Hubble Space Telescope

Launch from the Shuttle

The Hubble Space Telescope was carried into low Earth orbit in 1990 aboard the Space Shuttle Discovery, a joint project of NASA and the European Space Agency.

The mirror flaw, and the fix

Within weeks of launch it was clear something was wrong: images were blurred in a way no focus adjustment could correct. The primary mirror had been ground to slightly the wrong shape — an error of about two micrometres at the edge, traced to a miscalibrated test instrument used during manufacture. The result was spherical aberration, and it was an institutional failure as much as a technical one.

The first servicing mission in 1993 installed corrective optics that compensated for the error, and later instruments built the correction in rather than relying on an external fix. The recovery is routinely cited as the strongest practical argument for designing spacecraft that can be serviced.

Five servicing missions

Astronauts visited Hubble five times between 1993 and 2009, replacing instruments, gyroscopes, batteries and solar arrays. The detectors flown in 2009 were generations beyond those launched in 1990, so the observatory's capability increased over its lifetime instead of decaying — an almost unique trajectory for a space mission.

That option no longer exists. The Space Shuttle was retired in 2011 and no operational vehicle is equipped for the task, so Hubble now runs on its existing hardware, managing gyroscope failures with reduced-gyro observing modes while its orbit gradually decays. The contrast with JWST, which sits far beyond any servicing capability by design, is the clearest illustration of what that trade buys and costs.

Mission and instrument

This entry covers the mission and its servicing. For the observatory itself — its optics and what it observes — see the Hubble entry under Space Telescopes.