Hubble Servicing Mission 1: Endeavour’s Repair of a Flawed Mirror

Hubble Servicing Mission 1 lifted off on December 2, 1993, aboard the space shuttle Endeavour. Its job was to repair a telescope whose first images reached Earth looking wrong: the primary mirror had been ground too flat, producing a spherical aberration that put the images out of focus.

Built to be serviced

Engineers designed Hubble to be worked on by astronauts in space. It had handrails, and its instruments were made to be easily removed and replaced. NASA and astronomers wanted to upgrade the telescope throughout its life, installing the latest technologies and repairing parts that broke or were damaged.

A flaw that raised the stakes

After Hubble's launch and deployment in 1990, the ability to fix it became more critical than anyone had imagined. Public apprehension rose and NASA's competency was called into question. The biggest impact was the loss of spatial resolution in the wide field camera. Two of Hubble's gyroscopes were also failing, which made the servicing mission urgent. Seven astronauts trained for it.

What the astronauts did

Over five days of repairs and maintenance they:

• installed new solar arrays that would not expand and contract when going in and out of sunlight, letting Hubble stay steady when taking photos
• replaced failing gyroscopes and magnetometers, allowing more accurate control of the telescope's orientation
• installed Wide Field Planetary Camera 2, which had 48 color filters covering ultraviolet to visible wavelengths and housed extra mirrors to correct for the flaw in the main mirror
• adjusted Hubble's vision with the Corrective Optics Space Telescope Axial Replacement, or COSTAR, which acted almost like a pair of glasses for the primary mirror, fixing the spherical aberration for the rest of Hubble's instruments

Afterward the telescope was back up and running. The mission restored Hubble's original expectations and then more.