The five astronauts aboard the Space Shuttle Columbia began their fourth flight day at 4:31 p.m. CDT, preparing to make additional celestial observations through the shuttle's windows and continue work with a variety of experiments.

The day started off with a wake-up call sent up in honor of Pilot Jeff Ashby. It was a song called "Some Day Soon," written by Judy Collins and performed by Suzy Boguss.

The first job for Ashby and Mission Specialists Steve Hawley and Michel Tognini was to set up an exercise treadmill and the Treadmill Vibration Information System (TVIS) which will measure vibrations and changes in microgravity levels caused by on-orbit workouts. These workouts are needed to maintain astronauts' cardiovascular fitness and muscle tone, which can suffer in the absence of gravity. Each crewmember was scheduled to take a turn on the treadmill before it is put away at the end of the day.

Astronomer Hawley once again is scheduled to make observations of Jupiter, Venus and the Moon with the Southwest Ultraviolet Imaging System (SWUIS) as Commander Eileen Collins and Ashby put the shuttle in the proper orientation for his observations.

Tognini and Mission Specialist Cady Coleman will check on the bioprocessing experiments, and harvest mouse-ear cress plants as part of the Plant Growth Investigations in Microgravity experiment. These genetically engineered plants are expected to yield clues to the sensitive mechanisms the plants use to monitor their environment and help scientists develop plants that respond better to the stresses of space flight.

Collins and Ashby will fire the shuttle's engines so that the sophisticated sensors of the Midcourse Space Experiment (MSX) satellite will be able to collect ultraviolet, infrared and visible light data on the firing. The satellite was launched from Vandenberg Air Force Base in California in 1996. The commander and pilot also will practice landings on a laptop computer, simulation software and joystick combination called the Portable In-Flight Landing Operations Trainer (PILOT).

Meanwhile, Mission Operations' Wayne Hale reported that engineers on the ground continue to evaluate the short in one of the shuttle’s electrical systems, which occurred shortly after launch as well as the slightly reduced performance of the main engines. Neither problem poses any risk to the remainder of the mission, Hale said.

Hale said the crew's discovery that a circuit breaker had popped during the climb to orbit provides reassurance that the problem has been isolated and will not affect any of the shuttle's other electrical systems used for reentry and landing. He also said that the right engine's reduced performance may have been due to a small hydrogen leak in tubes that help cool the nozzle. While it won't be confirmed until the shuttle returns to Earth, Hale said the evidence pointing to the leak includes a slightly higher than normal temperature in that engine, and launch photos showing a white streak that could be escaping hydrogen.

At this point, Columbia is flying smoothly, orbiting the Earth every 90 minutes at an altitude of 182 statute miles.

The next STS-93 status report will be issued about 6 a.m. CDT Monday.

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