A team of engineers and scientists have developed concept vehicles for a crewed round trip to Mars using fusion power for in-space propulsion. Members of UAHuntsville, NASA’s George C. Marshall Space Flight Center and the University of Wisconsin have identified Z-pinch and Dense Plasma Focus (DPF) as two promising techniques for using fusion power for space propulsion.
“We are trying to develop a small, lightweight pulsed nuclear fusion system for deep space missions,” explained Dr. Jason Cassibry, an associate professor of engineering at UAHuntsville. “If this works we could reach Mars in six to eight weeks instead of six to eight months.”
A Dense Plasma Focus is a machine which produces a short lived plasma hot enough and dense enough to cause nuclear fusion. The premise of a Z-Pinch is to run very large currents (Megampere scale) through a plasma over short timescales (200 ns). The magnetic field resulting from the large current then compresses the plasma to fusion conditions. For a fusion propulsion system, the Z-Pinch would be formed using ring shaped nozzles with Deuterium-Tritium (D-T) fuel in the innermost nozzle and a Lithium mixture containing Lithium-6/7 in the outermost nozzle. The configuration would be focused in a conical manner so the D-T fuel and Lithium-6/7 mixture meet at a specific point that acts as a cathode so that the lithium mixture can serve as a current return path to complete the circuit.
In addition to serving as a current return path, the lithium liner also serves as a radiation shield. The advantage to this configuration is the reaction between neutrons and Lithium-6 resulting in the production of Tritium, thus adding further fuel to the fusion reaction, and boosting the energy output. In utilizing this method of fusion for propulsion, high thrusts and/or specific impulse can be produced.
A Z-Pinch engine would have a similar cycle to an Otto cycle, the team said in their designs, which can be found here: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110008825_2011009235.pdf
They conclude that due to the high cost of building such a vehicle it should be reusable and suitable for a variety of missions, similar to the now decommissioned space shuttle.