1990

The Hubble Space Telescope

What if you want to build a telescope that is not affected by the Earth’s atmosphere? The main reason for doing this is because the air that surrounds Earth blocks certain frequencies of light. Another reason is because changes in the atmosphere caused by wind and temperature differences distort the light that comes through, creating the twinkling effect we see in the night sky. It would also be nice to have a telescope that is not subject to light pollution and can see parts of the sky 24 hours a day.

The easy solution to these problems is to put a telescope in space. That sounds simple enough until you actually try to do it, however—then it becomes a massive engineering project.

The first problem is the mirror. Astronomers want it to be as big as possible, but there are limits based on size and weight restrictions in launch vehicles. Engineers chose a 94-inch (2.4 meter) mirror made of glass ground to a precision shape, slightly smaller than the mirror used in the Hooker telescope. A “Cassegrain” design reflects the light off the main mirror, to a smaller secondary mirror and back through a hole in the center of the main mirror to the Hubble’s cameras. The different cameras can see infrared light, ultraviolet light, and visible light.

Engineers then had to package this telescope for space flight, like any other satellite. There are the solar panels and batteries of the electrical system, the antennas and radios of the communication system, the rate gyros and thrusters of the pointing system—especially important so the telescope can point precisely at targets for long periods of time.

In the final instrument, everything works amazingly well. For example, NASA’s Hubble telescope was launched in 1990. It has precisely focused on one small section of space for more than a hundred hours to form the famous Hubble deep-field image. The image is mind boggling because it shows, for the first time, just how many galaxies are visible—thousands of them—in the tiniest patch of space.

SEE ALSO Hooker Telescope (1917), Space Satellite (1957), Lithium Ion Battery (1991).

An STS-125 crew member aboard the Space Shuttle Atlantis captured this still image of the Hubble Space Telescope as the two spacecraft continue their relative separation on May 19, 2009, after having been linked together for over a week.