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KENNEDY SPACE CENTER, FLA. -- Towering atop the mobile launcher platform and crawler transporter, Space Shuttle Discovery rolls out of the Vehicle Assembly Building on its way to Launch Pad 39B which is 4.2 miles (6.8 kilometers) away. While at the pad, the orbiter, external tank and solid rocket boosters will undergo final preparations for the STS-103 launch targeted for Dec. 6, 1999, at 2:37 a.m. EST. The mission is a "call-up" due to the need to replace portions of the pointing system the gyros which have begun to fail on the Hubble Space Telescope. Although Hubble is operating normally and conducting its scientific observations, only three of its six gyroscopes are working properly. The gyroscopes allow the telescope to point at stars, galaxies and planets. The STS-103 crew will also be installing a Fine Guidance Sensor, a new enhanced computer, a solid-state digital recorder, and a new spare transmitter to replace older equipment, and replacing degraded insulation on the telescope with new thermal insulation. The crew will also install a Battery Voltage/Temperature Improvement Kit to protect the spacecraft batteries from overcharging and overheating when the telescope goes into a safe mode. Four EVA's are planned to make the necessary repairs and replacements on the telescope. Comprising the STS-103 crew are Commander Curtis L. Brown Jr., Pilot Scott J. Kelly, Mission Specialist Steven L. Smith, Mission Specialist C. Michael Foale (Ph.D.), Mission Specialist John M. Grunsfeld (Ph.D.), Mission Specialist Claude Nicollier of Switzerland, with the European Space Agency, and Mission Specialist Jean-François Clervoy of France, with the European Space Agency