GTRI

Case Study

The Little Engine That Could: Decreasing Launch Costs and Extending Capabilities of Unmanned Space Vehicles

Published: August 11, 2003


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THE SUCCESSFUL COMPLETION of a miniature, 68-pound satellite's experimental mission earlier this year was an important first step in the development of a technology that promises to dramatically decrease launch costs and extend the capabilities of uninhabited space vehicles.

And at the helm of the mission was Georgia Tech Research Institute (GTRI) engineer Thom Davis, who - under the Intergovernmental Personnel Assignment (IPA) program - led the project for the Air Force Research Laboratory at Kirtland Air Force Base.

The XSS-10 spacecraft - compared in appearance to a Buick transmission - launched from Cape Canaveral in late January 2003. It was a first-of-a-kind, low-cost "microsatellite" carried aloft via a second-stage, modified Boeing Delta II rocket. The 24-hour mission demonstrated autonomous operations with newly developed guidance and control software. The expedition also revealed some "lessons learned" that are being incorporated into a follow-on mission called XSS-11, a one-year test of the technology.

"This launch was a small first step toward showing the capabilities of microsatellites," Davis says. "By operating autonomously, we eliminated a lot of the cost associated with a larger number of people on the ground to support the satellite."

The XSS-10 had capabilities similar to larger satellites, but its 3-foot-long by 18-inch circumference required developers to shrink its communication system from 12.5 to 2 pounds and reduce its power needs to one-tenth of a previous model's requirements.

Additionally, developers pre-programmed XSS-10's navigation and maneuvering operations into the microsatellite's on-board computer, creating its ability to operate autonomously. This capability contributed to the spacecraft's relatively inexpensive launch cost of $4 million (compared to $20 million for a traditional space vehicle launch). With help from on-board cameras, XSS-10 gathered real-time data to autonomously update the software's algorithms once the vehicle was in orbit.

"Previously, on-orbit maintenance of satellites was done with the inherent capabilities of the satellite with remote guidance from a human on the ground or by astronauts in a shuttle," explains Gen. George Harrison, director of research operations at GTRI. "....If the microsatellite can operate autonomously to examine and maintain itself, then you've really got something going. It is a step toward reducing human activity in space for routine tasks."

But microsatellite technology is still immature, Davis adds. His research team was successful in completing the XSS-10 mission objectives, including inspections, powering the spacecraft on and off, and communicating with the vehicle's computer via their own ground-based control center, rather than a central control center. But at 1 kilometer out from the rocket, the XSS-10 was not able to reacquire a telemetry signal from the Delta vehicle that launched it into orbit. Researchers have already devised a fix for this problem for future missions.

"We are excited about the success of the XSS-10 mission," Davis says. "We found there were a number of variables, some of which controlled us and many of which we were able to control. We learned we had to depend on each other, and we had some good luck. So we were successful."

Though the scientific results of the XSS-10 mission may seem small in comparison to those from a typical shuttle flight, they provided a critical first step toward autonomous satellite operations, Harrison notes.

"This is the way science progresses," he explains. "You set real, achievable goals and develop the science and technology to achieve them. Then you prove them through flight or orbital tests.... So then the next mission will have more capabilities and cost more, but it will have considerably more chances of success. Without this first mission, we might fall down in basic areas and lose important concepts. This is a staged, building-block process such as is done in any good scientific environment."

Davis is now working with the XSS-11 mission team to make his group's data useful to the next-generation vehicle launch scheduled for late 2004. The XSS-11 mission will involve navigating larger distances and performing more extreme maneuvers.

Meanwhile, the XSS-10 is in "de-orbit" mode, and it will eventually fall into the Earth's atmosphere and burn up. In the process, researchers can track its movement for up to 20 years, though they add that it poses no danger to other space objects.