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Delta 2 2nd stage imaged by XSS-10
XSS-10 took this image of the Delta 2 second stage that launched it during its brief mission in late January. (credit: Boeing)

Spied satellites

Is the inspection and servicing of spacecraft the killer app for smallsats?

Until recently it was easy to dismiss small satellites—those typically weighing no more than about 100 kilograms—as spacecraft of little practical interest. Work on small satellites was limited largely to amateur radio hobbyists as well as university students looking for thesis topics. The satellites typically had limited capabilities, assuming that the spacecraft actually made it out of the lab and into orbit. Improvements in and miniaturization of technology has changed that, though: groups around the world have built and launched a number of “picosatellites”, weighing as little as one kilogram but with all the critical functions of larger spacecraft.

Despite these advancements, though, smallsats are still seeking their niche in the market. The key advantages of smallsats, low costs and short development times, are still largely unrealized, primarily because of the difficulties involved in launching such spacecraft. Building a satellite in a year for under a million dollars is of limited benefit when it can take several years and several million dollars—if not more—to actually launch it. Moreover, many of the existing satellite applications rely on large spacecraft—a modern “small” communications satellite weighs in at a couple thousand kilograms—with few opportunities for true smallsats to find a foothold in the market. These factors have kept much of the work in smallsats trapped in university labs.

The key advantages of smallsats are still largely unrealized, keeping much of the innovative work in smallsats trapped in university labs.

The situation may be changing for smallsats, however. There are a number of encouraging prospects for more affordable, frequent space access in the foreseeable future, through either the use of former missiles or the development of new launch systems like SpaceX’s Falcon and DARPA’s RASCAL. In the meantime, spacecraft developers in both the government and private enterprise are exploring a new application for smallsats: using them to inspect, and possibly even service, other spacecraft. It’s an application that, with a few special exceptions, doesn’t exist today, and one for which small spacecraft may be uniquely suited. Just as proposed suborbital RLVs may bootstrap themselves by serving markets, like space tourism, that don’t exist today, smallsats may move to greater prominence by carving out a new market niche.

The XSS-10 trailblazer

The concept of using small satellites to test rendezvous and docking technologies and techniques is not new. In 1997 Japan launched the Experimental Test Satellite 7 (ETS-7), which consisted of separate “chaser” and “target” spacecraft designed to separate and then autonomously rendezvous and dock. ETS-7 carried out several successful docking tests in 1998 and 1999. The emphasis of the project, though, was on testing the docking techniques needed for Japan’s H-2A Transfer Vehicle (HTV), a far-larger automated spacecraft that will ferry supplies to the International Space Station.

A more recent, and more relevant, development was XSS-10. The spacecraft was launched in late January 2003 as a secondary payload on a Delta 2 whose primary payload was a GPS satellite. The microsatellite, shaped roughly like a cylinder 84 centimeters long and 43 centimeters in diameter, with a mass of just 31 kilograms, was attached to the side of the Delta 2’s second stage, designed to separate after the booster injected the GPS satellite into the proper orbit. The $100-million spacecraft, built by Boeing for the Air Force Research Laboratory, had just a 24-hour mission, testing a number of advanced technologies ranging from a first-of-its-kind lithium polymer battery to miniaturized communications.

XSS-10 program manager Thomas Davis called the results of the mission “quite positive”, saying that the spacecraft met all its mission success criteria.

On the morning of January 30, 18 hours after launch, mission controllers ejected XSS-10 from the Delta 2 second stage. The spacecraft drifted about 200 meters away from the stage before starting a series of maneuvers. The spacecraft acquired the spacecraft with its onboard camera and maneuvered around the stage at varying distances, returning images of the booster. The spacecraft went into a sleep mode and was later reawakened by ground controllers as a final test of its onboard software.

XSS-10 program manager Thomas Davis called the results of the mission “quite positive” during a talk about the spacecraft during the annual AIAA/Utah State University Conference on Small Satellites last month in Logan, Utah. He noted that the mission met all the minimum and full mission success criteria. He added it took a long time for the mission to actually come to fruition: the project started in 1996 and was initially intended to launch on the shuttle. The spacecraft was switched to a Delta 2 secondary payload in 1998, he explained, when ISS priorities pushed the spacecraft off the shuttle.

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