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A failure of a gyroscope used to point and stabilize the Hubble telescope has resulted in the closure of the observatory safely while engineers determine a solution.
Photo of the Hubble Space Telescope in Low Earth Orbit.
NASA
Any machine that runs almost continuously for 28 years will fail from time to time. And the Hubble Space Telescope is no exception.
On October 5th, Hubble went into safe mode after the failure of a gyroscope to point and stabilize the telescope while watching. In safe mode, the observatory hibernates while field engineers determine how to solve the problem.
"We are proceeding cautiously to stop hurting," said Tom Brown (Space Telescope Science Institute), who heads the Hubble Mission office. "Hubble will go back to science, whether the gyro works or not."
During the last Hubble maintenance mission in 2009, space shuttle astronauts Atlantis installed six new gyroscopes in the telescope. Generally, the observatory uses three at a time. In case of failure, it switches to one of its backups.
Last Friday, one of the three active gyroscopes failed. The failure was not a surprise: the gyroscope showed signs of wear over the past year. However, the replacement gyro did not work either. So, shortly after 6 pm EDT, the telescope suspended its operations to await new instructions from the Earth.
This is not the first time that a gyroscope breaks down, and it will certainly not be the last.
Hubble's pointing control system consists of gyroscopes, reaction wheels and fine guide sensors.
STScI
What engineers know so far is that the emergency gyro is too far from its target. "Ideally, the gyroscope goes in the desired direction," says Brown. In reality, however, all gyroscopes are slightly offset. The software can correct this offset as long as it is not too big. At the present time, the difference is outside the usable range.
NASA has assembled a team of engineers to review the telescope data as well as flight diagrams and software to determine the next step. The best option is to operate the replacement gyroscope so that the telescope can resume operation.
If that does not work, the agency already has a plan in place to operate the telescope with a single gyroscope, while the second one is waiting for help. In this mode, the observatory relies on additional information from magnetometers and guidance cameras for accurate pointing. According to Brown, the disadvantage is that Hubble can only look at half the sky at a given moment. However, when Earth and Hubble revolve around the sun, the same goes for the telescope viewing window. During a year, the entire sky (minus the forbidden area within 50 degrees of the Sun) becomes available.
At the moment, the atmosphere at NASA could be described as cautious optimism. "There is no sense of unhappiness, just a sense of worry," says Brown. All other instruments are in good condition. While engineers tinker with gyroscopes, a team of astronomers from around the world is already studying proposals for the future coveted telescope.
"We are still planning to last until the 2020s," said Brown. "We are expecting a lot of scientific observations from the observatory."
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