The crew is to perform radiation tests on the Hubble Space Telescope's Orbital Systems Test Platform, which will be installed on the telescope itself during another mission in 1999.

The crew also plans to release a small communications satellite called Spartan that is equipped with a solar observatory. Spartan was first released last November, but failed to operate correctly and had to be retrieved.

Crew members will also conduct experiments involving robotic instruments and the growing of optical crystals.

Glenn's will participate in a series of medical experiments designed by NASA and the National Institute on Aging intended to correlate the physical stress of space flight with those of aging. Focus will be on how Glenn copes with muscle atrophy, bone decalcification, balance disruption and sleep disturbances. Researchers hope to learn why the earthbound elderly suffer similar problems, along with deterioration of the heart, lungs and immune system.