Hubble Space Telescope Engineering Breakdown

The Hubble Space Telescope transformed a long-standing astronomical dream into an observatory operating above most of Earth's image-distorting atmosphere. NASA launched Hubble aboard Space Shuttle Discovery in April 1990 as a general-purpose observatory capable of studying ultraviolet, visible and near-infrared light. Its observations have helped scientists investigate planets, stars, nebulae, galaxies, black holes and the expansion of the universe. Hubble's story also became one of spaceflight's greatest repair successes: after engineers discovered that its primary mirror had been manufactured with the wrong curvature, astronauts installed corrective optics during the first servicing mission in 1993. Five astronaut servicing missions between 1993 and 2009 repaired systems and installed improved instruments, extending the observatory far beyond its original planned lifetime.

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.

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.