The U.S. Missile Defense Agency (MDA) is developing tiny spacecraft that could be used to demonstrate new satellite propulsion systems and help calibrate missile tracking sensors near the end of this decade, according to a senior MDA official.

The agency wants to launch two upcoming small satellite missions as secondary payloads on other military launches as part of the Pentagon’s Space Test Program, the official said in a March 16 interview. MDA expects that each satellite will cost less than $10 million, not including launch costs.

The two missions are for the Calibrated Orbiting Objects program and the Microsatellite Propulsion Experiment.

The Pentagon’s Space Experiments Review Board ranked the Calibrated Orbiting Objects program seventh on its 2004 priority list for space demonstrations seeking room on military launches. The Microsatellite Propulsion Experiment did not appear on the board’s 2004 list.

Like most of MDA’s space experiments, the Microsatellite Propulsion Experiment is intended to demonstrate technology that can be incorporated on a variety of future systems, rather than point the way to the development of a system based on the experimental spacecraft, the official said.

The importance of MDA’s mission requires extremely reliable systems, so technology risk must be wrung out through smaller projects before the agency can field a new capability, the official said.

The Microsatellite Propulsion Experiment will demonstrate new solid-fueled propulsion technology that could ultimately help the military reposition missile warning and tracking satellites at some point in the next decade, the MDA official said.

The solid fuel could help to move satellites much faster to monitor emerging threats than the liquid-fueled propulsion systems available today, the official said.

This responsive capability could also be helpful for military satellites outside of the missile defense arena, the official said.

The primary goal of the experiment is to leave at least one small satellite in orbit for a year or so to examine how radiation and lack of gravity in the space environment may affect the solid-fueled engine hardware like o-rings and gimbals, the official said. The agency wants to be sure that the harsh space environment will not cause deterioration in the propulsion systems that would prevent them from activating and operating very quickly, the official said.

The propulsion experiment has caught the eye of officials at some Washington think tanks who believe the experiment may be intended to demonstrate more than just satellite repositioning.

Industry officials familiar with the project say that experiment will feature a satellite that fires small projectiles, which critics of space-based missile interceptors say could be the first orbital demonstration of such a system. The MDA official declined to comment on potential designs for the system, saying that they are competition sensitive, but said that the experiment is not intended to demonstrate a space-based missile interceptor.

Theresa Hitchens, vice president of the Center for Defense Information, a think tank here, questioned the need for an experiment to focus on the space environment’s effects on a solid-fueled propulsion system when such effects could be simulated on the ground without conducting a space experiment that may lead some countries to believe that the United States is moving towards deploying space-based missile interceptors.

But the MDA official said ground facilities are best suited towards testing a single environmental effect on satellites at a time. Given the small size of the Microsatellite Propulsion Experiment and the relatively low cost of piggy-backing on another satellite launch, a space demonstration would be far more effective and not much more expensive than ground testing, the official said.

Unlike the Microsatellite Propulsion Experiment, the Calibrated Orbiting Objects project has not caused any controversy. That experiment will use at least one tiny satellite that will stand-in for a ballistic missile target as the Pentagon fine-tunes its missile warning and tracking sensors, the MDA official said.

Those sensors include the radar systems aboard the U.S. Navy’s Aegis ships and the Sea-Based X-band Radar that is expected to be ready near the end of this year, the official said.

The satellite or satellites used in the experiment are not expected to be very complex, but will include solar cells and reaction wheels that can give them some ability to maneuver, the official said. MDA wants to see some movement to give its sensors the ability to look at the satellite from different angles, the official said.