AAWSAP DIRD, Positron Aerospace Propulsion, March 2010

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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
significantly as long as the gas does not appreciably heat the walls.
Four versions of the gas-core concept are illustrated in Figure 12. Synchronous with
pulsed Ps injection are (a-c) pulses of LN2 or LNe or LH 2 with LXe gamma ray
attenuator and (d) pulses 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 this 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 conditions, 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 complete 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 thresholds for ionization of hydrogen, corresponding to l sp
of~ 2,500 sec.
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