NASA has partially restored the Hubble Space Telescope to scientific mode after a software bug temporarily halted observations, but engineers are continuing to study an issue that prevented the telescope’s aperture from closing and a separate issue with Hubble’s main camera.
NASA said Friday that Hubble resumed scientific observations at 8 p.m. EST Thursday (1 a.m. GMT Friday) after going into safe mode on Sunday. Safe mode is an event where Hubble puts itself in a safe configuration to await instructions from the ground up.
Hubble went into safe mode on Sunday after discovering a software bug in the spacecraft’s main computer, NASA said. Ground teams at NASA’s Goddard Space Flight Center in Maryland traced the software bug to code recently uploaded to Hubble to “help compensate for fluctuations from one of its gyroscopes,” NASA said.
Part of Hubble’s targeting system, the gyroscopes use reaction wheels to rotate the telescope to distant galaxies, stars and planets to collect scientific data and images. The gyroscopes measure the direction and speed of the spacecraft’s movement as it spins.
Engineers found that the software bug that caused Hubble to enter safe mode last weekend was an improvement that did not have permission to write to a specific location in the main computer’s memory, NASA said. Ground teams have removed the suspicious code from the computer to allow Hubble to quickly resume scientific operations, and will update the improvement to re-upload to the spacecraft in the future, officials said.
But NASA continues to study two separate problems that engineers discovered when Hubble was in safe mode.
One involves the opening door on the top of the telescope, which didn’t close automatically when Hubble went into safe mode on Sunday. The door prevents bright sunlight from damaging Hubble’s sensitive instruments, and closing the lid of the telescope during a safe mode is supposed to protect the telescope’s interior in case the spacecraft accidentally points to the sun.
NASA closed the aperture door when space shuttles visited Hubble for service missions, but the door never closed after it was determined that the spacecraft’s direction drifted too close to the sun, the agency said in a statement.
Further analysis by ground teams indicated that the lid remained closed despite orders and force sent to the opening door. Manual commands transferred from ground controllers to the door’s primary motor also failed to move the telescope cover, NASA said.
“However, the same commands sent to the backup engine from the ground did indicate movement, and that engine is now set as the primary engine. The team is exploring options to further reduce any associated risks, ”said NASA.
Engineers are also investigating a “low voltage problem” with Wide Field Camera 3, Hubble’s latest science camera and most widely used instrument. The flaw prevents the camera from resuming its observations, but Hubble’s other instruments are fully restored and operational, NASA said.
Developed by NASA with contributions from the European Space Agency, the famous orbiting observatory has been maintained and enhanced by five space shuttle missions. Wide Field Camera 3 was installed during the most recent astronaut service visit on board the shuttle Atlantis in 2009.
With the space shuttles retired, Hubble is in the twilight of its mission. NASA’s next advanced space observatory – the James Webb Space Telescope – will be launched in October to expand Hubble’s vision with a larger mirror and a more advanced array of scientific instruments.
Last year, at virtual celebrations to mark the 30th anniversary of Hubble’s launch, mission managers said they expected at least another five years to make valuable astronomical observations with the long-lived observatory. Only three of Hubble’s six gyroscopes are still operational, and the telescope needs three for normal operations.
That leaves Hubble with no redundancy in its gyro system. Engineers have figured out ways to continue some of the telescope’s observations with just one gyroscope, but that would put limitations on where Hubble could point as it orbits about 550 kilometers above Earth.
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