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A borked bit of code sent the Hubble Space Telescope into safe mode, revealing a bunch of other glitches

Writing to forbidden memory and not closing the door cause headaches for custodians of restored spacecraft

The Hubble Space Telescope resumed science operations this morning after a software error knocked the veteran spacecraft offline.

In what sounds for all the world like an on-orbit Blue Screen of Death, a software update uploaded to the spacecraft attempted to write to a location in computer memory to which it didn't have permission. The main flight computer took exception and sent the telescope into a safe mode on the morning of 7 March.

While engineers have recovered the spacecraft – after all, this is why "safe modes" exist – the problem has shown up other issues. Most seriously, the aperture door at the top of the spacecraft did not automatically close.

Images of the Hubble Space Telescope (HST) normally show this door open. It acts as a "safety net", closing in the event the HST accidentally points at the Sun (due to a hardware error or other problem). A blast of sunlight could do all manner of damage to the sensitive instruments inside the observatory.

"In more than 30 years Hubble has been in orbit," said NASA, "the aperture door has never closed because of the detection of such bright objects."

Despite commands being sent to close it, the door remained open. Instructions from the ground to the primary motor also failed to elicit a response, although the team did note movement when commanding the backup motor.

An "unexpected error" was also thrown up by the Wide Field Camera 3.

The code change itself was to compensate for fluctuations in one of the HST's gyroscopes, used in pointing the telescope. The patch has been prohibited from being used until a fix can be uploaded.

Six new gyroscopes and the Wide Field Camera 3 arrived with the final Space Shuttle servicing mission, 2009's STS 125. Three of those gyros have since failed and the HST needs the remaining three running for maximum efficiency, although can still do useful science with just one.

The 30th anniversary of the telescope's launch rolled around last year and engineers hope to keep the old thing going a while yet, even if the Shuttles that originally serviced it are long gone.

Its successor, the James Webb Space Telescope, has suffered repeated delays and cost overruns but looks set to launch this year after completing its final functional tests. ®

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