Chandra X-ray telescope is back at work: Engineers trace glitch to 3 seconds of error

An artist’s conception shows the Chandra X-Ray Observatory. (NASA / CXC / SAO Illustration)

NASA’s 19-year-old Chandra X-ray Observatory has been returned to its normal pointing mode after a data glitch forced a five-day outage, NASA said today.

The bus-sized spacecraft went into safe mode on Oct. 10, bringing science observations to a halt. The Chandra mission’s operation team determined that the outage was caused by a fault in one of the gyroscopes used by Chandra’s pointing system. That fault resulted in a three-second period of bad data, which led the onboard computer to calculate an incorrect value for the spacecraft’s momentum, NASA said in today’s status update.

The erroneous reading triggered the safe-mode condition, which caused Chandra to swap critical hardware operations to backup units and reconfigure its mirrors and solar panels to avoid the risk of damage.

Chandra’s operation team diagnosed the problem and switched gyroscopes to get the pointing system up and running again. The gyroscope that experienced the glitch has been placed in reserve.

Some technical detail for those interested in Chandra's recovery from #safemode: One of the two gyros that Chandra was using at the time of the glitch briefly reported an unexpected rate. A glitch of this size has not been observed on Chandra’s gyros before.

— Kim Kowal Arcand (@kimberlykowal) October 15, 2018

NASA said the team plans to apply a series of pre-tested software patches and return Chandra to full science operations by the end of the week.

Since its deployment from the shuttle Columbia in 1999, Chandra has charted X-ray emissions from a wide range of astronomical sources, including black holes and supernovae. Chandra observations were crucial to last year’s detection of what appears to be the closest-orbiting pair of supermassive black holes ever found.

Chandra isn’t designed to be serviced from space. The telescope was designed for a mission life of five years, but it’s on track to last four times that long.

The better-known Hubble Space Telescope also experienced a gyro breakdown last month. Hubble’s operations team is still diagnosing the problem, and the telescope is still in safe mode.

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