Chandra X-ray telescope experiences a glitch; Hubble troubleshooting continues


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

Even as experts worked on ways to get the Hubble Space Telescope back doing science, another one of NASA’s Great Observatories in space — the Chandra X-ray Observatory — went into safe mode as well.

NASA said the 19-year-old X-ray telescope put itself into hibernation on Oct. 10, possibly due to an issue with its gyroscopic pointing system. A gyro failure was behind the 28-year-old Hubble’s transition to safe mode last week.

Due to the glitch, Chandra swapped critical hardware operations to backup units and pointed its solar panels to soak up the maximum amount of sunlight, while pointing its mirrors away from the sun to minimize the risk of damage.

“All systems functioned as expected and the scientific instruments are safe,” NASA said in a status update issued Friday.

The Chandra telescope is named after Nobel Prize-winning Indian-American astrophysicist Subrahmanyan Chandrasekhar and operated for NASA by the Chandra X-ray Center at the Smithsonian Astrophysical Observatory. Chandra focuses on the powerful X-ray emissions from violent cosmic phenomena such as supernovae and black holes.

Scientists at the Harvard-Smithsonian Center for Astrophysics voiced optimism about Chandra’s prognosis on Twitter:

Chandra is safe, the issue is now characterized, we have a clear pathway to recovery, and we're working on it now. Chandra will return to its world-class science program soon.

— Grant Tremblay (@astrogrant) October 12, 2018

Chandra is 19 years old, which is well beyond the original design lifetime of 5 years. In 2001, NASA extended its lifetime to 10 years. It is now into its extended mission & is expected to continue carrying out forefront science for many years to come.

— Chandra Observatory (@chandraxray) October 12, 2018

So, as per the above tweets we went into safemode on Wednesday. I'm not free to give details at this point, but it's sitting happy on the B side in safemode, we just want to understand why it had a little twinge of unhappiness before getting back to work.

— Jonathan McDowell (@planet4589) October 12, 2018

My leading theory is that Chandra decided that if Hubble could have a little vacation, it wanted one too.

— Jonathan McDowell (@planet4589) October 12, 2018

NASA also updated the status of efforts to boost Hubble’s gyro capabilities and get it back to work. Last week, one of the telescope’s three active gyroscopic pointing systems went out of commission, prompting the telescope to go into safe mode.

Hubble needs three working gyros for optimal operation, and so experts have been trying to revive a gyro that was taken out of operation because of a glitch.

In Friday’s update, NASA said the gyro is properly tracking Hubble’s movement, but reporting rotation rates that are consistently higher than what they actually are.

“This is similar to a speedometer on your car continuously showing that your speed is 100 miles per hour faster than it actually is; it properly shows when your car speeds up or slows down, and by how much, but the actual speed is inaccurate,” NASA said.

Hubble’s pointing system can compensate for that effect when it targets a general area of the sky, but the gyro’s performance isn’t good enough for the fine-scale pointing that’s required for scientific observations.

NASA said an anomaly review board that includes professionals experienced in the manufacturing of such gyros, plus Hubble operations personnel, flight software engineers and other experts, is trying to identify the cause of the gyro’s behavior and determine what solutions can be implemented to correct or compensate for it.

If the experts come up with a fix, Hubble can be returned to three-gyro mode. But if not, Hubble will have to switch to one-gyro mode, with a second gyro held in reserve as a backup. In that scenario, scientific observations can still be made, albeit with lower efficiency.

Any fixes will have to be in the form of commands beamed up from the ground. NASA lost its capability for servicing Hubble when the space shuttle fleet was retired in 2011, and Chandra isn’t designed for in-space repair.

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