When the HST was tested after the servicing mission, the images were not only vastly improved, but they were utterly astonishing, giving scientists an unprecedented new view of the universe. Now, all of the instruments placed in the HST have built-in corrective optics for the mirror's defect, and COSTAR is no longer needed.
Another major mission came to correct Hubble's orbit. The HST uses six gyroscopes to point itself at stars and galaxies very accurately, and it must stay in an exact position while a picture is taken. Three of the gyroscopes must work perfectly to stabilize the satellite. Unfortunately, four of the gyroscopes broke at the same time. Hubble was put in a special "safe mode" for two months. In this mode, astronomers can't make any observations.
Astronauts trained for the mission in Johnson Space Center's giant swimming pool. The water helps to recreate the feel of being in space. They wear special underwater space suits and float around a model of the telescope, practicing their mission. The mission was troubled by shuttle delays, but the astronauts finally docked with HST and replaced all six gyroscopes. They also upgraded the main computer system and covered the telescope with some new insulation to help keep it safe.
Because the Hubble Space Telescope was designed for periodic servicing, the items to be replaced are easily accessible. The items range in size from a shoebox to a telephone booth. Most of these items can be removed or installed using special wrenches and power tools.
Initially Hubble cost $1.5 billion to build and put into orbit, and its total budget in one year is in the range of 230 to 250 million dollars. But that money does more than simply keep Hubble operating on a daily basis. It also includes funds for scientific data analysis, as well as for the development of future hardware and its associated software. More importantly, though, it provides us with images and knowledge of the universe around us. That data is simply priceless!
