Hubble Space Telescope
Space-based astronomical observing facility, orbiting the Earth at an altitude of 610 km/380 mi. It consists of a 2.4 m/94 in telescope and four complementary scientific instruments, is roughly cylindrical, 13 m/43 ft long and 4 m/13 ft in diameter, and has two large solar panels. HST produces a wealth of scientific data, and allows astronomers to observe the birth of stars, find planets around neighbouring stars, follow the expanding remnants of exploding stars, and search for black holes in the centre of galaxies. HST is a cooperative programme between the European Space Agency (ESA) and the US space agency NASA, and is the first spacecraft specifically designed to be serviced in orbit as a permanent space-based observatory. It was launched in 1990. It will re-enter the Earth's atmosphere some time after 2010 and be destroyed unless more servicing missions are flown to it – missions that are currently in doubt following the Columbia shuttle disaster.
By having a large telescope above Earth's atmosphere, astronomers are able to look at the universe with unprecedented clarity. Celestial observations by HST are unhampered by clouds and other atmospheric phenomena that distort and attenuate starlight. In particular, the apparent twinkling of starlight, caused by density fluctuations in the atmosphere, limits the clarity of ground-based telescopes. HST performs at least ten times better than such telescopes and can see almost back to the edge of the universe and to the beginning of time (see Big Bang).
Before HST could reach its full potential, a flaw in the shape of its main mirror, discovered two months after the launch, had to be corrected. In 1993, as part of a planned servicing and instrument upgrade mission, NASA astronauts aboard the space shuttle Endeavour installed a set of corrective lenses to compensate for the error in the mirror figure. COSTAR (corrective optics space telescope axial replacement), a device containing ten coin-sized mirrors, now feeds a corrected image from the main mirror to three of the HST's four scientific instruments. HST is also being used to detail the distribution of dust and stars in nearby galaxies, watch the collisions of galaxies in detail, infer the evolution of galaxies, and measure the age of the universe.
| In December 1995, HST was trained on an ‘empty’ area of sky near the Plough, now termed the Hubble Deep Field. Around 1,500 galaxies, mostly new discoveries, were photographed. |
| Two new instruments were added in February 1997. The near-infrared camera and multi-object spectrometer (NICMOS) will enable Hubble to see things even further away (and therefore older) than ever before. The space telescope imaging spectrograph will work 30 times faster than its predecessor as it can gather information about different stars at the same time. Three new cameras had to be fitted shortly afterwards as one of the original ones was found to be faulty. |
| In May 1997, three months after astronauts installed new equipment, US scientists reported that Hubble had made an extraordinary finding. Within 20 minutes of searching, it discovered evidence of a black hole 300 million times the mass of the Sun. It is located in the middle of galaxy M84 about 50 million light years from Earth. Further findings in December 1997 concerned different shapes of dying stars. Previously, astronomers had thought that most stars die with a round shell of burning gas expanding into space. The photographs taken by the HST show shapes such as pinwheels and jets. This may be indicative of how the Sun will die. |
| Galaxies photographed by the HST in 1998 were born at least 12 billion years ago. These were the remotest objects ever imaged. In April 2000, ten years after its launch, the telescope had taken 271,000 separate observations of 13,670 objects, and had been serviced by astronauts 13 times. |
| A US$19 million pair of powerful solar wings and an advanced camera were installed on the HST during an 11-day mission in early March 2002. The smaller wings, which are rigid, are more stable than the previous design and will provide 20% more power. |
| In January 2004, NASA announced that it was cancelling a 2006 mission to service and upgrade Hubble, on the grounds of astronaut safety. NASA also reported that no replacement date was being considered at that time. This produced fierce controversy in the scientific community, since without servicing, the Hubble Space Telescope will slowly deteriorate and will eventually fail. |
| The HST cost US$2.5 billion – five times the original estimate – and was launched seven years late by the space shuttle Discovery in April 1990. Its instruments include a wide-field/planetary camera designed to gather the sharpest astronomical images ever. The faint object camera was built by ESA and uses an image intensifier to image the faintest object resolvable by the telescope. The faint object spectrometer (FOS) measures spectra in a wide range of light, from ultraviolet to near infrared. The Goddard high-resolution spectrograph is similar to the FOS but is dedicated to ultraviolet and infrared astronomy. |
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