Emily Lakdawalla • Sep 10, 2013
Still no contact with Deep Impact
Oh, that dreaded phrase, "mission status report." It sounds so neutral, but it almost always means bad news. In this case, it's really bad: Deep Impact is not communicating with Earth. Here is the latest information from the status report, posted this afternoon by JPL.
Team Attempts to Restore Communications
Ground controllers have been unable to communicate with NASA's long-lived Deep Impact spacecraft. Last communication with the spacecraft was on Aug. 8, 2013. Deep Impact mission controllers will continue to uplink commands in an attempt to reestablish communications with the spacecraft.
Mission controllers postulate that there was an anomaly generated by the spacecraft's software which left the vehicle's computers in a condition where they are continuously rebooting themselves. If this is the case, the computers would not continue to command the vehicle's thrusters to fire and hold attitude. Lack of attitude hold makes attempts to reestablish communications more difficult because the orientation of the spacecraft's antennas is unknown. It also brings into question the vehicle's electrical power status, as the spacecraft derives its power from a solar array that is fixed, with its cells pointing in one direction.
When there is communication with a spacecraft, there is hope. When communication fails, so does hope. It doesn't sound good for Deep Impact, but they're still trying. The "continuously rebooting themselves" business reminds me of the situation with the Spirit sol 20 anomaly, when a problem with its flash memory had Spirit continuously rebooting. Principal Investigator Steve Squyres told the story of how the rover was saved from that in his book Roving Mars. It all hinged on the fact that, in response to problems encountered during Earth testing, a paranoid software architect (Glenn Reeves) had built in a command to boot the computer without the use of flash memory, and it was that command that saved the day. I doubt that the Deep Impact anomaly has anything in common with the Spirit anomaly. The odds that there are any back-door commands that can save the day here seem low. But not zero. But low.
The spacecraft has lasted long past its nominal mission, performing excellent bonus science over several mission extensions. It's not "too soon" for Deep Impact to be over -- it has accomplished much more than could have been expected. Still, losing a spacecraft is sad, and it's sadder to lose it to an anomaly rather than a planned end. While it was still doing good science, with science data still on board and not yet transmitted to Earth.
C'mon, Deep Impact. Talk to us.
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