Ad Astra Rocket Company will work through a series of development "gates" to build an advanced plasma-propulsion engine for in-flight testing on the International Space Station (ISS) by 2012.

William Gerstenmaier, associate NASA administrator for space operations, and Franklin Chang Diaz, Ad Astra president and CEO, signed a Space Act agreement Dec. 8 that will allow the Houston-based company to place a 200-kilowatt version of its Variable Specific Impulse Magnetoplasma Rocket (VASIMR) on the ISS to test its performance in space.

The engine, which uses RF energy to heat a plasma to extreme temperatures for high fuel efficiency, shielding the engine structure from the superhot gas with magnetic fields, will draw power from the station solar arrays to charge batteries that in turn will drive the engine.

In an interview Dec. 15 from the company's facility in Guanacaste, Costa Rica, Chang Diaz said the VF200 (VASIMR Flight 200 kw) should generate on the order of 4 Newtons of thrust (0.9 pounds), with a specific impulse of about 6,000 seconds. "That is quite sufficient to reboost the ISS," he said.

Under the arrangement with NASA, drafted under legislation creating a National Laboratory on the orbiting facility, Ad Astra will build and test the engine and deliver it to the ISS via one of the commercial or government vehicles in development to resupply it once the space shuttle fleet is retired.

If the engine tests out, Chang Diaz said, his company hopes to negotiate a reboost-services deal with NASA to help defray some of the $100 million - $150 million cost of developing the engine and testing it in space. For that purpose the company would install an advanced solar array on the station as a power source for the engine.

"As soon as this thing tests we would go for the solar array, and then we would provide a service of maintaining the ISS in orbit, which right now is a very expensive proposition," he said.

Potential launch vehicles include the vehicles being developed by SpaceX and Orbital Sciences with federal seed money under the Commercial Orbital Transportation Services (COTS) program at NASA, the PlanetSpace entry in NASA's Commercial Resupply Services competition for the ISS, and Japan's H-II Transfer Vehicle.

The testbed itself will weigh 3 to 4 metric tons, and be mounted on an unpressurized pallet that probably will be crafted at Ad Astra's facility in Costa Rica. The engine work itself will be done in Houston, where Chang Diaz -- a seven-time space shuttle astronaut -- started it while still at NASA.

The company will work through five "gates" to the station test under the Space Act agreement, starting early next year with a payload integration agreement and working toward critical design review by the end of 2009.

"As we have gone through this sequence of embodiments of the technology, we've gone up in the technology-readiness level" [TRL], Chang Diaz said. "We are now at TRL 6. When we left NASA we were at TRL between 2 and 3, so we've matured the technology by three TRL levels very quickly. And so the next level is TRL 7, which is flight."

Photo: NASA