Possible Scenarios to Cultivate Cyanobacteria on the Moon for Life Support

Home , ISS ECLSS, Lunar lava tube, Zvezda (moonbase)

Possible scenarios to cultivate cyanobacteria on the Moon for life support

Tom Schockaert

Promoter: Prof. Dr. S. Baatout Thesis presented in fulfillment of the Co-promoter: Dr. N. Leys the requirements for the degree of Master of Science in Space Studies

SCK•CEN Belgian Nuclear Research Centre

Academic year 2012-2013

Without written permission of the promoters and the author it is forbidden to reproduce or adapt in any form or by any means any part of this publication. Requests for obtaining the right to reproduce or utilize parts of this publication should be addressed to KU Leuven, Faculteit Wetenschappen, Geel Huis, Kasteelpark Arnsberg 11 bus 2100, 3001 Leuven (Heverlee), Telephone +32 16 32 14 01.

A written permission of the promoter is also required to use the methods, products, schematics and programs described in this work for industrial or commercial use, and for submitting this publication in scientific contests.

Acknowledgments

The Master of Space Studies is an international master after master program presented by the KU Leuven in collaboration with the University of Ghent. Despite the fact that I already obtained a master’s degree in Geography from the University of Ghent, I was delighted to be able to follow this program due to my interest for space, astronomy and everything that belongs with it. The Master of Space Studies was a fantastic experience with a lot of unique activities, meeting new people and broadening my knowledge about space. This thesis is a compulsory part of the program.

First of all I would like to thank my promoter Prof. Dr. S. Baatout who brought me in contact with Dr. Leys. She taught the lessons ‘Life Sciences and Biology in Space’ in the Master of Space Studies and because it was so fascinating, I preferred a thesis subject in this domain.

I would also like to thank my co-promoter, Dr. Natalie Leys. She searched for a fitting thesis subject. This study links microbiology with space exploration and even has topics that are related to my previous studies in geography. She also invited me at the Belgian Nuclear Research Centre (SCK•CEN) to get more familiar with the microbacteria Arthrospira, also known as ‘Spirulina’. During this period I was able to participate in the research of different PhD students. This was very interesting and I learned a lot about the different kinds of microorganisms that are used in the MELiSSA-system.

I like to thank Prof. Dr. C. Waelkens, program director of the Master of Science in Space Studies, who motivated me and followed up the thesis.

My final appreciation goes to the different employees and PhD students from SCK•CEN. If I had a question about a certain topic in microbiology, a lot of people were always ready to help me.

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Table of contents

Acknowledgments ...... iii

Table of contents ...... iv

List of figures ...... vii

List of tables ...... ix

Abstract ...... x

Keywords ...... xi

1. Human space exploration ...... 1

2. Back to the Moon? ...... 4

2.1. Future Moon plans ...... 4 2.2. Advantages of a Moon base ...... 5 2.2.1. Scientific benefits ...... 5 2.2.1.1. Lunar geology ...... 5 2.2.1.2. Astronomy ...... 6 2.2.2. Life sciences ...... 7 2.2.3. Economic benefits ...... 8 2.3. Possible locations on the Moon surface ...... 8 2.3.1. Equatorial regions ...... 8 2.3.2. Far side of the Moon ...... 9 2.3.3. Polar regions ...... 9 3. Life Support Systems ...... 11

3.1. Basic human needs ...... 11 3.2. Environmental Control and Life Support System of the International Space Station (ECLSS ISS) ...... 12 3.2.1. Temperature and Humidity Control (THC) and Fire Detection and Suppression (FDS) ...... 13 3.2.2. Atmosphere ...... 13 3.2.3. Water Recovery System ...... 14 3.3. History of Life Support Systems including cyanobacteria ...... 15 4. Bioregenerative Life Support System such as MELiSSA ...... 17

4.1. Compartment I ...... 19

4.2. Compartment II ...... 21 4.3. Compartment III ...... 22 4.4. Compartment IV ...... 22 4.5. Crew ...... 22 5. Arthrospira ...... 23

5.1. Phyllum of Cyanobacteria ...... 23 5.2. Morphology of Arthrospira ...... 23 5.3. Growth conditions of Arthrospira ...... 24 5.4. The value of Arthrospira ...... 25 5.4.1. Oxygen production ...... 25 5.4.2. Nutritious importance ...... 25 5.5. Arthrospira on the Moon ...... 26 6. Possible challenges to cultivate Arthrospira on the Moon...... 27

7. Illumination ...... 28

7.1. Illumination conditions on the Moon ...... 28 7.2. Visibility from Earth ...... 34 7.3. Implications for Arthrospira ...... 35 8. Temperature ...... 39

8.1. Temperature conditions on the Moon ...... 39 8.2. Implications for Arthrospira ...... 44 9. Radiation ...... 47

9.1. Radiation conditions on the Moon ...... 47 9.1.1. Galactic Cosmic Rays (GCR) ...... 48 9.1.2. The Sun ...... 49 9.1.3. Van Allen Radiation Belts ...... 50 9.1.4. The Moon ...... 51 9.2. Implications for Arthrospira ...... 52 10. Regolith ...... 55

10.1. Regolith on the Moon ...... 55 10.1.1. Origin of the Moon ...... 55 10.1.2. Regolith ...... 56 10.1.3. Composition ...... 56

10.1.4. Volatiles ...... 57 10.2. Implications for Arthrospira ...... 59 10.2.1. Chemical elements needed for Arthrospira ...... 59 10.2.2. Implantation on the Moon ...... 60 11. Gravity ...... 62

11.1. Gravity on the Moon ...... 62 11.2. Implications for Arthrospira ...... 62 12. Meteorites ...... 64

12.1. Meteorites on the Moon ...... 64 12.1.1. Asymmetries in meteorite fluxes ...... 64 12.1.1.1. Nearside/farside ...... 64 12.1.1.2. Equatorial versus polar regions ...... 64 12.1.1.3. Leading versus trailing effect ...... 65 12.1.2. Micrometeorites ...... 65 12.2. Implications for Arthrospira ...... 66 13. Magnetism ...... 67

13.1. Lunar magnetic anomalies ...... 67 13.2. Implications for Arthrospira ...... 69 14. Other obstacles ...... 70

14.1. Legal issues ...... 70 14.2. Launch, timing, implementation and deployment ...... 72 15. Possible scenarios to cultivate Arthrospira on the Moon...... 73

15.1. Preferred scenario using solar power ...... 75 15.2. Other possibilities using solar power ...... 77 15.3. General configuration of the photobioreactor using solar power ...... 78 15.4. Nuclear power sources ...... 79 Conclusions ...... 82

References ...... 84

List of figures

Figure 1: A possible future Moon base? ...... 4

Figure 2: 3D-printing robots print walls out of lunar material ...... 5

Figure 3: Regenerative Environmental Control and Life Support System Diagram for the ISS ...... 12

Figure 4: General architecture for the U.S. regenerative LSS on board the ISS ...... 15

Figure 5: Scheme of the different compartments in the MELiSSA loop ...... 18

Figure 6: Scheme with the different phases of a natural ecosystem ...... 19

Figure 7: Arthrospira platensis ...... 24

Figure 8: Difference in axial tilt between Moon and Earth ...... 29

Figure 9: Tower height needed on Poles ...... 29

Figure 10: Difference in altitudes obtained from the LOLA altimeter ...... 30

Figure 11a: North Pole average illumination ...... 31

Figure 11b: South Pole average illumination ...... 32

Figure 12: Areas with the most illumination on the North and South Pole ...... 33

Figure 13: Illustration of the modelled average illumination for the area around the Shackleton crater ...... 34

Figure 14: Visibility of Earth for both the North (a) as the South (b) Pole ...... 35

Figure 15: Storage of Arthrospira sp. PCC8005 at 4 °C and 20 °C ...... 36

Figure 16: Growth of subcultures of Arthrospira sp. PCC8005 after storage at 4 °C and 20 °C ...... 37

Figure 17: Surface temperature on the Moon’s equator for one lunar day ...... 41

Figure 18: Left, the minimum, mean and maximum temperature curves at the equator are shown for the Moon surface layer. Right, the curves are shown for 85°N ...... 42

Figure 19: Thermal image of the South Polar Region in summer solstice ...... 43

Figure 20: Thermal image of the North Polar Region in winter solstice ...... 44

Figure 21: Two different kinds of radiation sources (GCR and SEP) and the Earth’s magnetosphere ...... 47

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Figure 22: Inverted relation of Galactic Cosmic Rays with the sunspot cycle ...... 49

Figure 23: South Atlantic Anomaly and the Van Allen Belts ...... 51

Figure 24: Concentration of elements on lunar highland, lunar lowland and Earth...... 57

Figure 25: Gas release pattern for Apollo 11, soil sample 10086.16 ...... 58

Figure 26: Sketch of a possible entrance of a lunar lava tube ...... 61

Figure 27: Gravitational anomalies at the surface of the Moon ...... 62

Figure 28: Comparison between the cumulative micrometeoroid flux on the Earth (dotted line), and the rescaled cumulative micrometeoroid flux on the Moon (continuous line)...... 65

Figure 29: Lunar magnetic anomalies ...... 67

Figure 30: Reiner Gamma Swirl ...... 68

Figure 31: Sketch of the compartments of the photobioreactor ...... 79

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List of tables

Table 1: Chemical conversions in the different compartments of MELiSSA ...... 21

Table 2: Major forms of ionising radiation on the Moon ...... 51

Table 3: Ionising radiation used in ground experiments on Arthrospira platensis ...... 53

Table 4: Changes in Fv/Fm ratio and oxygen production during exposure to gamma radiation ...... 54

Table 5: Zarrouk medium for 1 liter water ...... 59

Table 6: Possible locations to cultivate Arthrospira on the Moon ...... 74

Abstract

For the first time in the scientific community, the possibility of cultivating the cyanobacterium, Arthrospira, on the Moon, is discussed. In the first part of the thesis the necessity of a Bioregenerative Life Support System for space exploration is explained. MELiSSA, developed by ESA and partners (e.g. SCK•CEN), is such a Bioregenerative Life Support System which generates food, oxygen and clean water for the crew, from the waste of the astronauts. Arthrospira is a key element in this MELiSSA system and whether or not this bacterium survives in outer space, or on the surface of the Moon as discussed in this thesis, is of great importance for the whole MELiSSA system and space exploration in general.

In the second part of the thesis the different hostile environmental factors on the surface of the Moon are described. Altered illumination from the Sun, diverse temperature conditions, ionising radiation, reduced gravity, different soil than here on Earth and increased meteorite risk could all be factors that endanger a permanent human base on the Moon, or endanger the implementation of a photobioreactor with Arthrospira on the surface of the Moon.

Some areas on the Moon would be more favourable than others and consequently, the main goal of this thesis is to explore a suitable location to implement a photobioreactor with Arthrospira. Because Arthrospira can only be cultivated at moderate temperatures, a temperature control system is vital. The power to that temperature control system can be provided by solar cells. A site with the most illumination would therefore be the most preferred spot. An area near the Shackleton crater on the South Pole seems to receive the largest percentage of illumination in the year. It is therefore the author’s opinion that this is the best suitable location if solar energy is used. Recently, however, there is a revival of interest in the use of nuclear power sources. If the possibility would exist, that the photobioreactor could be powered by a nuclear source, a limitation to the Poles is not needed anymore and other interesting locations can be searched for.

When the photobioreactor is implemented below the surface, possible harmful factors such as radiation, temperature variance, meteorites and abrasive regolith could be mitigated. In an optimal scenario where the photobioreactor is powered by solar energy, a mast with solar panels could be used to gather sunlight efficiently. The photobioreactor itself could be implemented below the surface on the South Pole to receive shielding from the hostile

environment and to collect as much sunlight as possible. If the timing of the mission could be arranged so that the South Pole finds itself in the summer season, favourable temperatures on the surface, or just below it, could be provided.

In a scenario where the photobioreactor is powered by a nuclear energy source, other exciting locations could be even more useful. Recently, a couple of lunar lava tubes were discovered in areas between the lunar high- and lowland. These lava tubes could be up to 400 metre wide and could be 40 metre buried below the surface. This makes it an excellent place to shield the photobioreactor, or a future Moon base, against ionising radiation, temperature variations and meteorites.

Keywords

Moon, cyanobacteria, Arthrospira, MELiSSA, hostile Moon environment, photobioreactor

xi Human space exploration

1. Human space exploration

It lies within the nature of mankind to explore its surroundings. Since the dawn of man, people travelled around the world to discover new places in search of wealth and prosperity. After a while, mankind did not only want to explore the Earth, but started looking to the sky to investigate the other celestial bodies. History changed on October 4, 1957, when the Soviet Union successfully launched Sputnik I (Garber, 2007) and this marked the beginning of the space age. Sputnik I was just a metal sphere with four radio antennae that did nothing more than transmit a beep signal. On April 12 in 1961, the USSR wrote history again with the launch of the cosmonaut Yuri Gagarin, who orbited once around the world and returned safely. This was the first manned space flight ever (Dick & Launius, 2006). However, in the years that followed, the payload of the satellites began to increase and only eight years later, on the 21th of July in 1969, Neil Armstrong set his first foot on the Moon. Still today, the Moon is the furthest mankind has travelled in space.

If the Human species wants to cross its boundaries of exploration, it has got to be ambitious and a manned spaceflight to Mars in the future seems inevitable. Nowadays, the exploration of Mars is certainly a hot topic. On the 6th of August in 2012, Curiosity, made by NASA’s Jet Propulsion Lab, landed on the surface of Mars in search of evidence for life (NASA, 2012). However, to achieve a manned flight to Mars, the space agencies will need to conquer all sorts of problems. An example of this can be found in a press conference of NASA on 31 may 2013 which stated that radiation exposure for human explorers to Mars could exceed NASA's career limit for astronauts, which is 1000 milliSieverts (mSv), if current propulsion systems are used. This is associated with a 5 % increase of risk in developing a fatal cancer (NASA, 2013). Missions to Mars would take several years to complete and, based on data from the Radiation Assessment Detector of the Mars Science Laboratory, astronauts would get a dose of 662 mSv on a journey of 6 months and this would not even include any step on the surface of Mars (NASA, 2013).

Another difficulty that the space agencies have to face is the autonomous survival in space. Indeed, astronauts have basic needs that need to be fulfilled in order to stay alive. A continuous supply of pressure and temperature control, oxygen, potable water, food, disposal of wastes and crew safety are some vital requirements for the independent existence in space. The equipment that is needed to regulate the environmental conditions in space is labelled as a

Possible scenarios to cultivate cyanobacteria on the Moon 1 Human space exploration

Life Support System (Eckart et al., 1996). The most advanced Life Support System can be found on board of the International Space Station (ISS). This physicochemical Life Support System is only useful for short duration missions and close to Earth destinations because regular taxi-flights remain still vital to supply the ISS with food and fresh water (Raatschen & Preis, 2001). However, if man wants to develop a permanent Moon or Mars base the development of a completely autonomous Life Support System is essential. A shift from physicochemical to a Bioregenerative Life Support System is inevitable. Reasons for this are the high launch costs for taking extra kilograms to space. Typical launch costs today are $10,000 USD to $25,000 USD per kilogram (Raatschen & Preis, 2001).

The European Space Agency (ESA) is developing a system called MELiSSA (Micro- Ecological Life Support System Alternative) which is the first of its kind to offer an approach for a compact Bioregenerative system for organic waste recycling with the use of microorganisms, living in interconnected controllable bioreactors (Mergeay et al., 1988). It aims to regenerate oxygen, potable water and food from waste, using bacterial and plant compartments, targeting up to 100 % degree of recycling.

MELiSSA consists out of a group of different interconnected biological reactors. The system recycles the wastewater, the organic matter and the carbon dioxide and converts it into oxygen, potable water and food. All kinds of bacteria in different compartments break down the waste into basic components such as nitrates, carbon dioxide and other minerals. These components are nutritious for cyanobacteria and plants which can produce oxygen through photosynthesis and are also a source of food. The cyanobacterium Arthrospira for example is a quality nutritious supplement containing many vitamins and water. In popular language it also goes by the name of ‘Spirulina’. This important bacterium is one of the most vital elements in the MELiSSA system. Research about this bacterium and whether or not it can survive in space is indispensable. If the space agencies want to fulfil their dream of putting a permanent human base on the surface of either the Moon or Mars, one of the first steps would be the investigation of the possibility of oxygen and food production, by cultivating cyanobacteria, on the surface of the Moon. This is the topic of this thesis.

Why the surface of the Moon is such an interesting place to install a bioreactor is explained in section 2. After an overview of the history of different Life Support Systems (section 3), MELiSSA and its different components will be described (section 4). Because cyanobacteria,

Possible scenarios to cultivate cyanobacteria on the Moon 2 Human space exploration

such as Arthrospira, are such a key element in this thesis, a separate chapter about the characteristics and its environment is dedicated to it in section 5. In a next step, this thesis aims to sum up the different challenges that the space agencies will encounter in implementing a bioreactor with Arthrospira on the Moon (section 6). Illumination (section 7), temperature (section 8), radiation (section 9), regolith of the Moon (section 10), microgravity and reduced gravity (section 11), meteorites (section 12) and magnetism (section 13) are all factors that could have an influence on the cultivation of Arthrospira on the Moon. In every section a number of possible solutions or countermeasures for these problems are described.

Possible scenarios to cultivate cyanobacteria on the Moon 3 Back to the Moon?

2. Back to the Moon?

2.1. Future Moon plans

Figure 1: A possible future Moon base? Source: ESA, 2013

It is 40 years since the last astronauts set foot on the lunar surface. After the Apollo 17 mission, mankind have not been back since, bringing the total amount of astronauts who stepped on the regolith of the Moon to twelve. However, many unmanned satellites since then have been, or still are, orbiting around the Moon (Chandrayaan-1 from India, SELENA from Japan, Lunar Reconnaissance Orbiter from NASA, etc.). On the 15th of April in 2010, President Barack Obama gave a speech wherein he boldly proclaimed that by 2025 it is possible to send astronauts to asteroids for the first time in history and by the mid-2030s, humans would orbit around Mars and even land on the surface (NASA, 2010). NASA administrator Charles Bolden dismissed the idea in a speech in 2013 of a planning by NASA to go back to the Moon with a human spaceflight anytime soon. Mankind has already been there and there is much more space that needs to be explored (NASA, 2013). Other countries such as Japan, China and Russia, however, do have interests in sending humans to the Moon. Even private companies like the Golden Spike Company are teaming up with Northrop Grumman for the design of a new lunar lander (Bergin, 2013). The European Space Agency announced in 2013 that it has plans to build a lunar base (figure 1) with 3D-printing (ESA,

Possible scenarios to cultivate cyanobacteria on the Moon 4 Back to the Moon?

2013). 3D-printing offers a potential means of facilitating lunar settlement with reduced logistics from Earth. In a first step the lunar material would be mixed with magnesium oxide and would turn into pulp. With this matter the 3D-printer would be able to print walls at a rate of 2 metres an hour. This ambitious concept can be seen in figure 2.

Figure 2: 3D-printing robots print walls out of lunar material Source: ESA, 2013

2.2. Advantages of a Moon base

Even though it sounds very ambitious to plant a base on the Moon, the benefits that would come together with a Moon base are massive. Although the political, social and industrial side would also benefit from this, in this thesis only the scientific and economic advantages are discussed.

2.2.1. Scientific benefits

2.2.1.1. Lunar geology

Although there are many hypotheses about the origin of the Moon, the most accepted theory suggests that the Moon is a remnant from a big impact nearly 4.5 billion years ago between the Earth and another Mars-sized object. Since then, the Moon was also subjected to meteorite fluxes in the past just as other celestial bodies. However, the Moon does not have any geological or atmospheric activity like Earth, Venus or Mars has. This makes the surface on the Moon extremely ancient and the Apollo missions even brought back rocks to Earth, dating back to 4.4 billion years ago (Ganapathy et al., 1970).

Possible scenarios to cultivate cyanobacteria on the Moon 5 Back to the Moon?

The outer layers of the Moon preserve a record of the solar system of billion years ago. In the lunar regolith, which is a layer of loose, heterogeneous material covering the solid rock on the Moon, evidences of old solar activity can be found. Indications of a solar wind flux from an ancient Sun, Galactic Cosmic Rays (GCRs) or Solar Energetic Particles (SEPs) from the past are probably the best preserved of the entire solar system (Crawford, 2004). If it would be possible to drill into the paleoregolith of the Moon, scientific research about the formation and ancient activity of our solar system would benefit hugely.

The Apollo missions discovered that there was a surface remnant of magnetisation on the Moon. Geomagnetic studies about whether or not the magnetisation is coming from an early core dynamo or induced by impact should be performed. The in situ study of the lunar rocks would be much more useful than just bringing them back to Earth because a preservation of the orientation of the magnetic fields would be guaranteed (Crawford, 2004).

2.2.1.2. Astronomy

It is suggested in the past that the Moon would be a very valuable location for astronomy. (ESA, 1992). The dark side of the Moon is probably one of the best places in the solar system where radio astronomy could take place. This is because it is continuously facing outer space and therefore shielded from Earth. The study of Galactic Cosmic Rays or other gamma rays would also benefit from an observatory station on the lunar surface because it lies outside the magnetosphere of the Earth.

For optical and infrared astronomy however, one can discuss that the Lagrange 2 point (L2) is a better location than the surface of the Moon. L2 marks a position where the combined gravitational pull of the Sun and the Earth provides precisely the centripetal force required to orbit with them. In this stable point the telescope is able to explore every direction, while a telescope on the Moon would be half blocked by the Moon itself. It is indeed the case that L2 is favourable but the Moon is still a much more suitable location than the Earth because of a couple of reasons. The Moon has no atmosphere like Earth. Gasses, dust and aerosols in Earth’s atmosphere absorb a lot of incoming photons from different wavelengths. For example, much of the far infrared light above 2 µm is absorbed by water vapour and carbon dioxide. Additionally, the ultraviolet light below 0.3 µm is absorbed by ozone (Crawford, 2004). A second problem with Earth’s atmosphere is the diffuse nature of the light. Light gets scattered by aerosols, dust particles and molecules and this scattering makes the light

Possible scenarios to cultivate cyanobacteria on the Moon 6 Back to the Moon?

undirected and it appears as it is coming from any region in the sky. Finally the weather in the troposphere is subjected to local variations, which blurs the images from the telescope. Although techniques like adaptive optics adjust to these local variations, a telescope on the Moon would still be more precise.

Infrared radiation detects any source of heat so if one wants to precisely study sources of the infrared wavelength, one would need a cryogenic telescope. There seem to be craters on the Poles of the Moon which are permanently shadowed that could be even colder than the surface of Pluto. Lunar Reconnaissance Orbiter measured the lowest summer temperatures at the craters on the South Pole at 35 K or -238 °C (ESA, 1992). This makes them favourable locations to place these cryogenic telescopes to study sensitive wavelengths such as the infrared.

2.2.2. Life sciences

Many of the physiological responses of organisms to the space environment have been studied. Gravity for instance can affect the cellular function at a molecular level, influencing fundamental cellular processes as signal transduction and gene expression (Fong, 2001). In the ISS, research has been done about the processes of life sciences in microgravity. However, the biological effects of reduced gravity instead of microgravity are largely unknown. Does reduced gravity cause the same biological changes similar to microgravity but slower? Or do these processes have a gravity threshold, which must be passed before they occur?

The unique radiation environment of the Moon would also provide opportunities for research in radiation (ESA, 1992).

Before astronauts are sent to Mars, it would be vital to study the human performances and adaptations to a reduced gravitational environment. The research is needed to enhance our knowledge of the fundamental human processes and could be even used to design medical therapies here on Earth. The use of Life Support Systems will elaborately be discussed in following chapters. When the day comes that the space agencies want to travel to Mars, it is necessary to be sure that the controlled ecological Life Support System cannot fail. The Moon also could be a testing-bed here (Crawford, 2004).

Possible scenarios to cultivate cyanobacteria on the Moon 7 Back to the Moon?

2.2.3. Economic benefits

Another advantage of a Moon base is the possibility to launch spacecraft from the Moon’s surface to further explore the solar system. The Moon would be some kind of steppingstone for further research. When a spacecraft is launched from Earth, the force and fuel that is needed to propel them out of the atmosphere is enormous because of the fairly strong gravitational field of the Earth (9.81 m/s2) and the friction and resistance of the atmosphere. The Moon, however, does not have an atmosphere and its gravitational pull is about one-sixth of that of the Earth. The escape velocity of the Earth is 11.2 km/s while that of the Moon is only 2.5 km/s (Zuber et al., 1994). Although less fuel and force is needed to launch a spacecraft from the Moon, one could ask himself if the amount of recourses like launch platforms and fuel needed for a launch from the lunar surface would not be more costly than a launch from Earth.

Although it sounds ambitious, a lot of studies have focused on the excavation of recourses from the Moon. One example of this is using the 3He in the lunar regolith as a potential fuel for future nuclear fusion reactors (Wittenberg et al., 1986; Schmitt, 2003). However, the concentration of 3He in the regolith samples returned by Apollo is very low (about four parts per billion) and it is far from clear whether significant excavation could ever be economic (Crawford, 2004).

2.3. Possible locations on the Moon surface

Some locations on the Moon have more benefits than others. In the next section a short review is given about the possible settings for a lunar base.

2.3.1. Equatorial regions

In the last section the possible excavation of 3He for nuclear fusion reaction was mentioned. On Earth 3He is rare and the abundance of helium-3 is thought to be higher on the surface of the Moon. This is because there is no plate tectonics or erosion from the atmosphere on the Moon and therefore the upper layer of the regolith contains amounts of 3He higher than here on Earth (Wenzhe & Yaqiu, 2010). The incidence angle in the equatorial regions of the Moon is much higher than on the Poles and as a result the 3He coming from the solar wind and Solar Energetic Particle Events will be more abundant than on the Poles (Lunar and Mars Exploration Office, 1990).

Possible scenarios to cultivate cyanobacteria on the Moon 8 Back to the Moon?

Traffic and launch from the lunar surface would also be easier. On Earth, space agencies prefer their launch platform as close to the equator as possible. For instance the European space agency has its launching base in Kourou, French Guyana and Russia has its launching area in Baikonur. The reason behind this is the increased momentum that the launch rocket receives from a rotation advantage. The Moon, however, has a very low rotation speed around its axis so the advantage here is minimal. Still the orbit would coincide with the ecliptic and would nearly coincides with the lunar orbit around Earth which makes a launch from this area favourable (Crawford, 2004). Also direct communication with the Earth is an additional advantage that favours a location on the Poles.

2.3.2. Far side of the Moon

In section 2.2.1.2 the benefits for a radio telescope on the far side have already been discussed. In a paper by Johnson et al. from 1999 the estimation of the highest concentrations of 3He should be found in the Maria on the far side. On the near side the magnetosphere of Earth shields the surface on the Moon during each orbit. The far side, however, is fully exposed and receives as a result a higher ion stream. A disadvantage here would be no direct communication with the Earth so an additional orbiting satellite around the Moon should provide for this.

2.3.3. Polar regions

Scientific research mostly agrees that a lunar base on the Poles would have the largest advantages. One of those benefits is the possibility of a constant sunlight on either the North or the South Pole of the Moon. These possible ‘peaks of constant sunlight’ make it feasible to power polar colonies almost exclusively with solar energy. An in-depth explanation about the luminosity conditions on the Moon is given in section 7.

Another big advantage is the evidence that water may be present in de large, dark and cold craters near the Poles (Watson et al., 2012). Although liquid water cannot persist on the surface of the Moon, ice water could be abundant in these craters. If there is indeed ice water available, the benefits for this water would be plural: (i) there would be no costly transportation of water needed from Earth, (ii) water consumption would be possible, (iii) it could be used as a rocket fuel or split into hydrogen and oxygen which further can be used for breathing potentials, etc.

Possible scenarios to cultivate cyanobacteria on the Moon 9 Back to the Moon?

Because the angle of incident sunlight is almost always the same, a stable thermal environment of -50 °C can be perceived (Watson et al., 2012). In section 8, the temperature on the Moon will be further discussed. .

Possible scenarios to cultivate cyanobacteria on the Moon 10 Life Support Systems

3. Life Support Systems

A Life Support System (LSS) is a set of machines and techniques that makes it possible for man to survive in space. Space agencies use the term Environmental Control Life Support System (ECLSS) (Barry, 2000). The function of this system is to control the atmosphere and temperature on the spacecraft, to provide the crew with oxygen, water and food, and to remove CO2 and other waste.

3.1. Basic human needs

The human body must be enveloped by appropriate pressure. The lack of pressure causes changes in the cardiovascular system, the musculoskeletal system and the nervous system. To accomplish this problem airtight enclosures or capsules where appropriate pressure can be artificially maintained must always surround the astronauts (Anderson, 2008).

Temperature in space varies constantly depending on the time and the place of the space vehicle. There are a couple of factors that influence these fluctuating temperatures. One example is the different materials that the space vehicle is made of. Some materials absorb more energy from sunlight than others. In addition, the angle of the spacecraft can influence the temperature. It is possible that temperatures of the space vehicle vary with 275 °C between the part that is facing the Sun and the part of the space ship that is facing outer space. A temperature control system to maintain the temperature is therefore needed to distribute the heat evenly and to get rid of excess heat. The temperature on board is usually maintained by active methods and by passive methods. Passive methods consist out of the insulating materials and active methods out of electrical heaters (Anderson, 2008).

A crewmember of typical size requires approximately 5 kg (total) of consumables (oxygen, water, and food) per day to perform the standard activities on a space mission, and outputs a similar amount in the form of waste solids, waste liquids, and carbon dioxide (Sulzman & Genin, 1994). The mass breakdown of these metabolic parameters is as follows: 0.84 kg of oxygen, 3.56 kg of water and 0.62 kg of food is consumed and is converted through the body's physiological processes to 1 kg of carbon dioxide, 3.87 kg of liquid wastes, and 0.11 kg of solid wastes. These levels can vary due to activity levels that is specific to mission assignment. Actual water use during space missions is typically around 26.0 kg per person a day, mainly due to non-crew-consumption use (e.g. personal cleanliness) (Hendrickx et al.,

Possible scenarios to cultivate cyanobacteria on the Moon 11 Life Support Systems

2006). Additionally, the volume and variety of waste products varies with mission duration to include hair, finger nails, skin flaking, and other biological wastes in missions exceeding one week in length.

Other environmental considerations such as radiation, gravity, noise, vibration, and lighting are also a factor into human physiological response in space, though not with the more immediate effect that the metabolic parameters have. Moreover, sleep is an important requirement for the human body. Sleeping bags with pillows are used to fasten the astronauts to a soft surface. Astronauts may wear blindfolds to block sunlight. Some astronauts prefer to float in air with few straps fastened to prevent bouncing (Anderson, 2008).

3.2. Environmental Control and Life Support System of the International Space Station (ECLSS ISS)

The ECLSS of the International Space Station ISS is to date the most sophisticated working LSS (figure 3) and is located in the U.S. Destiny modules and in the Russian Zvezda service module (Barry, 2000). Progression compared with previous Life Support Systems include the resupplying of oxygen (by electrolysis of water) and water (converting waste water to potable water) via the Oxygen Generation System (OGS) and the Water Recovery System (WRS) (NASA, 2008) (figure 4).

Figure 3: Regenerative Environmental Control and Life Support System Diagram for the ISS Source: NASA, 2008

Possible scenarios to cultivate cyanobacteria on the Moon 12 Life Support Systems

3.2.1. Temperature and Humidity Control (THC) and Fire Detection and Suppression (FDS)

Temperature and Humidity Control (THC) is the subsystem of the ISS ECLSS responsible for the maintenance of a steady air temperature and the control of the moisture in the station's air supply. Fire Detection and Suppression (FDS) is the subsystem devoted to identifying that there has been a fire and to take steps to fight it (figure 3).

3.2.2. Atmosphere

In the ISS a couple of machines and systems provide a tolerable environment for the human kind. The pressure is kept on a 101,3 kPa which is the same as on Earth’s sea level. An Earth like atmosphere (78 % nitrogen, 21 % oxygen) (Paul & Ferl, 2006) is favourable for the crew because the alternative, a pure oxygen atmosphere, has a greater risk of catching fire (like in Apollo1) and has harmful effects on the human body (oxygen intoxication) (Anderson, 1968).

The U.S. Oxygen Generation System (OGA) produces oxygen for breathing air for the crew and laboratory animals, as well as for replacement of oxygen lost due to experiment use, airlock depressurization, module leakage, and carbon dioxide venting. The system consists mainly of the Oxygen Generation Assembly (OGA) and a Power Supply Module. The heart of the Oxygen Generation Assembly is the cell stack, which electrolyzes, or breaks apart, water provided by the Water Recovery System, yielding oxygen and hydrogen as by-products. The oxygen is delivered to the cabin atmosphere while the hydrogen is vented overboard (figure 4). The Power Supply Module provides the power needed by the Oxygen Generation Assembly to electrolyze the water. The Oxygen Generation System is designed to generate oxygen at a selectable rate and is capable of operating both continuously and cyclically. It provides from 2.3 to 9 kg of oxygen per day during continuous operation and a normal rate of 5.4 kg of oxygen per day during cyclic operation (NASA, 2008). In 2011, the OGA was not running well for six months because the water that was fed to it was just slightly too acidic. During that period of six months the station crew was using oxygen, brought up aboard by visiting supply ships, a European cargo craft and the Russian Elektron oxygen generator, while awaiting delivery of the OGA repair equipment (Harwood, 2011). This is another example of the necessity of developing a completely reliable autonomous Life Support System because in a trip to Mars it would be nearly impossible to send supply ships. It also shows the need for parallel critical systems since a breakdown of the equipment is not unrealistic.

Possible scenarios to cultivate cyanobacteria on the Moon 13 Life Support Systems

Carbon dioxide and trace contaminants are removed by the Air Revitalisation System. This is a NASA rack, placed in Tranquillity, designed to provide a Carbon Dioxide Removal Assembly (CDRA), a Trace Contaminant Control Subassembly (TCCS) to remove hazardous trace contamination from the atmosphere and a Major Constituent Analyser (MCA) to monitor nitrogen, oxygen, carbon dioxide, methane, hydrogen, and water vapour.

The Air Revitalisation System and Oxygen Generation System are both developed by NASA. The Russian compartment also has an oxygen generator called Elektron. Just like the American one, it uses electrolysis to produce oxygen. This process splits water molecules reclaimed from other uses on board the station into oxygen and hydrogen via electrolysis. The oxygen is vented into the cabin and the hydrogen is vented into space (NASA, 2008). Both the NASA and Russian oxygen production systems on the ISS need clean water. The Bioregenerative systems, on the other hand, can work with wastewater without the loss of hydrogen.

3.2.3. Water Recovery System

Currently, in space, water for oxygen and drinking water production is being supplied from Earth and on board recycled and purified. Around 96.5 % of the water in the ISS is being filtered and can be reused with the help of physicochemical processes (Gustafson et al., 1989).

The Water Recovery System (WRS) recycles water from crewmember urine, cabin humidity condensate and crew perspiration during Extra Vehicular Activities (EVAs) so that it can be reused by the crew as potable water and as clean water for personal hygiene. Because of this system, the needed amount of consumables and water that has to be launched to the ISS has dropped enormously (6800 kg per year) (NASA, 2008). The WRS is divided into a Urine Processor Assembly (UPA) and a Water Processor Assembly (WPA). A low-pressure vacuum distillation process is used to recover water from urine. To mitigate the microgravity effect in space a rotating distillation assembly is used that aids in the separation of liquids and gasses in space. Liquid from the UPA is united with water from other water sources like the cabin humidity condensate and is delivered to the WPA for treatment. This Water Processor Assembly removes gas and solid materials such as hair and lint and purifies the water with different filters. Remaining organic contaminants and microorganisms are removed with a high-temperature catalytic reactor assembly.

Possible scenarios to cultivate cyanobacteria on the Moon 14 Life Support Systems

In a last step the purity of the water is tested by an electrical conductivity sensor. If it is pure enough it is sent to a storage tank and is ready to use by the ISS crew. Water that does not meet the standards is reprocessed (NASA, 2008). The Zvezda module, however, contains a water recovery system that processes waste water from showers, sinks, and other crew systems and water vapour from the atmosphere that could be used for drinking in an emergency but is normally fed to the Elektron system to produce oxygen (NASA, 2008).

Figure 4: General architecture for the U.S. regenerative LSS on board the ISS Source: Parker & O’Conner, 1999

3.3. History of Life Support Systems including cyanobacteria

Several test beds with cyanobacteria and algae have been studied in the past since the 1960’s. The Russian BIOS-1 was the first system that consisted out of different compartments with gas-exchange between CO2 producing organisms and O2 producing organisms. This system, prepared by the USSR in the space race, was based on the unicellular eukaryotic algae Chlorella. It proved that micro-algae could be used in space-flight to support one man with oxygen and water for six weeks (Gitelson et al., 1989). In BIOS-2 and -3 a plant compartment was also built in to the system and it provided for 95 % of the daily requirements of the crew with respect to food, water and oxygen. BIOS-3 was a milestone in the history of Closed

Possible scenarios to cultivate cyanobacteria on the Moon 15 Life Support Systems

Ecological Life Support Systems (CELSS) because it could support a three-man crew for four to six months (Gitelson et al., 1989).

Other systems with algae have also been studied in the past. The Closed Aquatic Ecosystem (CAES) for example is an experiment that aims to assess the functioning of a CELSS under microgravity. In this experiment a unicellular algae Chlorella pyrenoidosa and a freshwater snail were keeping each other alive in a bioreactor (Wang et al., 2008).

The Closed Ecological Recirculating Aquaculture System (CERAS) is developed in Japan by the Tokyo University of Marine Science and Technology as a CELSS prototype. It is a closed hydrosphere model for aquatic organisms with an aquatic higher plants culture, a microalgae culture, a zooplankton culture and a tilapia fish culture. Three different microalgae species have been investigated so far, e.g. the two eukaryotes Euglena gracilis, Chlorella vulgaris, and the cyanobacterium Arthrospira platensis. A. platensis appeared to be the most suitable food source for larval tilapia (Lu and Takeuchi, 2004) and could be used as a sole feed in order to simplify the whole system (Lu et al., 2003; Morin, 2009).

ESA and partners are also developing a Bioregenerative Life Support system for future space exploration, called MELiSSA. It consists out of different interconnected bioreactors, where Arthrospira is being cultivated in one of them. Next section will discuss the MELiSSA system in detail.

Possible scenarios to cultivate cyanobacteria on the Moon 16 MELiSSA

4. Bioregenerative Life Support System such as MELiSSA

Bioregenerative Life Support Systems are capable of converting metabolic waste products into oxygen, potable water and edible biomass. Physicochemical Life Support Systems, on the contrary, like the one on the ISS are unable to produce a nutritious food source. It would not make any sense to send fertilizers and water up to the ISS to grow plants since the cargo for these fertilizers and water could be more efficiently used as food itself. Thus culturing plants and algae for food only makes sense if it can be done from waste. This is why the development of Bioregenerative Life Support System is such an important matter.

The European MELiSSA-system (Micro-Ecological Life Support System Alternative) was the first of its kind, which offers an approach to design a compact Bioregenerative system for organic waste recycling with the use of microorganisms living in interconnected controllable bioreactors (figure 5) (Mergeay et al., 1988). MELiSSA uses a collective activity of different compartments. The crew can be seen as one compartment. Compartment IV consists out of higher plant compartments (IVa) and photoautotrophic bacteria such as Arthrospira (IVb), for oxygen and food production. In the other compartments (I, II, III), waste is broken down into several components, which are nutrients for compartment IV. The different compartments are tested and integrated in the MELiSSA Pilot Plant (MPP) that is located at the University of Barcelona in Spain (Morin, 2009).

Possible scenarios to cultivate cyanobacteria on the Moon 17 MELiSSA

Figure 5: Scheme of the different compartments in the MELiSSA loop Source: Hendrickx et al., 2006

Nature can give inspiration on how the MELiSSA loop could work. A water column of a soda lake could be used as an example for the MELiSSA system. On the bottom, biomass is built up in an anoxic region of degrading organic matter and on the surface, light is a major energy source where plant, algae and cyanobacteria such as Arthrospira are growing (Hendrickx et al., 2006). Food and oxygen are produced in the photosynthetic compartment (IV) in a similar way that a lake ecosystem would work (figure 6). Energy from the Sun is harvested by cyanobacteria, algae and plants, to produce biomass and O2 from CO2, H2O and minerals (Morin, 2009). The high ratio of plant material in lakes sediments, often difficult degradable organic matter, can give clues on how the MELiSSA loop could function. A soda lake can create ideal conditions for the growth of Arthrospira (production rates of 10 g C m-2 day-1) and are environments with a lot of microbial diversity (Zavarzin et al., 1999).

Possible scenarios to cultivate cyanobacteria on the Moon 18 MELiSSA

Figure 6: Scheme with the different phases of a natural ecosystem Source: Morin, 2009

4.1. Compartment I

The waste that consists out of inedible plant materials, hygienic paper, faecal matter and urine from the crew is collected in Compartment I. On Earth the waste is typically taken care of by anaerobic digestion (Verstraete & Vandevivere, 1999). This process involves several steps with different bacteria in every step. In the final steps carbon dioxide CO2 and energy-rich methane CH4 are produced (Smith et al., 1980). However, this process is not favourable due to the highly flammable characteristics of methane-gas. One could discuss, however, that the produced biogas can be used as an energy source but this is also not desirable because this means a loss of carbon in the MELiSSA loop that eventually will be used by the photosynthetic compartment. One could also argue that carbon could be used out of the methane gas but this involves additional compartments and that would just unnecessary complicate the MELiSSA loop. The use of full anaerobic digestion in a Life Support System is therefore unwanted (Hendrickx et al., 2006).

Possible scenarios to cultivate cyanobacteria on the Moon 19 MELiSSA

Partial anaerobic transformation is a better way of breaking down waste because the production of Volatile Fatty Acids (VFA) can be used by other compartments such as the photosynthetic compartment (IV). In MELiSSA the partial anaerobic process is achieved by reactor operations under slightly acidified conditions. The digestion under thermophilic (55 °C) instead of mesophilic conditions, creates higher metabolic rates, higher VFA, higher biogas production and pathogens are eliminated faster (Bendixen, 1994). This is the reason that thermophilic conditions are used although it also requires a higher energy input (Hendrickx et al., 2006).

The essential task of the thermophilic anaerobic bacteria is to transform the waste into ammonium, H2, CO2, Volatile Fatty Acids and minerals (table 1). It is the liquefaction stage of the MELiSSA loop and three different degradations are needed: proteolysis, saccharolysis, and cellulolysis (ESA, 2007). In MELiSSA’s first design, a consortium of thermophilic, cellulolytic, proteolytic and saccharolytic Clostridia were considered (Mergeay et al., 1988). However, experiments showed that there was only a maximum of 15 percent of degradation of the wastes. Therefore it was rapidly decided to extend the number of bacteria and to work with a consortium of strains. Now, the overall biodegradation efficiency by the selected inoculums reaches sufficient values. Better degradation values are currently limited by two factors: the very slow degradation of fibrous material (i.e. cellulose, xylan, and lignin) and the mechanical difficulty of extracting these non-degraded compounds for a specific and more adapted treatment (ESA, 2007).

Possible scenarios to cultivate cyanobacteria on the Moon 20 MELiSSA

Table 1: Chemical conversions in the different compartments of MELiSSA Source: Hendrickx et al., 2006

4.2. Compartment II

In the second compartment of the MELiSSA loop, the retrieved components from the first compartment are dealt with. Photo-heterotrophic bacteria are preferable: their growth is dependent on the light and is anoxygenic. Rhodospirillaceae are able to use fatty acids, organic acids or amino acids, sugars, alcohols and benzoate as a carbon source (Imhoff et al., 1989) which makes them useful bacteria for compartment II. Rhodospirillaceae can also be found in nature such as in stagnant water bodies where there is a relatively big amount of soluble organic matter. Rhodospirillum rubrum is one of the Rhodospirillaceae that is not producing any toxins and could even be used as a complementary food source (Vrati, 1984). The R. rubrum biomass has even been reported to have cholesterol-lowering properties, which is currently further investigated at SCK•CEN (Leys, personal communication). Anoxygenic photoauto- and heterotrophs transform the Volatile Fatty Acids, H2 and H2S evolved from the

Possible scenarios to cultivate cyanobacteria on the Moon 21 MELiSSA

+ liquefying compartment into biomass and into NH4 and minerals, available for the nitrifying compartment (Hendrickx et al., 2006).

4.3. Compartment III

In compartment IV of the MELiSSA system both the cyanobacteria as the higher plant compartment take up nitrogen as nitrate. Thus this means that ammonium, broken down in previous compartments, needs to be nitrified. With the help of Nitrosomonas, ammonia is being oxidized to nitrite. Nitrite on its turn is being oxidized to nitrate by nitrite oxidizers such as Nitrobacter. A culture mixture of Nitrosomonas europaea and a Nitrobacter winogradskyi was proposed to reside in the third compartment (Hendrickx et al., 2006). However, the bacteria in this compartment have a slower growth compared to the other compartments. Implementation is done by immobilized bacteria and therefore the bioreactors in this compartment are fixed bed columns (Albiol et al., 2000).

4.4. Compartment IV

Compartment IV consists out of two different parts (figure 5): Compartment IVa which consists out of a colonization of the cyanobacterium Arthrospira and a higher plants compartment IVb. The most important task in this compartment is the fixation of carbon out of CO2. It also has to generate an edible biomass and also needs to produce O2. Although plants can succeed in this, Arthrospira, called ‘Spirulina’ in popular language, is even more efficient. The bioreactor in compartment IV requires light supply and the cells need nitrate as a nitrogen source (MELiSSA, 1999). To fulfil a complete diet, the higher plant compartment that consists out of red beet, lettuce and wheat, was added to the loop (Hendrickx et al., 2006).

4.5. Crew

The MELiSSA system is built for the purpose of keeping a crew alive in a long time-space mission. Survival of the crew is essential and the other compartments are constructed for the production of food, water and O2 and for the degradation of the waste from the crew. A typical balanced diet consists out of carbohydrates, fat, proteins, vitamins and minerals. A high production rate of the biomass and delivering nitrous components is essential. The organisms should produce a high rate of O2 and should therefore fixate CO2 (Hendrickx et al., 2006).

Possible scenarios to cultivate cyanobacteria on the Moon 22 Arthrospira

5. Arthrospira

5.1. Phyllum of Cyanobacteria

Cyanobacteria, named after their blue-green color, are a big group of evolutionary ancient and ecologically important bacteria, which can carry out oxygenic photosynthesis, while using

CO2 as the only carbon source (Garcia-Pichel, 2000). The production of O2 as a by-product of photosynthesis by the cyanobacteria is thought to have converted the early reducing atmosphere into an oxidising one. This happened in an early anaerobic environment and changed the composition of life forms on Earth by creating biodiversity and leading to the near-extinction of oxygen-intolerant organisms. It is believed that the chloroplasts found in plants and eukaryotic algae evolved from cyanobacterial ancestors via endosymbiosis. (Margulis, 1975). Today cyanobacteria have become dominant in many extreme environments such as hot and cold deserts, hot springs and hypersaline environments.

5.2. Morphology of Arthrospira

The Arthrospira genus is a multicellular, filamentous microbacterium which filaments are composed of cells in a cylinder, arranged in helical trichomes (figure 7). The morphology is also the origin of the popular name for Arthrospira, which is ‘Spirulina’. The filaments are motile and glide around their axis (Ciferri, 1983). The helical shape of the trichomes is a typical attribute of the genus. The straightness and helical shape, however, can vary with different species and even within the same species it can differ. Helical parameters can be modified by changing the environmental conditions of Arthrospira such as the growth temperature. Trichomes of Arthrospira platensis can reach growths as long as 20 mm (Eykelenburg, 1979). The cytoplasm of A. platensis contains gas vacuoles which is absent in other species. These vacuoles make it possible to float vertically through the water column.

Possible scenarios to cultivate cyanobacteria on the Moon 23 Arthrospira

Figure 7: Arthrospira platensis Source: http://plantphys.info

5.3. Growth conditions of Arthrospira

The Arthrospira genus is a ubiquitous organism that can be found on many places on the Earth and in many different kinds of locations. Soil, sand, brackish water, seawater and freshwater, fishponds and tropical waters are all different kinds of environments where Arthrospira can be found. It seems that Arthrospira is a species that is capable to live in different habitats where other organisms are not able to live. A typical example of this is the occurrence of Arthrospira in certain alkaline lakes in Africa and in Mexico where they live practically as a monoculture. In mesahaline lakes with a salt concentration of 2.5 to 30 g/litre different kinds of cyanobacteria take over the environment (Iltis, 1971). However, in lakes with salt concentrations over 30 g/litre, Arthrospira seems to be a quasi-monoculture. It even has been found that Arthrospira can survive in salt concentrations up to 270 g/litre although salt concentrations from 20 to 70 seem to be optimal (Iltis, 1969). A high alkaline environment (pH-measures around 10) is favourable (Ciferri, 1983).

Arthrospira is a photoautotrophic bacterium which means it can grow in the light with CO2 as a sole source of carbon (Ogowa & Terui, 1972). The most favourable light intensity for cultivating Arthrospira is between 20 and 200 µE. Optimal temperatures during the day lay around 40°C while at night the optimum is around 25°C. Above 40 °C Arthrospira cultures do not grow anymore (Ogowa & Terui, 1970).

Possible scenarios to cultivate cyanobacteria on the Moon 24 Arthrospira

5.4. The value of Arthrospira

5.4.1. Oxygen production

It is a popular belief that trees are the best plants for absorbing atmospheric carbon dioxide. They can indeed fix from one to four tons of carbon per hectare per year. However, Arthrospira is even more efficient: an experiment in the Californian desert with industrially cultivated Arthrospira proved that it can fix 6.3 tons of carbon and produce 16.8 tons of oxygen per hectare per year (Hendrikson, 1997).

5.4.2. Nutritious importance

Even 500 years ago people already knew about the nutritious value of Arthrospira and made Spirulina cakes. In pre-Hispanic Mexico, the Aztecs ate ‘tecuitatl’, which consists out of algae that they found in Lake Texcoco. Bernal Díaz del Castillo, a member of Hernán Cortez´s troops, reported in 1521, that Spirulina maxima was harvested, dried and sold for human consumption in a Tenochtitlán (today Mexico City) market (Sánchez et al., 2003). It is also known that Kanembru tribeswomen in Chad made ‘dihé’ cakes, which also consisted out of Arthrospira. They found these algae in Lake Chad and used it because of their exceptional nutritious value (Garcia-Pichel, 2000). During 1964-65, a botanist on a Belgian Trans- Saharan expedition, Jean Léonard, reported finding a curious greenish, edible cakes being sold in native markets of Fort-Lamy (now N’Djamena) in Chad.

Arthrospira consists mainly on a rich content of protein, essential amino acids, minerals, vitamins, and essential fatty acids. Arthrospira platensis has a ratio of 60-70 % proteins by dry weight and contains a rich source of vitamins, for example vitamin B12 and provitamin A (β-carotene), and minerals, especially iron. It also contains a host of other phytochemicals that have potential health benefits. Arthrospira is able to produce 20 times more proteins per hectare as compared to soya (Hendrikson, 1997).

Arthrospira is also very easy to digest in contrast to many other microorganisms. This is because of its weak content in nucleic acids and lack of cellulose cell wall. Therefore no cooking is needed before human consumption and consequently allows the preservation of compounds such as vitamins and polyunsaturated fatty acids (Hendrikson, 1997).

Possible scenarios to cultivate cyanobacteria on the Moon 25 Arthrospira

5.5. Arthrospira on the Moon

The plans for the lunar bases discussed in section 2 seem extremely ambitious. Whether or not a permanently human base on the Moon is possible, a first step should be to make absolutely sure that a survivable environment is created for mankind. Shielding from radiation, temperature and atmosphere control, waste management, food and oxygen production are all vital components that need to be dealt with. This far from Earth only completely autonomous Life Support Systems can be cost-effective. A Bioregenerative, ecological controlled LSS like MELiSSA is in order here.

Although the other compartments of MELiSSA are also very important, Arthrospira in compartment IV produces edible nutrients, oxygen and water like no other organism here on Earth and is therefore the most important key element of MELiSSA. The advantage of not sending food, oxygen and water in taxi-flights to the Moon but regenerate them in situ is enormous. Whether or not MELiSSA operates well in space or on the Moon, depends a lot on the survival and robustness of Arthrospira in the space environment. Is it possible to cultivate Arthrospira on the Moon? The goal of this thesis is hence describing the potential problems Arthrospira could encounter and additionally propose some solutions to counteract these problems.

Due to the very harsh environment on the Moon’s surface there will be need for environmental control to sustain any microorganisms on the Moon. Arthrospira is very sensitive to temperature changes and no place on the Moon could provide the correct conditions. The non-existent atmosphere, the intense ultraviolet light, the Galactic Cosmic Radiation (GCRs) and Solar Energetic Particles events (SEPs), the lack of liquid water and lack of nutrients are other crucial factors which make it impossible to cultivate Arthrospira on the bare regolith of the Moon. The use of a photobioreactor supplied with nutrients for Arthrospira to grow in, could offer some protection against the extreme environment on the Moon

Possible scenarios to cultivate cyanobacteria on the Moon 26 Possible challenges to cultivate Arthrospira on the Moon

6. Possible challenges to cultivate Arthrospira on the Moon

If mankind dares to take the step to create a lunar base, a suitable location must firstly be found. Section 2.3 already suggests that a settling on the Poles would be preferable. A suitable location for a photobioreactor with a cultivation of Arthrospira should be the first steppingstone for finding an appropriate site for a lunar base. Implementing this photobioreactor on the surface of the Moon could face a couple of problems. A fitting location with appropriate illumination conditions needs to be sought out. This would probably be around the Poles, which in the past has been suggested that around those areas, possible ‘peaks of eternal light’ could exist (section 7). The thermal environment is a second difficulty that will be discussed in this thesis (section 8). Because of the long nights and days, temperatures around the equatorial regions vary enormously. Is the temperature on the Poles any better? On Earth, life is protected from harmful radiation by the geomagnetic field and the atmosphere. On the Moon, however, the environment for life is much more hostile. Whether or not Arthrospira can survive this environment is handled in section 9. Whether or not the regolith of the Moon contains nutrients for the survival of Arthrospira is dealt with in section 10. Microgravity and reduced gravity have a bad influence on the immune system of the human kind. The way bacteria react to microgravity or reduced gravity on the Moon is discussed in section 11. The atmosphere on Earth protects life for damaging meteorites. On the Moon, however, there is no existing atmosphere so the risk for meteorites is higher (section 12). The Moon has some magnetic anomalies, these are discussed in section 13. Any problems with the launch and the implantation of the photobioreactor on the surface is handled in section 14 together with any legal issues. Some solutions, concepts or explanation of the previous enlisted difficulties for Arthrospira to survive on the Moon will be discussed in section 15.

Possible scenarios to cultivate cyanobacteria on the Moon 27 Illumination

7. Illumination

7.1. Illumination conditions on the Moon

The location of a possible lunar base and thus the place for a photobioreactor with Arthrospira depends a lot on the illumination that is received by natural sunlight. The more sunlight received on the Moon, the more sunlight power that can be used from the solar panels. In this section an overview is given concerning the different illumination conditions on the Moon.

A lunar day is the time it takes for the Moon to make one complete orbit around the Earth and come back to the same position as it started. The Moon takes 27 Earth days, 7 hours and 43.2 minutes to complete an orbit around the Earth. However, the Earth in itself travels around the Sun in the meantime. The Moon therefore has to move further; from full Moon to full Moon takes an average of 29 days, 12 hours, and 44 minutes which is called a synodic day. During the year, these periods vary slightly due to gravitational factors (Cain, 2008).

The Earth is always faced to the same side of the Moon. The reason for this is that the Moon rotates about its spin axis at the same rate that the Moon orbits the Earth, which is called tidal locking. At some point in the distant past, the Moon rotated more rapidly than it currently does. The Earth’s gravity field caused a part of the Moon to bulge out. The pull of gravity caused the rotation of the Moon to slow down until this bulge was pointing directly at the Earth. At this point, the Moon was tidally locked to the Earth (Cain, 2008).

The two former facts imply that areas around the equator on the Moon receive almost 15 straight Earth-days of sunlight, followed by almost 15 Earth days of darkness.

Just as near the Poles on Earth, the Moon also has a midnight Sun. On one of the lunar Poles the Sun would be visible for 6 months straight in the local summer and in winter the Sun would drop below the horizon for the other half of the year. The Moon, however, has a very low angle of inclination (1.533 °) of the Moon’s equatorial plane with the solar ecliptic which means that the Sun in summer would never reach a higher altitude than 1.533 ° on the Poles (Reinhold, 1990). The difference in axial tilt between the Earth and the Moon can be clearly seen in figure 8.

Possible scenarios to cultivate cyanobacteria on the Moon 28 Illumination

Figure 8: Difference in axial tilt between Moon and Earth Source: http://nfo.edu/tilt.jpg

As said before, a continuous source of sunlight would be highly preferable to implement a bioreactor. Another possibility is building a high tower on the Poles with solar panels mounted on the top, providing the photobioreactor with artificial sunlight. If the assumption is made that the Moon is a perfect circle than we would need a tower of approximately 622 metres. This is the height that is needed for a tower on the Poles in winter to still receive sunlight.

Figure 9: Tower height needed on Poles Source: Reinhold, 1990

However, the Poles on the Moon, just as the rest of the surface, are covered with craters and it is possible that the height on the rims of these craters is high enough to receive continuous light. Indeed, around the Poles there seem to be craters which provide (1) areas where there is no sunlight at all, which means the possibility of water in ice form and other volatiles could

Possible scenarios to cultivate cyanobacteria on the Moon 29 Illumination

be trapped in there and (2) areas on the rims where there is a possibility for ‘peaks of eternal light’.

In a paper by Mazarico et al. from 2011 the illumination conditions for the lunar Poles were mapped with a Lunar Orbiter Laser Altimeter (LOLA) on board the Lunar Reconnaissance Orbiter developed by NASA. Due to the increased spatial and temporal extend of the simulations in comparison with other studies, the LOLA contributed a lot to the knowledge of illumination conditions on the lunar Poles. In figure 10 the elevation on the lunar Poles is presented. Note that the differences in altitudes on the South Pole is higher than on the North Pole.

Figure 10: Difference in altitudes obtained from the LOLA altimeter Source: Mazarico et al., 2011

The modelling of the illumination conditions depends on two different steps: (1) calculate and store the elevation of the horizon in a number of set directions, for every point in the region of interest (which is marked with the dashed rectangle); (2) interpolate those fixed-direction horizon elevations to a given Sun location, and calculate the ratio of the solar disc which is visible (Mazarico et al., 2011). In figure 11 the average illumination for 18.9 years is modelled for both the North and the South Pole. The figure represents the latitude from 88° till 90° for both Poles. Deep dark blue areas receive no direct sunlight at all while red areas on the rims of the craters were almost continuously lit for 18.9 years. Note that this figure represents a low surface area around the Poles and possible suited locations can also be found on lower latitudes.

Possible scenarios to cultivate cyanobacteria on the Moon 30 Illumination

Permanently shadowed regions are much of interest for the scientific community since it is suggested that these areas could be potential cold traps for volatiles. Because the Poles have a near-zero inclination with the Sun, sunlight never reaches deep craters on the North and South Pole (Feldman et al., 2000).

It seems that indeed the high crater rims close to the Poles receive the highest illumination values. The South Pole and its vicinity have a larger area of permanently shadowed regions as seen on figures 10 and 11. However, the higher topographic range on the South Pole enables generally better illumination for those high rim points than in the North.

Figure 11a: North Pole average illumination Source: Mazarico et al., 2011

Possible scenarios to cultivate cyanobacteria on the Moon 31 Illumination

Figure 11b: South Pole average illumination Source: Mazarico et al., 2011

In figure 10 the area of interest is indicated with a dashed rectangle. From every point in this region the horizon is modelled and its illumination by the Sun. Areas with the highest illumination are shown in figure 12. The gray scale map gives an indication of the received sunlight inside the craters and on the rims. Favourable areas on the North Pole are mostly in the vicinity of the Peary crater while most illuminated sites on the South Pole lay in the neighbourhood of the Shackleton crater. Earlier a tower of 622 metres was mentioned to receive constant sunlight on the Poles. Making use of the crater rims, such a high tower is not needed. Still, solar panels, mounted on a mast with an altitude of 10 metres would increase the illumination by the Sun with a decent amount. Not only the surface area is therefore modelled in the paper by Mazarico et al. but also the illumination from the Sun to the mast with a 10 metre altitude is calculated. Due to its height increase from the surface it is possible that the ranks of received illumination have changed. In figure 12 only the areas with the most surface illumination are shown while their correspondent numbers indicate the illumination rank on a 10 metre mast.

Possible scenarios to cultivate cyanobacteria on the Moon 32 Illumination

Figure 12: Areas with the most illumination on the North and South Pole Source: Mazarico et al., 2011 From all the locations studied, site 1 on the South Pole seems to receive the maximum amount of illumination. This area receives 92.66 % average solar visibility on the surface and 95.83 % average solar visibility from a 10 metre high mast. This location in the vicinity of the Shackleton crater has been suggested in the past as a good site for a future Moon base. Also for the implementation of a photobioreactor working on solar power this seems like a suitable spot. In figure 13, the 360° horizon elevation is shown for this spot. The surface level is represented with a dashed blue line while the horizon for the 10 metre mast is colour coded to indicate the distance to the obstacle on the horizon from very local (dark blue) to 150 km away (red). Due to different torques on the rotation axis of the Moon (which are not discussed in this thesis), the Sun has a different elevation each year. The gravity from the Moon and the Sun is responsible for this precession circle of 18.6 years. The path of the Sun over four precession cycles is indicated by small dots. When these dots are red the Sun from this location is visible. When the dots are black the Sun gets blocked due to the surrounding horizon. The longest total night at the surface of the most illuminated spot is 5.88 Earth days while the longest total night for a 10 metre mast is 2.75 Earth days.

Possible scenarios to cultivate cyanobacteria on the Moon 33 Illumination

Figure 13: Illustration of the modelled average illumination for the area around the Shackleton crater Source: Mazarico et al., 2011

7.2. Visibility from Earth

Although it is not such an important factor for cultivating Arthrospira, a high visibility of the site from Earth is also preferred for future lunar settlement. Mazarico et al. also modelled the visibility from Earth for both the North and South Pole for 18.6 years (figure 14). The areas with full visibility in the 18.6 years are represented by the colour white, while lack of visibility is indicated with a black colour. The elevation maps in the first step from modelling the illumination from the Sun are used again. However, in the second step the location from the source is changed from the Sun to the Earth. The more the Earth is visible from a certain location, the better possible communication to Earth can be established.

Possible scenarios to cultivate cyanobacteria on the Moon 34 Illumination

Figure 14: Visibility of Earth for both the North (a) as the South (b) Pole Source: Mazarico et al., 2011

7.3. Implications for Arthrospira

For this thesis the visibility from the photobioreactor to the Earth does not play a crucial role although data communication would be a lot easier. For a future Moon base, however, the communication to Earth would imply huge advantages. Although areas around the Shackleton crater receive the most illumination from the Sun, other locations with a better visibility from Earth could be more appropriate. On figure 12b areas on the South Pole with a high illumination percentage are shown. Areas in a lower latitude in the upper right corner (6, 18, 20, 23, and 33) have next to a high illumination a better visibility to Earth, which would make them more suitable locations for Earth communication sites.

The day and night cycle experienced by Arthrospira here on Earth would not be possible on the Moon. The illumination conditions on the equator are responsible for a night of almost 15 Earth days long, followed up by a daytime of also almost 15 Earth days. Can Arthrospira survive in these eccentric conditions? Arthrospira has been tested (e.g. in the MELISSA system) to grow in a continuously illuminated environment so it can produce the maximum of oxygen, water and edible biomass. Arthrospira would have no difficulties with the almost 15 Earth day long light conditions.

However, almost 15 Earth day long period in darkness would cause more of a problem. Arthrospira is a photoautotrophic bacteria which means it cannot grow in the dark even if organic sources of carbon are available in the medium. In SCK•CEN experiments are

Possible scenarios to cultivate cyanobacteria on the Moon 35 Illumination

performed to test the maximum storage time of Arthrospira sp. for the future ArtEMISS missions. In this experiment (conducted by Coninx in 2011) Arthrospira sp. was stored in the dark at 4 °C and at 20 °C. The test took 31 days and Arthrospira sp. was stored in a medium in closed tubes without headspace (thus without oxygen, except for dissolved oxygen in medium). In a first experiment the Optical Density at 750 nm was measured along a 31 day long period for both a culture kept at 4 °C and at 20 °C. The OD is an indication for bacterial cell concentration in a medium.

Figure 15: Storage of Arthrospira sp. PCC8005 at 4 °C and 20 °C Source: Coninx, 2011 (SCK•CEN experiment)

The OD of both the 4 °C and 20 °C cultures was measured on several time steps. The optical density remained relatively constant for the first 20 days in darkness, indicating the intact cells concentration remained stable. After this period the culture stored at 20 °C is starting to decrease in optical density, indicating that the cells and culture are dying. These data indicate that Arthrospira sp. could survive better at 4 °C than at 20 °C.

In a follow up on the experiment the growth of Arthrospira sp. subcultures were tested. From both the cultures in figure 15, a sample was taken out by a syringe every five days. This subculture was then exposed again to optimal Arthrospira sp. conditions (including a light source) and growth of this subculture was tested (Figure 16).

Possible scenarios to cultivate cyanobacteria on the Moon 36 Illumination

Figure 16: Growth of subcultures of Arthrospira sp. PCC8005 after storage at 4 °C and 20 °C Source: Coninx, 2011 (SCK•CEN experiment)

These data show, however, that for efficient recovery Arthrospira sp. PCC8005 is better stored at 20 °C than at 4 °C. At 4 °C, it can survive a period of 15 days in the dark and can grow again after the storage of 15 days. The subcultures from a 20 to 30 day storage period at 4 °C are only recovering very slowly. At 20 °C the culture can be stored for 20 days without any delay effects for recovery, but a culture stored for 31 days in the dark at 20 °C could not be recovered and was most likely dead (as was also suggested above).

This experiment proved that the dark/light regime, on the Moon are not devastating for Arthrospira sp. to survive. The equator regions have an almost 15 day dark period and an almost 15 day light period. The almost15 day dark period would probably not have any pernicious result if the temperature is kept at a reasonable level. In areas on the Poles on the rim of craters (e.g. Shackleton crater from previous section) the maximum night period would be less short and the continuous illumination for 100’s of days would provide a better location than in the vicinity of the equator. In the craters themselves there would be no illumination from the Sun at all what would obviously not be a good place for Arthrospira sp. to be cultivated in.

Possible scenarios to cultivate cyanobacteria on the Moon 37 Illumination

In this thesis, however, a photobioreactor is proposed. Due to the hostile environment of the Moon shielding would probably be needed. The solar panels could provide for the power of a LED lamp placed in the bioreactor. These solar panels could be mounted on the photobioreactor on the surface or on a couple of metre high mast to receive even more incoming light. A constant optimal light intensity between 20-200 µE could be provided by these solar panels.

The spectrum of the incoming sunlight for the cultivation of Arthrospira is also important. Arthrospira on Earth is commercially cultivated in large ponds. The sunlight that reaches the Earth’s surface has an essential spectrum range between 400-700 nm which is called the Photosynthetically Active Radiation (PAR). Organisms are able to use this spectrum for the process of photosynthesis. Ultraviolet (UV) radiation (100-400 nm) also reaches the surface of the Earth. However, as sunlight passes through the atmosphere, all UVC (100-280 nm) and approximately 90 % of UVB (280-315 nm) radiation are absorbed by ozone, water vapour, oxygen and carbon dioxide. UVA (315-400 nm) radiation is less affected by the atmosphere. Therefore, the UV radiation reaching the Earth’s surface is largely composed of UVA with a small UVB component. On the Moon there is no protective atmosphere like here on Earth. This means that the lunar surface also receives the extreme ultraviolet, UVC and UVB, radiation which is ionising. This UV radiation would cause filament breakage and would damage the cultivation of Arthrospira. However, if indirect illumination is selected, then a LED lamp in the photobioreactor can supply the needed light energy to cultivate Arthrospira and damaging UV radiation can be excluded.

Possible scenarios to cultivate cyanobacteria on the Moon 38 Temperature

8. Temperature

8.1. Temperature conditions on the Moon

The Moon has one of the most extreme surface thermal environments in the solar system. Temperature varies a lot due to the incoming sunlight and the relative position to the Sun. The Moon is not a geologically active body like the Earth and the internal heat source is minimal. The Moon has no atmosphere in addition. There is, however, an increase in atomic and molecular particles close to the surface in comparison with the interplanetary medium but for practical purposes the Moon is considered to be surrounded by a vacuum (Lucey et al., 2006). Heating on the Moon comes therefore entirely from the Sun. The equilibrium of incoming solar radiation is reached rather fast due to the rocky materials with a low conductivity and a relatively low heat capacity.

Pettit & Nicholson suggested in 1930 already that the temperature on the Moon could be calculated with the Stefan Boltzmann equation where I represents absorbed solar energy per unit area, T is the absolute surface temperature (Kelvin), ε is the emissivity, and σ is Stefan's Boltzmann constant, 5.67x10-8 in metric units.

I = εσT4

Since the Moon is orbiting around the Earth we can use the same solar constant as on Earth (1366 W/m2). The Moon can be assumed to be a black body (emissivity close to 1). Temperatures on the equator can then be calculated and the maximum day-time high on the Moon is around 394 K or 120 °C.

When the Sun is not directly overhead, whether you are at the equator during lunar morning or evening, near the Poles, or looking at a rock face sharply angled to the horizontal, the surface temperature will be lowered because the same solar energy is spread over a larger area. I = 1366cos(θ)W / m2

Where θ is the angle of the Sun's position relative to a line perpendicular to the surface. For an angle of 30°, (maximum temperature for a horizontal surface at latitude 30° N or S, or equatorial temperature at roughly plus or minus two Earth days from lunar "noon"), T is then

Possible scenarios to cultivate cyanobacteria on the Moon 39 Temperature

380 K, or 107 °C. At 60° angle, the temperature is still 331 K or 58 °C. At 75° we reach about 281 K or 8 °C. At 85° angle the equilibrated temperature drops to 214 K or -59 °C.

During the night the surface temperature drops further as the rocks radiate away the energy they have absorbed during the day time, with regions near the lunar equator dropping to about 120 K or -150 °C by the end of the night.

This strokes more or less with the model created by Vasavada et al. (1999) which calculates the surface and subsurface temperatures on the Moon. In their model, the temperature of the surface and subsurface layers depend on the solar, infrared and internal energy fluxes. These on their turn are determined by the thermophysical properties of the soil which are the solar albedo, the infrared emissivity, density, thermal conductivity and heat capacity. These parameters are derived from lunar in situ measurements and returned samples. It seems, however, that the thermophysical properties change abruptly near the surface. Accordingly, in the model of Vasavada et al. a difference is made between two layers which differ in thermal conductivity and bulk density. The first layer is a 2 cm top layer of regolith that is highly insulating. The second one is denser and has a higher conductivity then the top layer. The presence of these different two layers can be explained by the meteorite bombardment on the Moon (no atmosphere) that churns the top layer and compresses the bottom layer.

In figure 17 a temperature curve is shown for one lunar day on an area at the equator. These temperatures seem similar to the ones that were calculated earlier with the Stefan-Boltzmann constant. The full line resembles the two-layer model while the dashed line indicates temperatures where the entire surface layer is modelled with the thermophysical properties of the second layer. The dotted line shows temperatures where the entire surface layer is modelled with the thermophysical properties of the first layer.

Possible scenarios to cultivate cyanobacteria on the Moon 40 Temperature

Figure 17: Surface temperature on the Moon’s equator for one lunar day Source: Vasavada et al., 1999

With the model of Vasavada et al. the subsurface temperature is also calculated (figure 18). Left the temperature variation for 0 °N is shown and right the variation at 85 °N. The diurnal minimum, mean and maximum temperatures are plotted for both areas as function of depth on the Moon. Results show that in the two-layer model, the top 2 cm layer has low conductivity and the lower layer has a greater conductivity. The penetration depth increases with latitude on the Moon as the seasonal component of the insolation cycle becomes more significant. At the pole, the temperature oscillation penetrates approximately 3.5 times deeper into the regolith than at the equator. At the equator it seems that the lunar day and night have no effect anymore on the temperatures at 40 cm depth. The temperature reaches an equilibrium of 250 K or -23 °C. Temperatures at 85 °N are not influenced by the day and night cycle anymore, 1 metre in the regolith of the Moon.

Possible scenarios to cultivate cyanobacteria on the Moon 41 Temperature

Figure 18: Left, the minimum, mean and maximum temperature curves at the equator are shown for the Moon surface layer. Right, the curves are shown for 85°N Source: Vasavada et al., 1999

The Lunar Reconnaissance Orbiter, which is already mentioned in the illumination section, also has a Diviner Lunar Radiometer on board that measures lunar surface thermal emissions. Because of the axial tilt of 1.533° which is mentioned earlier, the lunar seasons are barely noticeable on most locations on the Moon. At the Poles, however, the inclination of the Sun changes by more than 3° over the period of one year. This affects the percentage of areas illuminated by the Sun and surface temperatures. The launch date and orbit of the Lunar Reconnaissance Orbiter were especially chosen so its Diviner could observe the summer solstice in the Southern hemisphere and the winter solstice in the Northern hemisphere.

Although the temperatures for the rest of the Moon were also mapped, in this thesis only the South Pole (figure 19) and North Pole (figure 20) are shown. This is because the topography on the Poles determines how much sunlight an area receives and therefore how the temperature is influenced. The rest of the Moon is discussed earlier and no difference is noticed with the map of the LRO.

Figure 19 shows a Diviner channel 8 thermal image of the South Polar Region. The images are taken during a period from 3 till 30 October in 2009. The rugged South Polar topography makes it one of the most spectacular regions on the Moon. The thermal measurements of Diviner show us areas on the rims of the craters which are warmed up by sunlight

Possible scenarios to cultivate cyanobacteria on the Moon 42 Temperature

(temperatures up to 300 K or 27 °C) and cold permanently shadowed regions (temperatures down to 35 K or -238 °C)

Figure 19: Thermal image of the South Polar Region in summer solstice Source: NASA/GSFC/UCLA

On the other side of the Moon, Diviner mapped the North Polar Region at winter solstice. In figure 20 a night-time false-colour channel 9 map can be seen. Again it shows regions inside the craters with temperatures as low as 25K (-258 °C). This low temperature was recorded on the floor of the Hermite Crater and is so far the coldest place on the Moon. One would have to travel to a distance beyond the Kuiper belt to find objects with surfaces this cold. Diviner measures the temperature from the top millimetre of the lunar surface. Temperatures below the surface are expected to be warmer due to heat retention from the spring and summer seasons (NASA/GSFC/UCLA, 2009). It is clear, however, that the temperatures on the rims of the craters will not reach 300K like they do in summer solstice. Maximum temperatures of not even 100K or -173 °C are recorded.

Possible scenarios to cultivate cyanobacteria on the Moon 43 Temperature

Figure 20: Thermal image of the North Polar Region in winter solstice Source: NASA/GSFC/UCLA

8.2. Implications for Arthrospira

Temperature is a major factor that controls the rate of photosynthesis and proliferation of cyanobacteria. It changes the rate of cellular reactions, the structure of the cell component, the nature of metabolism, nutrition requirement and composition of biomass. The optimal temperature for cultivating Arthrospira in continuous light is in the range of 30-38 °C (Vonshak et al., 1997). A freezing temperature for Arthrospira is not recommended because it

Possible scenarios to cultivate cyanobacteria on the Moon 44 Temperature

favours death (Rippka, 1988). The minimum growth temperature for Arthrospira is 8°C and the maximum is 40 °C (Andrade & Costa, 2007).

As seen in the previous section there is a high possibility that there is nowhere on the entire Moon, a favourable temperature climate for Arthrospira to grow in (temperatures should stay between 8 °C and 40 °C).

On the equator of the Moon (figure 17) the daytime reaches a temperature maximum of 120 °C and during the night it cools down to -150 °C on the surface. These are temperatures that are impossible to live in for Arthrospira. The variation in temperature also creates problems for the equipment so a more stable temperature condition is preferred. Areas with higher latitude have a lower maximum day temperature than on the equator. Still the temperature drops here also to -150 °C during the lunar night. At the Poles the situation is a little different. Temperatures depend a lot on the season and on the topography. The seasonal difference between figure 19 and 20 is clear. In summer (Southern hemisphere in figure 19) temperatures can reach up to 27 °C on the rims of the craters which is a possible environment for Arthrospira to grown in. For instance the area with most illumination that was discussed in section 7.1, near the Shackleton crater reaches these temperatures in summer.

Planting a photobioreactor on the surface of the Moon, would cause a lot of problems for the equipment and for Arthrospira itself to survive. Another concept is therefore proposed in this thesis. Since the regolith of the Moon has a really low conductivity, a photobioreactor below the surface of the Moon could be an advantage. It is discussed earlier that diurnal differences have no influences anymore below 1 metre under the surface. Figure 18 implies that on the equator, 1 metre under the surface the temperature would constantly be around 250K or -23 °C. On an 85° latitude the temperature would be around 140 K or -133 °C at 1 metre below the surface. It is hard though to estimate the subsurface temperatures on the Poles and around the craters due to the high variations in topography and illumination from sunlight.

If we want to succeed in cultivating Arthrospira on the Moon, the photobioreactor should provide a suitable thermal environment. The only chance to be sure that a sufficient thermal environment is created, is by the use of a temperature control system that would be powered by solar cells. Indeed in a previous section (7.2), the solar panels should already provide power for a LED lamp to continue photosynthesis with a constant light intensity. It is not

Possible scenarios to cultivate cyanobacteria on the Moon 45 Temperature

catastrophic though if Arthrospira does not receive any illumination for a couple of days. However, Arthrospira is very sensitive to temperature. If temperature drops below 0 °C it would most certainly die, on the other hand it cannot grow anymore above 40 °C. So the solar cells should provide power for the temperature control system, but one could ask himself how it could survive dark periods. Since there is no place on the Moon discovered with 100 % continuous illumination from the Sun, it is clear that there should be a battery on board the photobioreactor to store energy from the solar cells to mitigate the periods without sunlight. The walls of the photobioreactor should be rather thick to have as low thermal conductivity as possible and should retain the heat from the thermal control system as good as possible. The shielding should also stand against cryogenic temperatures.

Possible scenarios to cultivate cyanobacteria on the Moon 46 Radiation

9. Radiation

9.1. Radiation conditions on the Moon

Harmful radiation is one of the most important barriers that stand in the way for further space exploration with a human crew inside a spacecraft. So far, only in the Apollo missions did astronauts travel outside the protective magnetosphere of the Earth. The Apollo astronauts have been lucky in the past too: the solar storm of August in 1972 occurred in between two Apollo missions. The crew of Apollo 16 had returned to the Earth in April while the crew of Apollo 17 was preparing for a Moon landing in December. If an Apollo crew would have been on the Moon during the solar storm, death would probably be inevitable (Phillips, 2005). This is an example to show how significant the radiation factor is for the further colonisation of the solar system by the humankind.

The radiation in interplanetary space is divided into two main sources of radiation: Galactic Cosmic Radiation (GCR) and radiation from the Sun (figure 21). The particle types and energies vary widely. The magnetic field of the Earth and spacecraft shielding, affect the energies greatly. Travelling to the Moon requires also passing two layers of harmful energetic charged particles around the Earth which are called the Van Allen belts.

Figure 21: Two different kinds of radiation sources (GCR and SEP) and the Earth’s magnetosphere Source: www.nasa.gov

Possible scenarios to cultivate cyanobacteria on the Moon 47 Radiation

9.1.1. Galactic Cosmic Rays (GCR)

Galactic Cosmic Rays (or GCRs) are high-energy particles that originate from outside our Solar System. Most of the detected GCRs come from sources inside our galaxy although they also can be generated outside the Milky Way. They are essentially nuclei of atoms without their electrons, almost travelling at the speed of light. About 85 % of the detected GCRs are hydrogen nuclei (protons), 14 % helium (α-particles), and 1 % high energy ions which are called HZE particles (NASA, 2008). HZE particles include carbon, iron and nickel and higher heavy ions and possess significantly higher ionising power, greater penetration power, and a greater potential for radiation-induced damage. Another very small fraction of GCRs are stable particles of antimatter, such as positrons or antiprotons.

They are believed to have been created during the last million years of a supernova explosion (but not in the supernova itself). In that period GCRs are accelerated inside the expanding clouds of gas and magnetic fields of such a supernova remnant. The particles bounce back and forth in the magnetic field of supernova remnants until they gain too much energy and speed and become cosmic rays when the medium cannot hold them anymore. As they travel through the very thin gas of interstellar space, some of the GCR interact with the gas and emits gamma rays. Detection of that reaction is how we know that GCR passes through the Milky Way and other galaxies (NASA, 2008).

The energy levels in GCRs can vary from 103 eV to more than 1020 eV. An electronVolt is the amount of energy gained or lost by the charge of a single electron moved across an electric potential difference of one volt. The extremely high energies in GCRs, however, cannot be generated by supernova remnants. Where these energies come from is a big question. It is possible that they could be created in the super massive black holes from Active Galactic Nuclei, quasars or gamma ray bursts (Aharonian, 2004).

Because the GCRs are charged particles, they get affected by the magnetosphere of the Sun and the Earth. Therefore it is also quite hard to locate the exact location of the sources. The Sun has a strong magnetic field carried out well beyond Pluto by the solar wind and known as the Heliosphere. It looks like a bubble in the interstellar space that surrounds the solar system. This field slows and tends to exclude lower-energy particles (E < 109 eV). Solar activity varies on an 11-year cycle; this seems to strongly affect particles. In figure 22 the Cosmic Ray

Possible scenarios to cultivate cyanobacteria on the Moon 48 Radiation

Intensities are plotted together with the Smoothed Sunspot Number. It is clear that the sunspots, which are a proxy for the solar activity, determine how many GCRs are permitted inside the Heliosphere. The Earth’s field also affects direction and tends to exclude lower energy particles. The particles have greater difficulty penetrating the Earth’s field near the equator than they do near the magnetic Poles. Latitude affects the intensity by about 10 % (Kliewer, 1995).

Figure 22: Inverted relation of Galactic Cosmic Rays with the sunspot cycle Source: Climax, Colorado neutron monitor operated by the University of Chicago

The Moon, however, does not have a global magnetosphere like the Earth has and therefore the GCRs are not getting deflected. In addition, the Earth has an atmosphere and produces secondary cosmic rays. When primary cosmic rays enter the Earth's atmosphere they collide with molecules, mainly oxygen and nitrogen. The interaction produce a cascade of lighter particles, a so-called air shower (Morison, 2008). As described before, there is no abundant atmosphere on the Moon and thus it is not protected from primary cosmic rays like on Earth.

9.1.2. The Sun

Our Sun produces a constant flux of low energy particles, mostly protons and electrons of energies between 1.5 and 10 keV, which are called the solar wind. The stream of particles varies in density, temperature, and speed over time and over longitude. These particles can escape the Sun's gravity because of their high kinetic energy and the high temperature of the corona (Meyer-Vernet, 2007). However, the major radiation hazard is not coming from this wind but from solar particle events such as solar flares or Coronal Mass Ejections (CME).

Possible scenarios to cultivate cyanobacteria on the Moon 49 Radiation

The solar wind is sometimes distorted by bursts of plasma called CMEs or solar storms in popular language. They release huge quantities of matter and electromagnetic radiation and consist out of a plasma of mostly electrons and protons but also of heavier elements such as helium, oxygen and iron. The ejections originate from active regions on the Sun’s surface associated with sunspots. It is the magnetic reconnection of the field lines that causes a massive release of energy. When the solar cycle is at its maximum activity, the Sun generates around three CMEs a day and when it is at its minimum about one CME every five days (Fox, 2006). Coronal Mass Ejections are often associated with other forms of solar activity, most notably solar flares, but a causal relationship has not been established.

A solar particle event occurs when protons and nuclei like helium ions and HZE ions, emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated with Coronal Mass Ejections. These high energy protons and ions cause several effects. They can penetrate the Earth's magnetic field and cause ionisation in the ionosphere. Energetic solar protons are also a significant radiation hazard to spacecraft and especially astronauts, who can receive large amounts of absorbed dose from the ionising radiation (Bevill, 2013).

9.1.3. Van Allen Radiation Belts

A spacecraft, travelling to the Moon, needs to pass two radiation belts which surround the Earth (figure 23). They consist out of particles trapped in the magnetic field of the Earth. The inner belt is located between 1 and 3 Earth radii and contains primarily protons with energies exceeding 10 MeV. The outer belt contains mainly electrons with energies up to 10 MeV. It is produced by injection and energy events following geomagnetic storms, which makes it much more dynamic than the inner belt (it is also subject to day-night variations). Because of the difference between the geographical and magnetic axes magnetic axes, the inner belt reaches a minimum altitude of about 250 km above the Atlantic Ocean off the Brazilian Coast. This South Atlantic Anomaly (SAA) occupies a region through which low-orbiting satellites frequently pass. Energetic particles in this region can be a source of problems for the satellites and astronauts (Bevill, 2013).

Possible scenarios to cultivate cyanobacteria on the Moon 50 Radiation

Figure 23: South Atlantic Anomaly and the Van Allen Belts Source: www.nasa.gov

9.1.4. The Moon

The Moon finds itself at a distance of 384400 km from Earth. The effect of the radiation belts on the Moon is therefore negligible. The particles thus reaching the Moon are coming from the solar wind, Solar Particle Events (or Solar Cosmic Rays in table 2) or Galactic Cosmic rays. Table 2 gives an indication of the different particle energies and the abundances of different particles for the three major radiation sources.

Table 2: Major forms of ionising radiation on the Moon

Possible scenarios to cultivate cyanobacteria on the Moon 51 Radiation

It is quite difficult to characterise the radiation environment on the lunar surface because it is so complex. Radiation on the Moon also includes secondary particles produced by primary particles which interact with the surface of the Moon. As stated before, during the periods in the low solar cycle, the major detection of radiation is from the GCRs. They are primarily composed of high-energy protons in GeV range (table 2). During high solar activity, the CMEs and SPEs are more abundant. A large SPE produces a very intense charged particle radiation composed almost entirely of protons below 150 MeV (Straume, 2008).

The GCRs have huge amount of energies and will also penetrate deeper into material. A 1 GeV proton for example can go through 2 metres of lunar surface and secondary particles generated will penetrate even deeper. In some cases, these secondary radiations are even more damaging biologically than the primary radiations (Straume, 2008). The much lower energies from the solar wind, however, are easier to shield.

The dose-equivalent rate in interplanetary space in solar minimum is estimated to be in a range of 500 mSv to 1400 mSv (Binns et al., 2005). However, the lunar surface is protected by the body of the Moon itself and therefore the dose-equivalent rate is expected to be lower. Although it is difficult to model the combination of primary and secondary particles produced in the lunar regolith together with the topography, Adams et al. estimated the effective dose- equivalent in 2007 about 300 mSv/y average for the lunar surface. The Earth’s surface receives 3.8 mSv/y in comparison, which is about 100 times lower than the Moon. This is expected not to be dangerous in the short-term but health risks associated with radiation (cancer for example) may increase on the long-term. Because these doses are primarily from GCR, they are unlikely to be substantially reduced by shielding (Straume, 2008).

In solar maximum, however, the SPEs and CMEs pose a different challenge: Protons from SPEs can be shielded better than the GCRs but they still pose a substantial acute health risk for astronauts exposed during a lunar Extra Vehicular Activity (EVA). As earlier stated the Solar Particle Event in 1972 could have induced 15000 mSv to the skin and 2000 mSv to the marrow which could be lethal (Wilson et al., 2006).

9.2. Implications for Arthrospira

The long term presence in space requires a Life Support System that can handle the harmful radiation. In a paper by Rea et al. in 2008 space radiation experiments with cyanobacteria

Possible scenarios to cultivate cyanobacteria on the Moon 52 Radiation

were performed. In one of the experiments, sources of radiation on the ground were tested on Arthrospira platensis (Table 3). A source facility was the Dosimetry Division of the Joint Research Centre (JRC) at Ispra, Varese, Lombardy, Italy, where gamma radiation was obtained using a 60Co source. Another source facility was CERN (Conseil Européen pour la Recherche Nucléaire) where they made use of a Super Proton Synchrotron, to test neutrons

Table 3: Ionising radiation used in ground experiments on Arthrospira platensis Source: Rea et al., 2008

In table 4, the Fv/Fm and the oxygen production are shown which was measured on different kinds of radiated cyanobacteria. The Fv/Fm ratio is a parameter which is widely considered to be a sensitive indication of photosynthetic performance in comparison with healthy samples and is used as a stress factor. This ratio, together with the oxygen evolution, was measured during exposure to gamma radiation. The values were obtained as a difference between the photosynthetic efficiency of irradiated and non-irradiated samples as a percentage of the control. The exposure to gamma rays was for 20 minutes which created a total dose of 8400 mSv with illumination conditions at 70 µE. This dose is equal to a 28 year long stay on the surface of the Moon. The Fv/Fm ratio is the least reduced for Arthrospira platensis. The oxygen evolving capacity increased in all the irradiated strains and in particular in Chlorella.

Table 4: Changes in Fv/Fm ratio and oxygen production during exposure to 8400 mSv gamma radiation Source: Rea et al., 2008

Possible scenarios to cultivate cyanobacteria on the Moon 53 Radiation

The length of the mission depends on the amount of nutrients that are brought along in the photobioreactor. This is further discussed in section 10.2.1. A mission-time that would take a couple of months (e.g. 6 months) is a realistic estimate. Since it was earlier stated that the effective dose-equivalent was about 300 mSv/y average on the lunar surface, the effective dose-equivalent of a 6-month mission would not be bigger than 150 mSv. This is estimated for a period without any SPE in solar minimum.

Table 4 indicates that Arthrospira platensis is the least sensitive microorganism. It seems that the Arthrospira cells, with large cell cross-sections, and their high content of lipids, antioxidants and enzymes, can partially shield internal structures (such as DNA) from damage. SCK•CEN also performed radiation experiments on Arthrospira and results show that Arthrospira sp. PCC 8005 can survive acute doses up to 1600 Gy of 60Co gamma (dose rate 527 Gy/h) irradiation without any significant cell damage (Badri et al., unpublished). Moreover, several data in the literature address the potential of the multicellular, filamentous cyanobacterium Arthrospira platensis as a life supporting system since it shows also tolerance to heat, high light intensity and alkaline environment (Lehto et al., 2006). Other bacteria in the MELiSSA loop such as R. rubrum are more sensitive to the radiation (Mastroleo et al., unpublished).

Although Arthrospira inside the photobioreactor is resistant against high doses of radiation, the equipment and instruments are not. The photobioreactor should therefore be radiation hardened although the different techniques and shielding are not discussed in this thesis. In section 8.2, it was already suggested to plant the photobioreactor below the ground to create a stable thermal environment. Section 9.1 shows that in GCRs a 1 GeV proton can go through 2 metres of lunar surface and generates secondary particles in addition. Other radiation sources, however, cannot penetrate as deep into the surface as high energy GCR protons. A lot of radiation risks could therefore be mitigated by planting a photobioreactor below the surface.

Possible scenarios to cultivate cyanobacteria on the Moon 54 Regolith

10. Regolith

10.1. Regolith on the Moon

10.1.1. Origin of the Moon

The scientific consensus about the origin of the Moon is that it is probably formed 4.5 billion years ago. A collision of the Earth with a Mars-sized object could have ejected raw materials into space that eventually became the Moon. Shortly after the accretion of the Moon, its outer layers existed in the form of a magma-ocean as deep as 500 km (Christiansen & Hamblin, 2007). Crystallisation within this magma-ocean produced plagioclase feldspar crystals, which floated to the surface because they were lighter than the melt. Plagioclase feldspar formed an anorthositic crust about 50 km thick on the surface. Anorthosite forms a group of rocks with other plagioclase-rich rocks that belong to the oldest rocks (4.4 billion years old) on the lunar surface. It can be found in the highlands on the Moon, which are the bright areas on the surface of the Moon today. Part of the significance of anorthosite is that it records a thermal event very early in the Moon's history, long before the development of Maria basalts and even before the period of intense bombardment that formed the craters of the lunar highland (Christiansen & Hamblin, 2007).

The dark zones on the surface which are visible from Earth are Maria basalts. They are younger (less than 3.9 billion years old) than the anorthosite on the highlands. Exactly how these Maria basalts are formed and why they only appear on the near side of the Moon is still debated by the scientific community. In 2011, planetary scientists Erik Asphaug and Martin Jutzi published a study, proposing that the uneven distribution of Maria occurred because the Moon collided with another, smaller Moon of the Earth, a few million years after its formation. In this low-impact collision, the smaller Moon was crushed into the surface of the Moon, thickening the Moon's crust on one side. Subsequent impacts broke through the crust and released lava, only where the crust was thin, leading to the observed uneven distribution of Maria. Most of the igneous rocks collected from the Moon's Maria are very similar to terrestrial basalt, the most common rock in Earth's crust. Like anorthosite, basalts were once totally molten, as is indicated by their gas bubbles, interlocking crystalline textures, and compositions. Basalts differ from anorthosites in their mineral constituents. The principal minerals found in lunar basalt are plagioclase, pyroxene, ilmenite, and olivine, all found in terrestrial basalt. Only minor amounts of a few minerals previously unknown on Earth were

Possible scenarios to cultivate cyanobacteria on the Moon 55 Regolith

found (Christiansen & Hamblin, 2007). They are less reflective than the highlands as a result of their iron-rich compositions, and hence appear dark to the naked eye.

10.1.2. Regolith

The Moon's surface is covered with a thin layer of relatively loose, unconsolidated fragments of rock, crystals, and glass. These particles vary in size from large boulders to fine powder. This layer is called the regolith. The average thickness of the regolith depends upon the age of the surface on which it has been formed. The regolith on the Maria is averagely 5 metre thick and the regolith in the older highlands is possibly more than 10 metres thick. As a general rule, the older the surface, the thicker the regolith (Christiansen & Hamblin, 2007).

The surface of the Moon is modified by impacts that are the major factors in fragmenting solid rocks and developing a regolith. There is, in addition, a type of microscopic space weathering that occurs on the Moon. Since the surface of the Moon is unprotected by an atmosphere or global magnetic field, the regolith is continually bombarded by micrometeorites, solar winds, and GCRs. The net effect of this bombardment is to slowly change the regolith with time. One important change is the welding of particles together to glass generated by impact forming glass-bonded aggregates. Thus, the outer few centimetres of the lunar surface is where interactions between space processes and the Moon take place (Christiansen & Hamblin, 2007). Samples taken metres under the surface, however, could give information about the solar wind and solar interaction with the Moon billion years ago.

10.1.3. Composition

The chemical composition of the regolith is different, depending on where it can be found. The regolith in the Maria is rich in iron and magnesium and has a low percent in silica, just as the basaltic bedrock on which it is formed. The regolith in the highlands is rich in aluminium and silica, just as the rocks in those regions (Heiken et al., 1991). The average chemical concentration samples, taken back from the Apollo missions, are shown in figure 24. Note that there are much less samples from the lunar highlands due to the fact that almost all the missions landing spots were in the lowland Maria.

Possible scenarios to cultivate cyanobacteria on the Moon 56 Regolith

Figure 24: Concentration of elements on lunar highland, lunar lowland and Earth. Source: http://www.permanent.com/l-apollo.htm

10.1.4. Volatiles

As discussed earlier the solar wind consists out of mostly hydrogen, helium and some trace elements of heavy ions and atomic nuclei like carbon, chlorine, nitrogen, etc. They hit the lunar surface and insert themselves into the mineral grains for billions of years and can be extracted by heating (Feldman et al., 1998). Regolith samples from Apollo 11 and Apollo 12 were returned to Earth and analysed for the volatiles they emitted when heated in a vacuum (figure 25).

Possible scenarios to cultivate cyanobacteria on the Moon 57 Regolith

Figure 25: Gas release pattern for Apollo 11, soil sample 10086.16 Source: Gibson & Johnson, 1971

The regolith samples were exposed to Earth air and may have picked up some volatiles in transport. Any volatiles coming out below 125 °C was taken to be from Earth because, as earlier discussed, the regolith is heated to 125 °C on a lunar day. Between the temperatures of 125 °C and 700 °C substantial amounts of hydrogen, water, carbon dioxide, and helium came off the samples. In this temperature range the molecules must have been adsorbed on the surface of crystal grains and not bound in chemical compounds. These temperatures are probably achievable by the use of concentrated solar energy. Between the temperatures of 700 °C and 1400 °C additional volatile materials come off including substantial amounts of nitrogen, carbon monoxide, hydrogen sulphide, and finally oxygen. These volatiles probably represent the breakdown of more complex compounds (Gibson & Johnson, 1971).

In sections 7 and 8 the existence of permanently shadowed craters on the North and South Poles were discussed. Indeed these craters could reach temperatures down to 35 K or -238 °C. This is so cold that almost all volatiles that find their way there become trapped. Ongoing micrometeorite impacts cover them with dirt, further isolating them from exposure and possible escape. Indeed both Lunar Prospector and recently the Lunar Reconnaissance Orbiter indicate the presence of hydrogen at the Poles. Water cannot persist on the Moon surface but seems to be abundant as water ice in these permanently shadowed craters

Possible scenarios to cultivate cyanobacteria on the Moon 58 Regolith

10.2. Implications for Arthrospira

10.2.1. Chemical elements needed for Arthrospira

Arthrospira is an aquatic and photosynthetic organism. Liquid water is not available on the surface of the Moon but could be abundant in the form of water ice on the Poles. How exactly this water ice could be excavated will be a future topic of debate because the bottoms of the craters could be as cold as 35 K or -238 °C. Perhaps it is possible to warm up the craters in some kind of way to extract liquid water from the Moon, although this sounds rather ambitious.

In table 1, the chemical elements needed for the growth of Arthrospira are presented: carbon, oxygen, nitrogen and sulphur are all available in the lunar regolith. Volatiles like carbon and nitrogen (figure 24) can be heated out of the lunar regolith although the amount is respectively low. Their origin lies in the radiation from the solar wind. In Pole craters the volatiles could be deposited over billions of years. Sulphur and especially oxygen are relatively abundant on the Moon’s surface. Phosphor is available in very little amounts.

Although most essential elements are abundant, the efficient excavation of these volatiles would be rather difficult. Maybe in the future it is possible to use the volatiles as a life support, but in this thesis it is just proposed to use an optimised medium for Arthrospira to grow in. A Zarrouk medium (table 5) is proposed for this thesis. The amount of Zarrouk medium will have an influence on the duration of the experiment. Whenever the vital chemical elements for Arthrospira will be used up, the growth of Arthrospira will stop and death is inevitable. In the future, however, a full Bioregenerative Life Support System like MELiSSA would provide continuously the needed elements for Arthrospira, produced by the waste from the astronauts.

Table 5: Zarrouk medium for 1 litre water Source: Feng et al., 2006 Elements g/litre

NaHCO3 18.0

NaNO3 2.5

K2HPO4 0.5

K2SO4 1.0 NaCl 1.0

Possible scenarios to cultivate cyanobacteria on the Moon 59 Regolith

CaCl2 0.04

Na2EDTA 0.08

10.2.2. Implantation on the Moon

The lunar dust is very destructive and could cause difficulties for future missions. The abrasive nature of the dust particles may rub and wear down surfaces through friction and cause instrumental damage. It has a negative effect on gaskets which seal the equipment from space and is harmful for solar panels. In addition it would also be dangerous for the astronaut’s lungs, nervous and cardiovascular system (Taylor and James, 2005). There is some evidence that the Moon may have a tenuous atmosphere of moving dust particles constantly leaping up from and falling back to the Moon's surface which is called electrostatic levitation. This dust particles would stick on anything as witnessed in the Apollo missions.

In previous sections, the benefits of implanting a photobioreactor below the surface are already mentioned. Also, the harmful moving dust particles, would not cause any difficulties when the bioreactor is placed below the surface.

Another possibility is presented in this thesis in relevance to the lunar surface. Basaltic lava flows create sub-surface tunnels on the Moon which are called lunar lava tubes (figure 26). When the surface of the lava tube cools down, it forms a hard outside that contains the ongoing lava flow beneath the surface. After the lava-flow diminishes, the tunnel may become drained and forms a hollow void. Lunar lava tubes are formed on surfaces that have a slope that ranges in the angle from 0.4° to 6.5° (Greeley, 1971). One such area containing lava tubes and rilles is the Marius Hills region. In 2008, an opening to such a lava tube in this area may have been discovered by the Japanese Kaguya spacecraft (Handwerk, 2009). There may also be lava tubes in the Mare Serenitatis (Coombs & Hawke, 1992). Lunar lava tubes are typically found along the boundaries between lunar Maria and highland regions and could lay under 40 metres of basalt. This would give ready access to elevated regions for communications, basaltic plains for landing sites and regolith harvesting, as well as underground mineral resources (Walden et al., 1998). Figure 18 indicates that below the surface a stable temperature of -23 °C can be found for the equatorial regions. In addition would the lunar lava tubes shield human bases from radiation and meteorites.

Possible scenarios to cultivate cyanobacteria on the Moon 60 Regolith

The lunar lava tubes could be a possibility for a future human base. However, these tubes which are mostly found on the near side of the Moon around the Maria would not provide a lot of illumination. The cultivation of Arthrospira, which is highly dependent on illumination conditions, would therefore not be preferable here, if solar cells are used as a power source. If a nuclear reactor (section 15.4) is used, there is no illumination issue anymore and it would be possible to drive the photobioreactor in such a lunar lava tube.

Figure 26: Sketch of a possible entrance of a lunar lava tube Source: www.nasa.gov

Possible scenarios to cultivate cyanobacteria on the Moon 61 Gravity

11. Gravity

11.1. Gravity on the Moon

The Moon, with its 1737,10 km radius, has a lower gravitational field than Earth. The acceleration due to gravity on the surface of the Moon is 1.6249 m/s2. That is 16.7 % or about 1/6th of the gravitation here on Earth. Over the entire surface, the gravity variation is about 0.0253 m/s2. Because weight is directly dependent upon gravitational force, things on the Moon will weigh only 16.7 % of what they weigh on the Earth (Hirt & Featherstone, 2012). The red dots in figure 27 are mascons, which are large positive gravity anomalies associated with some of the giant impact basins.

Figure 27: Gravitational anomalies at the surface of the Moon Source: Hirt & Featherstone, 2012

11.2. Implications for Arthrospira

The microgravity space environment causes some difficulties for the human body: Muscle atrophy, bone loss, fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders and a weakening of the immune system. However, the biological effects of reduced gravity instead of microgravity are largely unknown. Whether the reduced gravity causes the same biological changes similar to

Possible scenarios to cultivate cyanobacteria on the Moon 62 Gravity

microgravity but slower or is there some kind of threshold involved that should be passed, is still a topic of debate.

The effects of microgravity on Arthrospira are currently being investigated by SCK•CEN. However, the reduced gravity on the Moon is not expected to danger the mission and would not be a critical factor in this thesis.

On the other hand, technical problems do have to be discussed in relation to cultivating Arthrospira in reduced- and microgravity. Gas/liquid separation processes on Earth are very much dependent on gravity, and are very challenging to be efficiently achieved in space. The

O2 generated by Arthrospira in the Zarrouk medium is toxic for this organism. In microgravity the produced O2 bubbles would stay in the medium and not ascend like here on

Earth. This would cause O2-stress and inhibition of the photosynthesis process. To efficiently harvest the oxygen gas from the medium (to be supplied to astronauts) a mixer could be used. Hence, porous membranes that let only gas through and keep the liquid inside the photobioreactor seemed preferable to dense membranes (Cogne et al., 2005).

Possible scenarios to cultivate cyanobacteria on the Moon 63 Meteorites

12. Meteorites

12.1. Meteorites on the Moon

Because the Moon has no real atmosphere like the Earth has, meteoroids do not burn up and more impacts are observed on the Moon. These objects range from submicron dust to large comets and asteroids. Lunar impacts can help planetary science because these impact craters provide windows into the crust. Different methods and techniques can be used to study the impacts. As the meteoroids impact the lunar surface, their kinetic energy is partitioned into the excavation of craters, the production of plumes associated with a flash of light, and the generation of seismic waves that propagate through the Lunar interior (Oberst et al., 2012).

In the past meteorites have been divided into three categories. The first category were stony meteorites which were mainly composed out of silicate mineral. Iron meteorites consist out of iron-nickel and stony-iron meteorites contain large amounts of metallic and rocky material. However, in the modern classification of meteorites, they are divided into groups according to the structure, mineralogy and chemical and isotopic composition. Meteorites smaller than 2 mm are classified as micrometeorites (Committee on Meteorite Nomenclature, 2012).

12.1.1. Asymmetries in meteorite fluxes

12.1.1.1. Nearside/farside

The Earth has a stronger gravity field than that of the Moon. It will therefore change the orbits of impactors on the Moon. In the past it has been suggested that the gravitational effect of the Earth would cause more meteorites to crash on the lunar nearside rather than the farside (Wiesel, 1971). Bandermann and Singer claimed in 1973 that whether the Earth’s gravity will act as a lens or a shield depends on the velocities of the meteorites and the distance between Earth and Moon. Recent studies, however, (Le Feuvre & Wieczorek, 2011) conclude that nearside/farside asymmetry is negligible in the present situation. In the very distant past, though, the Earth could have served as a gravitational shield for the Moon and this would reduce the nearside crater production.

12.1.1.2. Equatorial versus polar regions

Larger meteoroids typically approach from low inclination heliocentric orbits, which means that the flux at lower latitudes will be higher than on the Poles (Oberst et al., 2012). In a paper

Possible scenarios to cultivate cyanobacteria on the Moon 64 Meteorites

by Le Feuvre and Wieczorek in 2008 the latitudinal variation of cratering rate is modelled. They estimated a polar-to-equator ratio of 0.9. Primary cause to this asymmetry is the significant number of impactors with low inclination. In their paper of 2011 they estimated the ratio on 0.8 instead of 0.9.

12.1.1.3. Leading versus trailing effect

It was mentioned earlier in the illumination section that the Moon is tidally locked with the Earth. This synchronous rotation causes the leading side of the Moon to intercept more impactors than the trailing side. In addition the Moon revolves around the Earth with a speed of ~1 km/s and head to head collisions with meteorites on the leading side will therefore be more energetic than impacts on the trailing side (Oberst et al., 2012). Recent models show a small asymmetry indicated a leading to trailing ratio of ~1.3 to 1.4 (Le Feuvre & Wieczorek, 2008).

12.1.2. Micrometeorites

A micrometeorite has a size smaller than 2 mm. In a paper by Vanzani et al. in 1997 the micrometeroid flux on the lunar surface is modelled. They used the model of Love & Brownlee (1993) that calculated the flux of micrometeorites on the Earth and adapted that with lunar parameters. The cumulative lunar micrometeoroid flux for both the Moon and the Earth are shown in figure 28.

Figure 28: Comparison between the cumulative micrometeoroid flux on the Earth (dotted line), and the rescaled cumulative micrometeoroid flux on the Moon (continuous line). Source: Vanzani et al., 1997

Possible scenarios to cultivate cyanobacteria on the Moon 65 Meteorites

They conclude that a surface of about 150 m2 on the Moon is hit, on average, by one micrometeoroid larger than 0.5 mm in diameter per year. An object of that size, impacting with an average velocity of about 13 km/s, excavates in aluminium alloy material of an hypothetical lunar basis, a crater with diameter larger than about 1.8 mm and depth greater than about 1 mm. Micrometeoroids of about 0.1 mm in size can produce craters of 350 μm in diameter and of comparable depth in metal targets (Vanzani et al. 1997).

12.2. Implications for Arthrospira

If mankind wants to establish a lunar base it has to mitigate the risk of being hit by a meteoroid. Although the risk is fairly low, the longer the stay on the Moon, the greater the risk becomes of being hit by a meteoroid or micrometeoroid. From figure 28, it is clear that the flux of micrometeoroids is higher for smaller sizes of space dust. Although these small impact craters are no catastrophic events for lunar bases, they still could damage space suits en instruments and cause a lot of difficulties. A good solution to counteract these meteorites could be the establishment of a base below the surface. Indeed the lunar regolith would function as a shield against the micrometeorites. Larger impacts could still damage the base though. In section 10.2.2 the lunar lava tubes are mentioned and could also not only shield from radiation but additionally to meteorites. Some tubes exist for more than 100 million years and could be dozens of metres below the surface and could therefore also protect the settlement against larger meteoroids. For this thesis, the implementation of a bioreactor on the Moon, implies the same reasoning as mentioned before. A photobioreactor 1 metre below the surface could already mitigate the impacts of micrometeorites. The chance that a large meteorite could jeopardize the mission is very low but is still possible. If the photobioreactor is powered by solar cells, the location on the Poles is preferable. In case legal issues about nuclear power sources in space are resolved, it would be possible to use a nuclear reactor and an implementation in such a lunar lava tube would be possible. The 40 metres depth of such a lunar lava tube would provide more shielding against bigger meteorites than a location on the Poles, 1 metre below the surface.

Possible scenarios to cultivate cyanobacteria on the Moon 66 Magnetism

13. Magnetism

13.1. Lunar magnetic anomalies

The Moon does not have a global magnetic field like the Earth has today. The magnetosphere of the Earth looks like a dipole and is generated by the molten core of the Earth. The solar wind distorts the dipole and on the night side, the Earth has its magnetotail (figure 21). However, the Moon does seem to show some variations in magnetisation although this is almost entirely crustal in origin. Figure 29 shows the two Poles with lunar magnetic anomalies which are found on 30 kilometres altitude above the surface and could be a few hundred nano-Tesla (µT) on the surface (Phillips, 2006).

Figure 29: Lunar magnetic anomalies Source: Wieczorek et al., 2012

The origin of these patches of magnetic anomalies is still a cause for scientific debate and still no consensus is reached. The anomalies do seem the strongest on the antipodes of the lunar impact basins “Mare Imbrium” and “Mare Orientale”. Bob Lin of UC Berkeley, who has been studying the magnetic anomalies for almost 40 years gives a possible explanation:

"Almost four billion years ago, the Moon had a liquid iron core and a global magnetic field. Suppose an asteroid hit the Moon. The blast would make a cloud of electrically conducting gas ('plasma') that would sweep around the Moon, pushing the global magnetic field in front of it. Eventually, the cloud would converge at a point directly

Possible scenarios to cultivate cyanobacteria on the Moon 67 Magnetism

opposite the impact, concentrating the magnetic field at that point." Eons later, the Moon's core cooled and its global magnetic field faded away. Only the strongest, tangled patches remained” (Phillips, 2006)

Another theory by Wieczorek et al. in 2012 proposes that the anomalies on the Far side could be explained by highly magnetic extra-lunar materials from the asteroid that formed the largest and oldest impact crater on the Moon: the South Pole Aitken basin. This basin is indicated on figure 29 with a white ellipse.

Whatever the case is, it appears that these little patches of magnetisation may be capable of creating perhaps the smallest magnetospheres in the solar system and shielding little regions of the surface from the bombardment of the solar wind. These regions are marked by curious "swirl" patterns that are observable when looking at the reflectivity of the surface, and may be a result of this shielding (Farrell, 2012). Indeed these swirly patches are much whiter than the surrounding area and do not seem to have any correlation with topography or different kind of regolith. One of the most famous swirls, the Reiner Gamma Swirl, is shown in figure 30). The whiter areas could be explained by the magnetic anomalies in the following way: Moon dust is normally darkened by long exposure to the solar wind. The magnetic fields, however, could deflect the solar wind and would therefore get less exposure. If so, lunar swirls are merely a shadow of the magnetic forces arching above them (Phillips, 2006).

Figure 30: Reiner Gamma Swirl Source: http://www.astrosurf.com

Possible scenarios to cultivate cyanobacteria on the Moon 68 Magnetism

13.2. Implications for Arthrospira

Magnetotactic bacteria synthesise magnetic iron nanominerals, which function as tiny compass needless that allow the microbes to navigate using magnetic field lines (SCK•CEN, 2012). However, Arthrospira is not such a magnetotactic bacteria and therefore does not directly sense the magnetic field on Earth, and thus is not expected to experience direct effects of the magnetic field on the Moon. The lunar magnetic anomalies do protect the surface from harmful radiation coming from the solar wind, though. In future possible locations for a lunar base, these “swirls” could additionally protect astronauts from radiation and could mean the difference between life and death. In section 9.2, the survivability of Arthrospira against the harmful radiation was already discussed. It seems that Arthrospira is not so sensitive to the radiation and this factor is therefore not critical in this thesis.

Possible scenarios to cultivate cyanobacteria on the Moon 69 Other obstacles

14. Other obstacles

14.1. Legal issues

If all these harmful factors from previous sections could be overcome, there would still be a less obvious difficulty, namely the political and legal issue. The Outer Space Treaty which is signed in 1967 and ratified by 102 parties explicitly forbids any government from claiming a celestial resource such as the Moon, claiming that they are the "Common heritage of mankind" (Frakes, 2003). Art. II of the Treaty states that:

"Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means."

In previous chapters, the possible excavation of volatiles in the lunar regolith is discussed. However, a nation, or private company faring with the flag of that nation, cannot claim these resources since they are common heritage of mankind. A permanent lunar base would therefore also be a common heritage of mankind and no nation can claim an area on the Moon for its own private base.

Another legal issue that has to be addressed is the biological contamination of a celestial body. Because it is the wish of the scientific community to preserve the pure nature of a celestial body, a planetary protection principle was designed in the past. This principle finds also its legal basis in Article IX of the Outer Space Treaty which claims that:

“States Parties to the Treaty shall pursue studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose.”

In this article both the forward and back contamination are discussed. Forward contamination is the transfer of life from Earth to another celestial body and back contamination is the possibility to bring extraterrestrial organisms into the Earth’s biosphere. An example of this was the intentionally commanded crash from the Galileo spacecraft into Jupiter. Galileo had not been sterilized, so to prevent forward contamination of its Moons, a plan was formulated

Possible scenarios to cultivate cyanobacteria on the Moon 70 Other obstacles

to send it directly into Jupiter. This eliminated the possibility it would impact Europa and seed it with bacteria.

The Committee on Space Research (COSPAR) provides recommendations that are tailored to the type of space missions (flybys or landings) and to the different celestial bodies (COSPAR, 2002). These recommendations are categorized into five groups with category I having the least risk of contamination and category V the largest risk. Any mission to the Moon finds itself in category II. In this category there is an interest for studying prebiotic chemistry and the origin of life but for which there is an insignificant probability of contamination with Earth life.

The spacecraft should nonetheless be sterilized before leaving Earth in order to minimize the risk of depositing Earth-originating biological material at the destination. NASA has currently one approved method which is dry heating the satellite (Office of Planetary Protection, 2012). However, in this thesis the implementation of a photobioreactor with cyanobacteria is discussed and whether or not these bacteria are allowed on the surface of the Moon could be a source of discussion. It is clear that Arthrospira could not survive freely on the Moon without a photobioreactor. Anyhow extra levels of containment could be a possible solution for preventing potential leaking of the photobioreactor. And a final full inactivation of the culture on the Moon, after the end of the experiment, e.g. by high temperature (by shutting off the temperature control unit), could be added.

A scenario where the photobioreactor is powered by nuclear energy, could provide other possible locations than the Poles. However, article IV of the Outer Space Treaty claims that:

“States Parties to the Treaty undertake not to place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner.”

Although the photobioreactor is obviously not a nuclear weapon in this thesis, controversy still could arise whether or not the nuclear source could be used as a weapon. In addition, principle 3 of the “Principles Relevant to the Use of Nuclear Power Sources in Outer Space” claims that:

Possible scenarios to cultivate cyanobacteria on the Moon 71 Other obstacles

“In order to minimize the quantity of radioactive material in space and the risks involved, the use of nuclear power sources in outer space shall be restricted to those space missions which cannot be operated by non-nuclear energy sources in a reasonable way.”

This thesis discusses both the possibilities of using solar power and nuclear power. As will be discussed in section 15, implementing a photobioreactor with a solar power source could be possible and would therefore exclude the need of nuclear energy (principle3). Controversy and legal issues should be resolved first before a nuclear reactor could be used in this mission.

14.2. Launch, timing, implementation and deployment

When a biological experiment is sent to space (e.g. the International Space Station), typically the cells or organisms are launched sent in an inactive state (e.g. dried, frozen, dormant). This is because the rockets allow only minimal power to the payload during launch and flight, for safety and technical reasons. Once in orbit or in the station, e.g. in the biolab, located in the Columbus module of ISS, these cells or organisms are activated again and the cultivation process can begin. A similar scenario will probably have to be implemented for cultivating Arthrospira on the Moon in a photobioreactor. If temperature control is provided during the 3- day trip to the Moon, the bacterium can be stored in active form in the dark (for max. 15 days, as described above) and reactivation of the bacteria by adding growth medium and switching illumination would be feasible.

The duration of the mission would depend on the amount of nutrients that are provided for Arthrospira to grow in. A Zarrouk medium that would last for a month or a couple of months (e.g. 6 months) seems like an appropriate period for the duration of the experiment. Whenever the nutrients in the Zarrouk medium are all used up, the experiment is finished.

In section 8.1 the temperature in the summer at the Poles is described. Figure 19 shows that temperatures here can climb up to a steady 25 °C during the summer. If the mission could be timed, so that the experiment would take place in the summer, the thermal control system would need much less power to provide suitable temperature conditions for Arthrospira. If the mission would be timed in winter, the photobioreactor should be able to handle temperatures of -180 °C which is of course less favourable.

Possible scenarios to cultivate cyanobacteria on the Moon 72 Possible scenarios

15. Possible scenarios to cultivate Arthrospira on the Moon

It is clear from previous chapters that installing a photobioreactor with Arthrospira on a certain location on the Moon, is not a straightforward decision. The different parameters influence the selection of an adequate site. Some factors are beneficial for Arthrospira to cultivate, others threaten a successful mission. If mankind ever wants to establish a lunar base, one of the first steps should be to investigate the hostile environment and assess the risk and difficulties for the different locations on the Moon. Previous sections in this thesis gave an overview of these issues and a summary can be found in table 6. In a next step the operation of a successful completely autonomous Bioregenerative Life Support System (BLSS) like MELiSSA should be tested and confirmed. The objective in the future, is that Arthrospira would provide oxygen, water and food to a human crew in space and the waste of the human crew could be broken down by different compartments to eventually serve as nutritious components for Arthrospira. In this thesis, however, the goal was to assess the possibility of planting a photobioreactor with Arthrospira on the Moon, cultivated in a nutritious medium. As discussed earlier, Arthrospira is a key-component for MELiSSA and when Arthrospira would not survive on the Moon, it would jeopardize the whole MELiSSA concept. In the next section some locations and scenarios are proposed that would increase the possibility of cultivating Arthrospira on the Moon.

Possible scenarios to cultivate cyanobacteria on the Moon 73

Table 6: Possible locations to cultivate Arthrospira on the Moon Source: Schockaert, 2013 South Pole North Pole Near side (equator regions) Far side (Equator regions) Illumination  Up to 93 % of the year on  Up to 90 % of the year on Almost 15 Earth days light Almost 15 Earth days light rims of craters on surface rims of craters on surface followed by almost 15 Earth followed by almost 15 Earth  Permanently shadowed  Permanently shadowed days dark days dark regions in craters regions in craters Temperature on surface  On rims: Summer ~ +25 °C  On rims: Summer ~ +25 °C Day: ~ +120 °C Day: ~ +120 °C and winter ~ -180 °C and winter ~ -180 °C Night: ~ -150 °C Night: ~ -150 °C  In craters down to ~ -250  In craters down to ~ -250 °C °C Temperature at 1 metre Variable with topography but Variable with topography but ~ -23°C stable ~ -23°C stable below surface for 85 °S: ~ -125°C stable for 85 °N: ~ -125°C stable Radiation Least Least Less Most Regolith Depends on lunar highland/ Depends on lunar highland/ Depends on lunar highland/ Depends on lunar highland/ lowland instead of latitude lowland instead of latitude lowland instead of latitude lowland instead of latitude Volatiles Trapped in permanently Trapped in permanently Inserted by solar wind in Inserted by solar wind in shadowed regions shadowed regions mineral grains (< far side) mineral grains (> near side) Water Water ice in permanently Water ice in permanently Inserted by solar wind in Inserted by solar wind in shadowed regions shadowed regions mineral grains (< far side) mineral grains (> near side) Lunar lava tubes none none Found on boundaries between Found on boundaries between lunar highland/lowland lunar highland/lowland Magnetic field No lunar magnetic anomalies No lunar magnetic anomalies Some Lunar magnetic A lot of Lunar magnetic anomalies anomalies Meteorites 10-20 % less than on equator 10-20 % less than on equator 10-20 % more than on Poles 10-20% more than on Poles Communication to Earth High percent on elevated areas High percent on elevated areas Always Never

Possible scenarios

15.1. Preferred scenario using solar power

Although the rest of the parameters could also provide benefits or disadvantages, the critical factors on the Moon for cultivating Arthrospira are sufficient nutrients, illumination conditions and the temperature. Sunlight illumination is only essential if solar cells are used as a power supply. In the following scenarios, a solar energy source is used. In section 15.4 scenarios are suggested which rely on a nuclear power source.

There are some chemical elements abundant in the lunar soil that could be nutritious for Arthrospira (carbon, oxygen, nitrogen, sulphur). These quantities are very limited though and the possible excavation of these elements is still up for scientific debate. The lunar Maria are richer in magnesium and iron than the lunar highlands and would provide additional nutrients for Arthrospira. But for a first-step stand-alone bioreactor experiment, an optimized Zarrouk medium will need to be brought along from Earth to provide the nutrients. In the future integrated MELiSSA system, however, nutrients for cyanobacterial cultivation can be obtained from waste degradation.

Illumination conditions on the Moon are extremely different than here on Earth. The equator receives ~ 50 % illumination in a year but with periods of almost 15 Earth days that it receives sunlight, followed by almost 15 days it remains in the dark. Some areas on the Poles deep inside the craters receive no direct sunlight at all, while rims on the craters could receive sunlight almost the whole year through. Indeed an area next to the Shackleton crater on the South Pole receives 93 % sunlight in a year and that could increase with the use of a mast which would raise the amount of sunlight to almost 96 %. The longest total night at the surface of the most illuminated spot is 5.88 Earth days while the longest total night for a 10 metre mast is 2.75 Earth days. In section 7.2 the survivability of Arthrospira in long periods of darkness is discussed. Arthrospira can survive 5.88 Earth days in the dark and this would not cause any difficulties. The almost 15 days of darkness on the equator would also be survivable for Arthrospira but would obviously have a disadvantage in comparison with the Poles. It is impossible to cultivate Arthrospira with direct sunlight on the lunar surface because the extreme UV would break down the filaments and would cause death. Indirect illumination from a LED lamp inside the photobioreactor is thus preferred and could provide adequate light conditions, including an optimal intensity (20-200 µE) and correct spectrum (PAR), and continuous illumination. 75

Possible scenarios

Another big obstacle for installing a photobioreactor on the Moon is the temperature factor. Table 6 shows that no location on, or below, the surface would provide the thermal conditions for Arthrospira to grow in for the whole year through. Although the 25 °C on rims of craters on the Poles in the summer is survivable, the temperature drops to about -180 °C in the winter on these rims. On the equator the temperature rises and drops accordingly to the received illumination of the night and day cycle. Below the surface on the equator the temperature is not influenced anymore by the night and day cycle, about a half metre in the ground and would reach a stable -23 °C.

Thus it is clear that there needs to be a thermal control system that would generate enough heat for Arthrospira to grow in. On both the Poles and below the surface and on the equator only heating would be needed. On the surface of the equator, heating and cooling down would be needed.

The power that the illumination and thermal control systems need, could be generated by solar panels. The more illumination the solar panels receive, the more power that could be provided to the thermal control system. It is therefore proposed in this thesis that the photobioreactor is placed next to the Shackleton crater in the South Pole because this area receives the most illumination on the Moon. An additional mast with solar panels on the top which could adapt to the angle of incoming sunlight, would provide the most power for the thermal control system. Depending on the height of the mast, there would still be some small periods in the dark where no power could be delivered to the thermal control system. A battery that would store extra power from the solar cells is therefore indispensable.

Since the cultivation on Arthrospira now relies on solar panels, it is possible to plant the photobioreactor below the ground (approximately 1 metre). The continuously lit LED-lamp would also be powered by the solar cells. The photobioreactor should be well shielded from the cold and some additional benefits include that: Micrometeoroids and small meteoroids would not damage the photobioreactor, the radiation levels are lower below the surface and abrasive dust that could be electrical levitated from the surface would not stick on the reactor and damage it.

Possible scenarios

15.2. Other possibilities using solar power

Another location, similar to the preferred location next to the Shackleton crater on the South Pole, could be a site on the North Pole. The same difficulties, as discussed in previous section, apply here also. There could be some disadvantages in comparison with the South Pole, however. The first one could be the smaller percent of illumination during the year (up to 90 % on the surface). Another one is a lower topography on the North Pole (figure 10). The craters are deeper in the South Pole, which could mean that there are more trapped volatiles and water ice abundant in these permanently shadowed craters. The higher altitude on the rims could also provide more visibility and thus more direct communication to earth. Although the volatiles and water is not essential for a first stand-alone photobioreactor, the amount of water ice and trapped volatiles could be a huge factor for future lunar base designs. A last, small advantage of the South Pole is a possibility for astronomers to see the galactic centre from there.

Another possible scenario could be the implementation of the reactor below the surface around the equator regions. Advantages of this location are the stable ~ -23 °C all year long. A big disadvantage, however, is the day/night cycle of the Moon. It would be hard to store enough energy in the battery during the day to overcome 15 Earth days of darkness every lunar month. Another disadvantage would be the unavailability of water ice and trapped volatiles in comparison with the Poles for future Moon base plans, though it is not a priority in this thesis. A third disadvantage is the bigger impact risk of meteorites in comparison with the Poles. Some additional advantages could be the installation of the reactor in the lunar Maria. This is a safer landing spot (all the Apollo missions landed in the flat lunar Maria) and it has more iron and magnesium than the lunar highland regolith (possible nutrients for Arthrospira). If the reactor is additionally placed on the near side, there would be a constant visibility and communication from Earth possible.

Arthrospira can survive radiation doses up to 3200 Gy which is far above the lethal threshold for a human being. Although radiation is not the most crucial factor in this thesis, for mankind it forms one of the most difficult barriers to overcome for further space exploration. In this perspective, two further groups of possible locations on the Moon are discussed. Lunar lava tubes could be 300 metre in diameter and could lie under dozens of metre of lunar regolith. Some of them have been existing for hundreds of millions of years and could protect the crew

Possible scenarios

from radiation. A big difficulty here again could be the limited amount of energy from solar cells. Dozens metre of electric cables should be installed from the solar panels to the lunar base, deep inside the lunar lava tubes. Additionally the lunar lava tubes are found on hills between the boundaries of lunar Maria and the highland which would all have an almost 15 day/night cycle. If the photobioreactor is powered by nuclear energy, however, solar cells would not be needed and the big amount of electrical cables neither.

Possible reduced radiation can also be available at the lunar swirls. It is thought that these white areas receive less radiation because of the surrounding lunar magnetic anomaly. The magnetic field would deflect the radiation from the solar wind which would normally darken the regolith.

15.3. General configuration of the photobioreactor using solar power

Figure 31 shows a small sketch of the different modules needed in a photobioreactor for cultivation of Arthrospira on the Moon if solar energy is used. A solar panel that could follow the direction of incoming light from the Sun during the mission, should provide the most efficient power supply for the photobioreactor. A back up battery would be needed in case some dark periods would not be able to provide solar power. The reactor containing the cyanobacteria needs illumination (which is most efficiently provided by a LED), temperature control and a mixer to ensure an efficient uptake of nutrients and the removal of oxygen. The oxygen, which is waste for Arthrospira, but a valuable resource for the space crusaders, should be harvested via an exhaust outlet. A membrane is needed to keep the water inside the reactor while the oxygen-gas is able to escape. In the MELiSSA system, the vital oxygen would of course be delivered to the crew. A control system for the photobioreactor is also required. The bioprocess should follow up the pH-measurements, nitrate- and carbon dioxide concentrations, nutrients flow and measurement of the cell concentration of Arthrospira with an optic density metre. A camera, allowing macro-and microscopic imaging, is optional but could give some further insight in the behaviour of the culture. The control system for the bioreactor should also manage the oxygen valves. When the pressure of the produced oxygen- gas becomes too large, valves should open and release the oxygen through the exhaust outlet. The measurements of the cell concentration, temperature, pH, etc. should be transmitted back to Earth. A communication system should be on board to pass on the data. The whole bioreactor is placed below the ground to diminish the risk of radiation, meteorites, abrasive regolith and varying temperatures. 78

Possible scenarios

Figure 31: Sketch of the compartments of the photobioreactor Source: Schockaert, 2013

It would be a great advantage if the implementation of the photobioreactor on the Moon could be done without any human presence. It could for example be sent to the preferred location as a payload on a lunar lander. The mast, with solar panels mounted on it, could stay at the surface while the photobioreactor could be placed into the surface as a probe. However, more research about this issue should certainly be needed.

15.4. Nuclear power sources

This thesis mainly focuses on the power supply by solar cells. This limits the possibilities of implementing a bioreactor to the Poles, due to the higher yearly illumination in that area. On the equator, however, cultivating Arthrospira or creating a lunar base in the future, will be difficult if we rely on solar panels. Another possibility involving the use of nuclear power sources, is presented here. Even during the Apollo missions on the Moon, this source of energy was already used. SNAP-27 on board the Apollo 12 was one of a series of Radioisotope Thermoelectric Generators (RTGs) and marked the first use of a nuclear electrical power system on the Moon (Seaborg, 1969). It was designed to provide all the electricity for continuous one-year operation of the NASA scientific instruments and supporting subsystems deployed by the astronauts on the lunar surface. It is a cylindrical

Possible scenarios

generator, fuelled with the radioisotope plutonium-238, about 0.5 metre high and 40 cm in diameter, including the heat radiating fins. The generator, making maximum use of the lightweight material beryllium, weighs about 17 kg with fuel (the radioactive material). Thermocouples are placed in the walls of the container, with the outer end of each thermocouple connected to a heat sink. Radioactive decay of the fuel produces heat which flows through the thermocouples to the heat sink, generating electricity in the process. Such a thermocouple is a thermoelectric device that converts thermal energy directly into electrical energy (Seebeck effect). It is made of two kinds of metal (or semiconductors) that can both conduct electricity. They are connected to each other in a closed loop. If the two junctions are at different temperatures, an electric current will flow in the loop. The SNAP-27 produced 63 watts (Seaborg, 1969). This amount is not enough to provide sufficient power for a photobioreactor to maintain illumination and temperature conditions and the other necessary compartments (figure 31). Other RTGs, however, could produce more electrical power. The Galileo spacecraft which was launched in 1989, for example, carried a 570-watt RTG (World Nuclear Association, 2013).

For power requirements over a few kWe, fission systems have a cost advantage over RTGs. When an atom of U-235 or Pu-239 fuel fissions, neutrons are released that trigger additional fissions in a chain reaction at a rate that can be controlled with neutron absorbers. This chain reaction is not available in RTGs. This is an advantage in that power can be varied with demand or shut off entirely for maintenance. It is also a disadvantage in that care is needed to avoid uncontrolled operation at dangerously high power levels. Fission power sources have been mainly used by Russia in the past. An example of this were the Topaz reactors which were aimed to reach 40 kWe (World Nuclear Association, 2013).

Using nuclear power sources for space caused, and still causes, a lot of controversy. Accidents with nuclear sources could be disastrous. An example of that is the Kosmos 954 satellite launched by the Soviet Union in 1977. A malfunction prevented safe separation of its on board nuclear reactor. When the satellite re-entered the Earth's atmosphere the following year it scattered radioactive debris over Northern Canada, prompting an extensive cleanup operation.

For public safety concerns and an international treaty banning nuclear power in space stopped development. Recently nuclear power sources are getting a revival and a large part of the

Possible scenarios

scientific community believes that nuclear energy will be a next step for further space exploration.

In case the legal issues with a nuclear source are sorted out and provided that the concept is safe, a nuclear power source could also be useful for cultivating Arthrospira on the Moon. The constant power supply for many years and the fact that it does not need solar illumination, makes such a nuclear reactor very valuable. When there is no restriction to the Poles anymore, the photobioreactor could be placed anywhere on, or below, the surface.

A robotic mission to the Moon, where the photobioreactor could be carried around the surface by a Moon rover, could drive to nearly any place. A good location to place the photobioreactor would be in an, earlier discussed, lunar lava tube. Indeed the big disadvantage of such a lava tube is the difficult power supply if solar cells are used. Now that a nuclear reactor is used, this disadvantage is overcome. A 40 metres depth below the surface, would still give communication problems to Earth, though.

Conclusion

Conclusions

The goal of this thesis was to examine if there is a possibility that cyanobacteria such as Arthrospira (Spirulina in common language) could one day be cultivated on the Moon for life support purposes.

In the first sections the usefulness of Arthrospira is discussed. Arthrospira has a huge nutritious value, produces big amounts of oxygen and provides clean water. Due to these exceptional characteristics, Arthrospira is a key factor in the MELiSSA system. In this system, developed by ESA and partners (including SCK•CEN), the aim is to create a Bioregenerative Life Support System which provides food, drinking water and oxygen for the crew, by recycling the waste of the astronauts. If mankind ever wants to travel to Mars or construct a permanent base on the Moon, such a Bioregenerative Life Support System is indispensable.

In the second part of the thesis the hostile environment on the surface of the Moon is described. Different harmful factors create other living conditions than here on Earth. Diverse temperature conditions, ionising radiation, reduced gravity, altered illumination from the Sun, different soil than here on earth and increased meteorite risk could all be factors that endanger a permanent human base on the Moon or, as discussed, endanger the implementation of a photobioreactor with Arthrospira on the Moon surface.

These hostile factors differ from one place to another on the Moon. Some areas are therefore more favourable than others and consequently, the main goal of this thesis was to explore a suitable location to implement a photobioreactor with Arthrospira. Although there are multiple possible locations, it is the author’s opinion that illumination and temperature conditions are the crucial factors. Because Arthrospira can only be cultivated between 8 °C and 40 °C and cannot survive direct sunlight illumination conditions, a temperature and illumination control system is vital. The power to that temperature and illumination control system could be provided by solar panels. A site with the most illumination would therefore be the most preferred spot

An area near the Shackleton crater on the South Pole seems to receive the highest percentage of illumination in the year. It is therefore the author’s opinion that this is the most suitable

Conclusion

location. When this photobioreactor is implemented one metre below the surface, possible harmful factors such as radiation, temperature variance, meteorites and regolith could be diminished. If the timing of the mission could be arranged so that the South Pole finds itself in the summer season, favourable temperature on the surface could be provided.

Another possible power source is the use of a small nuclear reactor such as a Radioisotope Thermoelectric Generator (RTG). This way, the photobioreactor is not dependent anymore of illumination conditions and could be implemented anywhere on the surface. A lunar lava tube which could reach depths of 40 metre below the surface, could protect the photobioreactor against possible harmful factors such as radiation, temperature variance, meteorites and abrasive regolith.

In conclusion, in the future it could be possible to implement a photobioreactor with Arthrospira on the moon. However, the knowledge about the Moon is still not complete. Illumination conditions, temperature conditions, amount of volatiles in the craters, etc. are still not fully known. More Moon missions should provide more understanding about the surface of the Moon. Lunar lava tubes have been discovered since 2009, but the inside of such a lava tube is never seen. Robotic missions exploring these tubes are necessary, before a photobioreactor for cultivating Arthrospira is placed at those sites. More research about the cyanobacterium Arthrospira under space environmental conditions is also needed. SCK•CEN is currently investigating the lethal radiation doses on Arthrospira but other factors, such as the behaviour of Arthrospira in reduced gravity or microgravity, is still completely unknown. Flight experiments with Arthrospira in the ISS, such as the ARTEMISS project, could close the knowledge gap of the behaviour of this cyanobacterium in microgravity.

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