(11/17/1999) --- STS-103 Mission Commander Curtis L. Brown Jr. sits inside orbiter Discovery waiting for the start of a simulated countdown exercise. The simulation is part of Terminal Countdown Demonstration Test (TCDT) activities. The TCDT also provides the crew with emergency egress training and opportunities to inspect their mission payload in the orbiter's payload bay. Other crew members taking part in the TCDT are Pilot Scott J. Kelly, and Mission Specialists Steven L. Smith, C. Michael Foale (Ph.D.), John M. Grunsfeld (Ph.D.), Jean-François Clervoy of France, and Claude Nicollier of Switzerland. Clervoy and Nicollier are with the European Space Agency. STS-103 is a 'call-up' mission due to the need to replace and repair portions of the Hubble Space Telescope, including the gyroscopes that allow the telescope to point at stars, galaxies and planets. The STS-103 crew will be replacing a Fine Guidance Sensor, an older computer with a new enhanced model, an older data tape recorder with a solid-state digital recorder, a failed spare transmitter with a new one, and 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. The mission is targeted for launch Dec. 6 at 2:37 a.m. EST