Discovery launches with the Hubble Space Telescope

Discovery Lifts Hubble Into Orbit

On April 24, 1990, the space shuttle Discovery launched from Kennedy Space Center on STS-31 with the Hubble Space Telescope in its cargo bay. The telescope was deployed the following day. The difference between those dates matters: on April 24 the observatory was still cargo supported by the shuttle; afterward it was a separate spacecraft with its own power and orientation systems. Getting Hubble to orbit had been the work of many years and involved more than designing a fine optical instrument. It also meant building a telescope the shuttle could carry, release and, under later missions, reach again.

A Telescope Above the Turbulent Air

Earth's atmosphere distorts light and blocks some wavelengths. Moving a telescope above it gives astronomers access to a different set of observations, including wavelengths that cannot readily be studied from the ground. An orbiting telescope must supply its own stability, power and communication, and scientists cannot walk over to replace a component. Hubble was built with these constraints in mind. Its usefulness would depend not only on the mirror but on the ability to point accurately, keep instruments at suitable conditions and send data back. The launch solved the problem of location while leaving the performance of those systems to be tested.

A Flaw Revealed by the First Images

Soon after deployment, astronomers discovered that Hubble's primary mirror had a figure error that prevented light from coming to the intended sharp focus. The observatory still returned useful information, but important kinds of work were impaired. Engineers traced the error to the way the mirror had been tested during manufacture. The flaw was small in physical dimensions and large in consequence. It could not be removed by turning a simple focus control. Instead, instruments or corrective optics had to compensate for the known shape of the mirror and restore light to the path the original design required.

Why Serviceability Saved the Program

In 1993 a servicing crew installed corrective equipment and a new camera with its own correction. Later shuttle missions replaced instruments and other components. Hubble became a long-lived observatory partly because its design allowed it to be treated as equipment that could be maintained, rather than a single launch that had to remain unchanged. The 1990 lift-off was the prerequisite for all that followed. It did not by itself guarantee the well-known images of later decades. Those images came from a combination of the orbital platform, scientists learning what had gone wrong and astronauts making repairs the original vehicle had been designed to accept. That arrangement kept the people who designed new instruments connected to practical questions about what an astronaut could reach, remove and replace.