The Hubble Space Telescope is an orbiting observatory that was launched in 1990. Ground-based observations of the stars are 1.   because of the blurring effects of the earth's atmosphere. But because the Hubble telescope is in 2.   about 380 miles above the earth, it can produce sharper images than can telescopes on the surface. The large primary mirror of the Hubble telescope reflects light from space to a second 3.   . The light bounces off this mirror and passes through a hole in the center of the primary mirror. Special equipment then records the picture. But after the telescope was 4.   , NASA engineers discovered that the primary mirror was not focusing correctly. In 1993, astronauts in the space 5.   were sent to repair the optics--a job that was made easier because the telescope was designed to be repaired in space.