NASA has lost contact with the Deep Impact spacecraft, its eight-year-old deep-space comet hunter.
Scientists haven't communicated with the spacecraft since Aug. 8 despite continuing efforts to re-establish contact with the vehicle, which has traveled about 4.7 billion miles through space.
The spacecraft's controllers suspect a software glitch, which may be forcing its computers to continually reboot.
If that's the problem, the computers would not be able to fire the spacecraft's thrusters to change or maintain attitude, and therefore spin out of control.
Thus, scientists no longer know the orientation of Deep Impact's antennas, making it much harder to communicate with the craft.
NASA also noted that if the spacecraft can't point its solar array toward the sun, it may be running low on power.
Deep Impact, which completed both its primary and extended missions, is history's most traveled deep-space comet hunter, according to the space agency.
Launched in January 2005, the spacecraft traveled about 268 million miles to investigate the comet known as Tempel 1. In July of 2005, it deployed a sensor that was hit by the comet and sent data about it back to Earth.
The spacecraft also flew by the comet Hartley 2 on Nov. 4, 2010. In January 2012, it took images of comet C/2009 P1. Earlier this year, Deep Impact took images of comet ISON.
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