An observatory above the atmosphere
Earth’s atmosphere blurs starlight and absorbs parts of the spectrum. Hubble placed its mirror and instruments in orbit, using stable pointing and long exposures to study stars, galaxies and planets. It was also designed for maintenance by astronauts.
Power, attitude control and communications had to operate together. Solar arrays supplied energy, controls kept targets in view, and ground teams received data and scheduled observations.
Discovery releases the telescope
Discovery launched with Hubble on the STS-31 mission on April 24, 1990. The next day its crew used the robotic arm to lift the telescope from the payload bay, check deployment and release it into independent orbit.
April 25 marks orbital deployment; launch was the preceding day. After the shuttle departed, Hubble used its own power, pointing and communications systems for commissioning and observation.
Diagnosing and correcting the optics
The initial images revealed spherical aberration in the primary mirror, preventing light from forming the intended sharp focus. Teams diagnosed the problem and developed corrective optics and a new camera for servicing.
In December 1993, astronauts on Endeavour’s STS-61 mission installed equipment including the corrected new camera and COSTAR during spacewalks. Subsequent tests showed improved image quality.
An observatory with replaceable instruments
Servicing replaced cameras, batteries, solar arrays and control components, allowing the same telescope to operate with newer instruments. Engineering maintenance and scientific observation became continuing parts of the mission after launch.
Deployment and servicing reports preserve the release from the payload bay, independent operation and replacement of optical equipment. These engineering steps accompany the observatory’s accumulated measurements.