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NASA Puts Hands-Free Linkup to a Test

For its final approach, DART will use 16 gas thrusters, responding to signals from its "mission manager," the on-board software capable of tweaking the spacecraft's movements in response to information from its cameras and sensor arrays.

In two short jumps, DART will maneuver to a position two miles behind the target, then six-tenths of a mile behind. Then it will begin a series of 43 maneuvers that will twice bring it within 16 feet of the satellite.

An illustration shows how NASA's DART craft, set for launch tomorrow, will approach a target satellite. (Orbital Sciences Corp.)

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International Space Station
Space Exploration

The mission's top priority is to give DART's laser "eye," known as the Advanced Video Guidance Sensor, a complete workout. "Once you get a signal [from the reflector], you lock onto it and go into proximity operations," Snoddy said.

Besides the simulated dockings, the maneuvers include circumnavigating the satellite, approaches from the left and right, pulling away out of sensor range and then locking on again, and keeping station alongside at eight different distances, beginning at 16 feet.

"We're going to do everything two times," Snoddy said.

About 20 hours into the mission, DART will finish its last sideways approach to the satellite and retire to a position about 1,000 feet away to initiate its final withdrawal and eventual burn-up in Earth's atmosphere .

Although DART is only a demonstration, its implications could be far-reaching. "We've done 10 years of development to prove it can work," Snoddy said in a telephone interview. "And now it's on the shelf for the next guy to use."

The "next guy" is Orbital Express, a joint Defense Department-NASA project to develop an autonomous spacecraft capable of refueling and servicing Earth-orbiting satellites. It will use DART's laser eye as its main close-in navigation and station-keeping system.

Beginning in September 2006, Orbital Express's two elements -- NEXTSat, the target, and ASTRO, the robot spacecraft -- will conduct up to a year's worth of docking and refueling exercises, robotic equipment transfers and approaches and withdrawals.

"We repeat it over and over, until there is sufficient confidence to show we have reduced the technical uncertainty," said Orbital Express program manager Richard Matthews, of Boeing Co., the project's lead contractor.

This will be valuable knowledge, not only for the scheduled 2007 Hubble repair mission, but also for space exploration, NASA's Steidle said. "We need pre-positioning of supplies and water and in-space assembly. We need to validate our assumptions, and these [missions] are key pieces."

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