Defense Intelligence Reference Document Positron Aerospace Propulsion

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Positrons for a Manned Mars Mission
Positron propulsion systems improve engine performance, making them an attractive
substitute for chemical and nuclear systems for manned exploration of the planets. One
of the boldest challenges is a manned mission to Mars. On board propellant requires an
overall interplanetary system mass that prohibits use of any type of existing launch
vehicle, including the Saturn V. The need to protect astronauts from radiation hazards
in space inhibits use of low-impulse interplanetary trajectories to reduce propellant
mass. Missions must be established that can transport astronauts to Mars in less than
180 days.
Demands on a positron engine to get from LEO to Mars are based on two parameters:
mass of the spacecraft after burnout and the D..V provided by orbital mechanics. Efforts
to minimize burnout mass for a positron-based rocket spacecraft prompted examination
of previously designed systems. The NASA Mars Exploration Study Team studied such
systems in 1997-98.49, so
Conclusions reached by NASA and adopted for this study include:
• To make the Mars mission economically feasible, multiple payloads should be
launched to Mars instead of a single, "all-in-one" vehicle. This keeps payload masses
within reach of existing chemical launch systems.
• A solid-core nuclear-thermal rocket (NTR) was studied. The study adopted existing
NERVA rockets with lsp = 900 seconds and a core temperature near 2,800 °c. The
1993 study examined 15 kilopound-force klbt and 20 klbt rockets. 51
• Each launch had a payload consisting of the NTR with its Mars payload.
• Unpiloted cargo was sent on a low-energy ("C3") Hohmann-type transfer, generally
the slowest means of reaching Mars.
• The Mars excursion vehicle should be sent on a "fast transit" to Mars from LEO. A
fast, 180-day mission would not require artificial gravity on the spacecraft to protect
astronauts from weightlessness.
• The Earth return vehicle (ERV) sits in Mars orbit at 250-km periapsis and waits until
astronauts have docked from Mars using a liquid oxygen (LOX)/methane propulsion
system. The ERV uses a chemical propulsion system to return home to avoid use of
a fission-based propulsion plant in the atmosphere.
• Minimization of D..V to Mars is performed by launching during estimated planetary
conjunctions (every 778 days) and by using aerobraking.
• Aerobraking uses the chemical propulsion system of the cargo vessel or lander.
Payload is jettisoned from the NTR system (called the trans-Mars insertion system
[TMI]) sometime during the trip to Mars.
• To reduce the probability of impact with Earth, an additional D..V is given to the TMI
stage after the payload has separated.
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