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Product Name: STS-90 Day 16 Highlights

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With nearly all of their science studies complete, Columbia's astronauts were awakened at 3:29 a.m. CDT today to begin a busy day preparing for their return to the Kennedy Space Center.late Sunday morning. Commander Rick Searfoss is scheduled to route a line from Columbia's waste tank to a Contingency Waste Container (CWC) to offload about 80 pounds of waste water throughout the course of the day. This will ensure that the tank's capacity will be adequate to support as much as two additional days in orbit in the event Columbia cannot land as planned due to weather conditions. Columbia's science crew -- Mission Specialists Rick Linnehan and Dave Williams and Payload Specialists Jim Pawelczyk and Jay Buckey -- will wrap up science activities this morning when they complete some vestibular experiments. Crew members also will begin cabin stowage activities. Commander Rick Searfoss, Pilot Scott Altman and Mission Specialist Kay Hire will conduct a hot-fire test of the shuttle's reaction control system to ensure Columbia's readiness for tomorrow's entry and landing. About an hour later, they will activate one auxiliary power unit and check out the flight control system to make sure Columbia has full use of its flight control surfaces in anticipation of Sunday's landing. They also will conduct landing simulations with the Portable In-flight Landing Operations Trainer (PILOT). The astronauts will conduct a deorbit briefing among themselves early in the afternoon. Payload commander Rick Linnehan will replenish water supplies and carry out other routine husbandry tasks for the rodents on board and the science crew will put away experiment hardware and partially deactivate the Spacelab module. Columbia's KU-band communications antenna also will be stowed just before 11 a.m. today. Meteorologists are forecasting favorable conditions at the Kennedy Space Center on Sunday for a landing at 11:09 a.m. CDT. Columbia remains in a 150 x 131 nautical mile orbit, circling the Earth every 90 minutes. On Saturday, May 2, 1998, 5:00 p.m. CDT, STS-90 MCC Status Report # 32 reports: With all science activities complete on board, Columbia's seven astronauts readied their ship for a Sunday landing at Kennedy Space Center. The science crew ^V Mission Specialists Rick Linnehan and Dave Williams, and Payload Specialists Jim Pawelczyk and Jay Buckey -- wrapped up science activities this morning with final studies focusing on how the vestibular system adapts in a changing environment. To prepare for tomorrow's return to Earth, the flight crew Commander Rick Searfoss, Pilot Scott Altman and Mission Specialist Kay Hire conducted a successful test of the shuttle's reaction control system jets and flight control surfaces. For the check out of the flight control surfaces, the astronauts started Auxiliary Power Unit #3, one of three hydraulic units on board, to provide hydraulic power to the surfaces and to verify that its cooling system was working properly after an apparent freeze-up during Columbia's launch two weeks ago. The FCS checkout was completed successfully, but APU 3^Rs cooling system did not function as expected. The failure of the cooling system for APU 3 will not affect Columbia's landing tomorrow and a minor modification to managing the auxiliary power units will be implemented by entry Flight Director John Shannon. Following standard deorbit procedures, one APU will be started five minutes prior to the scheduled deorbit burn. At a point 13 minutes before Columbia encounters the first traces of the atmosphere, when the remaining two APU's are normally brought on line, only one additional APU will be started. APU 3 will be powered on about six minutes prior to landing when Columbia's speed is about Mach 2.5. The auxiliary power units are capable of operating for 10 to12 minutes before their cooling systems would be required. Commander Rick Searfoss successfully dumped about 70 pounds of waste water into a Contingency Waste Container (CWC) this morning, This will ensure sufficient stowage capacity in the waste tank to support as much as two additional days in orbit in the event Columbia does not land on Sunday. Payload commander Rick Linnehan replenished water supplies and performed some routine husbandry tasks for the rodents on board and completed a partial deactivation of the Spacelab module. Final deactivation of Spacelab systems is set for tomorrow morning. Columbia's Ku-band communications antenna also was stowed about 11:30 a.m. today. Columbia has two opportunities to land at the Kennedy Space Center on Sunday. The first would see a deorbit firing of the orbital maneuvering system engines at 10:11 a.m. CDT, with landing at 11:09 a.m. In the event flight controllers elect to bypass the first opportunity, there is a second opportunity that would see a deorbit burn at 11:44 a.m. with a landing to follow at 12:43 p.m. CDT. Preliminary weather forecasts for Sunday show clear skies in the vicinity of the Kennedy Space Center. with the only potential issue the possibility of high cross winds. The current forecast indicates the winds should stay within acceptable limits. By Monday, a weather front is expected to approach KSC, bringing with it the possibility of low cloud ceilings and rain showers. Weather at the alternate landing site at Edwards Air Force Base in California is expected to be good through Tuesday. The next STS-90 status report will be issued following Columbia^Rs landing at the Kennedy Space Center. or after a wave-off of Sunday landing opportunities.