Hubble Telescope, Disoriented by Mechanical Failure, Takes a Nap to Reboot

The News

  • As a result of gyroscope failure, The Hubble Space Telescope (HST) is temporarily out of service.


Key Highlights

  • HST is equipped with six gyroscopes to orient the telescope.
  • Out of the six gyroscopes, three are required for optimal operation of the telescope while other three are backup gyroscopes.
  • In the early years of operation till 2009 gyroscope failure was a commonplace. Thus as a part of its last servicing mission, NASA in 2009, installed 6 gyroscopes.
  • From 2009 two gyroscopes have failed the current failure being the third one.
  • As a result the ground controllers tried to bring the backup gyroscope online, however, it behaved erratically. Thus the HST was put into “safe mode”.


What do gyroscopes do?

  • In order to make precise observations of objects in space, pointing the telescope to an object and holding it steady is important
  • This job is done by the gyroscopes and steering devices called reaction wheels on HST.
  • By measuring the attitude when Hubble is changing its position the gyroscopes help control the telescope’s pointing while scientists are observing the objects in space.
  • Further when the telescope needs to be re-pointed to another object, the gyroscopes sense this and pass this message to the computer control system.
  • The control system then a command to give the reaction wheels a “push” or “spin.”
  • Further, as Hubble accelerates its reaction wheels in one direction, Hubble’s reaction is to rotate in the opposite direction.
  • This is in accordance with Newton’s third law.
  • Since the rotation axes of the four reaction wheels point in different directions, Hubble is able to use combinations of them to point itself toward any location in the sky
  • Thus three gyros are necessary for the telescope to operate optimally, though it can operate with one.



About Hubble Space Telescope

  • Hubble space telescope is named after Edwin Hubble, the astronomer who discovered the expansion of the universe.
  • The largest telescope yet placed in orbit, HST is a joint project of NASA and the European Space Agency (ESA).
  • HST is orbiting the earth 600 km above its surface since 1990.
  • The aperture of the mirror used in HST is about 2.4 m.
  • HST can observe objects in visible, near-ultraviolet, and near-infrared light.
  • The advantage in being above Earth’s surface is that it can observe space without the distortion caused by earth’s atmosphere.
  • Observing the space from its vantage point high above the atmosphere, angular resolution of the telescope would be limited only by diffraction.
  • This enables the mirror of the telescope to concentrate 70% of a star’s light into an image with an angular diameter of 0.1 arcsec.
  • Thus HST has been able to produce sharp images of extremely faint objects.
  • Important discoveries of HSTs include:
  • Discovery about the nature of planets like new moons of Pluto
  • Evolution of stars
  • Inner workings of galaxies
  • Expansion of the universe at a faster rate than several billion years ago
  • Recently Hubble Space Telescope spotted a galaxy that formed less than 500 million years after the birth of the universe giving a glimpse of early universe




James Web Telescope: The Future

  • After the success of HST the James Webb Space Telescope is all set to succeed the HST in 2021.
  • JWST will observe at visible and infrared wavelengths from 600 nm to 28 micros.
  • It has a 6.5-m objective mirror which 2.5 times the diameter of the HST objective mirrors.
  • Thus it is six times more powerful in terms of its the light-gathering capacity and thus can study even fainter objects than HST.
  • While HST is in low-altitude orbit around the Earth, JWST will orbit the Sun some 1.5 million km beyond the Earth.
  • In this orbit the telescope’s view will not be blocked by the Earth.
  • Furthermore, by remaining far from the radiant heat of the Earth it will be easier to keep JWST at the very cold temperatures required by its infrared detectors.

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