Technology

Tests at the US Sandia National Laboratories could lead to a more efficient interpretation of the 1960s concept of powering an interplanetary spacecraft using nuclear explosions. Project Orion, cancelled in 1965, envisaged powering a spacecraft by ejecting and exploding small nuclear bombs behind it.

The scaled-down Mini-Mag Orion propulsion concept being pursued by Andrews Space & Technology (AS&T) replaces the bombs with small pellets of fissile material that would be compressed beyond their supercritical point using a magnetic field. Another magnetic field would act as the nozzle, directing the resulting plasma away from the vehicle to generate thrust.

The tests, conducted under a NASA small business research contract, involved the magnetic compression technology fundamental to the Mini-Mag concept. The two tests used the world's largest operational pulse power machine to demonstrate compressing a simulated fissile material in a magnetic field.

The goal was to correlate the compression achieved with the current required. "A ratio of 10:1 would be useful, 30 would be great and 40 would be outstanding," says Ralph Ewig, AS&T principal investigator. Due to a diagnostic failure, experimenters were unable to quantify the degree of compression achieved, but it "fits the models", says Ewig. "It was not 100% proof, but it has not disproved the concept."

Seattle-based AS&T is now seeking extra funding to pursue development of a 250,000-500,000lb-thrust (1,000-2,000kN) engine using the Mini-Mag Orion concept. Such an engine would have a specific impulse - a measure of propulsive efficiency - of 10,000-30,000s, says Ewig, compared to under 500s for a conventional rocket motor. "The technology is working today. We could develop this engine in no more than 10 years," he says.