Disoriented satellite regains bearings but not vision

2019-02-27 10:19:02

By David Shiga NASA’s Swift satellite has regained its bearings following a glitch that prevented it from taking observations. But it will likely be several more weeks before it can resume studying cosmic explosions called gamma-ray bursts. Launched in November 2004, Swift studies brief bursts of gamma rays caused by the deaths of massive stars and collisions between dense stellar corpses. A key to Swift’s success is that it is able to rapidly swivel to train its instruments on the source of each fleeting burst. But on 10 August, Swift lost its bearings while turning to observe a new target (see Swift space telescope suffers debilitating glitch). It could no longer tell which direction it was pointing in the sky, a crippling problem for an astronomical satellite. The glitch was quickly traced to erroneous readings from one of Swift’s three gyroscopes, which control the spacecraft’s orientation. The spacecraft needs two of these gyroscopes to be working at any given time and uses the third as a spare. Now, the spacecraft has regained its bearings after turning on its spare gyroscope. But it is likely to take several weeks to get the spacecraft back to regular observations, since the new gyroscope has to be calibrated. In addition, while Swift was still disoriented on 11 August, its solar panels were briefly pointed away from the Sun, and the resulting power loss triggered its instruments to power down. As a result, its scientific instruments – a gamma-ray telescope, an X-ray telescope, and an ultraviolet and optical telescope – will need to be recalibrated before observations can begin. “To some extent, this turning off the instruments brings us back to how we were at the beginning of the mission,” says Swift mission director John Nousek of Pennsylvania State University in University Park, US. He notes that it took about a month to get Swift ready for observing after its launch in 2004. A similar amount of time may elapse between Swift’s 10 August glitch and a return to normal observing, he says. “But I see no fundamental roadblock preventing us from achieving full observatory performance once we carry out [these] jobs,