NASA’s Neil Gehrels Swift Observatory has run into difficulties after 17 years of largely smooth service. The orbiting explorer has entered safe mode after detecting a “possible failure” in one of the six reaction wheels used to change attitude. While it’s not clear exactly what (if anything) went wrong, NASA has halted direction-based scientific observations until it can either give the all-clear or continue operations with five wheels.

This is the first potential reaction wheel problem since the Swift Observatory began operations in February 2005, NASA said. The rest of the vehicle is otherwise working properly.

The Swift Observatory has played an important role in astronomy over the past two decades. It was primarily built to detect gamma-ray bursts and detects roughly 70 per day. However, it has increasingly been used as a catch-all observer across multiple wavelengths, spotting solar flares and hard-to-find stars. NASA won’t necessarily run into serious trouble if Swift has a lasting problem, but it would clearly benefit from keeping the spacecraft running as smoothly as possible.