Interstellar Spaceflight Using Nuclear Propulsion And Advanced Techniques more

62nd International Astronautical Congress, Cape Town, SA. Copyright ©2011 by the International Astronautical Federation. All rights reserved. IAC-11.D4.1.7 INTERSTELLAR SPACEFLIGHT USING NUCLEAR PROPULSION AND ADVANCED TECHNIQUES Seetesh Pande University of Petroleum & Energy Studies, India, seetesh.pande@gmail.com Ugur Guven University of Petroleum and Energy Studies, India, drguven@live.com Gurunadh Velidi University of Petroleum & Energy Studies, India, guru.velidi@live.in Our present space technology has just put its first step outside our heliopause. With 2012, Voyager will be the first manmade object to exit our Solar System for the first time. As space technology develops and as the future of humanity demands more and more; the only way that the humanity can expand would be toward the stars. Even though this may seem to be a dream at this point, the continuing trend in the technology suggests that this will be possible in the next century or towards the end of the 21st century. Thus, the modes of transportation for interstellar distances need to be considered now, so that the necessary technology can be developed correspondingly. In terms of specific impulse, conventional methods are totally useless for any distances that are outside our solar system. Thus, more exotic means of space transport conditions need to be realized in order to make interstellar travel a reality. With current technology, using advanced nuclear propulsion techniques seem to be the best way, as they possess the ability to create high specific impulses in a short period of time. Continued acceleration will be a key to success in such an endeavor and more importantly, with advanced nuclear propulsion, it can be possible to meet the necessary power requirements for the mission. In addition, combination of antimatter propulsion as well as fusion propulsion can be combined to give even a higher specific impulse, as well as an ability to meet power demands for decades, which will be necessary for travelling even at those high speeds. This paper will examine the most probable possibilities regarding interstellar travel based upon the available science and technology that we have today. In addition, this paper will treat some advanced but hypothetical forms of interstellar travel by the utilization of space curvature to some extent. In the end, the humanity has nowhere to go but to the stars. In this paper, we will try to demonstrate with calculations, the most probable way of achieving these objectives. I. INTRODUCTION Mankind has been looking towards the stars since the dawn of the civilization. Even in the Neanderthal age, men looked upon the heaven to the twinkling lights above and tried to understand what they represent. Since that time, it has been the yearning of the mankind to reach those stars. Of course, it was realised that they were stars somewhere around post circa Renaissance. However, since that time, countless scientists have looked toward the heavens to understand the stars. Perhaps with the work of the great scientist Isaac Newton, the law of gravitation has been found, which has given an idea on how these stars move in the heavens and how they affect each other, Then countless other physicists and scientists have worked toward understanding the mechanisms by which these stars work. However, with the idea that stars are formed after long processes, many cosmologists have worked on their theory of evolution of stars. With the contributions of another great scientist Albert Einstein, the General Theory of Relativity has been found, which has allowed IAC-11-D4.1.7 for the full understanding of the cosmology and the motion of the stars. However, still the big question remains, is it possible to go to these stars. Of course, since the launch of Sputnik in 1957, race to space has been underway by the various nations of the Earth [1]. In this space race, countless spacecraft, satellites and probes have been launched into space by countless nations of the Earth. During this race, several important landmarks have been reached including the famous landing on the moon, analysis of Martian soil by the Pathfinder and the swooping journey of the Voyager probe deep into the far reaches of the solar system. But, regardless of these accomplishments, mankind is still very far from reaching even the nearest star with the attainable specific impulses of today. Interstellar distances are very far as compared to the amount of distances that have been reached through the space programs of various nations. In fact, even with the Voyager series, which have travelled to the far reaches of the solar system, we are still very far from reaching the heliopause which marks the solar system boundary. Page 1 of 7 62nd International Astronautical Congress, Cape Town, SA. Copyright ©2011 by the International Astronautical Federation. All rights reserved. II. NEAREST STARS The reach for the stars must start with the nearest star system. Once this mission is accomplished, then it can be possible to think about going to other stars in the immediate neighbourhood [2]. Of course, even at the present level of technology that we have; the idea of going to the nearest star seems like a science fiction. The stars near our solar systems can be considered in a 10 light years radius and the nearest one of them is 4.3 light years away. Since these distances are vast, is it possible to dare to go to the nearest star with a manned mission; when mankind has not even been able to go to Mars yet with a manned mission [4]. is a red dwarf star that is about 4.3 light years away from Earth. In terms of kilometres, it is 41 million times million kilometres away from us. In terms of Astronomical Units, Proxima Centauri has the distance of 273,000 times the distance of Earth from the Sun [4]. If for example, the Voyager probe was to be hurtling toward Proxima Centauri, then it would take around 80,000 years for it to reach Proxima Centauri. If somehow, some sort of a light speed spacecraft existed, still it would take 4.3 years of travelling time to go there and it would take another 4.3 years to come back. So, in light of the Einstein’s Theory of Relativity, light speed is the absolute attainable speed in a spacecraft. Thus, even in a best case scenario, it would take roughly 9 years to get there and to come back [2]. It could also be possible to travel to the other two stars in the Alpha Centauri star system. However, because of their orbital relation, they are more further away as compared to Proxima Centauri. Hence, longer mission profiles will need to be planned in order to reach the other star systems in Alpha Centauri. However, one advantage of travelling to the Alpha Centauri system will be the ability to prove that interstellar flight is possible. Then, this mission can become a stepping stone to other stars [4]. II.II Barnard’s Star Even though Alpha Centauri system is the nearest star system, it doesn’t count as the nearest single star. According to the latest observations, the nearest star to our Solar system is the Barnard’s star. Barnard’s star is approximately 5.9 light years away. More importantly, according to Peter Van de Kamp’s observations, it is suspected that Barnard’s star harbours two planets in its orbit. Hence, by reaching the Barnard’s star, it can be possible to also reach these planets as well. The planets are suspected to be close to the mass of the planet Jupiter. However, with today’s attainable specific impulses, it would take around 115,000 years to reach the outskirts of the Barnard star system. III. SPECIFIC IMPULSE AND REQUIREMENTS OF KINETIC ENERGY The most important criterion when it comes to space travel is the concept of specific impulse. Without high specific impulses, it would not be possible to reach even the outskirts of our solar system. The basic definition of specific impulse is given in Equation 1 below and it is measured in seconds. Fig. 1: The Closest Star Systems to our Solar System In the first stage, it can be thought to use some sort of a robotic space probe in order to travel to the nearest star systems, since even under the best of conditions, travelling to the nearest star will take around 9 years back and fro (if it was possible to travel at the speed of light). However, even with today’s technology, it is possible to mount an interstellar mission to the nearest stars with a finite mission duration of 50 to 100 years. This can be taught to a long duration, but when one considers the vastness of the heavens, duration of 50 to 100 years can be thought of as nothing [4]. II.I Proxima Centauri The nearest star system to our solar system is the Alpha Centauri system. In fact, Alpha Centauri is not a single star, but rather a triple star system. The star in the Alpha Centauri system that is of any interest is Proxima Centauri. According to observations, Proxima Centauri IAC-11-D4.1.7 I sp Ft gmp F gm Ve g [1] The specific impulse of the existing spacecraft which use chemical propulsion methods is in the range of 300 to 550 seconds. This corresponds to a very low Page 2 of 7 62nd International Astronautical Congress, Cape Town, SA. Copyright ©2011 by the International Astronautical Federation. All rights reserved. speed and it would be next to impossible to travel to any star or even to outside of the solar system with these specific impulses. In order to reach long distances such as Proxima Centauri, Barnard’s Star or to farther destinations such as 47 Ursae Majoris, Epsilon Eridani and Lalande 21185; it is essential to have specific impulses of 30,000 and above. Otherwise, the travel time will take such long distances that it will become impossible to travel in a realistic time frame [7]. III.I Relativistic Speeds In addition, to the problems stated above, it must also be said that with low speed travels, the human crew’s life span will not be enough to oversee the journey. Even if generational spaceship crews were to be formed, still it would be such a huge endeavour to get such a space ark up and running. Hence, it would create a real problem in the sense of operation logistics for such an interstellar mission. However, if semi relativistic speeds were to be reached, this would allow the human crew aboard the interstellar space ship to feel less of the time that is passing away. Hence, 200 years in real time could be a matter of couple of years for the crew of the interstellar spacecraft that is travelling at near relativistic speeds. III.II Acceleration Rates The other thing of interest is the rate of the acceleration required to reach these distances. Due to the limitations of the human body, it would not be possible to create very high acceleration rates. Much of today’s space technology is based on acceleration techniques less than one g [14]. However, it can easily be seen that with such low acceleration rates, it would take extraordinarily long amounts of time to reach near relativistic speeds. It is well known from Earth conditions that human beings can easily adjust to an acceleration rate of 1g and in some cases 2g. Hence, besides the specific impulse of the spacecraft and besides the near relativistic speeds (0.1 c to 0.3c) that needs to be obtained; the correct acceleration rate is also of vital importance for success of the interstellar mission. IV. NUCLEAR PROPULSION AS A SOLUTION TO INTERSTELLAR FLIGHT As it can be seen from the various problems outlined above; it is essential to make sure that an advanced propulsion system that has the capability to reach high acceleration rates as well as high specific impulse with speeds translation to near relativistic speeds (0.1 c to 0.3c) is used. Obviously, no form of chemical propulsion or solar propulsion can impart the necessary kinetic energy for such missions. In retrospect, there are many advanced forms of propulsion such as nonIAC-11-D4.1.7 reaction drives as well as warp drives which have been proposed by various space agencies. However, within the realm of technological possibility, these interstellar flight propulsion techniques are beyond the realm of science and they enter the realm of science fiction. While they may become a reality someday, they do not represent a realistic approach for the next 100 years. In order to reach humanity’s goal for interstellar flight, a more realistic approach that is within the realm of today’s technology must be used. IV.I Previously Proposed Nuclear Propulsion Methods Within the realm of today’s space technology, the most realistic approach is the utilization of nuclear power for an interstellar propulsion technique. Since the NERVA program of the United States, there have been many different suggestions for long range nuclear flight from 1960’s and onwards. Even though, the utilization of a solid core nuclear reactor rocket is at the basis for these suggestions, some are more realistic then others. IV.I.I Nuclear Thermal Rocket Almost all of the proposed nuclear propulsion methods are based on the idea of thermal propulsion. The essence of the fact is that the exhaust velocity of the spacecraft is directly linked with the temperatures reached in the combustion chamber of the rocket. If the combustion chamber temperature is high enough, this will allow for a higher ejection speed, which then will be translated as higher specific impulse. In fact, all reaction drive based propulsion methods are based on high ejection of particles from the rocket nozzle, so that the speed of the spacecraft is as high as possible. In general, the specific impulse equation 1 can also be written in terms of molecular energy as seen in the equation below where J is the energy density [7]. I sp 2J [2] Hence, the impartment of energy density would be much more in an NTR as compared to chemical means. Fig. 2: Basic NTR Design for Deep Space Missions. Page 3 of 7 62nd International Astronautical Congress, Cape Town, SA. Copyright ©2011 by the International Astronautical Federation. All rights reserved. The basic application of a nuclear thermal rocket or NTR is thus based on using a simple fission reactor to get the necessary heat generation in the reactor core. Then, some form of a propellant (preferably hydrogen due to its low molecular weight) is accelerated through the reactor core itself and then it is passed through a nozzle. At this stage, the temperature of the flow itself becomes very high in the order of 900 to 3000 K and thus the excitation of the gas molecules creates a high speed flow in correspondence to the temperature of the flow. Due to the compressible nature of the flow of the propellant; it is immediately translated to supersonic speeds as it passes through some sort of a De Laval nozzle. This is discharged from the back of the rocket to create a high ejection velocity. Hence, in concordance with specific impulse equation (1), specific impulses of 500s or above are easily reached. However, the limitations of NTR cause it to be disregarded as an acceptable method for interstellar travel [7]. Due to the limitations of maximum temperatures that can be reached in a solid core nuclear reactor, the flow temperature can never go upwards of 3000K even under the best of conditions. Moreover, the microgravity effects of the nuclear reactor would also hamper this effect, since solid core reactors are designed to work best under 1g gravity conditions. Hence, while using NTR would be a good way to get to Mars; it would be a poor choice for an interstellar flight. The specific impulse reached would need to multiply by a factor of 100 in order to reach an acceptable range [14]. IV.I.II Nuclear Fission/Fusion Combination Another nuclear method that has been proposed by NASA was the Antiproton Catalysed Microfission / Fusion propulsion system. In this propulsion method, high temperatures were generated by the annihilation reaction of various antiprotons hitting a uranium isotope. This generation of heat would also start the chain reaction of the fusion of the hydrogen microspheres. The system would work on a fusion principle, but it would need the presence of antimatter in order to initiate the reaction. The reaction would be jump started by microfission. Even though this method would create very high specific impulses, it would be faced with many logistical challenges [19]. In the case of a full nuclear fusion, the needed temperatures are very high in the order of 100,000 K or more. Even with the availability of magnetic fields, containing such a reaction would be practically impossible under microgravity conditions. Moreover, the various by-products of fusion such as tritium would cause a large radiation signature in the exhaust of the spacecraft. Moreover, initiating such high temperatures is very difficult as very powerful fission reactions would need to be used (such as in the case of the atom bomb) The containing of such powerful explosions for IAC-11-D4.1.7 initiating the fusion reaction would also cause several difficulties and even in the best case scenario, it would cause the payload capacity of the interstellar spacecraft to be severely diminished [17]. On the antimatter front, there are promising developments and it can be possible to contain antiprotons by the use of a charged field. However, the cost of producing even a gram of antiproton would need the full resources of the Fermilab to work for the next 1000 years and the cost would be more than 5000 trillion US dollars with the best estimate. Hence, for the time being, antimatter is not a viable source. IV.II Gas Core Nuclear Propulsion Methods Within the realm of today’s technology, gas core reactors seem to be the most feasible option in terms of cost as well as technological logistics. If the proper design structure is used, gas core nuclear reactors would be able to generate temperatures in the range of 15,000K to 50,000K, which can be enough to reach the relativistic speed range of 01.c to 0.3 or even up to 0.4c. The overall specific impulse would be very high and more importantly 1g to 2g accelerations can be attained. Thus, the needed kinetic energy for the interstellar exploration would be reached and more importantly, there would be enough power to support all the internal systems of the spacecraft for hundreds of years [7]. In essence, a gas core nuclear reactor is a nuclear reactor that uses Uranium Hexafluoride as a nuclear fuel to initiate the fission reaction. Fission takes place with the bombardment of gaseous Uranium Hexafluoride with neutrons. The reaction kinetics is much more swift due to neutron cross sections obtained due to the core geometry. At a very high order of expansion, the available neutron population in the gaseous core increases and it causes a large expansion of a fission wave all across the core. Since the core itself has gaseous fuel, the temperature limitations of the core are greatly increased. With combination of magneto hydrodynamic methods and with the usage of specially space hardened core shielding, it can be possible to reach extremely high temperatures with the fission reaction that is taking place in the gaseous nuclear core. Once the fission reaction is initiated, it is essential to inject pure diatomic hydrogen into the nuclear reactor chamber. Hydrogen is easy to store due to its low molecular weight and more importantly, it can also be scooped up from the interstellar space of necessary. In essence, hydrogen is the most abundant element in the universe and this makes it a great choice for an interstellar fuel. Page 4 of 7 62nd International Astronautical Congress, Cape Town, SA. Copyright ©2011 by the International Astronautical Federation. All rights reserved. V. RELATIVISTIC EFFECTS II.I Relativistic Mass Expansion and Time Dilation Since the approachable speeds are in the range of 0.1c to 0.4 c in this particular nuclear propulsion method, it is essential to incorporate effects of relativity into the equations. Naturally, the most important relativistic effects are relativistic mass expansion as well as the relativistic time dilation. Both of these effects will have a direct effect on the interstellar mission. The relativistic mass expansion will indirectly cause more kinetic energy to be used in order to accelerate the spacecraft. Hence, in concordance with this, it may be necessary to increase the thermal capacity of the nuclear reactor in order to pump more kinetic energy into the flow. The mass expansion and velocity changes at relativistic speeds is given by [17]: Fig. 3: Gas Core Nuclear Propulsion System M Hence, the hydrogen will be injected in the nuclear core and this will cause the hydrogen molecules to reach very high temperatures. Care will be needed to design the core geometry, so that the prevalent turbulent floe conditions can be managed, while the kinetic energy characteristics of the propellant flow itself are magnified. This is also important as it is essential to increase J in order to attain higher specific impulses. In a gas core nuclear propulsion system, the effects of the fission reaction to overall kinetic energy would be magnified with the effects of the turbulent flow of H2UF6 mixture along with the rotational and translateral motion of the gaseous fluid mixture due to MHD effects as well. Approximately 100 molecules of H2 will be needed to get injected into the core for every molecule of UF6. If this injection is done in an uniform manner of a cylindrical reactor core with a length of 7 to 9 meters, the output to the nozzle can create high flow speeds necessary to obtain the needed specific impulses for interstellar flight. The separation ratio of H2 to UF6 will need to be calculated carefully, so that the nuclear fuel is preserved inside the spacecraft. The speed of the H2 in most cases will be 100 to 1000 times the speed of UF6, which can make this process easier. In case, the loss of UF6 is acceptable to some degree, this can also help improve J characteristics as well. There are also methods to create a second cycle from J in order to create electricity. Hence, this can also be used to power an electric thruster, which can also help increase the overall acceleration rate of the spacecraft. However, the increase in the mass of the spacecraft would serious penalize the payload bearing capacity of the spacecraft, so in this paper, this approach is neglected. M0 1 at c 2 [3] vrel _ hyp (t ) at at 1 ( )2 c [4] xrel _ hyp (t ) c2 a 1 at c 2 1 [5] Where M0= Mass of the space craft M= Mass Expansion a= Acceleration of the space craft t= Time Expansion Another point of interest is the relativistic time dilation. In a way, this will be an important advantage to the interstellar mission. By effectively increasing the time dilation, the amount of time the crew feels onboard the spacecraft will be decreased as compared to Earth bound time. This will actually reduce the physiological effects as well as the psychological effects of long, space bound travel on the crew of the spacecraft. The equation for time expansion is given by the following equation: (t ) c at a sinh a c [6] Hence, both the effects of the time dilation as well as the mass expansion will need to be incorporated in to the design of the mission parameters for best results. To IAC-11-D4.1.7 Page 5 of 7 62nd International Astronautical Congress, Cape Town, SA. Copyright ©2011 by the International Astronautical Federation. All rights reserved. some extent, there may also some relativistic effects on the fission reaction itself. Stars Distance from Earth (ly) 4.3 5.9 7 9.2 tEarth (ly) t Space Craft Lalande 21185 can also become the next targets of a mission. (ly) 11.1 15.1 17.9 25.4 9.841 13.33 15.96 22.83 Mass Exploration (0.4 c) 10,910.89 kg 10,910.89 kg 10,910.89 kg 10,910.89 kg α- Centauri Bernard’s Star Lalande 21185 Epsilon Eridani Table 1: Parameters of Travel to Nearby Star Systems Thus, in the case of interstellar travel, the following data can be seen in the table above, which depicts the mass expansion and time dilation effects for various nuclear propulsion interstellar missions in the expected range of 0.1c to 0.4c for a mission to Alpha Centauri and Bernard’s star respectively. This would also help in planning other interstellar missions in the 5 to 10 light years range of our solar system [17]. Fig. 5: On Board Space Craft Time With Reference to Space Craft at 0.4 c In case, there is a problem with lack of hydrogen propellant, it can easily be scooped off near stars as hydrogen will be found in abundance near stars. (It is also found in interstellar medium but without the required density). Once the hydrogen is available, the second problem would be nuclear fuel. However, about 400 kg of UF6 would be enough to supply power for many generations. V. CONCLUSION As stated above, mankind is looking for new and exotic ways to start an interstellar travel to the nearest stars. Even if at the end of the mission, nothing is found, it will at least prove to the mankind that travel to the stars is possible. Of course, many scientists will state Fermi’s paradox, since gradually evolving technology will allow for better ways to travel interstellar distances in a lesser period of time. However, this should not deter humankind from launching interstellar missions as soon as possible. Even if these missions are superseded by faster missions in the end; the past missions can help accumulate the needed experience for the future interstellar missions. This is why in this paper nuclear methods are discussed since only nuclear propulsion methods are viable within today’s technology. Even Fusion and Antimatter drives will not be possible for next 50 to 100 years and it will take at least that long to perfect them. Hence, at the least, robotic spacecraft using nuclear propulsion techniques should be sent to the nearest star system. Even if the mission is not successful, at least mankind can learn from the experience of failure, so that future missions can succeed. In the end, the future and the survival of mankind may depend on its quest for stars. It is hoped Fig. 4: Onboard Space Craft Time With Reference to Earth at 0.4 c However, it would be best if the interstellar travel was planned in such a way, so that it would be a one way journey. In this scenario, the first stop would be Alpha Centauri system and perhaps a probe can be left in an orbit to provide a communications beacon for other interstellar missions in the future. Then, once the flight to Alpha Centauri is completed and the beacon deployed; the second stop would be to go to Barnard’s star. Hence, the same strategy would be employed there and another communications beacon or a probe can be dispatched there as well. Then, slowly spreading out into a spiral other stars such as Epsilon Eridani and IAC-11-D4.1.7 Page 6 of 7 62nd International Astronautical Congress, Cape Town, SA. Copyright ©2011 by the International Astronautical Federation. All rights reserved. that this paper will provoke these thought processes for the realization of interstellar flight of mankind. VI. ACKNOWLEDGEMENTS We would like to thank University of Petroleum and Energy Studies for their unwavering support. Moreover, we would like to acknowledge the help of Prof. Dr Murat Aydin, Prof. Dr. Akif Atalay, Dr. Turgut Berat Karyot and Adil Erdem for their past contributions in the conceptual analysis. Also, the parents of Gurunadh, Mr. V G V Subrahamanyam, and V S V L Kameswari are thanked extensively for their support in higher education and for future research. VII. REFERENCES [1]. Deborah Cadbury, “Space Race: The Untold Story of Rivals and Their Struggle for the Moon”, Fourth Estate, 2005. [2]. Gurunadh Velidi, Ugur Guven, “Usage of Nuclear Reactors for Space Applications: Space Propulsion and Space Power Concepts”, in proc. International Conference on Mechanical and Aerospace Engineering, New Delhi, 2011, P.356-360. [3]. Stanley Schmidt, Robert Zubrin, “Islands in The Sky: Bold New Idea Colonizing Space”, Wiley, First Edition, 1996. [4]. Giancarlo Genta, Michael J. Rycroft, “Space, the final frontier?” Cambridge University Press, 2003. [5]. Paul A. Czysz, Claudio Bruno, Future Space Craft Propulsion Systems: Enabling Technologies for Space exploration, Second Edition, Praxis Publishing Ltd, Chichester, UK, 2009. [6]. A. Lyngvi, P. Falkner, A. Peacock, “The Interstellar Heliopause Probe Technology reference Study”, Advances in Space Research, 35 (2005) 2073-2077. [7]. Claudio Bruno, “Nuclear Space Power and Propulsion Systems”, Volume 225, Progresses in Astronautics and Aeronautics, American Institute of Aeronautics and Astronautics, 2008. [8].Ian A. Crawford, “Project Icarus: A review of Local Interstellar Medium Properties of Relevance for Space Missions to the Nearest Star”, Acta Astronautica 68(2011)691-699 [9]. Dana G. Andrews, “Cost Considerations for Interstellar Missions”, Acta Astronautica, 34(1994) 357365. [10].John Allen, Mark Nelson, Overview and Design Biospherics and Biosphere 2, mission one (1991-1993), Ecological Engineering 13(1999)15-29. [11]. A. Lyngvi, P. Falkner, S. Cambel , “The Interstellar Heliopause Probe”, Acta Astronautica, 57 (2005) 104-111. [12].R L McNutt, G.B. Andrew, “A Realistic Interstellar Explorer”, Advances in Space Research 34 (2004)192197. [13].Shannon M. Bragg-Sitton, James Paul Holloway, “Autonomous Reactor Control Using Model Based Predictive Control for Space Propulsion Applications”, Annals of Nuclear Energy,33(2006)1368-1378. [14]. W. Huntress, D.Setson, “The Next Steps in Exploring Deep Space- A Cosmic Study by the IAA”, Acta Astronautica, 58(2006) 304-377. [15]. G. Albarran, V.A. Basiuk, “Stability of Interstellar Fullerene under high Dose γ-irradiation”, Advances in Space Research, 33(2004)72-75. [16]. Vladimir. A. Basiuk, Guadalupe Albarram, “Stability of Interstellar Fullerenes under High Dose γirradiation: New Data”, Advances in Space Research 36(2005)173-177. [17]. Frank Drake, “Space Mission for SEIT”, Acta Astronautica, 44(1999)113-115. [18]. Olog G. Semyonov, “Radiation hazard of Relativistic Interstellar Flight”, Acta Astronautica, 64(2009)644-653. [19]. G. Gaidos, R.A Lewis and G. A Smith, “Antiproton-Catalyzed Micro fission/Fusion Propulsion Systems for Exploration of The Outer Solar System And Beyond”, American Institution of Physics, 420(1998)1365-1372. IAC-11-D4.1.7 Page 7 of 7