NASA has partially repaired the Hubble Space Telescope in scientific mode after a software error temporarily halted the observations, but engineers are studying a problem that is holding back the telescope’s aperture opening and a separate case with Hubble’s main camera.
NASA said Friday Hubble resumed scientific observations at 20:00 EST Thursday (0100 GMT Friday) after switching to safe mode on Sunday. Safe Mode is an event in which Hubble puts itself in a secure configuration to wait for instructions from the ground up.
Hubble went into safe mode on Sunday after detecting a software bug inside the spacecraft’s mainframe, NASA said. Ground crews at NASA’s Goddard Space Flight Center in Maryland tracked down the software bug to code recently uploaded to Hubble to ‘help compensate for fluctuations from one of its gyroscopes,’ NASA said.
The gyroscopes are part of Hubble’s directional system and 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 velocity of the spacecraft’s movement when it rotates.
Engineers found that the software bug that left Hubble in safe mode last weekend contained an enhancement that did not allow it to write to a specific location in the mainframe’s memory, NASA said. Ground crews have removed the suspicious code from the computer to enable Hubble to resume scientific operations quickly, and will upload the enhancement to the spacecraft in the future, officials said.
But NASA continues to study two separate issues that engineers discovered when Hubble was in safe mode.
The one is the aperture at the top of the telescope, which could not close automatically when Hubble went into safe mode on Sunday. The door prevents bright sunlight from damaging Hubble’s sensitive instruments, and the safe cover of the telescope during safe mode should protect the inside of the telescope if the spacecraft accidentally points to the sun.
NASA opened the door when spacecraft visited Hubble for service work, but it has never been instructed that the door would be locked after the spacecraft’s detection was too close to the sun, the agency said in a statement.
Further analysis by ground crews indicated that the cover remained closed despite orders and force sent to the opening door. NASA said hand commands linked from ground controllers to the primary car of the door also could not elicit the telescope cover.
“The same instructions that were sent from the ground to his backup car did indicate movement, and the car has now been set as the primary car. The team is looking at options to further reduce any associated risk, ”NASA said.
Engineers also rate a ‘low voltage issue’ with Wide Field Camera 3, Hubble’s latest science camera and most widely used instrument. The error prevented the camera from resuming its observations, but Hubble’s other instruments were fully recovered and in operation, NASA said.
The famous observatory, developed by NASA with contributions from the European Space Agency, was served and upgraded by five spacecraft missions. The most recent service visit by astronauts aboard the shuttle Atlantis in 2009 installed Wide Field Camera 3.
With the exit of the spacecraft, Hubble is in the twilight of its mission. NASA’s next advanced space-based observatory – the James Webb Space Telescope – will begin expanding Hubble’s vision in October with a larger mirror and a more sophisticated range of scientific instruments.
Last year, during virtual celebrations to mark the thirtieth anniversary of Hubble’s launch, mission managers said they expected to get at least another five years of valuable astronomical observations with the long observatory. Only three of Hubble’s six gyros are still in operation, and the telescope needs three for regular operations.
This leaves Hubble without redundancy in its gyro system. Engineers have devised ways to continue some of the telescope’s observations with just one gyro, but this will be limited to where Hubble can point if it orbits about 550 kilometers above the earth.
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