The Hubble Space Telescope: Our Window on the Universe

Hubble is big. Excluding its aperture door and solar arrays, the spacecraft is 43.5 feet (13.3 meters) long and 14 feet (4.3 meters) across at its widest point. Altogether, Hubble would weigh about 27,000 pounds (12,200 kilograms) on the ground, although it is weightless in orbit.

Hubble is a reflecting telescope. It uses mirrors to collect light from the universe and reflect that light to its cameras and other scientific instruments.

The primary mirror is 1,825 pounds and almost 8 feet (2.4 meters) across. It collects light from an astronomical target and reflects it to a secondary mirror that is 12 inches (0.3 meter) wide.

This secondary mirror then reflects the light through a hole in the primary mirror and then on to its scientific instruments.

Unlike most other spacecraft, Hubble was designed to be serviced periodically by astronauts. So it was built with modular components that are made for astronauts to handle and replace.

At the back end of the spacecraft are the scientific instruments. Four are rectangular, each the size of a large refrigerator. Just above them are four additional instruments (three of which are used to track guide stars) that are shaped like pie wedges.

Four 100-pound wheels (two illustrated in the center of this diagram), each two feet wide, are used to turn Hubble using Sir Isaac Newton's third law of motion: for every action there is an equal and opposite reaction. When one wheel spins clockwise, the spacecraft spins counterclockwise.

Hubble is powered by two gallium-arsenide solar arrays that produce more than 5,000 watts or power.

Hubble's observations are converted to radio waves and then beamed through one of the spacecraft’s high-gain antennas to a NASA communications satellite, which relays the data to the ground. Here one of the high-gain antennas appears in its stowed position.

Hubble’s aperture door is usually kept open, but it can close, if necessary, to prevent light from the Sun from entering and potentially damaging the telescope or its instruments.

Yellow handrails are attached all over Hubble to help astronauts traverse the spacecraft during servicing missions.

Serious technological and managerial challenges arose during the turbulent years of Hubble’s development, causing delays for the project. In January of 1986, the nation suffered the loss of the Space Shuttle Challenger, further delaying Hubble's launch.

When Hubble began taking images, they were blurred. The problem was spherical aberration — the edges of Hubble’s primary mirror were ground too flat by just a fraction of the width of a human hair. Although engineers had designed Hubble with replaceable components, the mirror was not one of them.

Scientists and engineers devised a set of nickel- and quarter-sized mirrors to remedy the blurring effects of the primary mirror. Called the Corrective Optics Space Telescope Axial Replacement (COSTAR), this device deployed the small mirrors into the light paths going to the scientific instruments.

In December 1993, astronauts aboard Space Shuttle Endeavour flew on a mission to install the corrective mirrors, add a new camera that had corrective mirrors already built into it, and perform other repairs to the spacecraft.

The camera was the Wide Field and Planetary Camera 2 (WFPC2), designed and built at NASA's Jet Propulsion Laboratory.

WFPC2, which actually contains four cameras, would go on to produce many of Hubble's breathtaking images, helping transform our view of the cosmos.

As seen in these before-and-after images of galaxy M100, the corrective mirrors successfully fixed Hubble's blurred vision.

During Hubble’s time in orbit, the telescope's discoveries have changed our fundamental understanding of the universe, and its memorable photos have reinvigorated the public’s interest in astronomy. Not since the days of Galileo has a telescope revolutionized our understanding of the cosmos and so broadly piqued the curiosity of the human race.