E N C Y C L O P E D I A

 

Hubble Space Telescope

The Hubble Space Telescope (HST, or the Hubble) is a telescope located at the outer edges of Earth's atmosphere, about 600 kilometerss above the ground, orbiting the Earth every 100 minutes. It was placed into orbit, in April 1990, as a joint project of NASA and the ESA. The telescope can achieve optical resolutions greater than 0.1 arcseconds. The HST is named after Edwin Hubble. It is scheduled for replacement, by the Next Generation Space Telescope (NGST), in 2009.

Working outside the atmosphere has advantages because the atmosphere obscures images and filters out electromagnetic radiation at certain wavelengths, mainly in the infrared.


Hubble Space Telescope as seen from the Space Shuttle Discovery on mission STS-82.


Pictures taken by the Hubble Space Telescope: Clockwise from the upper left, the "Tadpole" galaxy, the "Cone Nebula", two colliding spiral galaxies dubbed "The Mice", and stellar birth in the Omega Nebula. (Images courtesy of NASA)

Table of contents
1 Technical description
2 Discoveries
3 Launch and initial disappointment
4 Servicing Missions
5 The future beyond Hubble
6 External Links

Technical description

The unit weighs about 11,000 kilograms, is 13.2 meters long, has a maximum diameter of 4.2 meters and cost US 2 billion (2 × 109 dollars). The telescope is a reflector with two mirrors; the main mirror has a diameter of about 2.4 meters. It has various spectrometers and three cameras: one for faint objects in a small field, one wide field camera for planetary pictures, and one infrared camera.

It uses two solar panels to generate electricity, which is mainly needed to power the cameras and the four large flywheels used to orient and stabilize the telescope. The telescope's infrared camera and multi object spectrometer also need to be cooled down to minus 180 degrees Celsius for operation.

Discoveries

  • Hubble provided dramatic pictures of the collision of comet Shoemaker-Levy 9 and Jupiter in 1994.
  • Evidence of planets surrounding stars other than the Sun was obtained for the first time with Hubble.
  • Observations with Hubble also showed that the missing dark matter in our galaxy cannot consist solely of faint small stars.
  • Some of the observations leading to the current model of an accelerating universe were performed using the Hubble space telescope.
  • The theory that most galaxies host a black hole in their nucleus has been partially confirmed by many observations.
  • In December 1995, Hubble photographed the Hubble Deep Field, a region covering one 30-millionth of the area of the sky and containing several thousand faint galaxies. A similar patch of southern sky was also imaged and looked remarkably similar, strengthening the position that the Universe is uniform over large scales, and that Earth occupies a typical place in the Universe.

Click here for more

Launch and initial disappointment

The telescope was launched by Space Shuttle Discovery mission STS-31 on April 24, 1990. This had been postponed from a 1986 launch date by the Space Shuttle Challenger disaster in January that year.

The first images back from the telescope were generally regarded as a big disappointment for astronomers and all concerned in the project. They were blurred, and despite image processing could not match the predicted resolution. It was determined that the main mirror had been ground slightly too flat at the edges, a problem that could have been tested for on the ground if the funds had been available.

Servicing Missions

The telescope has been revisited several times by spacewalking astronauts in space shuttles in order to correct malfunctions and install new equipment. Because of atmospheric drag, the telescope slowly loses height (and gains speed) over time; the shuttle pulls it back to a higher orbit every time it visits.

  • Servicing Mission 1, December 1993 (STS-61) installed several instruments and other equipment. The most important astronomically were: the Corrective Optics Space Telescope Axial Replacement (COSTAR), which was a set of five corrective mirrors; and the Wide Field/Planetary Camera (WF/PC-II), an upgraded version of the previous ultraviolet detector which also incorporated the corrective optics. On January 13, 1994, NASA declared the mission a complete success, and showed the first of many much sharper images.
  • Servicing Mission 2, February 1997 (STS-82) replaced High Resolution Spectrograph and Faint Object Spectrograph with Space Telescope Imaging Spectrograph and added Near Infrared Camera / Multi-Object Spectrograph.
  • Servicing Mission 3A, December 1999 (STS-103) replaced faulty gyroscopes and fine guidance sensors (reusing one returned by SM-1), installed new computer.
  • Servicing Mission 3B, March 2002 (STS-109) repaired and upgraded several items, requiring lengthy and delicate spacewalks. Fixes to the telescope included:
    • Update of its Power Converter Unit, which was particularly tricky as it was not designed for in-orbit replacement, and also required taking the satellite completely off-line for the first time since it was put into operation.
    • Replacement of its solar arrays. The new arrays were derived from those built for the Iridium comsat system.