Hubble Space Telescope

A telescope above the air

The idea of a telescope in space was proposed by Lyman Spitzer in 1946. NASA and the European Space Agency built it, and it was named after Edwin Hubble in 1983. The telescope was launched on 24 April 1990 on the space shuttle Discovery (STS-31), into an orbit about 540 kilometres up.

Early images were blurred. The main mirror had been ground precisely, but to the wrong shape: it was too flat at the edge by about two micrometres, a spherical aberration caused by a test instrument assembled with a spacing error.

Repair in orbit

Hubble was designed to be serviced. In December 1993 astronauts on STS-61 installed corrective optics, a replacement camera and a package of small mirrors that restored sharp images. Four more servicing missions followed, the last in 2009, replacing cameras and spectrographs, gyroscopes and batteries.

The telescope's most famous picture is the Hubble Deep Field. In December 1995 it stared at an apparently empty patch of sky for ten days and recorded about 3,000 galaxies, at distances reaching nearly to the early universe.

Open data and a long life

Hubble's observations are archived at the Space Telescope Science Institute, and become public after a proprietary period, which is short or none for most programmes. Papers using Hubble data are among the most cited in astronomy. Hubble helped fix the Hubble constant, the rate of expansion of the universe, measured with Cepheids and supernovae, and its observations underlie the finding that the expansion is accelerating.

Ageing gyroscopes limit its pointing. In 2024 NASA put the telescope into a one-gyroscope mode to preserve its life, trading some efficiency for years of operation.

The servicing era is over

Hubble's five servicing missions kept it productive for nearly twenty years. After 2009 no further visits were possible because the space shuttle retired, and the telescope is now living on its remaining gyroscopes and its batteries. Its eventual end, by a controlled or uncontrolled reentry, is expected in the 2030s, after the shuttle's retirement removed the means to boost its orbit. The archive, by then, will include more than thirty years of observations, and each year reanalysis of old data yields discoveries the original observers did not seek. For an observatory in space, the archive is the part that lasts.

Instruments and technologies

• 2.4 m primary mirror A Ritchey–Chrétien design with a mirror of ultra-low-expansion glass, in a telescope kept at about room temperature.
• Wide Field Camera 3 A camera covering ultraviolet to near-infrared, installed in 2009.
• Fine guidance sensors Sensors that lock on guide stars to hold the telescope steady.

The people

• Edwin Hubble Astronomer for whom the telescope is named.
• Lyman Spitzer Astrophysicist who proposed a telescope in space in 1946.

Timeline

• 1983 Named after astronomer Edwin Hubble.
• 1990 Launched on STS-31; a flaw in the mirror's shape blurs early images.
• 1993 First servicing mission (STS-61) corrects the optics.
• 1995 Hubble Deep Field observed over ten days in December, revealing about 3,000 galaxies.
• 2009 Fifth and final servicing mission.

Key lessons for observation today

• Design for service Hubble could be repaired in orbit, and the repair saved the programme. Plan for access to instruments in the field.
• Test the test The flaw arose from the instrument used to test the mirror. Independent verification of calibration equipment is essential.
• Open archives outlive missions The archive supports science long after each instrument is retired. Plan the archive with the mission.

Sources

• NASA Science, Hubble history timeline
• Wikipedia, Hubble Space Telescope
• Wikipedia, Hubble Deep Field
• Wikipedia, Lyman Spitzer