Astronauts are on a mission to fix some very big eyes in the skies.

On May 12, NASA, the U.S. space agency, blasted a crew of astronauts into space. Four first-time fliers joined a crew of three veteran astronauts in the space shuttle Atlantis to journey thousands of miles away from Earth.

NASA workers prepared for Servicing Mission 4.

Their destination was the Hubble Space Telescope. The telescope orbits Earth at the rate of 5 miles per second. That means the telescope completes one orbit every 97 minutes. (If a car could go that fast, it could travel from New York to California in 10 minutes!) As part of Servicing Mission 4 (SM4), the astronauts carried spare parts and scientific instruments up to Hubble, including a newer and more powerful camera.

The telescope is about the size of a large school bus. It contains several cameras that take pictures from space and then send them to Earth. First, Hubble sends the data to a satellite. From there, it is sent to a station in New Mexico and then to the Goddard Space Flight Center in Greenbelt, Md. Finally, the images arrive at the Space Telescope Science Institute (STScI) in Baltimore. The institute then provides the Hubble data to astronomers all over the world.

Since 1990, the telescope has captured hundreds of thousands of pictures that have helped astronomers understand space better. Using Hubble's special technology, astronomers have been able to measure the age of the universe, identify quasars, and study distant galaxies.

Hubble's new camera is the size of a piano. It has greater power to examine several galaxies at the same time. Astronomers want to understand how the galaxies grow and change, said Donna Weaver, an STScI spokesperson.

The SM4 astronauts have a lot of work to finish while they're spacewalking around the telescope. One thing on their to-do list is changing Hubble's six batteries. It's a good thing everything floats in gravity-free space—each battery weighs about 150 pounds.

NASA says the repair mission will be the last one for the Hubble. Scientists expect the improved telescope to last at least five more years before it will slowly stop working. When that happens, the telescope will begin to spiral toward Earth. Astronauts will either bring it back to Earth or crash it safely into an ocean. NASA plans to replace the Hubble with the James Webb Space Telescope after 2014. The space agency hopes the new telescope will provide information about the birth of stars, among other fascinating facts about the universe.