Choosing a New Home: How to Determine Which Asteroid to Settle

UAE MBR Settlement Challenge 2018 Project Report

J.L. Galache, PhD Aten Engineering, Inc.

This project received seed funding from the Dubai Future Foundation through Guaana.com open research platform.

Contents

Introduction 1 WeRoam...... 1 Beyond the Horizon ...... 1 Asteroids, the Breadcrumbs of the Solar System ...... 4

Motivation and Goals 7

Method 9 Sources of Data ...... 9 A Matter of Time vs Energy ...... 9 A Matter of Some Gravity ...... 11 Search Parameters for Candidate Asteroids ...... 12 Small Settlement on Small NEA ...... 12 Large Settlement on Large Asteroid ...... 12 Mining Settlement on NEA ...... 13

Results 15

Conclusion 19

Bibliography 21

Appendix – Lists of Candidate Asteroids 23

iii

Introduction

We Roam

The human species has few characteristics that are unique to it, setting it apart from other species on our planet. Humans are not the only animals to use tools, or lan- guage, create societies, feel sorrow and joy, nor take care of our young, wounded and elderly. Sadly, we are also not the only ones to murder and wage war. But we are the only ones so far to write, clothe ourselves, blush, and purposely interrupt our natural sleep to wake up earlier than we would otherwise. While these and other traits have undoubtedly contributed to our perceived success with respect to other species, it is one characteristic in particular which has enabled all our other traits to shine: Our restlessness. The fossil record and DNA analysis show that already 2 million years ago some of our earliest human ancestors, the Homo Erectus, had left their birthplace in Africa and established themselves throughout Europe and reached as far away as China [16]. Humans have ultimately established themselves on every continent of our planet, even when the conditions were so harsh it would have made sense to ﬁnd another land to live in. This could be because humans have another unique characteristic: We can make our home anywhere, and the decision of where this is does not have to depend on the local climate. We are adaptable, we are hardy, and we are stubborn; if we have decided to make a life somewhere, we will do just that. Not all humans are restless; some like to stay just where they are, which is precisely why we have spread throughout the globe. Through circumstance or desire, our ancestors travelled the world, leaving individuals behind to create camps, which became towns, cities, countries, empires. And all throughout the millennia, a subset of people kept travelling and exploring and leaving footprints where none had been left before. Now that we have mastered every climate, every latitude, and every height, it is only natural that some of those restless souls among us look not towards the horizon for challenges, but upwards, away from the safety of Earth’s surface, with its fertile lands, plentiful oceans, and nourishing atmosphere. The allure to keep moving to new lands is as strong now as it was millions of years ago. We should not wave it aside or ignore it; it means we are still human!

Beyond the Horizon

Where in the Solar System would we live were it not on Earth? Mars has long been a favourite of crowds and science ﬁction writers alike; something about it is alluring, even if we can’t quite ﬁgure out what. Its rusty desert landscape is reminiscent of some areas on Earth, and it also hosts an atmosphere (albeit much

1 2 Introduction thinner than Earth’s) which, unlike Venus’s, is transparent, and even hosts familiar clouds floating by on the wind. Of course, the temperatures on Mars are quite extreme: At its warmest, on a Summer day it can reach 20◦C, while in Winter or at nighttime temperatures can plummet to −150◦C. Mars also happens to be quite close to Earth (in astronomical terms) with a one-way trip taking about 8 months. Notwithstanding all the challenges of living on Mars, its appeal remains strong and, apart from the Moon, it has been the favourite destination for human exploration craft since 1960, with 46 missions having successfully been launched towards the red planet since then, and seven more in development and planned to launch within the next few years [14]. The main driver, at least publicly, for many of these missions is the search for life on Mars, or some evidence that it once existed. Thus, Mars has been ripe for science fiction authors to use as their backdrop, or even a protagonist, in their stories. As early as the 19th century, authors were creating tales of trips to Mars, usually recounting the adventures of Earth travellers as they encounter the inhabitants of the red planet [4]. Edgar Rice Burroughs’s popular Barsoom series (11 books written between 1912 and 1964) proves the long- lasting interest of this genre, which inspired the likes of Carl Sagan to one day undertake the scientific exploration of Mars1. Starting in the 1950’s, as scientific knowledge of Mars was beginning to make an inhabited Mars an unlikely scenario (which was confirmed in the 1960’s and 70’s by NASA’s Mariner and Viking programs), fantasy and science fiction authors began incorporating this into their writings and new themes appeared, such as how to settle an empty planet, the challenges of surviving in such a harsh environment, and whether Mars should be terraformed or not. These themes have persisted until today, giving us such science fiction classics as Kim Stanley Robinson’s Red Mars, Green Mars, and Blue Mars trilogy in the 1990’s, all the way through to 2011’s The Martian, by Andy Weir, which could be classified as “realistic sci-fi”, portraying the struggles of an astronaut marooned on Mars and having to survive until a rescue mission arrives. It was only natural that when motion pictures were invented Mars would become a topic of this new medium. Indeed, in 1910 one of Thomas Edison’s pro- duction companies created A Trip to Mars, an almost 5-minute film that portrays a scientist floating to Mars after covering himself in antigravity powder2. Many a Mars-themed story or novel was adapted to the big screen: H.G. Wells’s The War of the Worlds has been adapted several times, Philip K. Dick’s We Can Remember It for You Wholesale became Total Recall; A Princess of Mars was adapted as John Carter; the hugely successful The Martian movie based on the eponymous novel by Andy Weir, etc. [17]. Many more were standalone movies, with over 30 being listed in reference [13]. It is therefore not unexpected that the likes of Elon Musk would grow up dreaming of settlements on Mars and, upon finding himself in a position to make that dream come true, would act upon it and create a series of companies to prop up the endeavour. NASA has long spoken of sending humans to Mars, but Musk actually started working on it. That there is interest beyond the confines of scientists and engineers in going to Mars was made apparent in 2013, when Mars One3, a private Dutch organization

1https://youtu.be/-5fbHkGpILc. 2https://youtu.be/np7VImsSMQM. 3https://www.mars-one.com. Beyond the Horizon 3 proposing to send people to Mars on a one-way trip, received over 200,000 initial submissions of interest from people around the world willing to make that one- way voyage [11]. Much of the interest in settling Mars has stemmed from a desire for adventure, but more pragmatic ideals are coming to the forefront, such as those who see Mars as a backup to Earth, a place where the human race, or at least a small portion of it, can survive in the event of a catastrophic disaster wiping out all life on our home planet. But would not the Moon make for an easier backup location? It is a mere 3 days travel away, compared to 8 months for Mars, and communications back and forth are almost instantaneous, whereas a radio message to Mars can take anywhere from 4 to 20 minutes to arrive there, and just as long to return. The Moon does have a “day” that lasts about 14 Earth days, and a night lasting equally long, while Mars’s day is a familiar 24 hours and 37 minutes long. There are pros and cons, but this has not stopped many from dreaming about lunar bases and frequent trips to the Moon, effectively dividing up Space enthusiasts into two camps: Team Moon and Team Mars. The Moon has had its fair share of literature and cinema dedicated to it, not to mention song and mythology. It has also fed the imagination of engineers and scientists, who have spent decades dreaming up permanent bases on the Moon, with both scientific and commercial purpose. Now these dreams seem closer than ever to becoming reality with both NASA and ESA emphasizing lunar projects in their near-term plans [12, 15, 2], with the added novelty of ISRU (In-Situ Resource Utilization) and private-public partnerships being essential components of their strategies. Even Venus, with its suffocating temperatures (around 450◦C at the surface) and corrosive atmosphere (mostly carbon dioxide with clouds of sulfuric acid) has been the subject of settlement plans, though human outposts would consist of air- filled structures, floating high up in the atmosphere, where temperatures are a balmy 20–30◦C [5]. So far we have only discussed settlements on planetary bodies, because, as Isaac Asimov once pointed out, we are “planetary chauvinists” [7]. Why would we not consider free-floating settlements in space? And indeed, someone has: In the 1970’s Gerard K. O’Neill advocated for the building of what came to be called O’Neill cylinders [6]; these gigantic cylinders would be 8 km wide, and 20–30 km long, and be paired up as parallel counter-rotating cylinders, located at Earth’s L4 or L5 Langrangian points4. The rotation would provide artificial gravity on the inside surface of the cylinders through centrifugal force, and their large diameter would allow for clouds and winds, and thus, weather patterns, to form, which together with the terraformed interior, complete with rivers, mountains and cities, would simulate an Earthly environment. Despite O’Neill cylinders gaining a cult following among space enthusiasts of the era, and promoting the settling of free space, they are still based on recreating an Earthly ecosystem in space, which still retains a tinge of planetary chauvinism. One final option that is left then is to create a habitat on an asteroid, or as suggested in some science fiction novels, inside an asteroid. In fact, a long asteroid could potentially be hollowed out and converted into an O’Neill cylinder. And unlike a

4The Lagrange points are 5 points in the Sun-Earth system where the gravitational pull of the two bodies is cancelled out and a spacecraft can remain at one of them using very little fuel. The L4 and L5 points are located along Earth’s orbit, 60◦ behind and ahead, respectively, of Earth. 4 Introduction settlement in free space, an asteroid could provide valuable resources to be mined by the settlers. Perhaps because asteroids are small compared to planets and moons, and much less flamboyant than their cousins the comets, they have failed to inspire authors the way Mars and the Moon have. Despite this, they have had their small share of literary appearances in Sci Fi; for example, in The Culture novels5 by Iain M. Banks, asteroids are hollowed out and spun up to provide artificial gravity on the inside of the shell through centrifugal force; they are also equipped with faster- than-light space drives and can thus be considered spaceships. Asteroids do figure prominently in The Expanse novel series6 by James S. A. Corey7, which was adapted for TV in 2015, and where asteroid settlement and mining is a central part of the plot. But what is an asteroid? Read on to find out.

Asteroids, the Breadcrumbs of the Solar System

The Solar System was formed some 4.6 billion years ago, out of a massive cloud of gas and dust, at the center of which a star had been born, our Sun. The material orbiting the Sun coalesced into the 8 major planets we now know over the course of a few million years. Other planets were likely created, but were ﬂung out into interstellar space, or into the Sun itself, by interactions by with Jupiter or one of the other giant planets, as their orbits settled into where they are today. Lots of material was left over, and also lots of debris was created when newly formed protoplanets (the progenitors of planets) were smashed to pieces in collisions oc- curring in their crowded orbits. All these smaller pieces of metal, rock, and ice (and combinations thereof) continued orbiting the Sun and came to be known as asteroids and comets. Comets formed farthest away from the Sun, beyond the orbit of Neptune, and thus contain many volatile elements such as water, ammonia, methane, carbon monoxide and dioxide, etc, as well as dust and rock. Asteroids, having formed closer to the Sun, where it was warmer, do not contain many of these volatile elements, as they boiled away, and instead contain mostly rock and metal, with plenty of dust. However, some asteroids do contain water as part of their mineralogical makeup, that is, the water molecules are part of their mineral structure, so it is not in free form as ice or liquid. That said, it is thought that some of the larger asteroids (probably larger than 100 km, and all located in the Main Belt and beyond) might still contain water ice trapped in their interiors [9]. The highest concentration of asteroids in the Solar System is found in the asteroid belt between the orbits of Mars and Jupiter, with over 730,000 asteroids having been found there thus far, and millions more awaiting discovery. But asteroids are ubiquitous in the Solar System, being found everywhere except inside Mercury’s orbit, where it is thought that the Sun’s heat is too high and it eventually breaks up any asteroid that might have wandered into such a close orbit. Of special interest to humans are the Near-Earth Asteroids (NEAs), which have paths that bring them close to, or even cross, Earth’s orbit. There could be as many as 30 million NEAs larger than 10 m [3], though we currently have only discovered around 20,0008.

5https://en.wikipedia.org/wiki/The_Culture. 6https://en.wikipedia.org/wiki/The_Expanse_(novel_series). 7This is the joint pen name of Daniel Abraham and Ty Franck. 8https://minorplanetcenter.net/mpc/summary. Asteroids, the Breadcrumbs of the Solar System 5

NEAs are discovered through the efforts of telescopic surveys that search for asteroids that might impact Earth, either soon or decades from now. The Minor Planet Center (MPC)9 in Cambridge, Massachusetts, logs all positional observations of asteroids and comets and announces new discoveries on an almost daily basis. NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, make long-term impact predictions and keeps a list of hazardous asteroids with even a small chance of impact10. Due to their orbital proximity to Earth, NEAs make easier targets for space missions, and there are currently two missions underway as of the beginning of 2018: JAXA’a Hayabusa2 is visiting asteroid Ryugu11, and NASA’s OSIRIS-Rex is visiting asteroid Bennu12. Asteroids can be broadly categorised into 3 types, based on their composition:

C-type (carbonaceous) They are dark (like asphalt or coal), fragile, and composed of rocky material mostly unchanged since the formation of the Solar System. Some of them contain water in the form of hydrated minerals that can be up to 20% of their weight. They contain metals, up to 30% iron, and signiﬁcant amounts of nickel and magnesium, and other elements too such as silicon, phosphorus, and carbon (only around 2–3%, but enough to give them their dark colour). S-type (stony or silicaceous) They are lighter in colour than C-types, their material stronger than concrete, and some have undergone heating while they formed part of the mantle of a protoplanet. They contain metals, up to 30% iron, with abundant magnesium and silicon, but no hydrated minerals, so no water. M-type (metallic) These asteroids are similar in tone to the S-types, but they are made almost entirely of iron and nickel, with at least 75% of the mass being iron, most of the rest being nickel, and under 1% being other metals. Some M-type asteroids also present evidence of rocky material on their surfaces. As you might expect from an all-metal asteroid, they are very hard. These asteroids likely originate from the cores of protoplanets, which differentiated into a core, a mantle and, possibly, a crust (just like Earth has all three), before being broken up into pieces through an impact with another protoplanet or large asteroid.

Most asteroids larger than about 100 m and smaller than 1 km are rubble piles, meaning they are not solid, but an agglomeration of dust, regolith13, pebbles, rocks and boulders weakly held together by gravity and chemical forces. Many asteroids smaller than 100 m are probably also rubble piles, but some monolithic objects must exist among them. It is expected that in the population of asteroids larger than 1 km there will still be many rubble piles, at least until they reach sizes of many hundreds kilometers. This poses a problem for those wanting to hollow out an asteroid, as it would be impossible to create a wide self-sustaining tunnel chamber through the asteroid. On the other hand, it makes mining easier as there is no need to break the asteroid up, because it already is.

9https://minorplanetcenter.net. 10https://cneos.jpl.nasa.gov/sentry/. 11http://www.hayabusa2.jaxa.jp/en/. 12https://www.asteroidmission.org. 13Regolith is the term used by geologists and planetary scientists to denote the “sand” found on the surface of planetary bodies.

Motivation and Goals

A settlement on the Moon has the advantage of staying close to Earth, and indeed, always in its view and within radio range. A trip to the Moon will take 3 days and can be launched practically at any moment in time. A Mars settlement, on the other hand, will require much more autonomy and independence from mother Earth, as two-way communications will take anywhere from 4.5 to 21 minutes (depending on where in their respective orbits Earth and Mars find each other) and trips will take about 8 months, with launch windows spaced every 2 years and 2 months. Mars also requires a much greater expenditure of energy to transport anything to its surface (about 80% more than to the Moon). Asteroids are their own unique destination. Some of them require less energy to arrive at than the Moon’s surface, and yet they suffer from similar communications constraints as Mars. They also have preferred launch windows, although these can be as short as a few months; much more benevolent than Mars’s. Unlike the Moon or Mars, asteroids do not have significant gravity, thus making them energetically easier to approach and depart from, although orbiting them becomes more complex than orbiting a body with a substantial gravitational pull, as does docking with them (as one does not really land on an asteroid). But perhaps the biggest attraction to settling on an asteroid is the presence of valuable resources that could be mined for sustenance, and profit, if the ap- propriate asteroid is chosen. An asteroid capable of providing air, water, and building materials to its settlers, and possibly even nutrients for its agricultural needs, would be a most valuable asset, enabling the settlement to become almost independent from Earth supplies. One can imagine settling an NEA with a Earth vicinity return period of 6–12 months, with abundant enough water that the settlement can draw a surplus after mining for its needs, and sell it to companies in LEO, using the profits to purchase necessities from Earth, or indeed, LEO, that it cannot manufacture on the asteroid. They might even be able to manufacture products from the asteroid’s metal and mineral reserves that can be sold in LEO, or to Moon settlements. This could allow the asteroid settlement to become self-sufficient through trade, like most countries on Earth are. Does such an asteroid exist? And if it does, have we discovered it yet? If not, how can we find it? And what other characteristics should such an asteroid have to make it a candidate for settling? This work intends to answer these questions and provide some options for destinations other than the hackneyed Moon or Mars. Please understand we are not against either of these celestial bodies; in fact, we believe humans should be exploring all reaches of the Solar System. We do not believe in “either/or”, but effusively defend “and/and”. All settlement destinations will have their pros and cons, but we can learn from all of them, and ultimately they all enable each other.

7 8 Motivation and Goals

That said, we will point out that because asteroids are ubiquitous throughout the Solar System, any species venturing out to explore its vastness would be well advised to learn how to proﬁt from the asteroids and use them in as many ways as possible, as one never knows when an emergency will arise and all that is available close by to ensure survival is a lowly asteroid. Method

Sources of Data

NASA’s JPL (Jet Propulsion Laboratory) provides orbital and physical data in their Small-Body Database Search Engine14. It should be noted that the vast majority of known asteroids do not have any physical data collected on them; the main goal of NASA’s Planetary Defense Coordination Ofﬁce (PDCO)15 is to discover NEAs and quickly asses whether they pose an impact threat to Earth or not; obtaining physical data on these asteroids is expensive and time-consuming, so is not a priority except for a relatively small number of them. JPL provides the following physical parameters, if they have been measured or calculated: size or dimensions, mass, albedo, rotational period, taxonomy (spectral classiﬁcation), and three colour indices (which could be a proxy for taxonomy, though we have not explored that in this work). Some further quantities were calculated from this dataset: ∆v16, this is a mea- sure of how much energy, and by extension, fuel, is required to travel to an asteroid from LEO (Low Earth Orbit); the lower the ∆v to get to an asteroid, the “closer” we say it is. The closest asteroids have a ∆v of around 3 km/s; for comparison, travelling from LEO and landing on the Moon requires a ∆v of around 6 km/s. Also added was the synodic period, which is calculated from an asteroid’s semimajor axis; this quantity is the time it takes for the asteroid, Earth and Sun to return to the same relative alignment in space. The synodic period can be used as an approximation of the time between two consecutive launch windows from Earth to an asteroid. It is, of course, theoretically possible to travel to any asteroid at any given time, but this will be at the expense of a higher ∆v, and usually a much longer travel time too. The dates when the journey requires the least ∆v are spaced apart approximately by the synodic period. This is important to know, especially at the beginning of a settlement, when help from Earth is likely to be required more frequently.

A Matter of Time vs Energy

As discussed above, when travelling to an asteroid, or indeed anywhere in the Solar System, there are two main variables that need be considered: The energy it will require to arrive at a destination (∆v), and the time it will take to get there. In general, these two variables ﬁght against each other: A fast trip will require a lot of energy (that is, fuel), while a trip that uses the least amount of energy possible

14https://ssd.jpl.nasa.gov/sbdb_query.cgi. 15https://www.nasa.gov/planetarydefense. 16We used the formulation proposed by Shoemaker & Helin in [10] to calculate the values of ∆v for the NEAs in the JPL dataset.

9 10 Method will take a long time. These two variables must be balanced against each other depending on the type of mission being ﬂown; a robotic science mission can take a long time to arrive at its destination, but a crewed mission would have to arrive as soon as possible to minimise travel time for the astronauts. This project did not examine travel times as these depend on the speciﬁc trajectories chosen, and calculating trajectories is beyond the scope of this work. Another way that energy will constrain where settlements are located is the separation in time between optimum launch windows, as measured approximately by the asteroid’s synodic period. Here too we run into a balancing act. In general, asteroids that are energetically easy to get to are those that are in orbits similar to Earth: About the same distance from the Sun, more round than elliptical, and not very inclined to the plane of the Solar System. Asteroids in these orbits will require less energy to get to, but their synodic periods will be longer. Fig. 1 shows the distribution of ∆v vs synodic period for NEAs, with each dot representing an NEA; while there is no analytical relationship, it can be seen that asteroids with a ∆v of less than 5 km/s have a synodic period longer than 2 years. The reason for choosing very low ∆v asteroids is because this will allow transporting the most supplies and equipment to them.

Figure 1: Plot of ∆v vs synodic period for NEAs.

At time of writing, there are currently two robotic spacecraft from planet Earth visiting NEAs. NASA’s OSIRIS-Rex17 mission is exploring Bennu, which is a 260 m, carbonaceous B type asteroid with a ∆v of 5.1 km/s. JAXA’s Hayabusa218 is exploring Ryugu, an 865 m, carbonaceous Cg type asteroid with a ∆v of 4.7 km/s. Table 1 lists all the missions that have successfully visited an asteroid, in order of increasing ∆v; note that some missions only performed distant ﬂybys. More im- portantly, note that the only missions to have touched an asteroid were those to an

17https://www.asteroidmission.org. 18http://www.hayabusa2.jaxa.jp/en/. A Matter of Some Gravity 11

Table 1: List of asteroids visited and imaged by spacecraft. Those in bold are NEAs.

∆v Launch year– Asteroid Mission Notes (km/s) Arrival year

Itokawa 4.6 2003–2005 orbit, land, sample return Ryugu 4.7 2014–2018 orbit, land, sample return Bennu 5.1 2016–2018 orbit, land, sample return Eros 6.1 1996–2000 orbit, land Toutatis 6.6 2010–2012 flyby Flyby after Moon orbit mission Gaspra 8.4 1989–1991 flyby Flyby on way to Jupiter Annefrank 9.0 1999–2002 flyby Flyby on way to comet Wild 2 Lutetia 9.0 2004–2010 flyby Flyby on way to comet 67P Mathilde 9.1 1996–1997 flyby Flyby on way to Eros Steins 9.3 2004–2008 flyby Flyby on way to comet 67P Vesta 9.4 2007–2011 orbit Ida 10.3 1989–1993 flyby Flyby on way to Jupiter Ceres 10.5 2007-2015 orbit After Dawn mission to Vesta Braille 10.9 1998–1999 flyby Tech demo mission for ion propulsion 2014 MU69 12.4 2006–2019 flyby Flyby after flying by Pluto Pluto 12..7 2006–2015 flyby

NEA, and these were NEAs with a low ∆v. The three lowest ∆v asteroids on the list are sample return missions, and the spacecraft all took over 2 years to reach their respective asteroids.

A Matter of Some Gravity

An often-seen scenario in space station design is that of a rotating, wheel-like station, where the outer rim is where the living quarters are, which, by virtue of the centrifugal force imparted by the space station’s spin, provides artificial gravity to its inhabitants. Something similar could be achieved on a large asteroid, like minor planet Ceres (the largest object in the Asteroid Belt) as depicted in the series of novels of The Expanse literary universe, and also portrayed in the TV series of the same name. In the books, the settlements are underground and upside down, because Ceres has been spun up so the centrifugal force on its inside edge provides artificial gravity. Unlike smaller asteroids, Ceres, which is 950 km in diameter and was visited by NASA’s Dawn mission in 201519, we now know is a solid body with geological layers, and not a rubble pile, so stable caverns could be dug out. However, the energy required to spin it up sufficiently to provide artificial gravity would be unrealistically large, and truly of science fiction proportions. Could the idea work on a small asteroid, say a few tens of meters in size? Maybe the space station could be anchored to the asteroid and make use of its inherent spin, then spin it up gradually until the centrifugal force is strong enough to provide appreciable gravity. The problem in this scenario is that it is believed most asteroids in this size range are rubble piles, which would make it impossible to attach a complex structure such as a space station to them. Furthermore, asteroids in this size range rotate at a speed of between 0.001 and 2 rpm (revolutions per minute); to attain 1 g (1 Earth gravity) artificial gravity on a space station ring 50 m across would require 6 rpm. It is believed that rubble pile asteroids spinning faster than around 0.007 rpm will break apart from the centrifugal force flinging the asteroid’s constituent rocks away. This means that a space station built around

19https://solarsystem.nasa.gov/missions/dawn/overview/. 12 Method

Table 2: Asteroid search parameters.

Settlement type q (AU) a (AU) Size (km) ∆v (km/s)

Small settlement on small NEA < 1.3 any any 4.0 Large settlement on large asteroid any < 5.2 > 10 8.5 Mining settlement on NEA < 1.3 any any 4.5

q: Perihelion of the orbit (closest the asteroid will get to the Sun). a: Semimajor axis of the orbit (half the length the orbital ellipse). ∆v: Delta-v of the trip, as calculated using the Shoemaker-Helin formulation. a spinning asteroid would require that asteroid to be a single, monolithic block. The simplest, and more realistic option, given the scenarion where the asteroid is a rubble pile, would be to bury the settlement a few meters below the surface, as the regolith would act as a shield against the harmful solar radiation. Settlers would have to live in microgravity conditions, just like astronauts on the ISS do.

Search Parameters for Candidate Asteroids

Depending on the use that is to be given to the asteroid, a different set of parameters will be required. Here we present a selection of three possible settlement scenarios and consider the various requirements for each asteroid. Table 2 lists the values used for each search parameter.

Small Settlement on Small NEA A small settlement could be placed on or around a small NEA and become eco- nomically self-sufﬁcient with some imaginative business ideas (see Fig. 2 for just such an idea from the Open Space Agency20). If gravity is desired, it could be obtained by choosing an asteroid with a single rotation axis and building the settlement as a ring around the asteroid such that centrifugal forces will provide some degree of artiﬁcial gravity. Due to the rapid spin speed required to achieve even a fraction of 1 g, a solid asteroid would be required, as a rubble pile would break up due to the rapid rotation. We place an upper limit of 4.0 km/s on the ∆v. This is quite low, but we expect a small settlement would want to remain “close” to Earth, if only for psychological reasons.

Large Settlement on Large Asteroid We choose, rather arbitrarily, 10 km as the minimum size for a “large” asteroid. Be- cause there are only two NEAs in this size range, we expand the search to asteroids beyond near-Earth space and into the Asteroid Belt. And because these asteroids cannot be sped up to provide artiﬁcial gravity, any near-future settlements on Ceres or similar bodies would need to contend with a very low gravity environment21. Due to this, a settlement on the surface will require anchoring, which may or may

20http://www.openspaceagency.com. 21The gravity on Ceres is about 1/6 that of the Moon, which in turn is 1/6 that of Earth. Search Parameters for Candidate Asteroids 13

Figure 2: A rotating space station around a small asteroid, as envisioned by the Open Space Agency. not be possible on rubble pile asteroids, but whether an asteroid is solid or a rubble pile is something that cannot be conﬁrmed from Earth for most asteroids. We expect asteroids that are several hundred kilometers in size to be solid, but those that are only tens of kilometers might be rubble piles. We limit the location of these large asteroids to be no further than Jupiter to make the settlement somewhat accessible to Earth trafﬁc; the Earth-Jupiter trip would take 2–3 years.

Mining Settlement on NEA Depending on the nature of the mining operation, asteroids of a particular composition would have to be chosen. And depending on the type of mining equipment being used, a certain set of physical parameters for the asteroid would be required; for example, if it should be a rubble pile or monolithic, spin slowly or rapidly, have a certain size to guarantee enough resources can be mined, etc. We increase the limit on the small NEA settlement ∆v to 4.5 km/s in order to increase the number of available targets. Also, if mining for water, it could be used as fuel and would thus allow travelling to more distant asteroids, as the craft returning to Earth could refuel at the asteroid instead of having to carry enough fuel for the return leg of the trip as well as the outbound leg.

Results

The searches performed using the parameters in Table 2 yielded 19 asteroids for small settlement on small NEA, 36 for large settlement on large asteroid, and 258 for mining settlement on NEA. The details for all these asteroids are listed in the three tables in Appendix – Lists of Candidate Asteroids. It should be noted that, given the search parameters in Table 2, the asteroids that result from the search for small settlement on small NEA are a subset of the results for the search for mining settlement on NEA given that only the upper limit on the value for ∆v changes. Of course, for a mining asteroid it is required that its composition be known, to determine if it has valuable resources worth mining. The first thing that stands out when looking at Tables 3 and 5, which list NEAs, is the dearth of physical data (size, spectral taxonomy and rotation period) available for these asteroids. Table 3 lists a single asteroid with a measured rotational period, and none with an observed taxonomy, out of a total of 19 candidate asteroids. Table 5 lists 19 asteroids with a rotational period (that is 7.4% of the 258 listed asteroids), and only one with spectral taxonomy. The situation is reversed for the candidate asteroids for large settlement on large asteroid, listed in Table 4. Here all but two of the asteroids have a measured size, and all but one have a measured rotational period; furthermore, 27 asteroids (75% of the 36 listed) have at least one taxonomic classification, although it is worth noting that almost all are S-type asteroids. This abundance of physical data is due to these being large, multi-km sized asteroids, which reflect more light than smaller NEAs and are thus brighter and easier to observe. Furthermore, apart from the NEA Eros, they are all Main Belt asteroids, and their synodic periods cluster around 1.43 years, meaning there are frequent opportunities for observation. Not only that, but most were discovered decades ago, so astronomers have had a very long time to observe them and obtain data; in contrast, about half the known NEAs were only discovered within the last decade. Contrast the low synodic periods of the Main Belt candidates with the synodic periods of the NEAs in Tables 3 and 5; the majority are longer than 3 years, with many of the lower ∆v ones having decades-long synodic periods. The synodic period for 2006 RH120 is 3.6 centuries long! We are fortunate to have a rotational period measured for it. The NEAs in these tables are also much smaller (only a handful are larger than 100 m), thus making them dimmer objects that are harder to observe. It is also worth noting that only 2 of the 258 candidate asteroids for mining settlement on NEA have a measured size. A very important factor in deciding whether to mine an asteroid or not will be the amount of a particular resource that is expected to be found in the asteroid; knowing the size is necessary for estimating the mass of the asteroid, and thus crucial for determining the reserve of resources available to mine. While the rotational period is mostly an engineering constraint,

15 16 Results composition and mass (of which taxonomy and size are proxies for) are financial constraints and must be known to the highest degree of certainty possible. Another notable result are the values of the condition code (see Appendix – Lists of Candidate Asteroids for a definition). The lower the value of the condition code (which goes from 0 to 9), the better known the location of the asteroid along its orbit will be; values of 3 or less are desirable if wanting to perform telescopic observations, a value of 0 is required if wanting to send a spacecraft to visit. If the condition code is 4–7, it will take a telescopic hunting expedition possibly lasting several nights to find the asteroid in the night sky; this, coupled with the long synodic periods, means that if it is not found during a first attempt, there will be a long wait until the next opportunity to look for it. Asteroids with condition codes of 8 or 9 are essentially “lost”, and we can only hope they are re-found again serendipitously by one of the NEA surveys. The more positional observations of an asteroid are made, and over a longer period of time, the lower the value of the condition code will become, and the more accurate its calculated orbit will be. If planning to travel to an asteroid, its position in space should ideally be known to within a few tens of meters (possibly a few hundred meters), or otherwise a spacecraft will find itself lost in space if the asteroid is not at the expected location. The problem of high condition codes that plagues the NEA results is not present in the large settlement on large asteroid results—all asteroids have a condition code of 0. Again, this is due to these asteroids being easily and more frequently (due to low synodic periods) observable than NEAs, and most having been observed for decades. While their ∆v is high, we at least know exactly where they are and would have no navigational problems travelling to them. Let us now examine the possibility of creating artificial gravity by installing a rotating station around an asteroid. As mentioned in section A Matter of Some Grav- ity, asteroids do not spin fast enough to allow sufficient gravity to be generated, so they would need to be spun up. We will examine the possibility of doing this to the fastest rotator in the candidate list for large settlement on large asteroid, Marmulla, which has a rotation period of 2.721 hours, and a diamter of 9.026 km. Marmulla is one of the few asteroids in this list without a taxonomy, so let us assume it is S-type, like almost all the others in the list; thus we would expect its bulk density to be around 3,000 kg/m3. We will also assume that it is cohesive enough that it would not fly apart if it were spun up. The gravity on the surface of Marmulla is 0.000096 g, where 1 g is the gravity on the surface of Earth, so its attraction opposing the artificially generated gravity will be negligible and can be ignored. The rotational period that Marmulla would need to have so as to provide artificial gravity of 1 g to an upside down settlement located on its surface is 134.8 s; for Mars-like gravity (about 1/4 Earth gravity) the rotational period would need to be 219.1 s; and finally, for lunar-like gravity (about 1/6 Earth gravity) it would need to be 331.6 s. These are much faster than the 2.721 hour period it currently has, so how much energy would be necessary to speed Marmulla up to achieve these faster spins? To achieve Earth gravity would require 1.02 × 1010 GJ (giga Joules); 3.87 × 109 GJ to achieve Mars gravity; and 1.69 × 109 GJ to achieve Lunar gravity. To put these values into perspective, the world’s yearly energy consumption is around 6 × 1011 GJ22; so, to spin Marmulla up to provide artificial Earth-like gravity would require about 1.7% of the world’s

22https://en.wikipedia.org/wiki/World_energy_consumption. 17 yearly energy expenditure, which is, to say the least, an unrealistic expectation for current or near-term technology. Could this be possible with a smaller asteroid? The only NEA for which we have a rotation period in the list of candidates for small settlement on small NEA is 2014 UV210, with a rotation of 0.5559 h and an estimated size of 22 m. Let us make the same composition and cohesion assumptions as for Marmulla, but instead of a settlement on the surface, let us imagine a ring station with a radius of 50 m, anchored to the asteroid, which would be at the center. The rotation period required for this space station to generate centrifugal gravity equal to Earth’s is 14.2 s; Mars gravity requires 23.1 s; and Lunar gravity, 34.9 s. The energy required to spin up 2014 UV210 to those speeds is, respectively, 0.36 GJ, 0.14 GJ and 0.06 GJ. Again, to place into perspective, the United States uses about 446 GJ of electricity per second23, so spinning up this asteroid to provide Earth-like centrifugal gravity would require 0.08% of the energy used each second by the United States, which would appear a more plausible amount of energy than that required to spin up asteroid Marmulla. NEAs with Earth-like orbits will have low ∆vs, but also long synodic periods. As the ∆v increases, in general so does the value of the semimajor axis and/or the eccentricity of the orbit. But what all low ∆v NEAs have in common is a low value of the inclination—they are all below 6◦; it is expensive energy-wise to change a spacecraft’s orbit from one plane to another and Table 5 conﬁrms that.

23https://en.wikipedia.org/wiki/List_of_countries_by_electricity_consumption.

Conclusion

Settling an asteroid, of any size, will be a monumental challenge and a techno- logical achievement of historical proportions. Humans have not travelled beyond Earth’s radiation belts in almost five decades, yet here we are dreaming of living on, and even off, asteroids. In this study we take a preliminary step towards identifying any known asteroids that might be suitable for a settlement, making choices based primarily on how easy it is to travel to them, how often this trip can be done, their size, and what the asteroids are made of. We have also considered whether it is possible to speed up an asteroid’s spin such that a settlement on its surface, or in a ring around it, might enjoy artificial gravity through centrifugal acceleration. What we have found is that NEAs make the best candidates for asteroids that require the least amount of energy to visit them, but they are also those with the longest synodic periods, which means any settlements on these asteroids must be self-sufficient from the moment of landing, because the time between launch windows is many years, even decades long. If the settlement needs provisions, they won’t be able to order them and receive them in short order. If the purpose of the settlement is to mine an NEA, there is a worrying lack of data on what asteroids are made of, how fast they spin, or even how large they are. Many also have poorly defined orbits, so it is impossible to travel to them, or even find them easily through a telescope. If what is wanted from an asteroid settlement is that it be accessible often, and have a known size, composition, and spin period to aid in the preparation of the settlement’s plans, then the choice would be one of several large asteroids in the Main Belt. The price to pay is a higher energy requirement to reach them; but it may be that new heavy lift rockets coming online in the near future (SpaceX’s BFR or Blue Origin’s New Glenn, for example) will bring these asteroids closer, so to speak, and open up the number of options available to settle. The biggest problem with choosing any of the asteroids in Table 4 is that none of those with a known taxonomy are C-type, so none of these asteroid contain hydrated minerals from which to extract water, and without water, a settlement will never be self sufficient. In order to settle and/or mine an NEA, there needs to be a change in strategy for observation and data collection: The acquisition of data to determine spectral class and rotational periods of low ∆v NEAs must become a priority. Without knowing what an asteroid is made out of, it is impossible to determine whether it should be mined or not. Without knowing the size to an accuracy better than the current ± 50%, it is impossible to determine whether it will be profitable to mine or not, and with poorly constrained orbits (high condition codes), spacecraft cannot be sent to them. With limited opportunities to observe asteroids with long synodic periods (and given the most attractive NEAs have long synodic periods) it is crucial to observe

19 20 Conclusion all candidate NEAs for settlement or mining at every possible opportunity to ensure that when one is finally chosen, its orbit is known with a high degree of confi- dence. As shown in [1], it is imperative to observe these NEAs and obtain spectra and light curves within days of discovery, or otherwise this might not be possible for years or decades to come. There is currently a project underway at the Lowell Observatory called MANOS (Mission Accessible Near-Earth Object Survey)24 that is doing just that. We look forward to when they publish they data as we expect that many of the low ∆v NEAs in this report will gain taxonomies and rotational periods. Lastly, this report looked into the possibility of speeding up an asteroid to use the centrifugal force to produce artificial gravity. For a large asteroid with a settlement on its surface we found the energy necessary to speed up the asteroid’s rotation to the required speed was prohibitive, and was more than many small countries use in a year. But for a small asteroid a few tens of meters in size, forming the center of a rotating space station 100 m in diameter, the energy necessary to speed the rotation up would be a fraction of the electrical consumption in the United States each second. In closing, we are unable to identify any NEAs that are suitable candidates for settling, largely because of lack of physical data. We do identify a number of Main Belt asteroids, except none of them are expected to contain water, making them unsuitable for a self-sustaining settlement, especially considering they require significantly more energy and time to travel to them than to NEAs. In order to discover more low ∆v NEAs, a dedicated survey searching exclusively close to the ecliptic would need to be conducted, and it would have to be operational over decades due to the long synodic period of these asteroids; however, estimates by [8] suggest there may be no more NEAs left to discover with ∆v below 4 km/s. If true, then in order to grow the number of NEA candidates, the limiting ∆v must be raised, and for that to be practical it will be necessary for more powerful and affordable rockets to become available, or for refuelling in Low Earth Orbit to become a reality. Settling an asteroid is still far away in the future, and we have identified some obstacles that keep us from even identifying suitable candidates, let alone travelling to them and living on them for years at a time. But these obstacles should not deter, but rather inspire us to work harder towards this goal of making humans a species living both on, and off world.

24https://manos.lowell.edu/. Bibliography

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[14] Wikipedia contributors. List of missions to Mars — Wikipedia, The Free Ency- clopedia. Accessed: 2018-10-23. 2018. url: https://en.wikipedia.org/w/ index.php?title=List_of_missions_to_Mars&oldid=864883293. [15] Jan Woerner. Moon Village: A vision for global cooperation and Space 4.0 | Jan Woerner’s blog. Accessed: 2018-10-31. Nov. 2016. url: http://blogs.esa. int/janwoerner/2016/11/23/moon-village/. [16] Zhaoyu Zhu et al. “Hominin occupation of the Chinese Loess Plateau since about 2.1 million years ago”. In: Nature 559.7715 (July 2018), pp. 608–612. doi: 10.1038/s41586-018-0299-4. [17] Glenn Zorpette. At Last, the Great Martian Movie - IEEE Spectrum. Accessed: 2018-10-24. Sept. 2015. url: https : / / spectrum . ieee . org / geek - life / history/at-last-the-great-martian-movie. Appendix – Lists of Candidate As- teroids

The following tables list the asteroids that were found when searching the JPL database using the criteria outlined in section Search Parameters for Candidate Aster- oids (and see Table 2); the objects in the tables below are listed in order of increasing ∆v. The columns are as follows: ID: The asteroid’s name (if available), number (if available) and provisional desig- nation in parentheses. Measured size: The measured size of the asteroid in meters. If spherical, this is the diameter; if not spherical, it is the mean diameter. Estimated size: The asteroid’s size in meters, as estimated from its absolute mag- nitude. ∆v: The asteroid’s ∆v, as calculated using the Shoemaker-Helin formulation [[10]]. a: Semimajor axis25 of the asteroid’s orbit, in AU26. e: Eccentricity27 of the asteroid’s orbit. i: Inclination, in degrees, of the asteroid’s orbit with respect to the ecliptic28. Synodic period: The asteroid’s synodic period29 with respect to Earth, in years. Rotational period: The asteroid’s rotational period in hours, as measured from light curves and/or radar observations. Taxonomy: The asteroid’s spectral type according to the classic Tholen classification, and/or the more modern SMASS30 classification. The taxonomy is related to the asteroid’s composition. Condition code: This value qualifies the quality of the orbital solution as it per- tains to locating the asteroid along its orbit. 0 is the highest quality and 9 the lowest; asteroids with a condition code 4 or higher will prove difficult-to- impossible to find in the sky with a survey telescope31.

25The semimajor axis is the longest axis of an ellipse. 26An Astronomical Unit is approximately the average distance between the Earth and Sun, and is defined as 149,597,870,700 km. 27The orbital eccentricity defines how much an orbit deviates from a perfect circle. A circle has an eccentricity of 0; values larger than 0 but less than 1 define ever more elongated ellipses; a value of 1 defines a parabola; values greater than 1 define hyperbolas. 28The ecliptic is the imaginary plane formed by the Earth’s orbit around the Sun. 29The synodic period is the time it takes for the asteroid, Earth and Sun to return to the same relative alignment in space. 30http://smass.mit.edu/smass.html. 31https://en.wikipedia.org/wiki/Uncertainty_parameter.

23 24 Appendix – Lists of Candidate Asteroids

Table 3: Asteroids found for small settlement on small NEA search parameters.

Measured Estimated ∆v a e i Synodic Rotational SMASS Tholen Condition ID size (m) size (m) (km/s) (AU) (AU) (◦) period (y) period (h) Tax. Tax. code

Table 4: Asteroids found for large settlement on large asteroid search parameters.

Measured Estimated ∆v a e i Synodic Rotational SMASS Tholen Condition ID size (m) size (m) (km/s) (AU) (AU) (◦) period (y) period (h) Tax. Tax. code

1. 433 Eros (1898 DQ) 16840 6.112 1.46 0.22 10.83 2.31 5.27 S S 0 2. 1204 Renzia (1931 TE) 21533 7.807 2.26 0.29 1.88 1.42 7.885 S 0 3. 1034 Mozartia (1924 SS) 7919 8.123 2.29 0.26 3.97 1.40 S 0 4. 2717 Tellervo (1940 WJ) 8991 8.145 2.21 0.22 3.28 1.44 4.213 0 5. 1110 Jaroslawa (1928 PD) 12306 8.150 2.22 0.24 5.86 1.43 97.4 S 0 6. 901 Brunsia (1918 EE) 13210 8.162 2.22 0.22 3.45 1.43 3.1363 S 0 7. 937 Bethgea (1920 HO) 11383 8.206 2.23 0.22 3.70 1.43 7.539 S 0 8. 800 Kressmannia (1915 WP) 15429 8.213 2.19 0.20 4.26 1.45 4.464 S 0 9. 512 Taurinensis (1903 LV) 23090 8.218 2.19 0.25 8.75 1.45 5.585 S S 0 10. 1147 Stavropolis (1929 LF) 13430 8.239 2.27 0.23 3.88 1.41 5.6607 S 0 11. 1055 Tynka (1925 WG) 13479 8.247 2.20 0.21 5.28 1.44 11.893 S S 0 12. 1130 Skuld (1929 RC) 10125 8.260 2.23 0.20 2.17 1.43 4.81 0 13. 1058 Grubba (1925 MA) 11910 8.274 2.20 0.19 3.69 1.44 46.3 S S 0 14. 422 Berolina (1896 DA) 10714 8.278 2.23 0.21 4.99 1.43 25.978 DX 0 15. 870 Manto (1917 BX) 13683 8.298 2.32 0.27 6.19 1.39 122.3 S 0 16. 685 Hermia (1909 HE) 10950 8.331 2.24 0.20 3.65 1.43 50.4 0 17. 1188 Gothlandia (1930 SB) 12670 8.347 2.19 0.18 4.82 1.45 3.4916 S 0 18. 341 California (1892 J) 15830 8.348 2.20 0.19 5.67 1.44 318.0 S 0 19. 1065 Amundsenia (1926 PD) 19639 8.363 2.36 0.30 8.36 1.38 7.7594 S 0 20. 1527 Malmquista (1939 UG) 10040 8.373 2.23 0.20 5.19 1.43 14.077 0 21. 1117 Reginita (1927 KA) 10193 8.383 2.25 0.20 4.34 1.42 2.946 0 22. 43 Ariadne 71340 8.387 2.20 0.17 3.47 1.44 5.76218 Sk S 0 23. 951 Gaspra (1916 S45) 12200 8.402 2.21 0.17 4.11 1.44 7.042 S S 0 24. 1153 Wallenbergia (1924 SL) 8037 8.403 2.20 0.16 3.34 1.44 4.096 0 25. 270 Anahita 51400 8.430 2.20 0.15 2.37 1.44 15.06 S 0 26. 736 Harvard (1912 PZ) 17111 8.437 2.20 0.17 4.38 1.44 6.7 S 0 27. 1703 Barry (1930 RB) 9211 8.446 2.21 0.17 4.52 1.44 107.1 0 28. 244 Sita 11077 8.448 2.17 0.14 2.85 1.45 129.51 Sa 0 29. 352 Gisela (1893 B) 26744 8.455 2.19 0.15 3.38 1.44 7.49 Sl S 0 30. 1631 Kopff (1936 UC) 8636 8.462 2.24 0.21 7.49 1.43 6.683 0 31. 1047 Geisha (1924 TE) 10729 8.463 2.24 0.19 5.67 1.42 25.62 S 0 32. 711 Marmulla (1911 LN) 9026 8.467 2.24 0.20 6.09 1.43 2.721 0 33. 1667 Pels (1930 SY) 8998 8.467 2.19 0.16 4.62 1.45 3.268 Sa 0 34. 913 Otila (1919 FL) 11636 8.477 2.20 0.17 5.81 1.44 4.872 Sa 0 35. 1088 Mitaka (1927 WA) 15137 8.487 2.20 0.20 7.65 1.44 3.0361 S S 0 36. 1653 Yakhontovia (1937 RA) 9010 8.496 2.61 0.32 4.07 1.31 15.41 X 0 25

Table 5: Asteroids found for mining settlement on NEA search parameters.

Measured Estimated ∆v a e i Synodic Rotational SMASS Tholen Condition ID size (m) size (m) (km/s) (AU) (AU) (◦) period (y) period (h) Tax. Tax. code

1. (2018 AV2) 9 3.743 1.03 0.03 0.12 23.35 4 2. (2010 UE51) 11 3.827 1.06 0.06 0.62 12.92 2 3. (2007 UN12) 9 3.829 1.05 0.06 0.24 13.22 5 4. (2012 TF79) 17 3.864 1.05 0.04 1.01 14.22 5 5. (2017 FJ3) 5 3.884 1.13 0.12 0.96 5.85 6 6. (2008 HU4) 11 3.916 1.07 0.06 1.39 10.17 0 7. (2010 VQ98) 12 3.919 1.02 0.03 1.48 29.66 4 8. (2014 UV210) 22 3.933 1.16 0.13 0.60 5.03 0.5559 1 9. (2014 WX202) 6 3.939 1.04 0.06 0.41 19.54 2 10. (2008 EL68) 15 3.940 1.04 0.06 1.04 18.05 9 11. (2016 TB18) 57 3.941 1.08 0.08 1.53 9.44 3 12. (2012 EC) 113 3.956 1.15 0.14 0.91 5.24 0 13. (2008 EA9) 15 3.959 1.06 0.08 0.42 12.11 6 14. (2017 SV19) 52 3.966 1.06 0.04 1.30 11.38 5 15. (2015 KK57) 16 3.968 1.09 0.06 1.03 8.11 3 16. (2015 VC2) 17 3.970 1.05 0.07 0.87 13.39 2 17. (2009 BD) 12 3.982 1.01 0.04 0.38 69.12 1 18. (1991 VG) 11 3.989 1.03 0.05 1.43 21.47 0 19. (2017 BN93) 43 3.993 1.04 0.05 2.12 15.83 7 20. (2017 FT102) 7 4.001 1.04 0.06 1.52 18.21 3 21. (2016 RD34) 16 4.003 1.05 0.03 1.96 15.23 3 22. (2014 YD) 71 4.009 1.07 0.09 1.74 10.08 2.12 3 23. (2015 PS228) 9 4.010 1.06 0.08 0.44 12.58 5 24. (2015 DU) 25 4.022 1.10 0.09 2.75 7.39 0.076 3 25. (2015 YO10) 25 4.022 1.12 0.10 2.43 6.32 7 26. (2013 EC20) 8 4.029 1.11 0.12 1.30 6.83 4 27. (2008 UA202) 7 4.032 1.03 0.07 0.26 20.93 6 28. (2013 DA1) 18 4.032 1.17 0.14 1.89 4.81 7 29. (2017 FB157) 15 4.032 1.21 0.17 1.11 4.08 8 30. (2016 JF38) 11 4.038 1.13 0.12 2.41 6.16 9 31. (2006 RH120) 7 4.053 1.00 0.04 1.09 358.97 0.04583 1 32. (2018 SN3) 6 4.058 1.16 0.15 0.43 5.10 7 33. (2017 FF3) 21 4.068 1.15 0.14 2.56 5.43 6 34. (2012 WR10) 9 4.071 1.09 0.11 0.31 8.65 6 35. (2016 CF137) 39 4.071 1.09 0.10 2.44 8.21 4 36. (2016 TB57) 31 4.076 1.10 0.12 0.30 7.36 3 37. (2013 XY20) 41 4.077 1.13 0.11 2.86 5.95 5 38. (2006 UB17) 28 4.081 1.14 0.10 1.99 5.60 7 39. (2018 DT) 20 4.084 1.22 0.18 1.77 3.88 5 40. (2001 GP2) 22 4.095 1.04 0.07 1.28 18.60 6 41. (2014 SU1) 49 4.095 1.21 0.17 2.18 4.08 5 42. (2013 RZ53) 3 4.097 1.02 0.03 2.11 41.41 3 43. (2016 EP84) 17 4.098 1.19 0.17 0.82 4.34 4 44. (2013 BS45) 34 4.102 0.99 0.08 0.77 79.81 0 45. (2014 QN266) 28 4.108 1.05 0.09 0.49 13.50 4 46. (2018 LQ2) 57 4.110 1.09 0.06 2.13 8.16 3 47. (2017 TP4) 28 4.115 1.08 0.04 1.56 9.29 5 48. (2013 CY) 11 4.118 1.11 0.13 0.78 6.69 5 49. (2005 LC) 23 4.121 1.13 0.10 2.80 5.82 7 50. (2014 WA366) 22 4.122 1.03 0.07 1.56 20.26 4 51. (2017 FL64) 10 4.123 1.13 0.13 2.33 6.10 6 52. (2011 CG2) 271 4.125 1.18 0.16 2.76 4.60 10.813 0 53. (2011 MD) 13 4.125 1.06 0.04 2.56 12.03 0.1937 2 54. (2017 YW3) 26 4.125 1.09 0.11 2.20 7.88 5 55. (2010 SZ3) 17 4.129 1.18 0.14 2.21 4.45 7 56. (2012 MY2) 27 4.132 1.26 0.20 0.18 3.41 4 57. (2016 GL222) 36 4.133 1.15 0.14 3.53 5.19 7 58. (2009 OS5) 65 4.135 1.14 0.10 1.70 5.46 1 59. (2010 AN61) 21 4.139 1.16 0.13 3.61 5.09 6 60. (2014 WU200) 8 4.139 1.03 0.07 1.27 24.68 3 61. (2011 UD21) 10 4.140 0.98 0.03 1.06 30.21 4 62. (2016 TM56) 22 4.145 1.12 0.13 2.35 6.43 5 63. (2005 QP87) 15 4.146 1.23 0.18 0.27 3.71 5 64. (2018 PK21) 33 4.146 0.99 0.08 1.20 54.73 4 65. (2012 FS35) 5 4.155 1.10 0.12 2.34 7.58 5 66. (2012 KT12) 28 4.161 1.25 0.20 1.72 3.50 6 67. (2000 SG344) 59 4.163 0.98 0.07 0.11 28.75 3 68. (2008 TS10) 8 4.164 1.26 0.20 1.47 3.43 8 69. (2016 WD7) 18 4.167 1.25 0.21 0.67 3.54 5 70. (2013 WA44) 94 4.168 1.10 0.06 2.30 7.48 0.35 3 71. (2018 LR3) 28 4.169 1.20 0.19 0.47 4.16 7 72. (2012 HG2) 21 4.174 1.19 0.18 0.11 4.37 0.0227 5 73. (2017 UM52) 7 4.176 1.05 0.05 3.43 13.28 9 74. (2014 KD45) 14 4.179 1.15 0.09 0.77 5.20 7 75. (2018 CQ3) 47 4.182 1.17 0.15 4.00 4.80 4 76. (2018 BC) 7 4.183 1.05 0.07 2.86 14.64 4 77. (2017 BF29) 39 4.184 1.18 0.13 2.61 4.53 5 78. (2012 XM55) 14 4.190 1.10 0.13 1.08 7.75 6 79. (2013 LE7) 16 4.203 1.16 0.11 1.67 4.90 0 80. (1998 KY26) 30 4.205 1.23 0.20 1.48 3.71 0.1784 3 81. (2015 PL57) 37 4.205 1.12 0.14 1.63 6.38 4 82. (2013 PZ6) 14 4.207 1.17 0.11 2.05 4.79 7 83. (2016 NM15) 16 4.215 1.23 0.17 1.90 3.72 6 84. (2015 EZ6) 10 4.216 1.24 0.19 3.12 3.63 6 85. (2003 SM84) 149 4.219 1.13 0.08 2.80 6.16 1 86. (2012 FN) 7 4.223 1.22 0.19 3.23 3.86 9 87. (2013 GH66) 13 4.226 1.05 0.04 3.45 13.88 3 88. (2017 UY4) 47 4.226 1.19 0.16 3.78 4.41 4

Continued on next page 26 Appendix – Lists of Candidate Asteroids

Table 5: Asteroids found for mining settlement on NEA search parameters.

Measured Estimated ∆v a e i Synodic Rotational SMASS Tholen Condition ID size (m) size (m) (km/s) (AU) (AU) (◦) period (y) period (h) Tax. Tax. code

89. (2001 QJ142) 94 4.227 1.06 0.09 3.10 11.57 0 90. (2016 TM) 16 4.227 1.15 0.17 0.37 5.22 6 91. (2017 TF1) 24 4.227 1.26 0.19 0.89 3.45 5 92. (2013 GN3) 98 4.235 1.23 0.18 3.79 3.79 3 93. (2015 XA379) 45 4.237 1.29 0.22 1.35 3.17 4 94. (2008 AF3) 31 4.241 1.21 0.19 2.07 4.07 4 95. (2010 DJ) 26 4.242 1.21 0.14 0.23 4.05 8 96. (2017 YD1) 5 4.242 1.08 0.10 3.23 9.55 6 97. (2012 BB14) 52 4.243 1.06 0.10 2.64 11.18 4 98. (2016 YP4) 21 4.243 1.28 0.21 1.00 3.22 5 99. (2011 BP40) 43 4.244 1.12 0.15 0.92 6.34 8 100. (2016 JB18) 18 4.246 1.12 0.15 1.89 6.25 6 101. (2000 AE205) 130 4.251 1.16 0.14 4.46 4.89 S 1 102. (2010 WC1) 15 4.252 1.14 0.16 2.09 5.46 8 103. (2014 SD304) 52 4.253 1.17 0.11 2.29 4.82 4 104. (2015 XZ378) 19 4.255 1.01 0.03 2.72 46.89 5 105. (2014 JR24) 7 4.258 1.07 0.12 0.93 10.87 5 106. (2012 AQ) 4 4.259 1.07 0.10 2.86 10.23 5 107. (2017 YK14) 10 4.259 1.23 0.20 3.09 3.77 9 108. (2015 VO142) 8 4.260 1.07 0.13 0.28 9.76 4 109. (2009 CV) 71 4.262 1.12 0.15 0.94 6.60 0 110. (2017 BG30) 7 4.267 1.06 0.11 1.63 12.88 6 111. (2017 RS2) 26 4.268 1.26 0.20 2.99 3.38 6 112. (2010 JW34) 12 4.270 0.98 0.05 2.26 34.59 4 113. (2013 EM89) 33 4.270 1.18 0.12 2.41 4.59 6 114. (2015 VV) 71 4.272 1.14 0.10 4.01 5.72 4 115. (2012 UW68) 57 4.274 1.14 0.16 2.47 5.74 4 116. (2017 UX42) 10 4.274 1.17 0.13 4.10 4.85 7 117. (2017 WX13) 68 4.277 1.28 0.21 2.47 3.24 6 118. (2018 AJ3) 15 4.277 1.15 0.13 4.83 5.36 6 119. (2011 CE22) 43 4.279 1.11 0.09 4.57 7.05 9 120. (2018 CU14) 16 4.282 1.12 0.15 1.03 6.45 7 121. (2014 MA6) 65 4.283 1.27 0.21 3.18 3.36 5 122. (2012 EL8) 11 4.286 1.19 0.15 4.25 4.39 7 123. (2017 WM13) 16 4.291 1.13 0.12 4.85 5.90 6 124. (2008 UD95) 39 4.293 1.14 0.14 4.35 5.50 8 125. (2010 CE55) 188 4.294 1.29 0.22 2.53 3.15 0 126. (2015 MC54) 23 4.305 1.12 0.07 3.02 6.54 5 127. (2014 CH13) 68 4.306 1.14 0.15 3.63 5.64 9 128. (2003 YS70) 8 4.307 1.29 0.24 0.35 3.17 5 129. (2005 YA37) 179 4.308 1.28 0.23 2.24 3.23 0 130. (2012 HK31) 43 4.309 1.07 0.12 2.21 9.88 7 131. (2008 XS) 20 4.310 1.28 0.21 3.32 3.25 7 132. (2018 QE) 14 4.312 1.31 0.25 0.18 2.98 7 133. (2014 HT46) 25 4.322 1.28 0.23 1.57 3.22 3 134. (2007 VU6) 26 4.324 0.98 0.09 1.22 27.21 6 135. (2008 JL24) 6 4.324 1.04 0.11 0.55 18.29 0.05385 4 136. (2012 HH31) 90 4.325 1.20 0.14 3.29 4.22 7 137. (2006 QQ56) 34 4.327 0.98 0.05 2.80 43.52 4 138. (2011 ED12) 23 4.328 1.10 0.13 2.82 7.63 6 139. (2014 UY) 43 4.328 1.17 0.17 3.56 4.67 0.0658 4 140. (2015 HS11) 20 4.329 1.16 0.13 4.94 4.93 5 141. (2012 LA) 16 4.332 1.04 0.02 3.12 17.59 2 142. (2005 GN22) 26 4.334 1.28 0.21 2.20 3.19 7 143. (2011 BL45) 21 4.334 1.04 0.02 3.05 18.49 6 144. (2008 TX3) 54 4.337 1.18 0.19 2.38 4.56 6 145. (2004 FN8) 20 4.338 1.17 0.14 5.26 4.79 7 146. (2009 QE34) 98 4.338 1.29 0.23 2.63 3.16 6 147. (2018 BQ) 37 4.338 1.33 0.25 1.64 2.87 5 148. (2005 ER95) 43 4.340 1.22 0.16 3.34 3.83 7 149. (2012 EP10) 8 4.343 1.05 0.12 1.03 14.09 6 150. (2005 RK3) 94 4.346 1.25 0.19 3.72 3.55 0 151. (2016 CF194) 78 4.351 1.29 0.20 1.64 3.15 4 152. (2015 ON22) 24 4.352 1.23 0.15 1.87 3.70 8 153. (2011 OK45) 16 4.358 1.29 0.21 2.87 3.14 8 154. (2015 LJ) 59 4.360 1.23 0.15 2.23 3.73 4 155. (2012 BP123) 20 4.361 1.12 0.16 2.59 6.28 9 156. (2015 MB54) 86 4.361 1.31 0.24 2.79 3.01 0 157. (2001 AV43) 62 4.362 1.28 0.24 0.20 3.20 0.1701 0 158. (2016 NL39) 16 4.362 1.34 0.25 0.79 2.80 6 159. (2018 DU) 11 4.364 1.17 0.18 3.20 4.67 6 160. (2006 JY26) 11 4.365 1.01 0.08 1.44 65.69 3 161. (2016 GC134) 30 4.365 1.17 0.16 4.77 4.85 7 162. (2014 LJ) 10 4.370 1.08 0.14 1.05 9.33 6 163. (2017 CF32) 31 4.371 1.15 0.18 1.19 5.22 2 164. (2018 GZ) 14 4.372 1.08 0.09 4.60 8.82 6 165. (2008 CM74) 12 4.373 1.09 0.15 0.85 8.32 6 166. (2011 PN1) 17 4.380 1.21 0.13 1.95 3.97 8 167. (2015 AP44) 30 4.385 1.28 0.24 1.11 3.26 7 168. (2004 BV18) 34 4.386 1.33 0.25 2.17 2.85 0.0565 6 169. (2018 GF4) 47 4.386 1.35 0.25 0.97 2.78 7 170. (2015 DJ215) 82 4.389 1.13 0.15 4.07 5.89 4 171. (2015 TB) 17 4.390 1.27 0.19 3.00 3.31 7 172. (2009 RT1) 98 4.392 1.16 0.11 4.15 5.13 6 173. (2015 VH2) 17 4.392 1.32 0.23 2.07 2.94 6 174. (2006 BZ147) 43 4.394 1.02 0.10 1.41 29.33 3 175. (2017 RL2) 31 4.395 1.11 0.05 2.91 7.13 5 176. (2006 DN) 65 4.396 1.38 0.28 0.27 2.61 7

Continued on next page 27

Table 5: Asteroids found for mining settlement on NEA search parameters.

Measured Estimated ∆v a e i Synodic Rotational SMASS Tholen Condition ID size (m) size (m) (km/s) (AU) (AU) (◦) period (y) period (h) Tax. Tax. code

177. (2008 HQ3) 16 4.397 1.36 0.26 1.79 2.73 8 178. (2013 SP19) 7 4.397 1.28 0.24 2.32 3.19 7 179. (2018 RR1) 5 4.400 1.08 0.14 0.67 9.68 6 180. (2018 EX) 21 4.403 1.28 0.20 3.13 3.20 6 181. (2014 KF39) 45 4.404 1.04 0.08 3.64 16.81 3 182. (2011 AM37) 6 4.408 1.10 0.15 2.63 7.50 7 183. (2015 XD169) 22 4.409 1.09 0.12 3.75 8.68 6 184. (2015 XX128) 33 4.410 1.27 0.23 3.13 3.35 4 185. (2016 GK135) 12 4.414 0.99 0.09 3.19 47.66 5 186. (2010 KV7) 13 4.417 1.21 0.22 0.31 3.96 8 187. (2016 YR) 19 4.417 1.03 0.07 3.45 25.84 6 188. (2011 CY7) 47 4.420 1.29 0.22 3.95 3.16 8 189. (2008 KT) 12 4.422 1.01 0.08 1.98 60.97 5 190. (2018 PU23) 12 4.422 0.96 0.08 0.83 17.51 6 191. (2004 WH1) 82 4.424 1.20 0.20 2.66 4.21 7 192. (2013 HP11) 43 4.424 1.18 0.13 4.16 4.46 5 193. (2010 PS66) 49 4.425 1.35 0.24 1.12 2.79 6 194. (2017 SF14) 68 4.425 1.32 0.23 2.81 2.96 5 195. (2006 UQ216) 18 4.426 1.10 0.16 0.47 7.28 7 196. (2017 HZ49) 41 4.426 1.20 0.20 3.94 4.10 7 197. (2018 RC1) 30 4.427 1.26 0.17 2.13 3.40 7 198. (2017 TA6) 20 4.431 1.12 0.17 0.99 6.44 4 199. (2011 MQ3) 57 4.434 1.12 0.11 5.68 6.29 6 200. (2013 PA7) 156 4.434 1.15 0.09 3.47 5.17 0 201. (2015 TJ1) 156 4.435 1.23 0.22 2.22 3.76 3 202. (2018 MC5) 49 4.435 1.37 0.26 1.03 2.64 5 203. (2011 HP24) 36 4.436 1.19 0.11 3.06 4.40 6 204. (2013 QM10) 68 4.436 1.19 0.17 5.57 4.37 4 205. (2013 SB21) 21 4.437 1.34 0.23 0.81 2.83 6 206. (2014 WN69) 13 4.438 1.38 0.28 1.16 2.59 8 207. (2006 HW50) 68 4.439 1.23 0.19 5.57 3.70 0.0291 0 208. 89136 (2001 US16) 471 4.443 1.36 0.25 1.91 2.73 14.39 0 209. 499998 (2011 PT) 86 4.443 1.31 0.21 2.21 2.99 0 210. (2004 EU22) 94 4.445 1.18 0.16 5.34 4.62 0 211. (2010 VC72) 130 4.445 1.16 0.14 5.93 5.03 2 212. (2010 VO21) 9 4.447 1.33 0.26 1.97 2.89 7 213. (2011 TP6) 41 4.448 1.32 0.22 2.59 2.93 5 214. (2016 DF) 21 4.448 1.09 0.07 4.58 8.07 6 215. (2014 FA44) 57 4.449 1.29 0.19 0.98 3.13 3.5 5 216. (2008 GL2) 19 4.451 1.12 0.13 5.17 6.25 7 217. (2009 DC12) 136 4.452 1.33 0.26 2.91 2.86 6 218. (2012 CR46) 27 4.454 1.34 0.24 2.67 2.82 7 219. (2014 DJ80) 28 4.454 0.98 0.07 3.03 28.21 5 220. (2015 RT82) 37 4.454 1.24 0.21 3.96 3.67 7 221. (2018 RR5) 28 4.454 1.32 0.24 3.97 2.93 7 222. (2017 LD) 16 4.457 1.39 0.28 0.07 2.55 4 223. (2018 LJ1) 26 4.457 1.28 0.18 2.21 3.24 5 224. (2015 VC1) 19 4.463 1.13 0.15 4.84 5.86 7 225. (2017 HU49) 26 4.463 0.97 0.06 2.63 22.54 4 226. (2018 LQ5) 54 4.465 1.23 0.15 3.47 3.74 7 227. (2017 TH2) 9 4.466 1.30 0.24 3.53 3.04 7 228. (2006 MV1) 23 4.467 1.32 0.24 4.27 2.96 0.0951 7 229. (2016 ST2) 57 4.467 1.14 0.07 3.43 5.68 5 230. (2010 RM80) 14 4.468 1.18 0.20 2.36 4.62 7 231. 363305 (2002 NV16) 271 4.469 1.24 0.22 3.50 3.66 0.9067 0 232. (2006 SK61) 31 4.469 1.38 0.26 0.35 2.61 6 233. (2017 SN10) 37 4.469 1.15 0.18 3.02 5.44 6 234. (2013 UX2) 7 4.471 1.12 0.15 4.11 6.45 5 235. (2014 FZ) 21 4.474 1.37 0.27 2.42 2.66 7 236. (2015 YK) 34 4.474 1.09 0.12 4.70 7.92 5 237. (2015 JD3) 41 4.475 1.06 0.01 2.72 12.24 4 238. (2016 CS247) 41 4.476 1.37 0.28 1.69 2.68 5 239. (2016 EJ156) 36 4.476 1.19 0.19 4.16 4.28 6 240. (2017 OE7) 30 4.476 1.40 0.28 0.65 2.52 6 241. (2012 XK134) 27 4.479 1.19 0.22 0.62 4.30 6 242. (2017 RP2) 90 4.479 1.12 0.17 2.22 6.32 4 243. (2009 SW171) 31 4.483 1.33 0.23 3.06 2.87 7 244. (2017 KJ5) 25 4.483 1.33 0.22 2.19 2.89 7 245. (2011 HH) 45 4.485 1.30 0.21 3.48 3.05 6 246. (2017 CO) 31 4.488 1.38 0.27 1.88 2.61 8 247. (2016 ES85) 6 4.489 0.97 0.09 2.24 20.73 5 248. (2017 FP127) 11 4.489 1.18 0.20 2.58 4.52 7 249. (2007 DD) 34 4.490 0.99 0.12 2.62 52.18 0.07429 2 250. (2008 NX) 49 4.492 1.32 0.21 0.60 2.93 6 251. (2005 EZ169) 45 4.494 1.32 0.22 2.74 2.96 7 252. (2014 UW57) 27 4.494 1.39 0.28 2.06 2.58 8 253. (2003 EZ16) 156 4.495 1.18 0.14 5.81 4.65 0 254. (2014 HL198) 18 4.495 1.29 0.24 3.79 3.17 9 255. (2015 HM182) 8 4.495 1.19 0.21 2.76 4.31 9 256. (2014 TR) 19 4.496 1.39 0.28 2.05 2.56 8 257. (2017 WF16) 8 4.497 1.23 0.20 5.21 3.79 6 258. (2015 FQ33) 24 4.500 1.30 0.23 4.80 3.09 8