DIA, 2010: dois estudos do AAWSAP sobre fusão “aneutrônica” concluem que ela serviria a satélites e a Marte, mas não às estrelas

UNCLASSIFIED//[FOR OFFICIAL USE ONLY, struck through] Defense Intelligence Reference Document Defense Futures 01 November 2010 ICOD: 20 July 2010 [DIA]-08-1011-003 Aneutronic Fusion Propulsion

Aneutronic Fusion Propulsion The Defense Intelligence Reference Document provides nonsubstantive but authoritative reference information related to intelligence topics or methodologies. Prepared by: Technology Warning Division (DWO-4) Defense Warning Office Directorate for Analysis Defense Intelligence Agency Author: AAP Person 83 Administrative Notes: (U) COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one in a series of advanced technology reports produced in FY 2010 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapon System Applications (AAWSA) Program. Comments or questions pertaining to this document should be addressed to [AAP Person 1] AAWSA Program Manager, Defense Intelligence Agency, ATTN: JUIAF - DI/DWO-3, Bldg 6000, Washington, DC 20340-5100.

Aneutronic Fusion Propulsion Introduction Space exploration is limited by existing propulsion technology. Up to now, chemical rockets have been used to reach low-Earth orbit, the Moon, and the outer regions of the solar system. Chemical rockets can use either solid or liquid fuel. Regardless of the type of fuel, their design is similar to that shown in Figure 1. Oxygen is combined with hydrogen or a hydrocarbon fuel in a combustion chamber where high temperatures and pressures cause the exhaust to be ejected through a supersonic nozzle to provide thrust to the rocket. The momentum of the fuel ejected through the nozzle provides the force or thrust that accelerates the rocket forward. There are many variations of chemical rockets, but they all suffer from the need to carry copious amounts of fuel. Other methods have been proposed to decrease the need to carry such a significant mass of fuel into space. Ion drives, for example, are used to provide the very low thrust required to maintain satellites in Earth orbit. The "fuel" that they carry is xenon gas accelerated by electric fields. Nuclear fission propulsion has been proposed for space missions, and thermal nuclear fission reactor rockets were constructed and tested at the Nevada Test Site through Project Rover between 1956 and 1971.[1] In these rockets, a nuclear reactor provides heat to liquid hydrogen through nuclear fission and ejects the hydrogen gas through a Laval nozzle to generate thrust. While these rockets must still carry hydrogen fuel as a propellant, these rockets can provide more than twice the performance of chemical rockets by using heat through fission rather than reactive chemicals. The results of the 72 reactor tests conducted under Project Rover were very promising and culminated in the successful 12-minute test of the Phoebus-2A NERVA (Nuclear Engine for Rocket Vehicle Application) reactor that generated over 4 gigawatts of thermal power. One problem associated with nuclear fission rockets is radioactive contaminants. These contaminants in the exhaust make this technology impossible to use in launching payloads from Earth. Additionally, for applications in space, radiation protection must be provided for the crew by adding heavy shielding materials or by locating the crew as far as possible from the reactor propulsion system. Nuclear fusion, as opposed to fission, provides another potential propulsion technology. In a fusion propulsion system, isotopes of light elements are fused together under extreme conditions to form heavier elements, releasing large amounts of thermal energy. This thermal energy can be used to heat liquid hydrogen to high temperatures and expand it through a Laval nozzle to provide thrust in a manner similar to that shown in Figure 1. Typically, isotopes of hydrogen and helium would be used in fusion propulsion systems. Deuterium is an isotope of hydrogen and can be separated from the hydrogen in water. Fusion reactions are difficult to initiate due to the high temperatures and pressures required. Thermonuclear bombs, for example, combine a fusion device with a nuclear fission bomb to provide the high temperatures required to initiate the fusion reaction. Regardless of the conditions required to induce nuclear fusion, the energy release is large. From propulsion standpoint, an advantage of fusion over fission is that for a given amount of thrust, the fusion reaction requires less fuel than either fission or chemical propulsion systems. Fusion reactors using deuterium or tritium fuels are easiest to initiate; however, they generate significant amounts of neutron radiation. This is a hazard for the crew on a space ship, and there is a high probability that neutrons produced by fusion reactors would escape into space without providing much of their energy to a hydrogen propellant. Other fusion reactions using isotopes of helium and lithium will generate only charged particles, such as protons, that travel very short distances before giving up all of their energy as heat. These "aneutronic fusion" reactions take place without neutron production and decrease the need to carry large amounts of radiation shielding material for the crew. The energy from charged particles generated by aneutronic fusion can also be captured in conductive coils and converted directly into electricity. Aneutronic fusion promises to be an important mechanism for future space propulsion, although novel accelerator or laser systems must be researched and developed in order to initiate, sustain, and control the fusion reaction. Another futuristic method of spacecraft propulsion involves the use of antimatter. Antimatter includes antiprotons, antineutrons, and positrons (anti-electrons). Although this propulsion process may be the most efficient, antimatter has some drawbacks. For example, antimatter is generated in only minute quantities at accelerator facilities around the world. Although it has been captured and stored, containment remains a problem. When antimatter combines with matter, it completely annihilates and converts to energy, which then can be converted into heat for a propulsion system. Antimatter reactions provide the greatest amount of energy per unit mass of any potential fuel, but the ability to generate significant quantities of antihydrogen or similar antimatter fuels at any accelerator facility is very limited. The focus of this study is on aneutronic fusion propulsion. Integral to this study are the topics of fuel, rocket design, and the organizations that research aneutronic fusion development. [Figure 1: diagram labeled Liquid H2, LOX, nozzle] Figure 1. Liquid-Fueled Chemical Rocket.

Chapter 7: Conclusions Among the various aneutronic fusion propulsion technologies developed, Robert Bussard and his colleagues appear to have the best developed proposals. All nuclear fusion designs rely on ignition of the fusion reactions that will consume less energy than is produced by fusion. This hurdle is significant and has thwarted the ability for fusion reactors to generate commercial electricity. Antimatter engines are a more promising technology, since the technique to harvest and store small amounts of antihydrogen already exists. Antimatter is a denser form of energy than fusion fuels and presents the possibility of creating a rocket that approaches the speed of light relative to Earth. The major hurdles to antimatter propulsion include the production of commercial quantities of antihydrogen and the safe transport of antimatter from the earth's surface into space.

UNCLASSIFIED//[FOR OFFICIAL USE ONLY, struck through] Defense Intelligence Reference Document Defense Futures 01 November 2010 ICOD: 20 July 2010 DIA-08-1011-004 Aneutronic Fusion Propulsion

(U) Aneutronic Fusion Propulsion The Defense Intelligence Reference Document provides nonsubstantive but authoritative reference information related to intelligence topics or methodologies. Prepared by: Technology Warning Division (DWO-4) Defense Warning Office Directorate for Analysis Defense Intelligence Agency Authors: AAP Person 85, AAP Person 88, AAP Person 89 COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one of a series of advanced technology reports produced in FY 2010 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapons System Applications (AAWSA) Program. Comments or questions pertaining to this document should be addressed to [AAP Person 1] AAWSA Program Manager, Defense Intelligence Agency, ATTN: JUIAF - DI/DWO-3, Bldg 6000, Washington, D.C. 20340-5100.

Aneutronic Fusion Propulsion Summary Controlled fusion energy production has been under development for 60 years. The primary objective has been gaining the ability to create terrestrial power plants using deuterium and tritium as fuel. Unfortunately, this objective has been eluded for both technical and economic reasons. However, the threshold for achieving success in applying fusion to propulsion is considerably relaxed, especially if fuels are used that do not use tritium. Tritium has to be continuously bred; these reactions yield fast neutrons, which require shielding and cause structural materials to be periodically replaced. Such "aneutronic" fusion fuels, such as hydrogen fusing with Boron-11, have been studied extensively for space propulsion applications since the 1980s. This report reviews the basic fusion plasma physics, design concepts that apply aneutronic fusion for propulsion, and the requirements for transitioning to space. The predominant concepts studied include magnetic field reversed configuration, dense plasma focus and inertial electrostatic confinement. All of these concepts have venture capital funded programs for terrestrial fusion power. When applied to space or near-space propulsion, they can exceed the performance of any conventional electric thruster. The future technology development of aneutronic fusion propulsion will initially be motivated by the very large GEO satellites that will be developed in the next 20 years for commercial and military broadband communication. Further development of very-high-power propulsion systems(> 100 kW) to Mars and beyond will require major developments in all technology areas for confinement pulsed power and ion fuel beam accelerators.

Chapter 1: Concept Overview Controlled thermonuclear fusion has been the aspiration for nuclear scientists and engineers for the last 60 years. During that time, tens of billions of dollars have been invested in this endeavor with the expected fruition being pushed even further into the future. When Lyman Spitzer invented the Stellarator in 1951, it was expected to take only 5 years of concentrated plasma physics experiments to harness the fusion of hydrogen ions confined by magnetic fields. However, the numerous new instabilities that arose under increasing higher magnetic confinement pressures have been a roadblock to the success of controlled fusion. In 1983, a rediscovery was made by Robert Bussard of a fusion device invented by Robert Hirsch in his 1966 Ph.D. thesis. The Fusor, as Hirsch named it with his thesis advisor and famous inventor Philo Farnsworth, simply used spherically concentric electrodes in a vacuum chamber. When a deuterium gas was supplied to the chamber and a few-microsecond pulse at 30 kV was applied to the electrodes, D-D fusion occurred, releasing He and neutrons. Although it released less energy than was needed to supply the initial electric pulse, it provided the evidence for a method to obtain supplementary heating to ignition of magnetically confined plasmas. The Fusor led to continued development of what is now called Inertial Electrostatic Confinement (IEC) devices. Amongst these was the Dense Plasma Focus (DPF), a plasma production tube invented in 1961, and several other devices. Magnetic confinement devices utilized the IEC method with imploding layers of lithium or applying intense beams from either end of a linear magnetic pinch device. This resurgence of alternate confinement concepts was immediately applied to fusion space propulsion since it was recognized that there would be an advantage over nuclear fission propulsion with its costly safety requirements. For mitigating shielding mass and tritium fuel launch-safety concerns, non-neutron-generating "aneutronic" fusion fuels were also adopted. Aneutronic fusion fuels include those isotopes of light elements that when fused produce no neutrons or a very few from the fusion of daughter products. Although there are eight such reactions for light nuclei, the most practical for fusion reactors include the following: D + 3He → 4He + p; P + 7Li → 2 4He; p + 11B → 3 4He In Chapter 2, we will review the fusion plasma physics needed to apply these aneutronic reactions to a confinement device to make a fusion reactor practicable for propulsion, which is described in Chapter 3. In Chapter 4, the relevance of these aneutronic fusion propulsion concepts will be reviewed and assessed for aerospace applications including near-space, orbital, and interplanetary propulsion, as well as the potential for interstellar use. In Chapter 5, we will summarize the recent national, international, and privately funded R&D that may expedite development, while in Chapter 6, we outline an R&D path forward for the aneutronic fusion technologies and systems needed for the next 50 years. Finally, we provide a summary in Chapter 7 that conveys aneutronic fusion propulsion: • May have near-term applications to replace current satellite ion thrusters and extend application to interplanetary flight. • Requires extensive technology development for air and near-space applications. • Will not be practical beyond the solar system unless breakthrough propulsion physics can assist the flight to the next stellar system, where fusion "ion thrusters" can then be used. Despite the attention propulsion has gotten from the scientific community, the problem has been insufficiently addressed by the space science community. Although it is certainly true that the fusion drive train must be successful from a theoretical and experimental perspective before consideration for adaptation to the space environment, many critical aspects such as Earth-based launch, space-based assembly, space materials science, safe flight operations, and mission success need to be introduced early in the design phase. More importantly, now that these fusion propulsion concepts are starting to look both feasible and attractive, the transition to space and the inherent aerospace application development need considerable focus. Toward this consideration, we now begin with a background on plasma physics that includes fusion efficiencies and confinement schemes for aneutronic fusion, which leads us to the application to the propulsion concept discussions that follow.

Chapter 7: Conclusions Much of the groundwork (literally) for aneutronic fusion propulsion has been accomplished, including conducting fusion experiments, development of design concepts, and the analysis of applications to aerospace propulsion. Transitioning these concepts to space is an immense challenge given the large mass, power requirements, and support engineering for power conversion, energy recovery, and fuel storage. This transition, however, may depend upon the success of the developments of privately funded ventures attempting to develop terrestrial power. Notwithstanding such developments, their application for both military and space or near-space applications requires a much lower threshold for return on investment than terrestrial power. Pulsed-powered DPF or IEC aneutronic fusion thrusters may have near-term applications to replace current satellite ion thrusters. This could be extended to the very high-power domain of beam-assisted FRC for manned interplanetary flight. The near-space domain will require major improvements in technology to reduce system mass since the size enters the MW range. The application to the aircraft domain will require further developments in technology to reduce system mass and/or the use of DT fuels, which present other potential safety issues. Aneutronic fusion propulsion will not be practical beyond the solar system unless breakthrough propulsion physics is developed that can assist the flight to the next stellar system where fusion thrusters can then be used. Whether it is reducing rows and rows of capacitor banks to pulse generators, shrinking immense superconducting magnets to a more compact and lightweight geometry, or engineering integrated fusion propulsion systems to fit onto a booster rocket, the physicists who pioneered much of the reactor and propulsion technology must now work side-by-side with the space systems companies to explore viable propulsion systems from implementation to on-orbit maintenance and attitude control. The future needs to be focused more on science and engineering and less on science fiction.