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Archive for Tuesday, May 16, 2006

Accident report in on spacecraft collision

May 16, 2006

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— A robotic NASA spacecraft designed to rendezvous with an orbiting satellite instead crashed into its target, according to a summary of the investigation released Monday.

Investigators blamed the collision on faulty navigational data that caused the DART spacecraft to believe that it was backing away from its target when it was actually bearing down on it.

"The inaccurate perception of its distance and speed ... prevented DART from taking effective action to avoid a collision," the summary said.

The 800-pound Demonstration for Autonomous Rendezvous Technology spacecraft was supposed to rendezvous with a defunct Pentagon satellite during a 24-hour period last year.

DART successfully located the target satellite orbiting 472 miles above Earth and moved within 300 feet of it. But problems arose when DART tried to circle the satellite.

Investigators concluded that DART spent too much fuel steering itself toward the satellite. The excessive firings of its engines were caused by inaccurate navigational data from its on-board computer.

Determining that it wouldn't have enough reserve fuel to complete the mission, DART began shutting down about 11 hours into the mission, but not before crashing into the satellite.

This artist rendering released by NASA shows the Demonstration for Autonomous Rendezvous (DART) spacecraft, foreground, as it might appear as it approaches a communications satellite in orbit above Earth. The NASA spacecraft designed to autonomously carry out a series of tasks crashed into its target after using too much fuel halfway through its mission, according to a report summary released Monday, May 15, 2006.  Investigators blamed the collision on faulty navigational data that caused the DART spacecraft to believe that it was backing away from its target when it was actually bearing down on it.

This artist rendering released by NASA shows the Demonstration for Autonomous Rendezvous (DART) spacecraft, foreground, as it might appear as it approaches a communications satellite in orbit above Earth. The NASA spacecraft designed to autonomously carry out a series of tasks crashed into its target after using too much fuel halfway through its mission, according to a report summary released Monday, May 15, 2006. Investigators blamed the collision on faulty navigational data that caused the DART spacecraft to believe that it was backing away from its target when it was actually bearing down on it.

Unbeknownst to engineers at the time, DART's main sensor mistakenly believed it was flying away from the satellite when it was actually moving 5 feet per second toward it, investigators found.

The collision pushed the target satellite into a higher orbit. NASA said neither spacecraft pose a threat to other satellites and both will burn up upon re-entry into the atmosphere.

In addition, the investigation also concluded that DART overestimated how much fuel it consumed, although the remaining amount would not have been enough to complete the mission.

Investigators also raised issues with the mission's management style, saying that lack of training and experience caused the DART design team to shun expert advice. They also found that internal checks and balances were inadequate in uncovering the mission's shortcomings.

The 10-page document summarizing DART's failure comes a year after the spacecraft was launched from Vandenberg Air Force Base in California.

Last month, NASA said it won't release the investigative board's full 70-page report, citing sensitive information protected by International Traffic in Arms Regulations. The summary was prepared by the space agency's exploration systems mission directorate.

Robotic technology plays a critical role in NASA's plan to send humans back to the moon and Mars. The $110 million DART mission was meant to test whether robots can perform some of the tasks astronauts currently must do.

DART was managed by NASA's Marshall Space Flight Center in Huntsville, Ala. It was built by Orbital Sciences Corp.

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