AAWSAP DIRD, Positron Aerospace Propulsion, March 2010

This Defense Intelligence Reference Document was prepared by the Defense Intelligence Agency's Defense Warning Office and dated 2 March 2010. It is one of a series of advanced technology reports produced under the Advanced Aerospace Weapon System Applications program. It looks at using positrons as fuel for air-breathing turbojets, ramjet-assisted missiles, single-stage reusable vehicles and rockets for a manned Mars mission, and it also covers positron production, costs and storage. It concludes that a first positron-powered flight around the globe could be possible within 10 years.

From the source: Release of 2026-09-18 Incident: 3/2/10, Las Vegas, Nevada. Released with redactions. 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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THE GAS-CORE POSITRON ROCKET
The gas-core positron concept follows nuclear gas-core concepts, 31, 32, 33 which are
different from the solid-core concept in that gamma rays directly heat a fluid under
pressure. The limit of the solid-core approach is melting temperatures of the solid
matrix gamma ray attenuator. By direct heating, temperatures can increase
sign ifi cantly as long as the gas does not appreciably heat the walls.
Four versions of the gas-core concept are illustrated in Figu re 12. Synchronous with
pulsed Ps injection are (a-c) pulses of LN 2 or LNe or LH 2 with LXe gamma ray
attenuator and (d) pu lses of LH2 where Ps is encapsulated in lead, a gamma ray
converter. For fluid injection, a turbo- pump (not shown) is located upstream, with
power obtained from a positron Brayton cycle system described later in th is paper.
Results from computational fluid dynamics codes reveal that high-density regions of the
fluid move away from the gamma ray source when the power in the system exceeds
300 megawatts . Under these cond itions, the propellant does not efficiently absorb
gamma rays. Furthermore, calculations of heat required for continuous operation
suggest the vortex configuration of (b) breaks down and reverts to two-fluid flow.
However, both the two-fluid, flow-through model and the Ps lead -cartridge concepts
show promise if the mass flow rate of the hydrogen propellant exceeds that of the
xenon or lead by a factor of five. By operating in a pulsed mode, one should be able to
control the positron delivery into the chamber core. With comp lete absorption of
gamma rays in the 2-cm lead casing, performance of the system matches that of
previously examined systems. 34, 35
Thrusts of 130 kN (1,000 atmospheres) are predicted for a single-engine system with
an efficiency of 85 percent. Burn times are 30 minutes for tiV = 3. 7 km/second (sec)
with 25 mg of positrons consumed for a 50,000-kg burnout mass. The limit of the gas
core concept occurs near the th resholds for ionization of hydrogen, corresponding to l sp
of~ 2,500 sec.
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