Journal of the British Interplanetary Society
VOLUME 71 NO.12 DECEMBER 2018 General interstellar issue
SOLAR SYSTEM ESCAPE MISSION WITH SOLAR SAIL SPACECRAFT within a framework of post-Newtonian Gravitational Theory Olga L. Starinova & Irina V. Gorbunova DO ALIEN CIVILISATIONS EXIST? Derek Pugsley HEAT TRANSFER IN FUSION STARSHIP Radiation Shielding Systems Michel Lamontagne THE HALO DRIVE: FUEL-FREE RELATIVISTIC PROPULSION of large masses via recycled boomerang photons David Kipping INDEX Volume 71, 2018
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Published by the British Interplanetary Society. Registered Company No: 402498. Registered Charity No: 250556. Printed by Latimer Trend & Company Ltd, Estover Road, Plymouth, PL6 7PY, England. © 2018 British Interplanetary Society. No part of this magazine may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or recording by any information storage or retrieval system without prior permission from the Publishers. CONTENTS VOLUME 71 NO.12 DECEMBER 2018
438 SOLAR SYSTEM ESCAPE MISSION WITH SOLAR SAIL SPACECRAFT within a framework of post-Newtonian Gravitational Theory Olga L. Starinova & Irina V. Gorbunova
443 DO ALIEN CIVILISATIONS EXIST? Derek Pugsley
450 HEAT TRANSFER IN FUSION STARSHIP Radiation Shielding Systems Michel Lamontagne
458 THE HALO DRIVE: FUEL-FREE RELATIVISTIC PROPULSION of large masses via recycled boomerang photons David Kipping
469 INDEX Vol 71, 2018
OUR MISSION STATEMENT The British Interplanetary Society promotes the exploration and use of space for the bene t of humanity, connecting people to create, educate and inspire, and advance knowledge in all aspects of astronautics.
JBIS Vol 71 No.12 December 2018 437 JBIS VOLUME 71 2018 PAGES 438–442
SOLAR SYSTEM ESCAPE MISSION WITH SOLAR SAIL SPACECRAFT within a framework of post-Newtonian Gravitational Theory
OLGA L. STARINOVA, IRINA V. CHERNYAKINA, Samara National Research University, Samara, 443086, Russian Federation.
Email [email protected]
The motion of the spacecraft with a solar sail under the action of the force of gravity of the Sun and the force of light pressure is considered. The force of gravity can be described in terms of the post Newtonian field theory of gravitation. We suppose that the solar sail has a planar and perfectly reflecting surface, the normal to the sail’s surface lies in the plane of motion, and the spacecraft has a planar heliocentric orbit. We consider the problem of achieving the spacecraft maximum total energy at a given time of flight. The initial phase coordinates of the spacecraft are the averaged heliocentric coordinates of the Earth. The spacecraft control is performed by changing the pitch angle between the normal vector to the surface of the solar sail and the radial direction. An optimal control is obtained in an analytical form using the Pontryagin’s maximum principle, under the assumption, that the plane of the movement of the spacecraft is normal to the axis of rotation of the Sun.
Keywords: Interstellar Mission, Solar Sail Spacecraft, Post-Newtonian Gravitational Theory
1 INTRODUCTION Dachwald [1, 2] show, that when spacecra is performing such a maneuver, there are sectors where the spacecra is moving Flight to the stars is the most exciting and fascinating chal- near the rotating gravitating body (the Sun) and the spacecra lenge for modern and possibly future aerospace science and velocity becomes comparable with the speed of light (up to 0.1 technology. Interstellar missions using chemical or even elec- c). In this case, the search for optimal control and modeling of tric propulsions require such high launch speeds and an enor- the movement should be carried out within the framework of mous huge amount of fuel, which is not provided by modern the post-Newtonian theory of gravity. e force of gravity can spacecra and rocket vehicles. But even if these requirements be described in terms of the post Newtonian eld theory of are met, ight to the nearest star system will last hundreds of gravitation, in the same way as in the works of Kezerashvili and years. Using solar sail spacecra is one of the real opportuni- Vázquez-Poritz [3, 4]. ties to perform interstellar ights in an acceptable time. e advantage of a solar sail spacecra is the lack of fuel that in- In order to gain the maximum cruise speed, the solar sail creases the payload in comparison with a jet propulsion space- should approach as close as possible to the Sun. For instance, a cra . e disadvantage of a solar sail spacecra is the depend- recent study [5] shows that a er sail deployment from parabolic ence of its acceleration on the distance to the Sun: the farther orbit with 0.1 AU perihelion, a 937 m radius beryllium hollow from the Sun, the less is the pressure of sunlight and, thereby, body solar sail with a sail mass of 150 kg and a payload mass of the acceleration of the sail. Beyond the solar system, the pres- 150 kg reaches the inner Oort Comet Cloud at 2550 AU in 30 sure of sunlight and, accordingly, the e ciency of the solar years. In Refs. [1, 2, 5-9] it is shown that in order to achieve the sail will approach to zero. In addition, the e ciency of a solar maximum distance from the Sun in a minimum time, the solar sail depends on the sail loading (areal density), which is the sail must pass at a distance of less than 0.1 AU from the Sun. total mass of spacecra divided by the sail area. e smaller For example, the trajectory of the solar probe was presented in this ratio, the greater the acceleration due to the force of light Ref. [10], which includes repetitive pole orbits at a perihelion pressure and the faster the sail will arrive at a chosen star. of 4 solar radii, which is slightly less than 0.02 AU. e speed of motion at the perihelion of such a trajectory is so great that One of the opportunities for comparatively rapid transfer various eects of the surrounding environment around the Sun to other planetary systems is using the spacecra with a solar become noticeable [7-9]. In particular, we should consider the sail. e rst stage of this type of mission is the escape maneu- curvature of space-time in the region near the Sun. e eects ver from the Solar System and getting to the maximum space- of curved space-time in combination with the solar radiation cra cruising speed. In many works, for example, Sauer and pressure on solar sails in coupled heliocentric and non-Kep- lerian orbits have recently been considered [4, 11], where it was shown that they lead to deviations from Kepler's third law. is paper was presented at the Foundations of Interstellar Studies Despite the fact that the solar sail in the ight path is close to Workshop at CUNY City Tech, New York City, 13-15 June 2017. the Sun for only a short time, the disturbance of its movement
438 Vol 71 No.12 December 2018 JBIS SOLAR SYSTEM ESCAPE MISSION WITH SOLAR SAIL SPACECRAFT within a framework of post-Newtonian Gravitational Theory
during this period, when the acceleration due to the solar radi- parameter of the solar sail at r = r0 as measured by a distant ation pressure is the greatest, can lead to signicant changes in observer. Since the trajectory far from the Sun.
In this paper, we consider the problem of determining the at r = r0, we nd that for the angular momentum parameter L maximum escape velocity of the solar sail from the Sun for and for the energy E the following expressions: a given time, taking into account eects of spacetime curva- ture and special relativistic kinematics. At the initial time, the (5) spacecra is on the heliocentric orbit of the Earth and moves with its velocity. where . In Eq. (5) is the eective 2 MATHEMATICAL MODEL OF MOTION mass of the Sun and
e geometry of spacetime in the vicinity of the slowly rotating 26 Sun is described up to linear order in the angular momentum where Ls= 3.842 × 10 is the solar luminosity and σ is the areal J of the Sun by the large-distance limit of the Kerr metric [12], density. can be given in spherical coordinates (r, θ, ϕ,) as follows: In Ref. [4] the acceleration of the solar sail spacecra due to (1) the Sun illumination is determined as:
(2) (6) where t is time as measured by a distant static observer, G is the gravitational constant, M = 1.99 × 1030 kg is the mass of the Sun, c is speed of light, and J = (1.9 ± 0.015) × 1041 kg/m2 is the Sun’s angular momentum [13]. When the angular momentum J = 0, this metric reduces to the Schwarzschild metric, which de- scribes the exterior spacetime of a spherical and non-rotating where Ψ is an angle between the normal direction to the sur- sun. e second term in the metric (1), describes the rotating face of the solar sail n and the radial direction, Φ is an angle Sun and exhibits the frame dragging – a prediction of General between n and the transversal direction, γ is an angle between Relativity. To maximize frame dragging eect let us consider n and the direction of the solar radiation, σ is a mass per area the trajectories of the spacecra that lie within the equatorial parameter of solar sail, η = 0.5 corresponds to the total absorp- plane of the Sun. By introducing one can tion of photons by the sail and η = 1 corresponds to total re- write the 4-momentum of the solar sail as: ection, α is the angle between the solar radiation propagation and the radial direction. In the special relativistic framework one obtains: where τ is the proper time measured in the frame of reference of the solar sail. Following Ref. [4] for the component of the acceleration 4-vector of a solar sail one obtains: (7)
(3)
In Eq.(7) λ1 and λ2 are the steering angles in a local rotating frame, λ1 is the angle between the projection of the acceleration onto the instantaneous orbital plane and the spacecra radi- us vector, and λ2 is the angle between acceleration and orbital In Eq. (3), plane. and from the metric (1), for example, for the case when J = 0 e optimal control program of solar sail is considered as a one can nd how the proper time interval is related to the co- vector [14]: ordinate time interval: (8) (4) In Eq. (8) u(t) is the unit vector of the direction of operating acceleration, which can be expressed in terms of the steering By restricting ourselves to the case in which the force due angles λ1 and λ2 in a local rotating frame. to the solar radiation pressure is purely in the radial direction, the angular momentum L is a conserved quantity and we can To estimate of the maximum value escape velocity , we consider it as a parameter. However, since the solar radiation considered a case when θ = π/2, λ2 = 0 , and solar sail spacecra pressure is transferring energy to the solar sail, the energy E is performs a planar motion in ecliptic plane. In this case, equa- no longer a conserved quantity. In particular, E is the energy tions (3) and (6) can be reduced to:
JBIS Vol 71 No.12 December 2018 439 OLGA L. STARINOVA, IRINA V. CHERNYAKINA
3 OPTIMIZATION PROBLEM FORMALIZATION
A six dimensional state vector describes a solar sail motion in (9) the heliocentric frame. We consider the criterion of optimality which corresponds to the maximum output velocity from the Sun for a given ight time:
(14)
If sail is perfectly re ective, then η=1 and Eq. (9) can be sim- plied as: or
(10) (15)
As the next step, let us consider the approximation: According to the Pontryagin’s maximum principle [15], it is relevant to assign costate variables vector Ψ(t) to all elements of the state vector x in order to form a Hamiltonian:
is means that space and time are considered independent- (16) ly. Passing to the rst order system of dierential equations of plane motion and assuming that , we obtain: First of all, it is necessary to determine the Hamiltonian and, a er that, to dene partial derivatives and dene control angles equations [16]. In planar case, when the motion is described by Eq. (13) we have:
(11)
All the calculations are easier to do in a dimensionless form. We proceed to dimensionless variables and motion equations (17) according to the following agreement:
e system of costate variables: (12)
e symbol ✴ denotes the dimensional variables, is a dis- tance equal to one astronomical unit. e equations (11) take (18) the following form:
Since we do not need to provide specic heliocentric coor- (13) dinates and the speed of the spacecra , they are free at the nal time and for the corresponding costate variables the transver- sality conditions must be fullled:
In Eq. (13) the dimensionless light velocity, nominal sail accel- (19) eration and Sun’s angular momentum are:
where o is a 2-dimentional zero vector. According to Pontry- agin’s maximum principle, the optimal control law allows us to obtain the maximum of the Hamiltonian: respectively. ese equations we used to optimize the motion for the simplest planar case.
440 Vol 71 No.12 December 2018 JBIS SOLAR SYSTEM ESCAPE MISSION WITH SOLAR SAIL SPACECRAFT within a framework of post-Newtonian Gravitational Theory
(21)
(20)
e problem of ballistic optimization of the mission could Eq. (21) is the two-point boundary problem. ey have four be formulated as follows. We need to determine the vector (20), unknown parameters for the planar case, as well as for non-co- which provides the minimum criterion (14), the transversality planar case. All solutions were obtained by using Newton conditions (19), state’s and costate’s systems (13, 18) and the method. e system of dierential equations were solved by predetermined ight duration. Consequently, 8 dierential the Runge-Kutta method and a custom code was developed to equations in the multidimensional set are obtained: 2 equa- perform all calculations. tions of spacecra ’s position, 2 equations of spacecra ’s veloci- ties and 4 costate’s equations. Results of simulation for the planar cases, which describe the escape missions for solar sail spacecra with dierent mass 4 RESULTS OF SIMULATION per area parameters, are shown in Figs. 1-3. Fig. 1 presents the optimal planar escape trajectories for the several mass per area e spacecra assigns with the state vector x0 at the initial mo- parameters from σ = 0.1 kg/m2 to σ = 0.002 kg/m2. It can be ment (start position). e values of x0 equal the heliocentric seen that the spacecra approach to the Sun at the initial stage Earth state. In case of the estimation of the maximum value of allows it to accelerate and gain the maximal speed. e smaller , the nal state coordinates are not xed. As pre- the parameter σ, the closer the spacecra approaches the Sun. viously noted, costate variables are placed in correspondence is feature of the optimal motion is clearly visible in Fig. 2, with the radius and velocity vectors. erefore, the boundary which shows how the distance from the solar sail to the Sun conditions are represented for the case when iteration process depends on time of ight. Figure 3 shows the change of velocity convergence is reached: components during the initial stage of movement.
Fig.1 Optimal planar escape trajectories for a solar sail spacecra : a) σ = 0.1 kg/m2, b) σ = 0.02 kg/m2, c) σ = 0.01 kg/m2, d) σ = 0.002 kg/m2.
Fig.2 e heliocentric radius in the optimal planar escape trajectories: a) σ = 0.1 kg/m2, b) σ = 0.02 kg/m2, c) σ = 0.01 kg/m2, d) σ = 0.002 kg/m2.
Fig.3 e velocity components in the optimal planar escape trajectories: a) σ = 0.1 kg/m2, b) σ = 0.02 kg/m2, c) σ = 0.01 kg/m2, d) σ = 0.002 kg/m2.
JBIS Vol 71 No.12 December 2018 441 OLGA L. STARINOVA, IRINA V. CHERNYAKINA
e data are in good agreement with the results of the work border (about 90 AU and 37 years of ight) the spacecra will [1] obtained in the framework of Newtonian gravity theory. have velocity 28548 m/s 6 AU/Y. On this trajectory with the For example, it is shown that when the mass per area parameter perihelion 0.505 AU the maximum velocity of the spacecra is is 0.01 kg/m2, the device assumes a zero total energy at a dis- 491260 m/s 0.00163 c. tance of 1.89 AU and at the time of crossing the Solar System’s
REFERENCES
1. C. Sauer, “Solar sail trajectories for solar polar and interstellar probe 9. R.Ya Kezerashvili, G.L. Matlo, “Solar radiation and the beryllium missions,” 1999. hollow-body sail: 2. Diusion, recombination and erosion processes,” 2. B. Dachwald, “Optimal solar sail trajectories for missions to the outer Journal of the British Interplanetary Society, 61(2), pp.47-57, 2008. solar system,” Journal of Guidance, Control, and Dynamics, 28(6), 10. Y. Guo, R.W. Farquhar, “Current mission design of the solar probe pp.1187-1193, 2005. mission,” Acta Astronautica, 55(3), pp.211-219, 2004. 3. R.Ya. Kezerashvili, J.F. Vázquez-Poritz, “Can solar sails be used to test 11. R.Ya. Kezerashvili, J.F. Vázquez-Poritz, “Solar radiation pressure and fundamental physics?,” Acta Astronautica, 83, pp.54-64, 2013. deviations from Keplerian orbits”, Physics Letters B, 675(1), pp.18-21, 4. R.Ya Kezerashvili, J.F. Vázquez-Poritz, “Bound orbits of solar sails and 2009. general relativity,” Advances in Space Research, 46(3), pp.346-361, 2010. 12. R.P. Kerr, “Gravitational field of a spinning mass as an example of 5. G.L. Matlo, R.Ya. Kezerashvili, C. Maccone, L. Johnson, “ e algebraically special metrics,” Phys. Rev. Lett., 11, pp.237–238, 1963. beryllium hollow-body solar sail: exploration of the Sun's gravitational 13. F.P. Pijpers “Helioseismic determination of the solar gravitational focus and the inner Oort Cloud”, arXiv preprint arXiv:0809.3535., 2008. quadrupole moment” Monthly Notices of the Royal Astronomical Society, 6. W.K. Wilkie, J.E. Warren, M.W. omson, P.D. Lisman, P.E. 297(3), pp.L76-L80, 1998. Walkemeyer, D.V. Guerrant, D.A. Lawrence, “ e Heliogyro reloaded”, 14. O.L. Starinova et al., “Application of Electric Propulsion for Motion AIAA Paper 20110023680, 2011. Control of Spacecra which Function on Non Keplerian Orbits,” 7. Koblik V. V. et al. “Controlled solar sailing transfer ights into near-sun Procedia Engineering, 185, pp.291-298, 2017. orbits under restrictions on sail temperature,” Cosmic Research, 34(6), 15. R.E. Kopp, “Pontryagin maximum principle,” Mathematics in Science pp.572-578, 1996. and Engineering, 5, pp.255-279, 1962. 8. R.Ya Kezerashvili, G.L. Matlo, “Solar Radiation and the Beryllium 16. G. Leitmann, “Optimization techniques: with applications to aerospace Hollow-Body Sail-1. e Ionization and Disintegration Eects,” Journal systems,” Academic Press, 5, 1962. of the British Interplanetary Society, 60, pp.169-179, 2007.
Received 30 October 2018 Approved 30 October 2018
442 Vol 71 No.12 December 2018 JBIS JBIS VOLUME 71 2018 PAGES 443-449
DO ALIEN INDUSTRIAL CIVILISATIONS EXIST?
DEREK PUGSLEY 6 Parklands Avenue. Bognor Regis, UK
Email [email protected]
Discussions about the existence of alien civilisations are over optimistic. They assume life is inevitable, that every intelligent civilisation is capable of developing technology like our own, and often overlook the influence of a civilisation’s culture and social dynamics on technological development. This paper will identify and examine the sequence of events that resulted in our modern Techno-Industrial Society (TIS) and assess the implications for the development of alien industrial civilisations. Each event is so dependent on chance or a special set of circumstances it suggests industrialisation is a freak accident that may happen only once in the lifetime of our Galaxy. The circumstances determining the occurrence of each event will be identified by posing four questions: Is complex life rare? Is technology an inevitable consequence of intelligence? Do all intelligent societies become a TIS? How does resource depletion affect TIS development?
Keywords: SETI, Alien Civilisations, Fermi Paradox, Scientific Reasoning, Industrial Revolution
1 INTRODUCTION If other animals are intelligent this posits an important question: why is Homo sapiens the only species to make and Given the size and age of our galaxy it seems logical to believe use sophisticated tools? e standard response to this ques- there must be other intelligent civilisations in our Galaxy. It also tion is that only humans have the cognitive skills and manual seems reasonable to assume some of them will have achieved dexterity to use tools. However intelligence, bipedality, large a level of technology advanced enough to build spaceships brains, opposable thumbs, tool making and the use of re were and radio telescopes. ese arguments are based on a priori not a su cient selective advantage to ensure the survival of knowledge, there is no evidence to support the notion of an any other hominin species. Anatomically modern Homo sapi- inevitable progression from a planet with the right conditions ens (AMH) is the only extant hominin species. is suggests for life to an industrialised civilisation similar to ours. Viewed something more than intelligence is required before a techno- objectively, without the distorting lens of anthropomorphism, logical society can evolve. e development of increasingly so- the nal outcome of the process, a Techno-Industrial Society phisticated tools by early modern humans may have been the (TIS), seems somewhat improbable. e evolution of complex result of their evolutionary history and instinctive behaviours. life is possibly rarer than we like to believe and technology and It was this particular set of conditions that produced selective industrialisation are not guaranteed outcomes of intelligence. pressures driving the evolution of an advantageous trait unique e importance of tool making, machines and advanced tech- to AMH. is paper proposes the trait could be the cognitive nology as indicators of intelligence is overstated resulting in ability for scientic reasoning and was the key to the survival the belief that using tools proves humans are the only intel- of AMH in the rapidly changing environments following the ligent terrestrial animal. is belief is the basis for the Search end of the last ice age. However human history suggests that for Extraterrestrial Intelligence (SETI), which assumes intel- even with this trait there is no guarantee every civilisation will ligence is the only attribute required to develop a civilisation use technology to industrialise in the same way humans have based on science and technology. ese assumptions would be since the 18th century. is will be discussed in Section 4. reasonable if humans are the only intelligent animal on Earth. However since the 1960s, with more research due to better We tend to think technology ensures the success of a spe- funding and improved technology, we are beginning to real- cies, mainly because, so far at least, this is true for human be- ise intelligence is not restricted to human beings. Animals are ings. However resource depletion caused by the use of technol- more complex, more intelligent, more sentient than previously ogy may limit the number of industrial civilisations a planet believed and intelligent behaviour is now recognised in many could support over its habitable lifetime. A er the collapse of non-primate species such as dolphins, elephants, the octopus a global civilisation it would take geological timescales for nat- [1], several species of birds and even bees [2]. Intelligence is ural resources to be replenished. During the recovery period an important survival trait. It comprises cognitive abilities, industrialisation by subsequent civilisations that depended on such as problem solving and learning new skills, that enable resources such as metallic ores and fossil fuels would be prob- animals to adapt to changes in their environment. A er mil- lematic. is will be discussed more fully in Section 5. lions of years of natural selection it should come as no surprise such a functionally advantageous trait appears in more than For the purpose of this paper the following denitions will one species. be used:
JBIS Vol 71 No.12 December 2018 443 DEREK PUGSLEY
• Technology is the various ways social groups use science to acquisition of one simple cell by another. is is a rare anoma- provide themselves with the material objects of their civili- ly, suggestive of a freak accident. All multicellular life on Earth sation. evolved from a common eukaryote ancestor and without the • Industrialisation is a period of social and economic one-o event that produced this ancestor multicellular life will change that transforms a social group from an artisan not be possible – simple cells do not have the right cellular society into a mechanised society, involving the extensive architecture to evolve into more complex forms. According to re-organisation of its economy for the purpose of large Lane [6] this is because there is an energy barrier that pre- scale production of goods and services. vents simple cells, like bacteria, growing more complex. On • Culture is the set of shared attitudes, values, goals, and Earth this problem was overcome when a serendipitous event practices that characterises a social group. resulted in one simple cell somehow ending up inside another. • Civilisation is any complex society organized in densely e bacterium acquired by the host cell evolved into tiny pow- populated settlements with a symbolic system of commu- er generators – mitochondria. Only once this occurred could nication, for example a writing system. (is denition multicellular organisms evolve, with the transition possibly excludes any reference to social stratication and a ruling happening quickly [7]. elite. Although human civilisations are organised in this way alien civilisations may not be.) 3 IS TECHNOLOGY AN INEVITABLE CONSEQUENCE OF • Technophiles are any social group or society who want and INTELLIGENCE? are enthusiastic about using technological innovations. e human species has migrated to all parts of the world and 2 IS COMPLEX LIFE RARE? adapted to a wide range of environments. We attribute this to our intelligence and use of technology. is combination of Even if a planet has all the right conditions for life, random abilities is clearly a selective advantage, so natural selection chance and natural selection have to overcome two major ob- should ensure it emerges in any intelligent species. Many ani- stacles before multicellular life can appear: mals are now regarded as displaying intelligent behaviour and yet a er hundreds of millions of years of evolution only one • Homochirality species, AMH, has developed sophisticated tools. e stand- • Endosymbiosis ard explanation of this has been that only humans have both intelligence and the necessary physical capabilities, such as 2.1 Homochirality and the evolution of simple life opposable thumbs, to make and use complex tools. Howev- er many primate species other than Homo sapiens have op- We tend to presume life will arise on a planet with the right posable thumbs, and there are also non-primates, such as the conditions and once simple cells evolve there is an inevitable opossum, giant panda, koala and murids, with exible digits evolutionary trajectory to complex life. Even if the conditions that work like opposable thumbs enabling the animal to ma- are right, random chance has to produce a solution to the nipulate and grasp objects. e octopus, an invertebrate with problem of homochirality before single celled life can evolve. a large brain, can fold together the two sides of every one of Life almost exclusively synthesizes L-amino acids and D-sug- its one hundred suckers to form a pincer grasp like the human ars and this homochirality, or one-handiness, is essential for thumb and forenger. So organisms with intelligence and ap- the functioning of proteins as amino acid polymers, and for pendages with the dexterity to grasp objects are not unusual. the structure of DNA and RNA, which require incorporation of D-sugars. So before metabolic pathways could evolve there e fully opposable thumb probably appeared in Homo had to be an amplication mechanism, a catalyst, that pro- habilis about two million years ago but none of its hominin duced an enantiomeric excess. Research indicates there are descendants were able to develop their technology beyond several plausible mechanisms for the emergence of homochi- simple tools, apart from Homo sapiens. Intelligence, the abil- rality [3] [4] on a prebiotic planet but there is no agreement ity to grasp tools and the use of technology to make them on the actual mechanism that resulted in the origin of life on were not functionally advantageous enough traits to enable Earth. Until we are certain what the catalyst was on Earth we other hominins to adapt to the environmental changes of the should be cautious about assuming amplication mechanisms Pleistocene era. is suggests the evolution of a trait unique are commonplace in the Galaxy. Since such a mechanism is an to AMH, probably between one hundred thousand and one essential prerequisite for the emergence of life if one does not hundred and y thousand years ago, that gave it a selective exist on an alien world even simple life will never evolve. advantage over other hominins and improved its reproductive success. is trait was the cognitive ability for scientic rea- 2.2 Endosymbiosis and the evolution of complex life soning. For this trait to spread through the earliest members of the AMH population it must have provided an extremely e emergence of complex life is more problematic, requir- strong selective advantage otherwise genetic dri —random ing the acquisition of one simple cell by another to produce a events—would have overwhelmed the force of selection. eukaryotic cell, the building block of all multicellular life on Earth. Although such associations are common among com- If a er millions of years of evolution only one species has ever plex cells they are very rare in simple ones and the outcome evolved the cognitive ability for scientic reasoning it suggests was by no means certain: the two cells went through a lot of the trait arose because of a unique set of conditions. Accord- di cult co-adaptation before their descendants could our- ing to Louis Liebenberg scientic reasoning is an adaptation ish. According to Nick Lane [5] there is no inevitable evolu- driven by natural selection [8] [9]. It evolved in AMH as the tionary trajectory from simple to complex life. If simple cells tracking method used in hunting developed from simple and had slowly evolved into more complex ones over billions of systematic tracking into speculative tracking in response to years intermediate cells would have existed and some should changes in the environment. is advanced method of track- still be around today but there are none. So just once in four ing is based on hypothetico-deductive reasoning and involves billion years of evolution has random chance resulted in the a fundamentally new way of thinking. It requires the hunter to
444 Vol 71 No.12 December 2018 JBIS DO ALIEN INDUSTRIAL CIVILISATIONS EXIST? predict where tracks were most likely to be found and inter- may not see any benet in these changes. A society’s cul- pret other signs to locate prey. Liebenberg believes the ability ture is an important determinant of the philosophy of to interpret tracks and signs played a signicant role in the de- science it adopts and whether the physical expression of velopment of the scientic intellect. He argues the art of track- technology by the civilisation progresses towards more ing and modern science involve the same reasoning processes sophisticated technology and eventually large scale in- and require the same intellectual abilities such as visual and dustrialisation. Intelligence and use of simple technolo- thematic imagination and the use of analogy. If he is correct gy do not necessarily guarantee a civilisation will have a then it is possible the development of speculative tracking by strong desire to do this. AMH was the driving force behind the evolution of its cogni- tive abilities to engage in scientic reasoning. 3. A planet’s ecosystems are too hostile to allow the devel- opment of communities. Human civilisations have all e evolution of this trait would not have been possible if been built around the cultivation of a high-yield agricul- members of the hominin genus had not already beneted from tural crop that depends on the regional climate. Rice in a series of adaptions that began when grassland expanded in Asia, corn in North and South America, wheat in Europe Africa about three million years ago. ese included bare skin, and North Africa. In the Pacic, smaller communities an increase in sweat glands and longer legs, adaptions that al- were built around sweet potatoes and yams. Human civ- lowed for sustained walking and running, and craniodental ilisations also had docile herd animals like cows, sheep, adaptions enabling hominins to eat a wider variety of foods. pigs and goats that could be enclosed in pens. If a plan- Early hominins, such as Australopithecines, probably supple- et’s environmental conditions and ora and fauna are not mented their diet with meat from scavenging. Later hominins conducive to the formation of villages or cities civilisa- such as members of the Homo genus may have used system- tions will never develop. is may be the reason Aus- atic tracking for scavenging and persistence hunting. ese tralian aborigines never built settlements and remained were the subsistence methods various Homo species took hunter-gatherers [10]. with them when they migrated from Africa. For a while sever- al Homo species coexisted, all probably using the same range e evolution of a planet’s ecosystems depends on of subsistence methods. However only one of these groups, many factor including solar radiation reaching the sur- AMH, developed speculative tracking enabling it to adapt to a face, orientation, shape and size of continents, land to wider range of habitats than other hominins. sea ratio, presence and size of a moon or moons and seis- mic and volcanic activity. ere must be many possible e development of technology advanced enough to create scenarios where this combination of factors produces an industrialised society depends not just on intelligence and ecosystems that would inhibit the development of civi- the ability to use simple tools but also requires the evolution lisations. e Australian continent is an example of this of a particular trait, scientic reasoning. is appears to have on Earth. evolved in AMH due to a set of circumstances unique to our species suggesting its evolution is a very rare event. 4. Depletion of a planet’s natural resources by previous or contemporary civilisations. is will be discussed in Sec- 4 DO ALL INTELLIGENT SOCIETIES BECOME A TIS? tion 5.
e ‘I ‘in SETI refers to intelligence but it should refer to in- e belief that alien civilisations must follow the same tech- dustrialised societies because only such societies are capable of nological path as Western civilisation is based on several im- building radio telescopes and spaceships. To achieve the abili- plicit assumptions about such civilisations: ty to do this a civilisation requires not only intelligence, scien- tic reasoning and technology but also a period of social and • ey are technophiles like human beings. economic change that transforms all its social groups into an • eir technology is based on a notion of science similar industrial society. Industrialisation also depends on the devel- to the one developed during the Scientic Revolution in opment of three primary technologies, industrial power, metal Europe. working and machine tools for making precision parts. SETI • All social groups regard industrialisation as a positive is really looking for a TIS that has developed along these lines. development. However the history of human civilisations suggests there is no guarantee such a society will develop. e Scientic and Since the Industrial Revolution there has been world-wide Industrial Revolutions that took place in Western Europe did acceptance of the paradigm of scientic methodology devel- not occur in any previous civilisation. To explain this we need oped in Europe. is has resulted in industrial globalisation to look at how the culture of a society determines its notion of as people benet from, and want more, advanced technology. science and use of technology. ere are four possible reasons It is assumed that an alien civilisation would at some point why an intelligent society may not develop into a TIS. in its history experience a scientic revolution followed by an industrial revolution similar to that which took place across 1. If the alien species that constitutes the civilisation has Europe. It is also assumed, due to the perceived superiority of not evolved the cognitive abilities for scientic reasoning European science over all other forms, that an alien civilisa- it will have no notion of science with which to develop tion’s notion of science will be very similar to ours. Both are technology as we know it. shaky assumptions, the rst is based on a posteriori reasoning and the second an a priori argument. 2. Industrialisation involves such things as the increased use of machines over hand production methods, the de- Nathan Sivin’s [11] arguments for a scientic revolution in velopment of machines tools and the introduction of the 17th century China demonstrate that by looking at science in factory system. It requires signicant structural changes the context of the culture at the time, early modern science to a society and the political elite within the civilisation was not conned to a small corner of north-western Europe.
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Science revolutions did occur in other civilisations at other 4.2.3 Cultural times, notably Ancient Greek, Chinese, Indian, and Islam- ic. ese other revolutions are largely ignored because their Chinese society was founded on the beliefs of philosophers science was based on dierent philosophical principles to the like Confucius, Mencius, Han Feizi (Legalism), Lao Tzu (Tao- West’s. It seems reasonable to presume that because modern ism), and Buddha (Buddhism). e new science in Europe science emerged in Europe the Industrial Revolution would demanded truth above all and created knowledge that had have also started there. However, none of the cultural varieties no value except truth. e Chinese considered the idea of of modern science stimulated an industrial revolution and the objective knowledge without wisdom and moral or aesthetic sorts of institutional and social changes that appeared in the signicance as grotesque. is may explain why early China West. had sciences but no science, no unifying philosophy that in- tegrated all the sciences into an overarching concept. Scien- Chinese and Ancient Greek civilisations are examples of hu- tic and technological interests were connected to a person’s man civilisations that had the potential to industrialise but responsibilities, o en civil service appointments. As a result whose cultural evolution took their development of technol- innovations occurred in response to the everyday problems of ogy in dierent directions compared to Western Europe. It is, society arising from such things as construction, agriculture, therefore, worthwhile identifying the reasons why these two shipbuilding and armaments. civilisations did not industrialise. 4.3 Why industrialisation started in England 4.1 Why industrialisation did not happen in ancient Greece e Industrial Revolution in England was aided by revolutions e ancient Greeks were not technophiles. ey perceived in agriculture, transportation, communications and technol- hand-made artefacts as having more aesthetic value than ones ogy pioneered by English farmers and engineers. It was also produced using a machine. e notion of a factory produc- helped by its economic system and English culture. e ag- ing mass-produced goods for general consumption would ricultural revolution led to high productivity and low food have been an anathema to their ideals. Aristotle said science prices giving ordinary people su cient disposable income shouldn’t be used, because work is something for the lower to buy manufactured goods. Other economic assets were an classes. Learned people didn’t work, and working people didn’t eective central bank, a well-developed credit market, a free learn. eir economy, like many other ancient and medieval market economy, a free labour market with a surplus of labour, economies, was dependent on slave labour, particularly for ag- and easy access to high quality coal. ere were also less tan- riculture. Since the wealth of ruling classes was based on slave gible reasons why England became the ‘rst industrial nation’. ownership they would have seen mechanisation as a threat that ese are mainly cultural reasons. Although the industrial would reduce, rather than increase, their wealth and power. As revolution was clearly an unplanned and spontaneous event, it urbanisation increased and the Greek empire expanded they would never have taken place had there not been people who pioneered the technologies society needed to overcome prob- wanted such a thing to occur. ere were obviously those who lems or were cultural requirements at a particular time. Inno- saw opportunities not only for advances in technology but vations were primarily concerned with food production, water also the prots those advances might create. e English, like management, weapons, ship building and religious buildings. the Dutch of the same period, were a very commercial peo- It was their developing culture that aected the types of tech- ple. ey saw little problem with making money, taking their nologies pursued and the timing of their innovation rather surplus and reinvesting it. Whether this was to do with culture than a desire for progress or to acquire more personal wealth. and religion or it was a specically English trait is debatable, So although Greek engineers, such as Heron of Alexandria, but the fact remains that English entrepreneurs had a much knew steam could power machines they saw no potential in wider scope of activities than did their Continental counter- developing the technology for wider use in society. parts at the same time [12]. In the open society of 18th and 19th century England entrepreneurs like James Watt became 4.2 Why industrialisation did not happen in China wealthy men as a result of their inventions, unlike Heron of Alexandra in1st century ancient Greece who died in poverty. e reasons are political, economic and cultural. At the time no other European country had this combination of economic and social advantages. 4.2.1 Political 4.4 Summary For most of its history China was a unied empire run by a professional civil service based on meritocracy. is system e reasons why an industrial revolution did not occur before provided the security and stability, rather than progress, that the 18th century are complex. e culture of each previous Chinese society wanted. civilisation was dierent and so their reasons for not indus- trialising dier. Although it is possible to identify some of the 4.2.2 Economic tangible reasons it occurred in England when it did, the real problem is not how the Industrial Revolution took place but Although slaves were a part of Chinese society throughout why earlier civilisations did not want such a revolution. For its history they were never as signicant part of the econo- the ancient Greeks it was perhaps because machines did not my as in Greek and Roman society. ey were mostly used appeal to their sense of aesthetics. eir economy was also in domestic service, and possibly in mines and quarries and based on slave labour, as were most other ancient and medi- other workplaces with unsafe environments. e indigenous eval societies, and mechanisation would have been seen as a Chinese population was large enough, workers cheap enough, threat to the stability of this system. However this was not the and agrarian productivity high enough not to require mecha- case in China, slaves were never important to its economy. It is nization—thousands of Chinese workers were perfectly able tempting to explain China’s lack of industrialisation on the fact to quickly perform any needed task. that it did not have an integrated notion of science. However
446 Vol 71 No.12 December 2018 JBIS DO ALIEN INDUSTRIAL CIVILISATIONS EXIST? this did not stop China inventing cast iron, the printing press, lifetime of a planet. ese consecutive or contemporary civili- paper, the compass, gunpowder and chrome plating [13]. sations would consume resources to a lesser or greater degree. Given these circumstances there are two scenarios that could Earlier civilisations seem to have used innovations only when lead to resource depletion. society needed them, for example agriculture and construc- tion. ere was no need for innovations to develop machines 1. A succession of low to medium level technological civi- for mass-production because there was plenty of cheap man lisations rise and fall over many millennia gradually using re- power to do the job. is also meant there was no point in sources. mass-producing goods for general use because there were too few people who could aord them. Slaves had no income and 2. A civilisation has access to su cient natural resources to peasants spent nearly all their income on food. In societies de- develop more advanced technology and begin to industrialise pendent on slave labour or where social mobility is restricted on a local and then global scale. As it expands to become a by rigid social hierarchies there can be no notion of consum- global economy the extraction of resources becomes increas- erism. Within these types of society cultural evolution is about ingly dependent on evermore advanced mining machinery. security and stability not progress and constant change. e level of its technology is also su cient to make it a su- per-predator resulting in a mass extinction event that almost e Industrial Revolution was an unplanned and spontane- certainly results in the collapse of the civilisation. It is possible ous event. ere was no inexorably unfolding inner logic to no civilisation survives large scale industrialisation because a the process, rather a muddled series of decisions and actions. TIS inevitably becomes a super-predator. According to Adam Why did the people of England and then the rest of Europe Lipowski [14] a super-e cient predator emerges as a natural want such a revolution? e political, economic and social consequence of ecosystem dynamics. Human beings are argu- framework that provided the right conditions for industriali- ably such a predator because we are causing a reduction in the sation had been evolving in England for some time. It created population size of a large number of species. However it is not an open society and laws that rewarded innovation and en- the mass extinction event itself that is the problem. Even if the trepreneurship by allowing individuals to accumulate capital species that created the super-predator civilisation causes its and ideas. ere was also a desire for progress and as indi- own extinction, life will recover and another intelligent spe- vidual wealth increased a demand for products and services cies will step in and take its place. e real problem is resource that required innovations to increase productivity. Unlike depletion. slave-based economies there was no perceived threat to social stability from mechanisation because the English economy In both these scenarios succeeding civilisations would not was not dependent on slave labour. A free and mobile labour have the level of technology required to locate and extract the market meant workers could move from agriculture to better remaining resources. Natural resources such as fossil fuels paid jobs in the new factories. Improvements in agriculture take hundreds of millions of years to replenish and metallic meant food was cheaper, more varied and more plentiful and ores and other minerals are created by processes which take for the rst time ordinary people had spare money to spend on place over geological timescales and are o en widely dis- goods and services. Cultural evolution in England had created persed and di cult to locate. Resource depletion could be a society that believed hard work and ideas could improve a a constraint on the number of industrial civilisations that a citizen’s standard of living. e rest of Europe quickly saw the planet can support. e number of civilisations supported benets of industrialisation. At the time Europe was fragment- would depend on several factors including the chemical com- ed with continuous competition between jealous emerging na- position of the planet, whether the formation of fossil fuels is tions. is competitive system encouraged scientic progress commonplace, the habitable duration of the planet and the and industrialisation and acceptance of the social changes that time taken for natural resources to recover. e recovery time came with them. depends on ongoing ore-creating geological processes such as tectonic and magmatic activity, sedimentary processes, hy- Intelligent societies only industrialise if they want to. Human draulic sorting and hydrothermal alteration. It is possible that civilisations seem to have always found far more reasons to resources recovered a er depletion due to industrialisation maintain the status quo than industrialise. Why do we think could have become less concentrated and more widely dis- all alien civilisations will follow the example of 19th century persed, making it more di cult for later civilisations to locate Western Europe? and extract them.
5 HOW DOES RESOURCE DEPLETION AFFECT TIS 6 CONCLUSIONS DEVELOPMENT is paper has identied four improbable events that are cru- e disadvantages of technology that could lead to the col- cial stages in the evolution of a TIS. ree of these events, lapse of a TIS, such as nuclear war or climate change, are re- the evolution of single-celled life, the emergence of complex garded as problems that a society can avoid. However using cells, and development of the cognitive ability for scientic technology requires the consumption of a planet’s natural re- reasoning, were driven by natural selection. e emergence of sources and eventually results in the depletion of reserves of intelligence however is a highly probable event, evolution is fossil fuels and minerals. is could occur before a civilisation bound to stumble upon this because it is a useful survival trait has the capability to mine the resources of its solar system. like ight or eyes. It is signicant that the trait for scientic e possibility of resource depletion as a causative factor in reasoning evolved in only one terrestrial animal, AMH. is the non-existence of industrialised societies in the Galaxy is implies the trait is not as useful an adaption as intelligence and underestimated or overlooked. It is assumed only one species its evolution depends on a specic set of circumstances. For on each habitable planet builds a TIS. However because in- a terrestrial organism, based on the evolution of AMH, these telligence will evolve in more than one species there could be could be: any number of civilisations built by dierent species over the • e evolution of an early ancestor that is not a specialist
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predator, which becomes adapted for terrestrial locomo- social groups in these civilisations decided, for economic and tion. cultural reasons, they did not want industrialisation to hap- • e evolution of opposable digits for grasping and ma- pen. e Industrial Revolution started in England because a nipulating objects. period of cultural evolution had created an environment con- • Changes in a planet’s climate resulting in a decrease in ducive to technological progress. e social changes included forests and increase in grassland. such things as an open society, free labour market, intellectu- • An ancestor adapts to these changes in the environment al property rights and less inequality in income distribution. by losing its hair, walking upright and developing into a Based on this unique set of circumstances an alien civilisation long distance runner. would need a similar cultural evolution to create a society with • Later ancestors, who eat meat and supplement their diet the following characteristics: by hunting, develop the art of tracking. • One of these later ancestors develops persistence hunting • A desire for progress. and the art of speculative tracking. • Citizens can make money from their ideas. • ere is a need to increase productivity through innova- is set of conditions would exclude a true predator or veg- tion in order to meet demand for a product or service. etarian animal from developing scientic reasoning. As far • An economic, social, and political system that facilitates as natural selection is concerned a natural predator is ‘good- innovation and entrepreneurship. enough’ at its role in an ecosystem not to require the evolution • An economy that is not dependent on slave labour. of additional traits to make it a better predator. A vegetarian • Mechanisation is not seen as a threat to stability. organism would never need to develop its hunting skills. ese conditions do not exclude marine organisms. For example, the is specic set of circumstances has occurred only once octopus has manipulative appendages and is a hunter which in the history of human civilisations, suggesting cultural pres- does not have the speed to chase down its prey and so depends sures are a more important determinant of industrialisation on intelligence to trap them. What it lacks at the moment is the than a notion of science or intelligence. ability for scientic reasoning. Speculative tracking evolved in AMH because its social skills enabled close cooperation be- Analysis of the factors involved in each event result in the tween individuals during the hunt. e octopus is a solitary following observations: predator so there is no selective advantage driving develop- ment of the trait. 1. If homochirality is a problem we will discover planets with water but none with life. e other event, industrialisation, depends on the culture and social dynamics of civilisations. e development of science 2. If we nd planets with simple life like bacteria but nev- and technology and industrialisation by a civilisation is deter- er complex life then the evolution of a eukaryotic cell mined by a set of special circumstances and is too dependent through primary endosymbiosis is a uke event and in- on its social and historical origins to be considered universal. telligent civilisations in the Galaxy will be very rare. For example the direction taken by the Science Revolution in Europe depended on philosophical ideas of the ancient Greeks 3. Even if life is fairly common and the evolution of scientif- and Europe’s religious culture at the time. In the West the di- ic reasoning is not unusual SETI will probably never nd chotomies between mind and body, and objective and subjec- another TIS. An alien civilisation is unlikely to have the tive were already entrenched in scientic thought by the time same notion of science and undergo a process of indus- of Plato. St. Gregory of Nyssa and St. Augustine introduced the trialisation like human beings because its cultural evolu- early Christian church to Plato’s concept of a body-soul dichot- tion and social dynamics depend on a set of conditions omy and the immortality of the soul. Galileo, Descartes and unique to that society. Previous human civilisations have their successors opportunely used this ancient Greek idea of had dierent world views about the benets of science dualism as an argument for separating physical science from and technology to their society so we should not expect the province of the soul. ese early modern scientists realised an alien civilisation to have exactly the same world view they could not get round the authority of the Church on the as the Western European paradigm. strength of ideas alone. ey begun constructing a new intel- lectual community outside the old establishment. By emphasis- 4. Resource depletion means that over the lifetime of a ing the distinctions between mind and body they could claim planet there could be an upper limit on the number of authority over the physical world on the ground that purely civilisations that get the chance to industrialise. Using natural knowledge could not con ict with, and therefore could computer models to estimate the recovery time a er not threaten, the authority of established religion. In China a depletion and the distribution of replenished resources dierent philosophical and religious culture allowed Chinese could be one method of determining if resource deple- science to get along without the mind and body dichotomy. So tion is a signicant constraint. if the Catholic Church had been less resistance to the new ide- as of the Reformation, the science revolution in Europe could ese observations indicate we should be more objective in have been based on Aristotle’s idea that the body and soul are our a priori reasoning about the possibility of nding a TIS. not distinct entities but are dierent aspects of the same thing. We need to understand why only Western society chose to in- e Industrial Revolution, if it occurred all, would then have dustrialise—what was dierent about its social dynamics com- followed a very dierent course. pared to all other civilisations? Tool-use has been documented in a very small percentage of species so it probably does not A dierent notion of science to the modern Western view is confer any signicant evolutionary advantage like other traits not in itself a barrier to industrialisation. Previous civilisations such as the eye or wings. Why then do we believe tool using be- used machines, even knew the concept of a steam engine, and haviour is inevitable in alien ecosystems? More empirical data used assembly-line processes when necessary. However key is required to answer these questions.
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REFERENCES 1. "Are octopuses smart?",https://www.scienticamerican.com/article/are- 8. L. Liebenberg, e Origin of Science, CyberTracker, 2005. octopuses-smart/ (Last Accessed 14th September 2018). 9. L. Liebenberg, e Art of Tracking, David Philip, 1990. 2. R. Schiman, “Buzz o”, New Scientist, June 7 2018, pp40-41. 10. “Why didn’t Aborigines build cities?”, http://www.convictcreations.com/ 3. D. G. Blackmond, “ e Origin of Biological Homochirality”, Cold Spring aborigines/cities.htm (Last Accessed 15th September 2018). Harb Perspect Biol 2010;2:a002147. 11. N. Sivin, “Why the Scientic Revolution Did Not Take Place in China — 4. R. Pohl, “Homochirality as Prerequisite for the Origin of Life”, or Didn't It?”, Chinese Science, 1982, 5: 45-66 (revised August 24 2005). Conference ‘Extraterrestrial Life – Beyond our expectations?’ Vienna, 12. “ e Origins of the Industrial Revolution in England”, http://www. April 21 -22 2012. historyguide.org/intellect/lecture17a.html (Last Accessed 17th 5. N. Lane, “Life: is it inevitable or just a uke?”, New Scientist, June 23 September 2018). 2012. pp32-37. 13. “Stunning Metallurgical Advances of Ancient China”, http://www.china. 6. N. Lane, “Energetics and genetics across the prokaryote-eukaryote org.cn/english/culture/123047.htm (Last Accessed 20th September divide”, Biology Direct, 2011, 6:35. 2018). 7. W. C. Ratclie, R. Ford Denison, M. Borello and M. Travisano, 14. A. Lipowski, “Periodicity of mass extinctions without an extraterrestrial “Experimental Evolution of Multicellularity”, Proceedings of the National cause”, May 2005, Physical Review, E 71 052902 Academy of Sciences USA, Vol. 109, No. 5, pp 1595-1600 (2012).
Received 29 September 2018 Approved 2 November 2018
JBIS Vol 71 No.12 December 2018 449 JBIS VOLUME 71 2018 PAGES 450–457
HEAT TRANSFER IN FUSION STARSHIP Radiation Shielding Systems
MICHEL LAMONTAGNE, Icarus Interstellar.
Email [email protected]
Fusion starship designs require radiation shielding from neutrons and X-rays created by the drive. Even nominally aneutronic fusion reactions, such as Deuterium+He3, produce neutron fluxes through side reactions that may create large cooling requirements in drive structural elements. This paper aims to quantify these emissions and describe the heat transfer systems required to handle these heat loads. Neutrons and X-ray emissions are established for three fusion drive designs, Daedalus, a Daedalus variant named l’Espérance and Icarus Firefly. From nearly zero for Daedalus, they rise to 220 GW for l’Espérance and to 8400 GW for Firefly. The geometric structure of the vehicles is analyzed in order to determine the impingement rate for the neutron and X-Ray radiation. The open nozzle proposed by Miernik is used as an example of design, allowing up to 97% of the radiation to escape. Firefly, the most severely heat loaded design, requires 260 GW
of cooling. Two methods are compared to remove the heat to the radiators. Temperature change using Q=mf×cp×∆t for
gas and liquid flows, and Q=mf×Ve for phase change. The fluid paths are determined and pump and compressor power requirements are calculated. Then radiator areas and masses are determined. The physical arrangements of radiators are examined in regards to view factors, radiator placement and the influence of these on radiative power. Phase change in liquid metals provides the most powerful heat extraction method for the powers levels involved in starship propulsion, and radiators need to be placed as close to the drive as possible to avoid important mass penalties.
Keywords: Fusion, Heat transfer, Heat transport, Radiation
DAEDALUS
L'ESPERANCE
FIREFLY
Fig.1 General vehicle arrangements. 1 INTRODUCTION
Fusion starship designs require radiation shielding from Bremsstrahlung radiation from the electrons in the plasma neutrons and x-rays created by the drive. Even nominally also contributes to the radiation load. aneutronic fusion reactions, such as Deuterium+He3, can produce neutron uxes through side reactions that will cre- For this paper, three ship design were used, that cover the ate large cooling requirements in drive structural elements. spectrum of possible heat loads. e original Daedalus from the JBIS study [1], a Daedalus variant called l’Espérance, and Robert Freeland’s Icarus Fire y [2] (Fig. 1). is paper was presented at the Foundations of Interstellar Studies Workshop at CUNY City Tech, New York City, 13-15 June 2017. e three ships have similar characteristics, although
450 Vol 71 No.12 December 2018 JBIS HEAT TRANSFER IN FUSION STARSHIP Radiation Shielding Systems
TABLE 1 Ship characteristics and basic performance equations (for Daedalus the nozzle wall is also the radiator) Value Unit Daedalus L’Espérance Icarus Firefly Stage 1 Stage 2 Ship overall mass M tonnes 52,700 5450 30,000 24,000 Propellant m tonnes 46,000 4,000 27,660 21,725 Ship dry mass tonnes 2,500 1,450 2,340 2,275 Propellant mass kg/s 0.72 0.072 0.044 0.05 flow Main fusion D+He3 D+He3 D+D D+D reaction Fusion energy WEf GJ/kg 353,000 353,000 320,000 320,000 release Burnup fraction bf 0.15 0.09 0.22 0.8 Power P= ×bf×WEf GW 44,000 3,100 3,700 12,900 Neutron, x-ray loss 0 0 6% 65% fraction Radiation loss GW 0 0 220 8,400 Power to nozzle GW 44,000 3,100 3,480 3,600 Thermal load GW 9 1 17 260 Radius of nozzle m 50 20 20 25 Temperature K 1,600 2,000 2,450 2,600 Mass (nozzle + tonnes 22 accessories) Nozzle wall Area m2 15,700 2,500 500 240 Coolant - - Helium Beryllium Radiator area m2 (1) (1) 40,000 174,000 Radiator K - - 1,750 2,500 temperature Radiator system tonnes - - 800 1,591 mass
Daedalus is a 2 stage ship, summarized in Table 1: neutrons cross section for neutron capture; 80 Barns [1]. With the large diameter of the ICF pellets used by Daedalus and the 2 THE FUSION HEAT LOAD compression level chosen (2000 times the initial density of the pellet for the second stage), this eectively rendered the fusion e neutrons and x-ray emission levels for the three vehicles reaction aneutronic. e value of 80 barns has been called into vary widely; from nearly zero for Daedalus to 220 GW for l’Es- question in latter studies, notably the hypothesis that most of pérance and to 8400 GW for Fire y. e large variations are the neutrons would be thermalised in the pellet core and that almost entirely due to dierences in neutron and x-ray absorp- Bremsstrahlung radiation would also be absorbed in the pro- tion levels in the fusion reactions. pellant pellet [3, 4]. ese studies propose that up to 2.5% of the reaction energy may be lost as neutrons. Daedalus uses Inertial Connement Fusion of frozen fuel pellets and reaction 4 from Table 2, D+He3, as its main power To study the eect of neutron loads, L’Espérance was de- source. However, some side reactions of reactions 1, 2 and 3 veloped as an alternative design to Daedalus, with neutron are inevitable, so some neutrons are liberated. Neutrons ab- emission levels based on deuterium deuterium fusion using sorption was calculated in the original study using a very wide ICF pellets. Reaction 5 from table 2 summarizes the cascade
TABLE 2 Fusion reactions Reaction Products Total Energy N release Energy → Energy Energy MeV GJ/kg MeV/ MeV/ MeV/ fusion fusion fusion 1 D + T → He4 3.49 + n0 14.10 17.59 340,000 5 2 D + D → He3 0.82 + n0 2.45 3.27 79,000 4 3 D + D → T 1.01 + p+ 3.02 4.03 97,000 4 4 D + He3 → He4 3.60 + p+ 14.70 18.30 353,000 5 5 6D → 2He4 8.92 + 2n0 16.55 + 2p+ 17.72 43.22 348,000 12
JBIS Vol 71 No.12 December 2018 451 MICHEL LAMONTAGNE
Fig.1 Examples of Closed and open nozzles; Daedalus and l’Espérance. e Daedalus image also shows the heat shield, protecting the fuel tanks from the thermal radiation from the nozzle walls. reaction of deuterium+deuterium. About 40% of the reactions unhindered. Radiation that does hit structural elements is products are high energy neutrons. Using high energy neutron transformed into heat that must be removed. Detailed cal- cross sections of about 1.5 Barns, the radiation load that es- culations should show some neutron re ection and re-radi- capes the pellet core is about 6% of the fusion energy [5] or ation, depending on the materials, reducing the heat load. 220 GW. It is also assumed, as for Daedalus, that most of the is has not been taken into account in the present evalua- Bremsstrahlung radiation is absorbed in the pellet outer layers. tion. e impingement is a function of geometry; for a point source, the hemispherical nozzle of Daedalus covers 50% of Icarus Fire y uses a Z-pinch continuous fusion drive that has radiative area. If such a nozzle was used for Icarus Fire y, the no neutron capture capabilities and the same D+D fusion re- thermal loading would be 4,200 GW and totally unmanagea- action as L’Espérance. So it presents the upper limit of neutron ble. e Fire y nozzle and reaction areas were designed to be emissions. It also emits a signicant amount of Bremsstrahlung as open as possible and have only 6% of impingement area. radiation. Up to 65% of the fusion energy is lost as high energy is is at the extreme limit of stability for such a structure. neutrons or as x-rays, or 8 400 GW. As Fire y has a very high With an open nozzle, the thermal load is reduced to 260 GW, burnup fraction, the resultant thrust is similar to the other ve- still a large number, but less excessive. Due to the form of the hicles despite the high losses. pinch, a long thin line, the radiation is not a point source but a line source. is increases the thermal load on the structure 3 GEOMETRY and complicates the geometry. e thin structure required to reduce the heat load is susceptible to buckling. e reaction 3.1 Overall Vehicle Geometry takes place outside the nozzle, while for ICF the reaction hap- pens inside the nozzle. is increases the number of irradiated Daedalus is a very compact vehicle, with close proximity be- surfaces for Fire y. tween the fuel tanks and the drive. is conguration is possi- ble because there is only a thermal radiation load, and no high e l’Espérance nozzle has a structurally more conservative energy radiation load, on the vehicle. impingement area of 15%. e sum of the cooling loads is 17 GW for a nozzle about the same size of the one of the Daedalus Fire y and l’Espérance adopt stretched out congurations, second stage. using the inverse square law to reduce the size and loading of the radiation shields and their associated mass, and to allow e area subjected to radiation includes the nozzle, the reac- space for radiators. tion area, the payload and propellant radiation shield, structur- al elements, superconducting magnets and conductors as well 3.2 Nozzle and Shield Geometries as the energy recovery system. e superconducting elements require protection from all radiation, as the low temperature For Daedalus, the nozzle has closed walls. e nozzle also requires refrigeration, adding to the heat load and energy re- serves as the reaction chamber and as the drive radiator. e quirements, and superconductors are sensitive to high ener- metallic structure of the nozzle heats up to 1600 K in order gy radiation damage, eventually losing their superconducting to dissipate some x-ray radiation and induced eddy currents properties. Room temperature conducting superconductors in the nozzle wall. In fact, the size of the Daedalus nozzle was would not change the situation signicantly. chosen in order to allow for the radiative cooling of the nozzle walls. e rst stage can radiate 9 GW while the second stage e structure of l’Espérance and Fire y needs to be actively is sized for 1 GW. cooled, as the neutron radiation gain is much higher than the radiation loss at temperatures below the melting point of even e open nozzle concept of l’Espérance and Fire y has the most refractory materials. For the Daedalus nozzle/reac- been used for a number of design studies [4, 6, 7]. It allows tion chamber the Molybdenum walls at 1600 K are in thermal most of the high energy radiation to leave the reaction area equilibrium.
452 Vol 71 No.12 December 2018 JBIS HEAT TRANSFER IN FUSION STARSHIP Radiation Shielding Systems
Fig.1 Magnetic coil shielding. A superconducting magnetic coil and its shielding. In the shield, the liquid metal coolant absorbs neutrons, the high density metal (probably tungsten) absorbs x-rays, heating up considerably. e coolant evaporates and the gas carries away the heat to be radiated into space at the radiators. e multilayer insulation protects the superconductors from the thermal radiation from the hot shield, and the liquid nitrogen coolant removes any le over heat, to be radiated away by low temperature radiators. In the image, the fusion reaction is to the right.
e payload and fuel tanks radiation shield is another source impinge on another one, and how the overall performance will of heat load. Beyond the obvious need to protect the payload, be aected. View factors are tabulated for a number of standard it is important to shield the fuel tanks from neutron radiation. cases [8]. e three Fire y radiators lose about 15% of their ef- All the fusion starship designs use cryogenic fuels that must be ciency due to their view factor. e four l’Espérance radiators protected from the drive radiation. At the low temperature of lose about 10% of their e ciency due to their view factor. the tanks, and the much higher temperature required to keep the radiators at a reasonable size, the cycle e ciency is low and 5 COOLING SYSTEM DESIGN the power used to create the cryogenic conditions is consid- erably larger than the heat gain that is removed from the fuel e design of the cooling system begins with the lowest tem- tanks. is power must be radiated away as well. Existing re- perature in the system, the radiator exit temperature, and with frigeration systems have a number of ine ciencies that further the highest temperature, the shield elements that absorb the increase the radiation load. For example, with a tank at 4 K neutron and x-ray radiations. ese temperatures are limited and radiators at 300 K the power required to remove 1 MW by material considerations: melting points, material deforma- is about 123 MW. e total radiation is then 124 MW. See the tion under stress and high temperature corrosion. e Daeda- Carnot Cycle equation in appendix A. e geometry of these lus team chose Molybdenum, l’Espérance uses carbon-carbon tank radiators must be such that they are not themselves heated composites and Fire y a mix of Zirconium Carbide and car- by the thermal radiation from the drive radiators or from the bon-carbon. neutron shields. e design is an iterative process, where each choice in u- 4 THERMAL SHIELDS ences a number of parameters. One a rough radiator tempera- ture has been set, the radiator area can be determined using the 4.1 Multilayer Insulation Stefan Boltzmann law and the view factors. e choice of the heat transfer method is the next step. Multilayer insulation can provide protection from thermal ra- diation loads, as in Fig. 2, where it protects the tanks, and Fig. 5.1 Phase Change vs Temperature Change 3 where it protects the superconductors from the thermal loads coming from hot shielding elements. Daedalus used a thermal ere are two possible methods that can be used to remove the shield composed of 120 layers of re ective lm between the heat from the radiation shields in L’Espérance and Fire y. Tem- nozzle and the tanks, as well as some more layers on the tanks perature change for gas and liquid ows, described by: themselves, to bring thermal radiation gain down to practically zero. e other ships use very similar designs, and such ther- (1) mal barriers are in common use on satellites today. and liquid to gas phase change using: 4.2 View Factors for Radiators and Shields (2) e view factor indicates how much of a radiation source will
JBIS Vol 71 No.12 December 2018 453 MICHEL LAMONTAGNE
TABLE 3 Mass flow required to carry 100 GW of power Substance Boiling point Latent Heat of Specific heat (cp) Temperature Mass flow for Mass flow vaporisation (Ve) difference phase change required to equal for 500 C temp. vaporisation difference in fluid K kJ/kg kJ/kg°C °C Tonnes/s Tonnes/s Helium 4 21 5.19 4 39 4,762 Hydrogen 20 449 14 32 14 223 Water 373 2,270 4.18 543 48 44 FLiBe 1,703 11,433 2.40 4,630 84 9 Lithium 1,615 21,159 3.58 5,910 56 5 Beryllium* 2,742 32,444 1.82 17,827 110 3 Aluminium 2,792 10,500 0.897 11,706 223 10 * Firefly’s cooling circuit operates at half an atmosphere at the radiators, so the Beryllium phase change happens at a lower temperature, 2,500 K
Table 3. lists some uids that could be used for spaceship transfer coe cient. A similar temperature dierence will exist cooling using the vaporization phase change or a 500C temper- between the radiation shield and the coolant, so care must be ature change, for 100 GW of power. taken to ensure the shield is not hotter than its material limits. Liquids have much higher heat transfer coe cient than gas- Phase change in liquid metals provides the most powerful es, so this favors liquid coolants and phase change coolants. heat extraction method using the lowest coolant mass ow. Many of these equations are approximations, and need to be ey are good choices for the powers levels involved in starship conrmed by experiment. propulsion. However, to avoid the risk of corrosion, Helium can be an interesting alternative, in particular for lower heat Using the Stefan Boltzmann law, and since the heat transfer loads. to the wall is equal to the heat transfer to space, we can solve the following equations to nd the uid temperature Watson’s Equation for heat of vaporization combined with the Clausius-Clapeyron equation for vaporization temperature (3) can be used to modify the phase change temperature by var- ying the pressure used in the radiator system, (see equations (4) in appendix A). However, the heat liberated by phase change goes down as pressure goes up. Eventually, we will reach the when Pr=Pt. triple point of the uid, and there will no longer be a gas phase change but a circulating supercritical uid. e thermal environment of the operating vehicle is subject to many heat sources, using the average temperature used at Phase change is also advantageous for radiator performance Earth orbit, 200K, is a safe design choice for Ts, and has little as it happens at a xed temperature. e entire surface of the impact on the results. radiator is at the phase change temperature, while for temper- ature change heat transfer the radiator temperature varies over 5.3 Pipe sizing the whole surface, with an average temperature of about two thirds of the entry temperature. is increases the required Pipe sizing allows us to determine the velocity of the coolant area of the radiator system by about 50% and the system mass as well as its overall mass, since the volume of the pipe can be in the same proportion. determined from the circuit length and pipe diameter. It also determines the coolant circuit time, which is simply the circuit Once a heat transfer method is chosen, the mass ow re- length divided by velocity. Radiator placement also in uenc- quired for heat transfer is calculated from either equation (1) es the mass of the cooling system. Taking Icarus Fire y as an or (2). e density of the uid at the chosen temperature must example, it requires 8 tonnes per second of beryllium phase then be determined. With the mass ow and density, the next change. Placing the radiators at 500 m from the reaction area, step is to choose the velocity of the heat transfer uid in the sys- with a piping velocity of 5 m/s, would require a circuit time of tem. e velocity sets the pressure drop across the system, and 200 seconds, and an extra coolant mass of 1600 tonnes. Plus the therefore the size of the pumping system required to move the weight of the pipes. uid. e velocity is itself a function of pipe diameter, so this step is basically choosing a pipe size. is paper uses 10 m/s for e structural resistance of the piping limits the possible uid ows and 100 m/s for gas ows. operating pressures for the coolants. Small bore piping can be quite thin, but large diameter pipes can be problematic. e 5.2 Coolant and Shield Temperatures hoop stress equation can be used to determine a rst order re- quirements for the pipe sizes. e coolant temperature will be higher than the radiator sur- face temperature. e heat transfer coe cient of the coolant (5) also forces an additional temperature dierence between the average uid temperature and the wall of the radiator. For If the piping is chosen too small, the pumping power will gases in particular, this dierence in temperature can be sig- increase dramatically, the required pressure will also increase nicant. See the Gnielinski correlation to calculate the heat and the pipe walls will need to be thicker, adding mass to the
454 Vol 71 No.12 December 2018 JBIS HEAT TRANSFER IN FUSION STARSHIP Radiation Shielding Systems vehicle. For this paper the hoop stresses chosen were kept un- Pumping system mass is a factor of technological develop- der 200 MPa. ment; in particular new superconducting pumps are lighter than their equivalent classical counterparts. A value of 2 kW/ 5.4 Pumps, Pipes and Compressors kg was used for this paper.
To nd the pump or compressor power to circulate the coolant 7 DISCUSSION the following equations can be used: Despite having an order of magnitude less heat load, the heli- (6) um cooled l’Espérance has a similar system mass to Fire y. e very large volume of helium increases component masses, the which is valid for both the compressors used for gases and the high pressures require stronger pipe walls and the lower radia- pumps used for liquids. Pump or compressor e ciency ƞ is tor temperature reduces their e ciency. Helium has been used usually between 0.6 and 0.8. as a coolant in very high temperature reactors (VHTR) at about 1250 K, and is therefore a much better known coolant than the e most important consideration is uid velocity. Pump- exotic molten beryllium of Fire y. If liquid Beryllium was used ing pressure goes up to the square of the velocity and pumping for heat transfer for l’Espérance rather than helium, the cooling power to the cube of the velocity. So we need to keep the veloc- system would weigh about 100 tonnes. ity as low as possible, without oversizing the pipework. Since we know the required coolant ow Q, the only unknown is the e maximum radiator temperature (Twall) is a function of pressure drop Δp. To nd the pressure drop we need to solve a available materials. Structural strain and thermal uence re- series of classical uid dynamic and heat transfer equations and duce the maximum temperatures that materials can withstand. to do multiple iterations until we nd optimum values. e re- eoretical maximum strain values are reduced by up to 75% quired steps are: First determine the viscosity of the uid at the at high temperatures. Corrosion is another signicant problem operating temperature, then calculate Reynold’s number and at high temperatures. Heat pipe research has provided some in- the friction factor, and from these determine the pressure drop sightful information, but the number of applications for them using the Darcy Weisbach equation. is limited, so their development is not very advanced.
TABLE 4 The most important results in the design of the cooling systems Value Unit L’Espérance Icarus Firefly
Cooling heat load Pr GW 17 260 Cooling method Temperature change Phase change Main structural material Carbon Zirconium carbide Melting point K about 4,000 3,800 Coolant Helium Beryllium Mass flow m tonnes/s 6.5 8 Pressure max p kPa 2,000 1,000 Pressure min p kPa 50 Density p kg/m3 0.49 1,560 Volume flow m3/s 13,000 5.1 Specific heat Cp W/kgK 5.2 3.3 Viscosity μ kg/m*s 0.00006 0.0011 Heat of vaporization kJ/kg n/a 32,400 Radiator temperature Tw K 1,750 2,450 (average) Heat shield temperature K 2,450 2,600 Coolant temperature, to K 2,200 2,550 radiator Coolant temperature, from K 1,700 2,500 radiator Convective temperature K 180 16 difference Mains, dia pipe size liquid Dm m n/a 0.47 Mains dia. pipe size gas Dm m 4 0.25 Radiators, pipe size Dr m 0.015 0.015 Pumping power Pp MW 46 7 Pump mass tonnes 16 80 Radiator area m2 40,000 174,000 Radiator system mass tonnes 800 1,600
JBIS Vol 71 No.12 December 2018 455 MICHEL LAMONTAGNE
e possibility of recovering thermal energy is o en raised patible, such as hydrogen and carbon. Use of high temperature in the context of the large radiative powers required for these coatings has been successful in the aircra industry for the pro- vehicles. However, thermoelectric systems and turbine based tection of turbine blades, and might be transferable to starships. systems require large temperature dierences. is means the cold side radiators will be very large, increasing the overall 8 CONCLUSIONS mass of the ship. erefore there is no point to try to recov- er the thermal energy, since the overall mass gain will cancel It is possible for fusion starships with neutron and x-ray loads any benet from the energy gain by increasing the fuel require- to have adequate performances despite mass penalties due to ments. Direct energy conversion oers a far better path to re- the cooling systems. Neutron and x-ray heating has important covering energy from the drive. eects on vehicle mass and the reduction of neutron and x-ray emissions in the drive is a key part of fusion starship design. Corrosion for high temperature gases such as hydrogen, gas- Research is needed in the behaviour of materials at high tem- eous lithium or gaseous beryllium is a serious concern, and re- peratures if the designs sketched out in this paper are ever to quires renements of existing materials. Some mixes are incom- be realized.
APPENDICES
APPENDIX A Heat transfer equations
2 Conduction 7) dp = f × (L/D) × ((p×v )/2) Ve = vaporisation energy at standard pressure 1) P = U × A × (Ti-To) dp =pressure drop (Pa) (kJ/mol) P = Power (kW) f = friction factor Tn =boiling temp. standard pressure (°K) U = Heat transfer coe cient = k/x L = Length of pipe (m) T2 = New temperature (°K) x = material thickness (m) D = Diameter of pipe (m) Watson’s Equation for heat of vaporization 3 0.38 k = thermal conductivity (W/m°K) p = density (kg/m ) 13) Ve2 = Ve × ((Tc - T2)/(Tc - Tn)) 2 A = Area (m ) v = average velocity (m/s) Ve 2 = vaporisation energy at new pressure Ti = Interior temperature (°K) (kJ/kg) To = Outside temperature (°K) Haaland friction equation Ve = standard vaporisation energy (J/kg) 8) f = (-1.8×log(((e/D)/3.7)1.11 + (6.9/Re)))-2 Tn =standard pressure boiling point (°K) Convection e = pipe roughness factor (m) T2 = New temperature (°K) 2) P = h × A × (Ts-Tf) Re = Reynolds number (dimensionless) Tc = temperature at critical point (°K) h= convective heat transfer coe cient D = pipe diameter (m) Ts=Surface temperature (°K) Gnielinski correlation (3) – Convective Tf= Environment temperature (°K) Reynolds number (Re) heat transfer in pipes 9) Re = ρvD/μ 14) h = ((f/8) × (Re - 1000) x Pr) / (1+(12.7 × Radiation ρ = density (kg/m3) (f/8)1/2 × (Pr 2/3 -1))) × k/D 3) P = A × e × B(Tr4-Tf4) v = average uid velocity (m/s) h = convective heat transfer rate for a gas in a e = emissivity (no units) D = Diameter of pipe (m) pipe (W/m2K) B = Boltzman constant = 5.67e-8 W/m2K4 μ = dynamic viscosity (kg/m × s) or (Pa × s) f = friction factor Tr = Temperature of radiator (°K) see table 5 for μ and p Re = Reynolds number Tf = Environment temperature (°K) Pr = Prandtl number = approx. 1 for Sutherland gas viscosity turbulent ows 3/2 Phase change 10) μ=μ0 × ((T0 + C)/(T + C)) × (T/To) D= Pipe diameter (m) 4) P = m × Ve T = actual gas temperature (K) k = ermal conductivity of the coolant (W/ m = mass ow (kg/s) T0= reference gas temperature (K) mK) Ve = Vaporisation energy (kJ/kg) μ = actual gas viscosity (Ns/m2) see table 4 for k (gases) 2 see table 5 for Ve μ0 =reference gas viscosity (Ns/m ) see table 3 for C and To Carnot cycle Mass/energy ow (15) COP = TL/(TH-TL) 5) P = m × Cp × (T1-T2) Perfect Gas Law and m = mass ow (kg/s) 11) d = Mw × p / R×T (16) Q=Qc/COP Cp = specic heat (kJ/kg°K) d = density (kg/m3) COP = Coe cient of performance T1 = Initial temperature (°K) R= perfect gas constant = 8.314(J/°K×mol) TL = Temperature of the cold system (K) T2 = Final temperature (°K) Mw = molecular weight (g/mol) TH = Temperature of the hot system (K) p = pressure (kPa) Q = External power required (W) (J/s) Compressor or pump power T = temperature (°K) Qc = Power from the cold system (J/s) 6) P = (Q × dp)/n see table 2 for Mw dp = pressure change (kPa) Multilayer insulation Q= Volume ow (m3/s) Clapeyron’s Equation – vaporization 17) U = 4BT3/N(2e-1) + 1 n=pump/compressor e ciency temperature T is the average temperature between the two (usually between 0.6 and 0.8) 12) p2 = pn × e^Ve/R(1/Tn-1/T2) surfaces, Ts+Ti/2 p2 = new pressure at boiling point (kPa) e = Emissivity of the layers Pressure drop Darcy – Weisbach equation pn = atmospheric pressure = 101 (kPa) N = number of layers
456 Vol 71 No.12 December 2018 JBIS APPENDIX B Gas properties for heat transfer (For Sutherland’s viscosity equation)
Gas Sutherland Reference Reference Specific heat Molecular Thermal constant temperature viscosity capacity weight conductivity C T0 μ0 Cp w K (kg/m×s) (kJ/kgK) (g/mole) (mW/cmK) Air 120 291.15 0.00001827 1.2 28.97 Nitrogen (N2) 111 300.55 0.00001781 1.3 28 0.051+0.7438x103T-0.1573x106T2 Oxygen (O2) 127 292.25 0.00002018 32 0.07979+0.6671x103T-0.05479x106T2 Carbon dioxide 240 293.15 0.0000148 44 (CO2) Hydrogen (H2) 72 293.85 0.00000876 14 2 0.7897+0.03623x103T+0.01809x10 6T2 Deuterium(D2) * 5.1 4 0.7073+0.02368x103T+0.1048x10 6T2 Ammonia (NH3) 370 293.15 0.00000982 4.,5 17 Helium 79.4 273 0.000019 5.4 4 2.684x10-3*T0.71 Argon 0.5 40 * The viscosity of deuterium is approximately 1.4 times that of hydrogen.
APPENDIX C Liquids properties for heat transfer
Substance Boiling point Latent Heat of Specific heat Dynamic Triple point vaporisation (cp) viscosity temperature (Ve) K kJ/kg kJ/kg°C kg/m×s K Water 373 2270 4.18 0,00013 FLiBe* 1703 11433 2.4 0,003 Lithium 1615 21159 3.58 0,00035 Beryllium** 2742 32444 1.82 0,0011 Aluminium 2792 10500 0.897 0,0027 * FliBe is a Fluorine Lithium+ Beryllium salt. ** Firefly’s cooling circuit operates at half an atmosphere, so the Beryllium phase change happens at a lower temperature, 2500 K
REFERENCES
1. A. Bond & A. R. Martin. “Project Daedalus.” JBIS, 31, S5-S7, 1978. 7. C. D. Orth, “Interplanetary Space Transport Using Inertial Fusion 2. R. M. Freeland et al.,“Fire y Icarus: An Unmanned Interstellar Probe Propulsion, ICENES-98.” e Ninth International Conference on using Z-Pinch Fusion Propulsion”, JBIS, 68, pp.68-80 2015 Emerging Nuclear Energy Systems, Proceedings, Tel-Aviv, Israel. 1998. e Vista spaceship. 3. T. H. Rider, “Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium.” Physics of plasmas 4.4 (1997): 1039-1046. 8. J. R. Howell, A catalog of radiation conguration factors, McGraw-Hill, 1982. (web.) Siegel, R., Howell, J.R., ermal Radiation Heat Transfer, 4. R. B. Adams, et al. “Conceptual design of in-space vehicles for human Taylor & Francis, 2002. exploration of the outer planets.” (2003). 9. W. Hoelner, “Materials for the very high temperature reactor (VHTR): 5. T. H. Rider, “Fundamental limitations on plasma fusion systems not in A versatile nuclear power station for combined cycle electricity and heat thermodynamic equilibrium.” Physics of plasmas 4.4 (1997): 1039-1046. production.” CHIMIA International Journal for Chemistry 59.12 (2005): 6. J. Miernik, et al. “Z-Pinch fusion-based nuclear propulsion.” Acta 977-982. Astronautica 82.2 (2013): 173-182.
Received 7 April 2018 Approved 30 October 2018
JBIS Vol 71 No.12 December 2018 457 JBIS VOLUME 71 2018 PAGES 458-468
THE HALO DRIVE: FUEL-FREE RELATIVISTIC PROPULSION of large masses via recycled boomerang photons
DAVID KIPPING Department of Astronomy, Columbia University, New York, USA
Email [email protected]
Gravitational slingshots around a neutron star in a compact binary have been proposed as a means of accelerating large masses to potentially relativistic speeds. Such a slingshot is attractive since fuel is not expended for the acceleration, however it does entail a spacecraft diving into close proximity of the binary, which could be hazardous. It is proposed here that such a slingshot can be performed remotely using a beam of light which follows a boomerang null geodesic. Using a moving black hole as a gravitational mirror, kinetic energy from the black hole is transferred to the beam of light as a blueshift and upon return the recycled photons not only accelerate, but also add energy to, the spacecraft. It is shown here that this gained energy can be later expended to reach a terminal velocity of approximately 133% the velocity of the black hole. A civilization could exploit black holes as galactic way points but would be difficult to detect remotely, except for an elevated binary merger rate and excess binary eccentricity.
Keywords: Interstellar travel, Space vehicles, Black holes
1 INTRODUCTION up to relativistic speeds (assuming the binary is su ciently compact). is “Dyson slingshot” maneuver is theoretically In recent months, there has been increased interest in light sail- attractive but swinging round a neutron star in close proximi- ing propulsion systems, including using direct energy, thanks ty is potentially hazardous due to extreme tidal forces and the (in part) to the Breakthrough Starshot project announced in circumbinary radiation environment. 2016. Since the early 20th century, it has been recognized that the momentum carried by light could be used to accelerate In this work, it is shown that the Dyson slingshot can be spacecra [1]. Although the momentum exchanges are tiny, performed remotely using the ideas from directed energy light what makes radiation pressure attractive as a propulsion sys- sailing and gravitational mirrors. Gravitational mirrors were tem is the fact that fuel need not be carried by the spacecra rst described by Stuckey [10], who showed that null geodes- itself. Either through Solar radiation [2] or directed energy ics exists around Schwarzschild black holes enabling one to see [3-5] such systems could be used to overcome the limitations one’s own re ection. Photons just skimming the photon sphere imposed by the Tsiolkovsky rocket equation aecting conven- perform a full revolution and can make their way back to the tional reaction drives. source, dubbed as “boomerang photons” by the author. Using this eect, it is argued here that a moving black hole can be Achieving relativistic speeds through such a system is theo- used like a moving mirror, causing light to not only return to retically achievable by directing high powered lasers at space- the source but also receive a blue shi due to the black hole’s cra (see [6,7]). For non-relativistic speeds, the energy re- relative motion. Photons are recycled by the spacecra and re- quired to accelerate a spacecra of mass m to velocity βc equals peatedly emitted and re-absorbed from the gravitational mir- βmc2/2 (via a rst-order expansion in β of Equation (6) of [8]). ror, accelerating the spacecra up to speeds ultimately exceed- is highlights that accelerating massive objects to relativistic ing that of the black hole itself. speeds is certainly challenging since one needs to rst store energy comparable to the rest mass. Accelerating a low-mass For convenience, this setup is referred to as a “halo drive” in (~gram) spacecra may be feasible albeit at considerable en- what follows, as a result of the ring of light which wraps around ergetic cost (~10 TJ), but larger masses pose severe challenges. the black hole and the propulsive nature of the nal outcome. Such a system is capable of achieving the Dyson slingshot but An idealized propulsion system would be able to acceler- without requiring a spacecra to become in close proximity of ate arbitrarily large masses to relativistic speeds at little to no the binary itself. Whilst slingshots could be performed around energy cost. At rst, this statement may seem fanciful yet es- an isolated moving black hole, binaries are focused on in this sentially free speed-boosts have been exploited for decades in work due to their potential for compact congurations where the Solar System via gravitational assists, although not to the relativistic speeds could be achieved (although the expressions speeds associated with relativistic ight. Perhaps the ultimate derived throughout are equally applicable to isolated black incarnation of the gravity assist was proposed by Dyson [9] holes too). With O[108] black holes estimated to reside within who argued that a compact binary of white dwarfs or neutron the Milky Way [11], a large network of way-points potentially stars could be exploited to accelerate arbitrarily large masses exist to permit intra-galactic travel. is work describes some
458 Vol 71 No.12 December 2018 JBIS THE HALO DRIVE: FUEL-FREE RELATIVISTIC PROPULSION of large masses via recycled boomerang photons
tion meaning that the angle of emission equals the angle of re- ception [10]. e basic setup is depicted in Figure 1.
In order for the de ection to be strong enough to consti- tute a boomerang, this requires the light’s closest approach to the black hole to be within a couple of Schwarzschild radii, RS ≡ 2GM/c2. Light which makes a closest approach smaller than 3GM/c2 becomes trapped in orbit, known as the photon sphere, and thus typical boomerang geodesics skim just above this crit- ical distance.
Stuckey showed [10] that boomerang null geodesics could be computed by numerically integrating the rate of change of the radial coordinate with respect to the azimuthal coordinate, dr/dφ (a simple algorithm is described in the Appendix of that work). To illustrate this, numerical integrations of the geodesic were performed with 106 steps for a series of dierent initial stando distances, d. As shown in Figure 2, the critical de ec- tion necessary to perform a boomerang appears to be propor- tional to 1/d to a good approximation (particularly when d >> 2 GM/c ), with a constant of proportionality given by δ0 = 286.5°.
More importantly for this work, the experiment described above demonstrates that δ → 0 as d becomes large and thus the angle α depicted in Figure 1 approaches π radians (since α = π − 2δ). is simplication will be exploited this later in Section 3.
Even in the idealized Schwarzschild case, the results shown above are not generally applicable to a practical halo drive. is is because the photon should not return to the precise same lo- cation but rather a greater radial distance, since the spacecra Fig.1 Outline of the halo drive. A spaceship traveling at a velocity will experience a back-reaction a er emission (or exhaust) of β1 emits a photon of frequency νi at a specic angle δ such that the the photon. us, the angle should be chosen according to the photon completes a halo around the black hole, returning shi ed to rate of acceleration desired. νf due to the forward motion of the black hole, βBH. For the sake of demonstrating the principle of the halo drive, this paper does not concern itself with the precise angular cor- of the basic mathematics behind the halo drive concept and rection needed to accomplish this. the consequences for both the spacecra and the binary itself.
2 DEFLECTION OFF A MOVING BLACK HOLE
2.1 A halo from boomerang photons
e majority of this paper will concern itself will computing the velocities which can be achieved by a spacecra using the halo drive described in Section 1. However, it is worth rst es- tablishing that boomerang photon geodesics exist and consid- ering the shape of such paths.
Boomerang null geodesics were rst introduced by Stuckey [10], who considered the Schwarzschild metric and demon- strated that such geodesics exist and eectively turn black holes in gravitational mirrors. Indeed, theoretically an innite number of distinct boomerang geodesics exist, corresponding to how many loops around the black hole are conducted. If one writes the critical impact parameter for photon capture as bc, then the number of loops of a scattered photon equals N ~ − log(−1 + b/ bc)/2π [12]. However, for the sake of this work, the scope is limited to that of the rst-order geodesic which does not perform multiple revolutions. Fig.2 Top panel shows three numerically integrated boomerang Light is emitted from the source at an angle δ relative to null geodesics where the initial stando distance, d, is varied. the radial direction and experiences strong de ection as it ap- Solving for the boomerang deection angle for a series of di erent proaches the event horizon. For a Schwarzschild boomerang d values, it may be seen that the angle drops o as 1/d to a good geodesic, there is rotational symmetry about the radial direc- approximation, especially when d >> GM/c2.
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It is worth highlighting that boomerang geodesics can be constructed in the more general case of a Kerr metric, as dis- cussed by Cramer [13]. Since the halo drive exploits a compact binary, both components should be included in a more precise calculation. For the sake of this work, it is su cient to note that such a) geodesics exist and are computable b) the angle α π when d >> GM/c2, simplifying subsequent calculations. Note that point a) could be calculated onboard the spacecra either using a metric known to be completely correct, or using a pilot low-power laser to ne-tune the correct angle.
2.2. Deflections in the black hole’s rest frame
Let us now turn to calculating the movement of a spacecra in response to emitting a boomerang photon (or halo) around a moving black hole. Before considering the eect on the space- cra , one needs to rst derive the changes imparted onto a photon which conducts such a loop.
Let us work in the rest frame of the black hole and assuming that an incident photon passes by with an impact parameter exceeding 3√3GM/c2, such that the closest approach exceeds 2 3GM/c . In such a case, it is expected that the photon to be de- Fig.3 An incident photon of frequency νi’ is deected around a ected by some arbitrary angle (see [14]) which is labelled as Schwarzschild black hole by an angle α’, depicted here in the rest α’, as depicted in Figure 3. frame of the BH.
As described in Section 2.1, the angle α' is set by the mass of (5) the BH and the impact parameter of the encounter. To start, let us consider what the frequency of the de ected photon, νf', will (6) be. is can be computed by conserving relativistic four-mo- mentum before and a er the encounter. e initial four-mo- (7) mentum of the photon, working in units of c, is given by: Taking the last two lines, then squaring and summing, one may write:
(8) (1) One may now use the relation E2 = p2 + M2 and our earlier energy expression to write that:
and that of the black hole by: (9)
Solving the above for νf' yields the familiar Compton scat- tering equation: (2) (10)
Let us write the nal four-momentum vectors of these com- where the c units have been re-added. ponents as: 2.3 Deflections around a moving black hole
(3) e general principle of the halo drive is to siphon kinetic en- ergy from the black hole and thus one ultimately requires com- puting de ections around a moving black hole. Armed with the result from the previous subsection, this can be easily ac- and complished using Lorentz transforms.
Let us assume that the black hole is moving along the -ŷ di- T rection such that its velocity vector is given by v = (0, -βBHc, 0) . (4) In such a case, the incident photon’s energy in the observer’s frame, νi, may be related to that in the black’s hole (initial) rest frame, νi', using:
Conserving each component of the total four-momentum, (11) one nds:
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e de ected photon returns at an arbitrary angle and so using the more general boosting expression yields: (19)
(12) In other words, it is simply a multiplicative factor of the original frequency. e photon is then shi ed by the de ection One may now account for the photon’s de ection by substi- encounter according to Equation (19), which is again simply tuting νf' using Equation (10) to obtain: a multiplicative factor of frequency. Finally, upon return the equal and opposite gravitational redshi occurs (since the pho- (13) ton returns to the same location), cancelling out the previous blue shi .
2 Accordingly, in the limit of Mc >> hνi and the photon return- It is worth highlighting that in the limit of M → ∞ (an innite ing to the same location, gravitational blue/red shi has zero net mass mirror) and α → π (a normal re ection), Equation (13) re- eect. is symmetry is broken when one includes the Ki term, produces same familiar result as that of Einstein’s famous 1905 and again this could be correctly accounted for using numerical paper [15] i.e. integrations, however it is a fairly extreme case that is technical- ly forbidden as long as the spaceship has a low mass compared (14) to the BH i.e. m >> M (see Section 3.5 for justication).
If the photon does not return to the same location but at a Finally, one needs to relate α', the angle of de ection in the greater radial distance (as expected since the spacecra will be black hole’s initial rest frame, to α, the angle of de ection in the in motion), then there will be a net eect even in the limit of 2 observer’s frame. Consider the setup as depicted in Figure 3, Mc >> hνi. is is discussed later in Section 3.5. where α' is obtuse. If one denes an angle θ' = π − α as the acute and opposite angle, this angle along the direction of motion 3 FORMALISM FOR THE HALO DRIVE should be expected to be squeezed in the moving frame as a result of relativistic aberration. Accordingly, one would expect 3.1 Response of a spacecraft the observer’s frame to have θ' > θ, or more explicitly using the aberration formula: Consider an initial setup where a spacecra of mass m1 resides in a wide orbit around a binary BH. At one of the quadrature (15) point in the binary orbit, the BH will be approaching the space- cra at a relative velocity of βBH. More generally, the spacecra Plugging this into our earlier result for the frequency shi may have already begun to accelerate away from the black hole given by Equation (13), one may write: and thus have a velocity of β1 in the same direction.
(16) e source (or spacecra ) emits a photon of energy νi and this will lead to a slight back impulse on the source. e source must also slightly decrease in mass as a result of the emission, where reducing from m1 to m2, culminating in the source increasing (17) in speed from β1 to β2. Conserving relativistic energy and mo- mentum, one may write that: 2 In the limit where hνi >> Mc (the innite mass limit), then the photon’s frequency upon return is well-approximated by: (20) (18)
2.4 Gravitational redshifting during the deflection where m is the mass of the source. Solving the above and sim- plifying, one nds a speed of: One eect that has been ignored thus far is gravitational blue/ red shi . If the photon is assumed to return to the same lo- (21) cation it originated from, then the net change in gravitational potential energy from emission to re ection is zero. However, during the approach of the photon, it will become increasingly and a mass of: blue, potentially aecting our expressions. It is argued here that this eect is extremely small and can be safely ignored for the (22) purposes of this paper, although could be accounted for using numerical integrations. where in both expressions: Let us take the quite reasonable assumption that Mc2 >> hνi, such that Equation (17) can be approximated to Equation (23) (19). Let us denote the radial separation of the photon from the black hole as d[t] i.e. as a function of time. erefore, dur- e spacecra has nite mass and so cannot emit photons of ing the approach, one expects the photon’s frequency to be arbitrary energy. Taking the resulting equation for m2/m1, one blue shi ed as: may solve that the limiting case is when the mass approaches
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zero, the maximum allowed photon emission corresponds to:
(24) (30)
In this where the mass is totally converted into energy, the nal speed of the now massless spacecra can be shown to equal c, since it is essentially just the returning photon. Note that m3 equals m1 if κi1 → 0, demonstrating again that e results can be combined with the change once the pho- if the back-reaction eect of [16] is ignored, the mass of the ton returns with a modied frequency νf. Consider the sim- spacecra would be unchanged not allowing for any energy plied case where the nal and initial position of the source gains. Further, it is noted that in the limit of β1 → 0 and βBH → are both su ciently out of the gravitational well that the ef- 0, no mass gain should be possible and indeed this is apparent 2 1/2 fects of gravitational redshi can be ignored. Further, the since the solution becomes m3 = m1 (1 − 4κi1 ) i.e. m3
(31) giving (26) giving a nal mass of:
and (32)
2 -1/2 (27) where γ = (1- βBH ) . Evaluating the corresponding velocity, which is labelled as the “equilibrium velocity” in what follows (βeq): where in both expressions (33)
(28) which has an intuitive interpretation since at parity speed νf =νi.
3.3. Terminal velocity Note that the latter of the new equations reveals that limm2→0 m3 = 0, which happens when κi1→κi1,max. In other words, if the is gained mass can now be used to induce further accelera- spacecra converts all of its mass into energy and returns as tion. Whilst this could be achieved by simply exhausting pho- a pure photon, there is no mechanism here for the photon tons, the most e cient means would be again to use the BH to somehow return back to massive spacecra . Substituting mirror and exploit the halo drive. in the earlier equations, and a er much simplication, one nds that: Let us take Equation (31), set β1 → βBH since the starting speed is the equilibrium speed, and solve the expression to be (29) equal to 1/γBH with respect to κi1. e photon energy needed is easily found to be given by:
In the limit of the photon’s carrying no momentum (κi1 → 0), then the nal velocity is unchanged from the initial velocity, as (34) expected. In the limit of the intermediate mass, m2, being zero implying a complete conversion into energy, the nal speed is c as expected for a massless particle. It is worth highlighting that and plugging into our β3 equation where β1 is to again initiated in the limit of κi1 → 0, which is to say the back-reaction eect from βBH, one obtains a “terminal velocity”, βterm, of: described in [16] is ignored, then β3 → β1 and no acceleration is achieved, underlining the importance of the eect described (35) in that paper.
Although the velocity change in Equation (30) is small for which is bound to be 0≤βterm <1 for all 0≤βBH <1, as expected. low choices of κi1, it is emphasized that any number of photons Expanding to third-order in βBH, βterm may be written as: can be red and at any frequency and these velocity dierenc- es accumulate. At each stage, not only is the source accelerat- (36) ed, but it is also gains mass (or energy). Specically, the mass change is given by:
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To rst order then, the terminal velocity equals twice that where the square root term accounts for the relativistic Dop- of the black hole, consistent with the rst-order result for a pler shi . When this photon returns, the nal mass, m3, can conventional gravitational slingshot. In essence then, one is be calculated using Equation (28) except the photon energy is conducting a remote slingshot using the halo rather than phys- substituted using Equation (41), yielding: ically approaching the BH and risk tidal disruption (as well as an increased ight time and heavy time dilation by diving into (41) the gravitational well).
From [16], one expects the following two statement to be Solving m3 = m1 with respect to κi1 yields: true, if the principle of ensemble equivalence holds. First, rather than accelerating from rest to equilibrium speed with one photon, and then equilibrium to terminal with a second (42) photon, the same acceleration could be achieved for the same energy using a large number of smaller photon energies. is point is important because it is impractical to emit such a high Plugging this result into Equation (27) yields a revised ter- energy photon in a single step. Second, if this principle holds, minal velocity (a er much simplication) of: then the reverse should also be true and both steps should be achievable in a single photon i.e. we should be able to accelerate (43) from rest to terminal with a single photon emission.
is latter statement may be veried by solving limβ1→0 m3 = which is again bound to be 0≤βterm <1 for all 0≤βBH <1. Expand- m1 with respect to κi1 - the single high energy photon, which ing to third-order for low βBH, βterm may be written as: yields a quadratic solution of: (44) (37)
In the limit of high γBH, the expression is well-approximated e zero result clearly corresponds to no motion at all. Plug- by ging the latter result into our β3 equation in the limit where β1 → 0 yields the same terminal velocity as that stated in Equation ese results show that the Doppler shi s decrease the amount (36), in accordance with the principle. of energy transferred to the spacecra , but nevertheless speeds in excess of the black hole’s velocity can be achieved. It’s worth comparing this single photon emission to that of the maximum photon emission earlier, κi1,max . One may easi- 3.5 Accounting for gravitational red/blue-shifts ly show that limβ1→0 κi1,max equals this single photon energy if, and only if, βBH = 1. is therefore re-enforces that this physical As discussed earlier in Section 2.4, gravitational red/blue shi s limit cannot be practically achieved. can be shown to be an extremely small eect so long as Mc2 >> hνi and the photon returns to the same radial distance. Accord- 2 3.4 Accounting for relativistic Doppler shifts ing to Equation (25), κi1 < ½ and thus mc < hνi/2. Accordingly, the valid regime can also be stated as M >> m. However, since One important eect thus far ignored is the relativistic Dop- the objective of the halo drive is to accelerate the spacecra to pler shi of the returning photon in the spacecra ’s frame of relativistic velocities, then clearly the geodesic will be chosen motion. Even for a single photon emission, the emission caus- such that the photon does not in fact return to the same loca- es a back-reaction which accelerates the spacecra away from tion but rather a greater radial distance. rest up to β2. Accordingly, when the photon returns it is not reabsorbed as νf but as νf", where the dashes indicate a Lorentz Consider starting from rest and attempting to accelerate transform to the rest frame of the spacecra . to terminal velocity with a single photon of energy given by Equation (43). e intermediate velocity of the spacecra is β2, Following the principle of photon equivalence, one can which here can be evaluated to be: simplify the derivation by considering a single photon emis- sion to accelerate up to terminal velocity – dened as the max- imum speed for which m3 = m1. Starting from rest, β2 and m2 (45) are the same as Equations (22) & (23) found earlier, except that β1 → 0, giving:
(38) e time interval for the photon to return is approximately (2d0 + ∆d)/c and thus the distance traversed is:
(39) (46) Before, it was assumed that the photon returned with a fre- quency given by Equation (19) in the limit of α → π. One may e gravitational redshi from d0 to d0 + ∆d, when the pho- now modify this to: ton returns, is given by:
(40) (47)
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is eect can be considered to be insignicant if the rel- ativistic Doppler correction made in the previous subsection far exceeds the change caused by the gravitational red shi , i.e. when:
(48)
Solving for d0 in the limit of β1 → 0, one can show that equates to the condition that d >> RS, where RS is the Schwarzschild radius. If the ratio between the RHS and the LHS of the above is labelled as f, then Figure 4 demonstrates that this argument works well even for relatively high βBH. Ac- cordingly, it is argued that the terminal velocity derived in Equation (45) is accurate so long as d0 >> RS, in which case Fig.4 Initial stand-o distance from the black hole such that additional eects such as changes in the relative binary po- gravitational redshi e ects are f times smaller than those of sition leading to time-dependent gravitational red-shi s can Doppler e ects when using the halo drive. e approximation d0 >> also be safely ignored. RS found analytically in the limit of βBH → 0 generally holds up well except for extreme cases. 3.6 Numerical tests
roughout this work, it has been assumed that the principle of ensemble equivalence described in [16] also holds here, al- (49) though this has not been tested. e problem closely resembles that described in [16] and thus generally it is expected to hold. Further, Section 3.3 showed that a single-photon acceleration produced the same results as that of the double-photon acceler- ation curve. Of course, a single photon emitted with an energy e binding energy of a binary system is given by: comparable to the rest mass of the spacecra is not feasible (or indeed desirable) and generally implementation would involve (50) the emission of a large sequence of lower energy photons to produce a more gradual acceleration. where a is the binary separation and M2 is the mass of the sec- It is therefore worthwhile to test whether the terminal ve- ondary component. If the binary evolves from a to (a − ∆a) locity predicted from a single photon model indeed equals that as a result of the kick, then one may show that to rst-order when a large number of sequential emissions are performed in ∆E/E instead. Using the equations described throughout this work, a calculation was performed for the acceleration for N photons (51) 2 of equal frequencies set to ν = (mc κi1)/(hN), where κi1 is set to the value derived earlier necessary to achieve terminal velocity in the case of a single photon. If the principle holds, then the If one writes that a = ãGM/c2 (i.e. in half Schwarzschild ra- nal velocity a er numerically integrating N sequential steps dii), then should equal the terminal velocity (to within oating point precision). (52) As shown in Figure 5, it is easy to verify that the principle holds and more over it is possible to accurately predict the ter- minal velocity of the spacecra using our formulae. Expanding the ∆E term to second-order in βBH, accurate to 3% for all βBH < 0.5, yields: 4 DISCUSSION (53) 4.1 Response of the binary & observational signatures
e halo drive causes a spacecra of essentially arbitrary mass is reveals that the binary will be kicked into a slightly ec- (so long as m << M◉) to accelerate up to relativistic speeds (for centric orbit with the periapsis position located at the extrac- suitably compact binaries) without losing any fuel in the pro- tion point, with the new semi-major axis shrinking by that de- cess (although solutions do exist for moving m ~ M◉ via an scribed by Equation (54). In general, these changes are small alternative mechanism, as described in [17,18]). At face value, for all m << M2 or eectively all m << M◉. this makes remote detection of halo drives seemingly impossi- ble. But, there is no such thing a free lunch and of course some- A civilization using a network of binaries may not only ac- thing here has lost energy and that’s the binary itself. By the celerate from them but also decelerate upon return, thus poten- time it reaches terminal velocity, the spacecra has increased tially undoing the slight distortions made to the binary. Even 2 2 its energy from mc to mc γterm, and accordingly one can write so, the binary temporarily spends time at closer semi-major that the binary must have lost an energy of: axis where gravitational radiation is more eective and thus
464 Vol 71 No.12 December 2018 JBIS THE HALO DRIVE: FUEL-FREE RELATIVISTIC PROPULSION of large masses via recycled boomerang photons one still expects elevated merger rates to result.
One-way trips, perhaps from a central hub, would lead to an even higher rate of binary in-spiral on-top of the natural gravitational radiation. If journeys are made isotropically, an eccentric binary may not result but accelerated in-spiral would persist. However, only a discrete set of highways exist between galactic binary black holes and thus the distortions can never be perfectly isotropic meaning that excess eccentricity would likely persist.
4.2 From infinitesimal to finite beams
One eect ignored in the earlier derivation is that it was as- sumed that the beam has an innitesimal width. In reality, the beam has a nite width and that width will diverge in a physically real system. It is therefore critical that the beam di- vergence over the entire path length is less than the size of the spacecra ’s receiver, L, else signicant energy losses would occur.
Beams will diverge due to two eects. e rst of these is via diraction, and for a diraction limited beam one expects the width to diverge a er a distance 2d to:
(54) Fig.5 Numerical tests of the principle of ensemble equivalence for βBH = 0.8. As expected, photons can be released either in a where Dt is the diameter of the transmitter and W denotes the small number at high energies or in a large number of equivalent width of the beam at reception and transmission. If the space- cumulative energy, but the results are the same. e dashed lines cra has a physical width of L, then one requires: show the predictions from our earlier derivations in the case of a single photon assumption. Accounting for Doppler shi s leads to (55) signicant changes in the results. or Let’s say that the edge of the beam is oset from the center by a distance Wt/2. A light ray emitted from this point crosses the (56) radial line between the black hole and the center of the beam at a distance d + Wt/(2 tan δ). Accordingly, the correct angle this photon should be emitted at to perform a boomerang is not δ, In the neighborhood of the black hole, within a hundred but rather (using the result from Figure 2): Schwarzschild radii, it should be easy to produce collimated electromagnetic radiation at such wavelengths. is is can be (57) extended to much greater distances if the receiver is much larger than the transmitter (L >> DT). is latter point is par- ticularly relevant because the halo drive is able to accelerate Accordingly, the beam would potentially miss the spacecra eectively arbitrarily large masses up to βterm (so long as m << upon return. e key problem is that the photons at the edge M◉) allowing for extremely large (e.g. planet-sized) vehicles. of the beam were emitted at the wrong angle, δ, whereas the Ultimately, diraction can be overcome by simply using short- correct boomerang angle would have been δedge. er wavelength light, or even particle beams. For this reason, although diraction is an unavoidable eect, it could be miti- is point reveals that the problem actually stems from the gated against unless halo drives are attempted at extreme dis- way in which we chose to setup the beam - a planar source tances where it may become impractical to emit/absorb such such that the entire beam has the same initial emission angle. high energy radiation. For this reason, the divergence is not unavoidable in the same sense as diraction is, but rather is primarily an engineering A second eect that leads to beam divergence comes from problem that could be surmountable through careful beam essentially a tidal eect. Consider a beam which has nite width shaping (see [19]). e purpose of this work is not to provide and is emitted at a single angle, δ, tailored such that the center an actual blueprint for the halo drive, but rather merely high- of the beam will perform a boomerang geodesic (e.g. using the light that no physical barrier exists to prevent such a scheme. method described in Section 2.1). Photons emitted slightly Nevertheless, one possible solution could be a large number o to the side beam’s center will encounter the black hole at of micro-emitters with independent actuators that would be slightly dierent impact parameters. Since the beam angle is combined to form the overall beam, where each micro-emit- chosen such that only the center line performs a boomerang, ter has a unique angular displacement to correct for the eect, then the edges will saddle the separatrix and experience dis- analogous to how adaptive optics corrects wavefront errors tinct de ection angles, leading to the eect of achromatic beam in the Earth’s atmosphere using individual actuators. Clear- divergence. ly, such a system would require a very advanced control sys-
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tem to make the necessary calculations for each actuator, but liberately manipulate black holes into specic congurations, again there’s no obvious physical barrier to overcoming this analogous to optical tweezers. is could be particularly eec- problem. tive if halo bridges are established between nearby pairs of bi- naries, causing one binary to excite the other. Such cases could 4.3 Ignored effects lead to rapid transformation of binary orbits, including the de- liberate liberation of a binary. It is important to highlight several approximations made in this work. e purpose of this paper is to introduce the concept It is also highlighted that acceleration could be performed in of using halos as described, and thus several small eects were a two-body process where the source is a very massive emitter ignored to facilitate the calculations that are brie y discussed in the system but the halo strikes a second nearby and lower here. mass vehicle. is vehicle could then be accelerated to even faster velocities than the terminal velocity computed earlier. First, this work has assumed that extremely e cient absorp- Such a system would lead to the more massive source also ex- tion of the photon is assumed by the spacecra upon reception. periencing a kick back into a higher orbit, as well transferring An idealized system needs to be able to recycle the photons some fraction of its initial mass to the accelerated vehicle. us, with thermal losses (see [20]) much smaller than the total en- the system would have a nite lifetime before the accelerator ergy transferred to the spacecra , ∆E. would reach very large orbital radii where halos would become di cult to establish via diraction constraint of Equation (57). A second eect ignored is the energy to overcome the grav- itational potential energy of the binary in order to escape the 4.5 Kerr metrics system. Tacitly, it was assumed that the velocities achieved far exceed the escape velocity from the initial stand-o distance. is work has focused on halo drives being applied to a Requiring ∆E of Equation (50) to be much greater than the Schwarzschild black hole [23] in a compact binary system. gravitational potential energy of a binary where M2 = qM, one However, it is hypothesized here that lone, isolated Kerr black may show that: holes [24] could likely serve the same function. By riding along the frame dragged space- time surrounding the black hole, light should be blue shi ed (in the case of same sense revolu- tion), permitting the rotational energy of the black to be tapped (58) (it is highlighted that Cramer calculate boomerang geodesics for Kerr black holes [13] but the blue shi eect was not con- sidered). is joins the numerous ways previously proposed to extract energy from Kerr black holes, such as the Penrose where on the second line, right hand bracket has been Taylor process [25], superradiance with amplifying incident waves for expanded to rst-order as well as assuming q ~ 1. For low βBH, various elds [26-30] and the Blandford-Znajek process [31]. such as βBH = 0.05, this requires a large stand-o distance of a Calculation of the Kerr-case was beyond the scope of this work couple of thousand Schwarzschild radii. In the mildly relativis- but would be an interesting problem for the future. tic scenario of βBH = 0.2, stando distances greater than around a hundred Schwarzschild radii would make the gravitational 5 CONCLUSIONS potential energy factor much smaller than the gained energy. Nevertheless, it could be worthwhile to include this generally e search for intelligence amongst the cosmos is o en guided small contribution in future work. by considering the possible activities of hypothetical advanced civilizations and the associated technosignatures that would re- A third assumption is that the circumbinary environment is sult (e.g. [32-34]). At the same time, there is growing interest devoid of opaque material that would lead to beam losses. For in developing the means for humanity to take our rst steps example, an accretion disk around the black hole would certain- into becoming an interstellar civilization (e.g. Breakthrough ly make it a sub-optimal target for a halo drive. Accordingly, if Starshot; see [35]). ese two enterprises can o en overlap, one requires compact binaries for relativistic acceleration, the since advanced propulsion systems may lead to observable other component would need to be another black hole or neu- technosignatures (e.g. [36]). Along these lines, this work has tron star to avoid mass transfers forming a disk. considered how an advanced civilization might utilize the light sailing concept to conduct relativistic and extremely e cient 4.4 Other applications of the halos propulsion.
Numerous earlier works have highlighted the potential use of e proposed system is that a spacecra emits a collimated black holes for advanced technological applications (e.g. see beam of energy towards at a black hole at a carefully selected [21,22]) and the halo drive provides another example. angle, such that the beam returns to the spacecra - a so-called boomerang geodesic [10]. If the black hole is moving towards Although not the focus of this work, it is worth highlight- the spacecra , as could be easily accomplished by exploiting a ing that halo drives could have other purposes besides from compact binary, this halo of particles will return with a high- just accelerating spacecra . For example, the back reaction er energy (and momentum). is energy is then transferred to on the black hole taps energy from it, essentially mining the the spacecra allowing for acceleration. Overall then, the halo gravitational binding energy of the binary. Similarly, forward drive transfers kinetic energy from the moving black hole to reactions could be used to not only decelerate incoming space- the spacecra by way of a gravitational assist. cra but eectively store energy in the binary like a y-wheel, turning the binary into a cosmic battery. e analysis presented assumes the halo is photonic, but the beam could be comprised of massive particles too and achieve Another possibility is that the halos could be used to de- the same eect. Either way, the system described echoes the
466 Vol 71 No.12 December 2018 JBIS THE HALO DRIVE: FUEL-FREE RELATIVISTIC PROPULSION of large masses via recycled boomerang photons
are likely O[107] in the Milky Way [37], serving as both accel- Dyson slingshot [9], except that the spacecra does not phys- eration and deceleration stations. Alternatively, they could use ically slingshot around the compact object, but rather let’s the the larger population of BHs which do not reside in compact light beam do the slingshot on its behalf. binaries [11] via their proper motions, although this would not permit for such high velocities. An appealing aspect of the halo drive is that no fuel is spent. e spacecra gradually gains energy during its initial acceler- Each departure from a binary in a particular direction kicks ation and then discharges that energy for further acceleration the binary into a slightly eccentric orbit and accelerates it’s up to terminal velocity - the speed at which the spacecra re- in-spiral merger rate. In principle, each arrival from the same turns to its original mass. direction would undo this eect leading to no observable sig- nature. However, nite time dierences between the departure e terminal velocity of the spacecra is 133% the black and arrival would cause the binary to spend time at a tighter hole’s speed, to rst-order. Critically, this velocity in not sen- semi-major axis than it would naturally, during which time it sitive to the mass of the spacecra , with the only assumption would experience more rapid gravitational radiation in-spiral. being that said mass is much less than that of the black hole. Accordingly, a possible technosignature of the halo drive would Accordingly, a major advantage of the halo drive is that Jupi- be an enhanced rate of black hole binary in-spiral, versus say ter-mass spacecra could be accelerated to relativistic speeds. their neutron star counterparts.
Beam divergence due to tidal eects on a nite beam width ACKNOWLEDGMENTS could be mitigated by careful beam shaping. Divergence due to diraction is not expected to lead to noticeable losses for large DMK is supported by the Alfred P. Sloan Foundation. anks spacecra using optical lasers within a hundred Schwarzschild to Zephyr Penoyre, Nick Stone, Zoltan Haiman, Jerry Ostriker, radii. Nevertheless, for this reason, the system is argued to be Janna Levin, Avi Loeb and Claes Cramer for helpful conversa- impractical at distances much greater than this, thereby neces- tions in preparing this manuscript. I would also like to thank sitating relatively expedient acceleration. Bill Stuckey for his correspondence regarding gravitational mirrors, and Freeman Dyson, Michael Hippke and Duncan An advanced civilization utilizing such a system would rst Forgan for constructive comments on an early dra of this pa- have to have achieved interstellar ight to journey towards the per. Finally, thanks to the anonymous reviewers for their help- nearest suitable BH. ey could then could use BHs in binary ful feedback. systems as way-points throughout the galaxy, of which there
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Received 6 September 2018 Approved 21 December 2018
468 Vol 71 No.12 December 2018 JBIS INDEX ndex IVOLUME 71 NO.12 DECEMBER 2018
Contents by theme
Issue Number Theme 1...... General Papers 2...... Interstellar 3...... General Papers 4...... Tennessee Valley Interstellar Workshop 2017 5...... BIS Mars Symposium 2017 6...... Fermi Paradox Special Issue 7...... Selected papers from RiSpace Conference 2017 8...... Foundations of Interstellar Studies, New York 2017 9...... General Papers 10 ...... General Interstellar 11 ...... Selected papers from RiSpace Conference 2018 12 ...... General Interstellar
Contents by subject A British Interplanetary Society 159 Additive manufacturing 27, 416 Alpha Centauri 288 C Amino acids 151 Carbon dioxide freezing 89 Archaea 216 Commercial spaceflight 399 Artificial intelligence 71 Containment Asteroids microspheres 92 albedo alteration 82 Control systems 323 capture 20 Correspondence 358 deflection 82 COTS components 262 resources 20 Cubesats 239, 250, 410, 416 B D Bacteria 216 Daedalus 450 Biogenesis 216, 222 De-orbiting methods 234 Bio-markers 112 Diffractive solar sail 130 Black hole Docking system 314 halo drive 458 Dust erosion 133, 280 Breakthrough Starshot 294 Dust removal 36,89
JBIS Vol 71 No.12 December 2018 469 INDEX Contents by theme (cond.)
Interstellar communications 375 E Interstellar dust 133, 280 Earth observation 255 Interstellar medium 133 Economics 399 Interstellar precursor mission 275, 369 Electron emission 234 Interstellar propulsion 119, 438, 450, 458 Epsilon 426 Interstellar travel 45, 53,1 19,1 33, 140, 294, Ethics 53, 358 306, 358, 382, 394, 458 Evolution 216 Exposomes 112 Extinction 207 I Extrasolar planets 140,361 Japan Extra-terrestrial civilisation 375,443 Epsilon vehicle 426 Extra-terrestrial intelligence 71,200 Extra-terrestrial life 151, 212, 222, 348 Extra-terrestrial probes 375 L Extra-terrestrial UFOs 225 Laser, pulsed 280 Launch vehicles Epsilon 426 F manoeuvring upper stage 410 Fermi paradox 65, 200, 207, 212, 216, 222, 225,375, 443 market 399 Firefly Icarus 288,450 payload environment 426 Fusion propellants 298 SL-OMV 410 L'Espérance 450 G Gateway Earth 100 M Generation ship 45,53,358,382,394 Mars Genetics 45,382 access, transport 166 Governance 431 colonisation 178,190,348 Graphene 394 crewed landing 159,186 Gravitation 20,438 dust detection 36 Gravitational lens 275,361,369 dust removal 36, 89 Great Filter hypothesis 207,348 exploration 2 Guidance systems (GNC) 323 resources, propellant 186 resources, water 186 rover 36 H simulated mission 2 Halo drive 458 Mars Direct 159,166 Harpoon 406 Materials Heat transfer 450 metallic hydrogen 92 History metastable 92 Industrial Revolution 443 polyetherimide 416 science 65,443 Measurement techniques Human spaceflight distance 262 interstellar 45,53,358 Medical aspects 112 Mars colonisation 178 Metallic hydrogen 92 Mars exploration 2 METI (Messaging to ETI) 71 Mars lander 159,166,186 Mission analysis 2, 323 Moon 166 Mission design 140 safety 112 Moon space station 100 access, transport 166 Hydrogen, metallic 92 Hygiene 178 N I Necropolis 314 Icarus 288 Impact simulation 280 O Industrial Revolution 443 Orbital mechanics 20, 323, 438 Infrastructure Outer Space Treaty 348, 431 Gateway Earth 100 space station 100 In Situ Resource Utilisation 89,186 P, Q International Space Station 27 Paintballs 82
470 Vol 71 No.12 December 2018 JBIS INDEX
Planetary protection 348 universal units 43 Planets SL-OMV 410 extrasolar 140, 361 Solar array 36, 89 PocketQubes 239 Solar sails 130, 306, 394, 438 Poland Solar System satellites 268 elemental abundance 298 space industry 268 habitats for life 222 space policy 268 resources 298 Policy Space access 100 international co-operation 268 Space agriculture 382 space industry 268 Space colonisation 45, 53, 151, 358, 382 Polyetherimide 416 Space debris Poynting-Robertson Effect 306 removal 262, 314, 406 Progspexion 2 Space exploration 166 Propulsion methods Space law 190, 431 fission 126 Space manufacturing 27 fusion 119, 288, 298, 450 Space safety fusion/fission hybrid 119 health risks 112, 178 green propellant 410 hygiene 178 halo drive 458 Space servicing 100 interstellar 119, 438, 450, 458 Space settlements 45, 166, 382 magneto-hydrodynamic 225 Space station propellantless 234, 458 geostationary 100 rocket nozzles 119 ISS 27 solid propellant 426 Space Traffic Management 431 solar sail 130, 306, 394, 438 Stellar forces 294 Z-Pinch fusion 288 Structures Proxima Centauri 45 Cubesat 416 deployable boom 234 R Sun Radiation 450 gravitational lens 275, 361, 369 Relativity 438 Remote sensing 255 RemoveDebris 406 T Rendezvous techniques 323 Terraforming 151, 348 Robotics 250 Test facilities Rocket dust impact 280 fission fragment 126 Tether, electrodynamic magnetic nozzle 119 234 metallic hydrogen 92 Trajectories RSat (Repair Satellite) 250 stellar fly-by 294 S Satellites U architecture 239 United Kingdom constellations 255,410 launch vehicles 399 geosynchronous 314 Space Agency 410 integration 239 Universal scientific units 43 on-orbit assembly 250 sensors 262 testing 416 V video imaging 255 Vacuum engineering 394 Science fiction 159 Scientific units 43 Sensors 262 W SETI World ships 53, 358 Drake equation 65,212,216 Fermi paradox 65, 200, 207, 212, 216, 222, 225, 375, 443 X, Y, Z methods 375 Z-Pinch fusion 288 METI 71 3-D printing 27, 416 risks 71 (8) Flora 20
JBIS Vol 71 No.12 December 2018 471 INDEX
Contents by author
Arias F. J. Magnetic Mars Dust Removal Technology 36 Arias F. J. A Method of Attaining High Pressurized CO2 on Mars With Particular Application to Dust Cleaning System of Solar Arrays 89 Ashworth S. An Earth-Moon-Mars Passenger Transport Pyramid 165 Ashworth S. Scenario Block Diagram Analysis of the Galactic Evolution of Life 212 Baxter S. The Martians: Space Age Visions of Journeys to the Red Planet 159 Becedas J. Redesign and Space Qualification of a 3D Printed Satellite Structure with Polietherimide 416 Bernardini F. Implications for Resource Utilisation on Mars: Recent Discoveries and Hypotheses 186 Bond A. Alien Aircraft: Have they been observed on Earth? 225 Bouwmeester J. et al A New Approach on the Physical Architecture of CubeSats & PocketQubes 239 Cain J.R. Use of Exposomes to Assess Astronaut Health 112 Cain J.R. Mars Colonisation – Health Hazards and Exposure Control 178 Cassibry J. Pulsed Magnetic Nozzle for Fusion Propulsion 119 Chiu H-Y. Capture of Asteroids and Transport of Asteroid Materials to Earth 20 Clements D. L. Life Before Fermi – Back to the Solar System 222 Cornogolub A. et al Rigid Boom Electrodynamic Tethers 234 Costa R. The Law of Mars Colonization 190 Eckersley S. et al Future Rendezvous and Docking Missions enabled by low-cost but safety compliant Guidance Navigation and Control (GNC) architectures 323 Freeland R. M. Plasma Dynamics in Firefly's Z-pinch Fusion Engine 288 Friedman L. & Turyshev S. G. First Stop on the Interstellar Journey: The Solar Gravity Lens Focus 275 Gertz J. ET Probes, Nodes, and Landbases: a Proposed Galactic Communications Architecture and Implied Search Strategies 375 Grimm M. Applying Commercial Off-The-Shelf Sensors for Close Range Distance Measurement in Space 262 Hall A. The RemoveDEBRIS Space Harpoon 406 Hempsell M. et al Next Steps in Preserving Geostationary Orbit 314 Higgins A. J. Experimental Simulation of Dust Impacts at Starflight Velocities 280 Jackson A. A. Gram-scale Nano-Spacecraft Entry into Star Systems 294 Kamassa M. Defining the Polish Space Policy. In Search of Technological Niches for Emerging National Space Sector 268 Kennedy A. J. The Fusion Fuel Resource Base of our Solar System 298 Kezerashvili R. Y. Tests of Fundamental Physics in Interstellar Flight 306 Kipping D. The Halo Drive: Fuel-free Relativistic Propusion of large masses via recycled boomerang photons 457 London R. & Early J.T Evaluation of the Hazard of Dust Impacts on Interstellar Spacecraft 133 Laine P. E. Fission Fragment Rocket: Fuel Production and Structural Considerations 126 Landis G. A. A Telescope at the Solar Gravitaional Lens: Problems and Solutions 369 Loghry C. & Stender M. Rapid Constellation Deployment from the UK 410 Lamontagne M. Heat Transfer in Fusion Starship Radiation Shielding Systems 450 Mansfield K. Terraforming Mars in a Climate of Existential Risk 348 Marin F. & C. Beluffi Computing the minimal crew for a multi-generational space travel towards Proxima Centauri b 45 Marin F. et al Numerical Constraints on the Size of Generation Ships from Total Energy Expenditure on Board, Annual Food Production and Space Farming Techniques 382 Martin A. R. The Origin of the “Fermi Paradox” 200 Matloff G.L. Effects of Enhanced Graphene Reflection on the Performance of Sun-launched Interstellar Arks 394 Newlands R. The potential of metastable metallic atomic hydrogen as a rocket propellant 92 Paek S. W. A Multi-Functional Paintball Cloud for Asteroid Deflection 82 Peacock K. A. Fermi and Lotka: the Long Odds of Survival in a Dangerous Universe 207 Prater T. Toward a Multimaterial Fabrication Laboratory: In-Space Manufacturing as an Enabling Technology for Long Endurance Human Space Flight. 27 Pugsley D. Do Alien Civilisation Exist? 443 Roy K. & Smith C. Contact with Alien Biomes: Possible Biochemical Incompatibilities 151 Schwartz J. Worldship Ethics 101: The Shipborn 53 Silva Curiel A. da Video from Space 255 Smith L. J. The Norms of Behaviour in Space: Our space – Whose rules? 431 Starinova O. L. & Gorbunova I. V. Solar System Escape Mission with Solar Sail Spacecraft within a framework of post-Newtonian Gravitational Theory 438 Swartzlander G. Flying on a Rainbow – A Solar-Driven Diffractive Sailcraft 130 Tatum E. T. Searching for E.T: a Universal Units Proposal 43 Turchin A. The Global Catastrophic Risks Connected with Possibility of Finding Alien AI During SETI 71 Turyshev S. G. et al Direct Multipixel Imaging of an Exo-Earth with a Solar Gravitational Lens Telescope 361 Van Belle D. A. The Social Dynamics of Science, Exoplanetary Environments and the Drake Equation 65 Vidmar M. Propellant in the Fuel-Tank 100 Watson J. A. Crewed Mars Mission Concept Development and Experimentation 2 Weinstein-Weiss S. et al A Science-Driven Mission Concept to an Exoplanet 140 Weinzierl R.O.J. Extremophiles: The Resilience of Life under “Adverse” Conditions 216 Wenberg D. et al Advancing on Orbit assembly with the Intelligent Space Assembly Robotic System: the Path to Flight 250 Yamashiro R. & Takayuki I. Epsilon Launch Vehicle’s Status and Future 426 Zakirov V. The Market for a UK Launcher 399
REFEREED CORRESPONDENCE Ashworth S. Correspondence on Worldship Ethics 358 Schwartz J. Correspondence on Worldship Ethics 358
472 Vol 71 No.12 December 2018 JBIS Have you got what it takes?
A er two years spent successfully steering JBIS towards its new look, Editor Roger Longsta is moving on to fresh challenges. The Society is now looking for someone to replace him. This is a part-time position, typically taking two days a week, that would suit someone who is either in part- time employment, self-employed or retired but still takes a keen interest in the eld of astronautics, and who has a background in related academia, astronautics or the space industry itself. Administrative help will be provided and the position attracts remuneration for each issue published. If you think you might t the bill, please contact Executive Secretary Gill Norman at [email protected] for more details. Journal of the British Interplanetary Society
VOLUME 71 NO.12 DECEMBER 2018
SOLAR SYSTEM ESCAPE MISSION WITH SOLAR SAIL SPACECRAFT within a framework of post-Newtonian Gravitational Theory Olga L. Starinova & Irina V. Gorbunova DO ALIEN CIVILISATIONS EXIST? Derek Pugsley HEAT TRANSFER IN FUSION STARSHIP Radiation Shielding Systems Michel Lamontagne THE HALO DRIVE: FUEL-FREE RELATIVISTIC PROPULSION of large masses via recycled boomerang photons David Kipping INDEX Volume 71, 2018
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