DOW-UAP-D123, AAWSAP DIRD, Positron Aerospace Propulsion, March 2010

This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD examines positrons as a possible fuel for advanced aerospace propulsion, arguing that antimatter offers extraordinary energy density and could, in principle, support applications ranging from long-endurance aircraft and missiles to single-stage launch vehicles, onboard power systems, and crewed Mars missions. At the same time, it makes clear that the concept depends on resolving major unsolved problems in producing positrons in sufficient quantities and storing them safely for long periods, and much of the document’s discussion of flight systems and Mars missions remains conceptual rather than closely tied to demonstrated engineering practice. Its overall conclusion is that positron propulsion is theoretically attractive, but remains highly speculative as a practical technology because its core production and storage requirements remain unsolved.

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Defense
Intelligence
Reference
Document
Acquisition Threat Support
2 March 2010
!COD: 1 December 2009
DIA-08-1003-002
Positron Aerospace Propulsion
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Positron Aerospace Propulsion
Prepared by:
Acquisition Support Division (DW0-3)
Defense Warning Office
Directorate for Analysis
Defense Intelligence Agency
Author:
AAP Person 69
Administrative Note
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 2009
under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace
Weapon System Applications (AAWSA Pro ram. Comments or uestions pertaining to
this document should be addressed to AAP Person 1 , AAWSA Program
Manager, Defense Intelligence Agency, ATTN: CLAR/DWO-3, Bldg 6000, Washington,
DC 20340-5100.
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Contents
Introduction ............................................................................................................v
Antimatter.............................................................................................................. 1
Positron Air-Breathing Propulsion.......................................................................... 2
PTRE Applications .................................................................................................. 5
Unmanned Aerial Vehicle (UAV) ......................................................................... 5
Ramjet-Assisted Missile (RAM) .......................................................................... 7
Single-Stage Reusable Vehicle (SSRV) ............................................................... 8
Positron-Powered Rockets ................................................................................... 11
The Solid-Core Positron Rocket ........................................................................ 12
The Gas-Core Positron Rocket .......................................................................... 14
The Sanger Photon Positron Rocket ................................................................. 16
Positron Rocket System Comparison ................................................................ 17
Positron Energy Conversion for Onboard Power............................................... 18
Positrons for a Manned Mars Mission ................................................................... 19
Positron Production.............................................................................................. 22
Positron Costs ...................................................................................................... 23
Positron Storage .................................................................................................. 24
Formation of Positronium in Porous Media ....................................................... 25
Long-Term Storage of Positronium .................................................................. 25
Conclusions .......................................................................................................... 27
Figures
Figure 1. Specific Energy for Chemical, Nuclear and Antimatter Materials............. 1
Figure 2. Tory-IIC Ready for Testing ...................................................................... 3
Figure 3. PTRE Turbojet and Turbo-Ramjet Modes ................................................. 3
Figure 4. Details of the PTRE Engine.......................,............................................... 4
Figure 5. Combustion Turbo-Ramjet....................................................................... 4
Figure 6. UAV Range vs. Positron Mass .................................................................. 5
Figure 7. LOCAAS Turbojet Engine ......................................................................... 6
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Figure 8. BOMARC and Talos Ramjet-Assisted Missiles........................................... 8
Figure 9. Positron SSRV Flight Profile .................................................................. 10
Figure 10. Artist's Rendition of a Four-Engine Positron SSRV............................... 11
Figure 11. Solid-Core Positron Rocket Engine With a Hot-Bleed Configuration..... 12
Figure 12. Fluid Systems ...................................................................................... 15
Figure 13. Modified Sanger Photon Rocket Concept ............................................. 17
Figure 14. Closed Brayton Cycle Using Positron Annihilation ............................... 18
Figure 15. Conceptual 110 Watt Positron Closed Cycle Generator Based on the
NASA Glenn Research Center Stirling Radioisotope Generator (SRG) .. 18
Figure 16. Mars Trajectories (X-Coordinates Defined in Direction of Aries) ......... 20
Figure 17. Spacecrafts Using Positron Engines..................................................... 21
Figure 18. Proposed Undulator-Based Positron Source for the International
Linear Collider ..................................................................................... 22
Figure 19. Penning Trap ....................................................................................... 24
Figure 20. A Positron Forms Ps ............................................................................ 25
Figure 21. Computer Simulation of Ps Atoms ....................................................... 26
Figure 22. TEM of Silica Aerogel ........................................................................... 26
Tables
Table 1. GLOW for Chemical SSRV .......................................................................... 9
Table 2. GLOW for Positron SSRV ........................................................................... 9
Table 3. Total Positron Requirement for SSRV With a Dry Mass of 60,500 kg ....... 10
Table 4. Comparison of Space Propulsion and Power Systems - Solid Core ......... 13
Table 5. Comparison of Three Positron Propulsion Concepts for Mars Mission ..... 17
Table 6. Positron and Antiproton Expected Costs in the Next 10 Years ................ 23
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Positron Aerospace Propulsion
Introduction
Antimatter is considered an extremely attractive fuel for aerospace propulsion
because of its enormous advantage in energy density over all other known
sources of energy. However, because antimatter does not occur naturally and
is unstable in the presence of matter, no vehicles have ever flown using it.
After a short overview of the various aerospace applications of antimatter, this
paper provides a detailed analysis of air-breathing turbojets and turbo-ramjet
missiles, as well as rockets for manned interplanetary missions. It discusses
new methods of producing and storing large numbers of antielectrons, or
positrons, and compares their costs with those of antiprotons. Finally, the
paper considers the prospects for the first, modest demonstration of positron
propulsive flight within the next 10 years. Interplanetary missions on
positron-propelled spaceships are described in detail, with estimates of
positron requirements for each mission. Standalone positron power systems
are described briefly.
Studies of positrons as a fuel for aerospace propulsion applications have been
sponsored by the Air Force Research Laboratory, Eglin Air Force Base, Florida,
and the NASA Institute for Advanced Concepts, Atlanta, Georgia. This paper is
an anthology of that work and not a general review of antimatter propulsion.
The positron was predicted by Dirac in 19291 and discovered by Anderson in
1932.2 Along with the antiproton, which was discovered in 1954,3 the positron
has the largest specific energy of any known material. Because aerospace
propulsion performance is ultimately limited by specific power, this advantage
was immediately appreciated. However, compared with chemical sources of
energy, positrons presented new and serious production and storage
challenges.
Antimatter has a long history of appearing in science fiction literature, dating
to a 1942 short story in Astounding Science Fiction and the 1949 book Seetee.
It later appeared in the Star Trek television and film series and continues to be
an appealing subject for contemporary books and films, such as Angels and
Demons.
Positron aerospace propulsion is now entering a critical period owing to new
technologies that bear on production and storage issues. To their advantage,
positrons, unlike nuclear fission and antiprotons, present no radiation or
environmental safety problems.
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Antimatter
Antimatter appears in the form of fundamental particles that have their sign of electric
charge reversed from their matter counterpart. For example, the positron, e+, is the
antiparticle to the electron, e·. According to the CPT theorem,4 properties of matter and
their counterpart antimatter particles are identical. This has been tested in the
laboratory to an accuracy of roughly 1 part in 10 million.
Antimatter is appealing for aerospace uses because its specific energy by annihilation is
180 MJ/µg, or 10 orders of magnitude larger than chemical energy, as shown in Figure
1.
1.00E+03 ~---------------
1.00E+02 +--------------
1.00E+01 +--------------
1.00E+O0 -+--------------
1.00E-01 -+------
Energy Density _OOE-02 -----
MJ/µg 1.00E-03 -----
_OOE-04 +-------
1.00E-05 +------
1.00E-06 -+------
1.00E-07 -+------
1.00E-08
-1-----.,----
Olerrical Fission Fusion Fbsitron
Annihilation
Figure 1. Specific Energy for Chemical, Nuclear, and Antimatter Materials
In the presence of matter, the positron binds with an electron to form a short-lived
atom called positronium (Ps). Depending on the relative spin orientations of the
positron and electron, Ps has a mean lifetime in a vacuum of 125 picoseconds (para-Ps,
spins antiparallel), or 142 nanoseconds (ortho-Ps, spins parallel).
From quantum number conservation, para-Ps decays into two gamma rays of equal
energy, 511 kiloelectronvolts (keV), whereas ortho-Ps decays into three gamma rays
whose energies add up to 1022 keV. Hence, when Ps self-annihilates, there is 100
percent conversion of mass into electromagnetic energy given by Einstein's famous
equation, E = mc2, where c is the speed of light.
Although the energies of positron annihilation gamma rays are on the nuclear scale,
they have none of the undesirable features associated with nuclear energy. First, the
annihilation evolves rapidly (nanoseconds) and is controllable under predictable
electromagnetic forces. There is no long-term inertia as with nuclear reactors.
Consequently, positron-generated thrust can be throttled.
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Second, low-energy gamma rays from positron annihilation cannot make residual
radioactivity in surrounding air and containment vessels. In contrast, antiprotons
annihilate into a host of high-energy particles, including n-mesons and gamma rays that
can induce residual radioactivity in nearby materials.
Finally, low-energy gamma rays from positron annihilation can be readily converted into
useful forms of energy, including heat and electricity required for propulsion systems.
This contrasts with large, complex systems required for conversion of antiproton
annihilation and nuclear fission/fusion energy.
There are two reasons why positrons have yet to be used for aerospace applications,
First, it has not been possible to produce them in the numbers required. However,
recent developments in high-energy physics research are resulting in expanding levels
of positron production. Second, methods for storing positrons for basic research do not
hold enough positrons long enough for propulsion applications. Recent developments in
storage techniques may significantly improve the situation, with lifetimes up to months
and possibly years.
Positron Air-Breathing Propulsion
Aeronautical engines burn a mixture of aviation fuel and oxygen in air to heat a working
fluid. To keep engines small, the combustion rate in the engine needs to be high .5 At
sea level for a fuel-air mass ratio of 0.068, it is 500,000 kJ/m3-s. To maintain speed,
the thrust specific fuel consumption (TSFC) for turbojets and turbo-ramjets is in the
range of 0.075 - 0.11 and 0.17 - 0.26 kilogram/hour-Newton (kg/hr-N), respectively.
All aeronautical engines are limited in range and flight duration by the fuel on board.
Because of the aforementioned performance bounds of combustion engines, the
aeronautic industry has worked diligently to increase the range and payload of aircraft
by maximizing the performance of combustion engines and optimizing aerodynamic
design. Beyond this, the only way a combustion-powered aircraft can extend its range
and endurance is by in-flight refueling.
Two projects investigated nuclear power as a way to increase performance. In 1946,
the U.S. Air Force established the Nuclear Energy for Propulsion of Aircraft program.
However, this program was disbanded in 1951 in favor of the joint Atomic Energy
Commission-Air Force Aircraft Nuclear Propulsion program. Implementing nuclear
fission to power an aircraft required two approaches. One was direct cycle, whereby air
was heated by passing it through a nuclear reactor; the other was indirect cycle,
whereby the reactor heated a liquid metal that in turn heated air in a secondary heat
exchanger. The program never produced a prototype and was canceled in 1961.
In 1957, the Pentagon started development of a nuclear ramjet missile (SLAM,
Supersonic Low-Altitude Missile) to fly below Soviet defenses. The Lawrence Livermore
National Laboratory Pluto program successfully tested two engines, Tory-IIA and Tory­
IIC (Figure 2), at the Nevada Test Site. The program was canceled in 1964.6• 7
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Figure 2. Tory-IIC Ready for Testing (courtesy LLNL)
In a positron turbojet/ramjet engine (PTRE),8 tungsten shells are heated by gamma
rays, with heat transferred to air by convection.9, 10
tungsten shells
turbojet turbine
us d for healing
--
turbojet compressor
turbojet healing
chamber
Figure 3. PTRE Turbojet (green) and Turbo-Ramjet (red) Modes (courtesy Positronics Research LLC)11
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Tur ·n Pow r dElectric I
Co nn I r Tungst n H g G r Pow Sourc
Surf nsf Conv r ion Tra n 8 tr c
H To
01)
El tr cMotor
Dr' n
ompr sor
Po i on
Tr
H d r xp nds ru
rbin nd no
Int P • ro n Conv rs n
Chm ,
Air w
Comp, sor nd turb n can be t ath red to conv rt
urbo j Ito r m I
Figure 4. Details of the PTRE Engine {courtesy Positronics Research LLC}12
A com