The Hubble Space Telescope (HST) was the first and flagship mission of NASA's Great Observatories program. Designed to complement the wavelength capabilities of the other spacecraft in the program (CGRO, AXAF, and SIRTF), HST was a 2.4 m, f/24 Ritchey-Chretien telescope capable of performing observations in the visible, near-ultraviolet, and near-infrared (1150 A to 1 mm).
Placed into a low-earth orbit by the space shuttle Discovery on April 24, 1990, HST was designed to be modular so that on subsequent shuttle missions it could be recovered, have faulty or obsolete parts replaced with new and/or improved instruments, and be re-released.
HST was roughly cylindrical in shape, 13.1 m end-to-end and 4.3 m in diameter at its widest point.
HST used an elaborate scheme for attitude control to improve the stability of the spacecraft during observations. Maneuvering was performed by four of six gyros, or reaction wheels. Pointing could be maintained in this mode (coarse track) or the Fine Guidance Sensors (FGSs) could be used to lock onto guide stars (fine lock) to reduce the spacecraft drift and increase the pointing accuracy.
Power to the two on-board computers and the scientific instruments was provided by two 2.4 x 12.1 m solar panels. The power generated by the arrays was also used to charge six nickel-hydrogen batteries which provided power to the spacecraft during the roughly 25 minutes per orbit in which HST was within the Earth's shadow.
Communications with the satellite were maintained with the TDRS satellites. Observations taken during the time when neither TDRS was visible from the spacecraft were recorded on tape recorder and dumped during periods of visibility. The spacecraft also supported real-time interactions with the ground system during times of TDRS visibility, enabling observers to make small offsets in the spacecraft pointing to perform their observations. HST was the first scientific spacecraft designed to utilize the full capabilities of TDRSS, communicating over either multiple-access or single-access channels at any of the supported transmission rates.
The construction of the telescope was problematic, being delayed and over-budget. The mission was troubled soon after launch by the discovery that the primary mirror was spherically aberrated. The main mirror was ground incorrectly, and tests that demonstrated the problem were ignored; the problem was discovered only after the telescope was launched. In addition, problems with the solar panels flexing as the spacecraft passed from the Earth's shadow into sunlight caused problems with the pointing stability.
Fortunately, Hubble was designed to be serviced by astronauts - the only telescope so designed. Steps were taken to correct these problems, including replacement of the solar panels, replacement of the Wide Field and Planetary Camera with a second-generation version with built-in corrective optics, and replacement of the High-Speed Photometer with COSTAR (Corrective Optics Space Telescope Axial Replacement) to correct the aberration for the remaining instruments.
Hubble included a number of instruments, including the Wide Field and Planetary Camera, High Speed Photometer, Faint Object Camera, Faint Object Spectrograph, and Goddard High Resolution Spectrograph. All of these have since been replaced by other instruments (COSTAR was replaced by the Cosmic Origins Spectrograph). The other instruments in the current suite are the Wide Field Camera 3 (WFC3), Near Infrared Camera and Multi-Object Spectrometer (NICMOS), Advanced Camera for Surveys (ACS), and Space Telescope Imaging Spectrograph (STIS). Of these, the NICMOS has cooling problems and the High Resolution Channel of the ACS is offline due to electronics failures.
Hubble has made numerous important discoveries, including demonstrating the prevalence of black holes in nearby galaxies, observation of the collision of Comet Shoemaker-Levy 9 with Jupiter, refining estimates of the age of the universe and observing its accelerating expansion, and observing protoplanetary disks. It has produced the Hubble Deep Field and Hubble Ultra-Deep Field images. Hubble is unique among NASA's "Great Observatory" space telescopes in the range of frequencies it can detect - from near-infrared to near-ultraviolet.
There have been a total of five servicing missions to Hubble, in 1993, 1997, 1999, 2002, and 2009. Hubble was originally planned to be returned to Earth in a space shuttle, but this is no longer possible due to the cancellation of the Shuttle program. Now, it is planned to be de-orbited.
Alternate Names
Hubble Space Telescope
Space Telescope
Facts in Brief
Launch Date: 1990-04-25
Launch Vehicle: Shuttle
Launch Site: Cape Canaveral, United States
Mass: 11600.0 kg
Nominal Power: 2400.0 W