Hubble Space Telescope

Hubble's position above most of Earth's atmosphere gives it a clearer and more stable view of space than ground-based telescopes receive through moving air. It can also observe ultraviolet wavelengths that Earth's atmosphere blocks or strongly absorbs. Its 2.4-meter (7.9-foot) primary mirror collects light and directs it toward instruments that produce images and spectra.

Hubble's position above most of Earth's atmosphere gives it a clearer and more stable view of space than ground-based telescopes receive through moving air. It can also observe ultraviolet wavelengths that Earth's atmosphere blocks or strongly absorbs. Its 2.4-meter (7.9-foot) primary mirror collects light and directs it toward instruments that produce images and spectra.

NASA describes Hubble as orbiting roughly 483 km (300 mi) above Earth, moving at about 27,000 km/h (17,000 mph), or approximately 8 km/s (5 mi/s). It circles Earth about once every 95 minutes, completing roughly 15 orbits per day. Its live catalog altitude and calculated orbital values can differ because atmospheric drag and earlier servicing-mission reboosts change the orbit over time.

Hubble must hold its line of sight extraordinarily steady while traveling around Earth at orbital speed. Gyroscopes measure rotation, reaction wheels turn the observatory without using continuous thruster firings, and fine-guidance sensors lock onto guide stars. This combination lets Hubble keep distant targets centered during long observations.

Astronomers use spectroscopy to separate incoming light into wavelengths. The resulting spectrum can reveal an object's chemical composition, temperature and motion. Changes in spectral lines also help scientists measure whether distant objects are moving toward or away from Earth.

The primary mirror's initial spherical aberration blurred Hubble's early images because light reflected from different parts of the mirror did not focus at the same point. During Servicing Mission 1 in December 1993, astronauts installed corrective optics and a new camera with built-in correction, restoring the telescope's intended image quality.

Each science mission is designed around particular research questions and instruments. The spacecraft provides the pointing, power, communications, and environmental control those instruments need.

• Hubble's position above most of Earth's atmosphere gives it a clearer and more stable view of space than ground-based telescopes receive through moving air. It can also observe ultraviolet wavelengths that Earth's atmosphere blocks or strongly absorbs. Its 2.4-meter (7.9-foot) primary mirror collects light and directs it toward instruments that produce images and spectra.
• NASA describes Hubble as orbiting roughly 483 km (300 mi) above Earth, moving at about 27,000 km/h (17,000 mph), or approximately 8 km/s (5 mi/s). It circles Earth about once every 95 minutes, completing roughly 15 orbits per day. Its live catalog altitude and calculated orbital values can differ because atmospheric drag and earlier servicing-mission reboosts change the orbit over time.
• Hubble must hold its line of sight extraordinarily steady while traveling around Earth at orbital speed. Gyroscopes measure rotation, reaction wheels turn the observatory without using continuous thruster firings, and fine-guidance sensors lock onto guide stars. This combination lets Hubble keep distant targets centered during long observations.
• Astronomers use spectroscopy to separate incoming light into wavelengths. The resulting spectrum can reveal an object's chemical composition, temperature and motion. Changes in spectral lines also help scientists measure whether distant objects are moving toward or away from Earth.
• The primary mirror's initial spherical aberration blurred Hubble's early images because light reflected from different parts of the mirror did not focus at the same point. During Servicing Mission 1 in December 1993, astronauts installed corrective optics and a new camera with built-in correction, restoring the telescope's intended image quality.

Hubble's position above most of Earth's atmosphere gives it a clearer and more stable view of space than ground-based telescopes receive through moving air. It can also observe ultraviolet wavelengths that Earth's atmosphere blocks or strongly absorbs. Its 2.4-meter (7.9-foot) primary mirror collects light and directs it toward instruments that produce images and spectra. NASA describes Hubble as orbiting roughly 483 km (300 mi) above Earth, moving at about 27,000 km/h (17,000 mph), or approximately 8 km/s (5 mi/s). It circles Earth about once every 95 minutes, completing roughly 15 orbits per day. Its live catalog altitude and calculated orbital values can differ because atmospheric drag and earlier servicing-mission reboosts change the orbit over time. Hubble must hold its line of sight extraordinarily steady while traveling around Earth at orbital speed. Gyroscopes measure rotation, reaction wheels turn the observatory without using continuous thruster firings, and fine-guidance sensors lock onto guide stars. This combination lets Hubble keep distant targets centered during long observations. Astronomers use spectroscopy to separate incoming light into wavelengths. The resulting spectrum can reveal an object's chemical composition, temperature and motion. Changes in spectral lines also help scientists measure whether distant objects are moving toward or away from Earth. The primary mirror's initial spherical aberration blurred Hubble's early images because light reflected from different parts of the mirror did not focus at the same point. During Servicing Mission 1 in December 1993, astronauts installed corrective optics and a new camera with built-in correction, restoring the telescope's intended image quality.

The current two-line element set reports approximately 15.3168 revolutions per day. Dividing 1,440 minutes by that value gives an estimated orbital period of 94 minutes.

Space Shuttle Discovery launched on mission STS-31 from Launch Pad 39B at Kennedy Space Center on 24 April 1990 at 8:33:51 a.m. EDT. The five-person crew deployed Hubble from Discovery's payload bay on 25 April. A launch attempt scheduled for 10 April was scrubbed at T-minus four minutes because of a faulty valve in auxiliary power unit number one. Engineers replaced the APU and recharged the payload batteries before the successful launch. During the final countdown on 24 April, a ground-support fuel-valve issue briefly stopped the count at T-minus 31 seconds; engineers commanded the valve closed and the countdown continued.

Low Earth orbit is the region closest to Earth used by most crewed spacecraft, many science missions, Earth-observation satellites, and large constellations. Objects move quickly and commonly complete an orbit in roughly 90 to 130 minutes.

LEO can provide detailed Earth views, lower communications delay, and easier access than higher orbits, but it covers less area per spacecraft and is more affected by atmospheric drag.

• What can a space instrument observe that a ground instrument cannot?
• How does the mission’s orbit support its scientific goal?

Current identity and orbital elements come from CelesTrak’s public GP data. Calculated orbit values are derived from the current TLE and may change after catalog updates. Mission-history claims are added separately and require authoritative sources.

• CelesTrak NORAD GP Element Sets
• Hubble Observatory · NASA Science
• STS-31 · NASA
• Servicing Mission 1 · NASA Science