Swift enters safe mode over gyro issue while NASA preps patch to shake it off

Gamma-ray burst watcher almost two decades past use-by date

NASA's Neil Gehrels Swift Observatory has dropped into safe mode after one of the spacecraft's three gyroscopes showed signs of degradation.

The fix will require a software update to permit the spacecraft to continue with its two remaining gyros.

The spacecraft, which was launched in 2004 for a planned two-year mission, is designed to study gamma-ray bursts (GRBs). It was originally called the Swift Gamma-Ray Burst Explorer but was later renamed for its Principal Investigator, Neil Gehrels.

As with several other NASA missions – for example, Chandra – Swift's future is uncertain. Although a 2022 Senior Review panel deemed Swift the top-ranked satellite among operating missions other than Hubble and Chandra, its extended mission operations only run through FY2025. NASA is due to conduct the next Senior Review in spring next year.

According to NASA's FY2025 congressional justification [PDF]: "Science highlights from the last year include the discovery of a star torn apart on repeated orbits around a distant supermassive black hole (a repeating tidal disruption event)."

Swift [PDF] has three instruments onboard for studying gamma-ray bursts and their afterglow. The Burst Alert Telescope (BAT), which can survey a sixth of the entire sky at one time, is used to detect a burst. The spacecraft will then swiftly (geddit?) repoint itself to enable the X-ray telescope (XRT) and Ultraviolet/Optical telescope (UVOT) to perform additional observations.

However, pointing the spacecraft requires gyros, and on March 15, engineers noted increased "noise" from one of the trio of gyroscopes. The degraded performance made it difficult for the spacecraft to acquire a star tracker lock, meaning science observations were impacted. Thus, the spacecraft was put into safe mode while engineers devised a solution.

The good news is that Swift can handle a failed gyroscope and still meet its mission goals. The bad news is that the flight software will need a patch to allow Swift to operate correctly with just two gyros.

NASA said: "Until that patch has been successfully deployed, science operations are expected to be very limited."

Gyros are pesky things in spacecraft since they are moving parts that will inevitably eventually experience wear – even if that wear occurs many years beyond their designers' expectations. While gyroless operations have extended the lives of some spacecraft, for example – ESA's Mars Express – the mission requirements of others, particularly observatories, make alternative operation modes difficult or impossible to implement.

The Register contacted NASA to check on the health of the remaining Swift gyros and what options exist should another gyro show signs of failure. We will update this piece should the agency respond. ®

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