Discovery's astronauts and ground controllers successfully completed testing Friday of an atmospheric research satellite in preparation for its release from the shuttle this weekend.
National Aeronautics and Space Administration officials said the extensive checkout, involving more than 200 computer commands, showed the observatory to be in excellent shape.
"There has not been, as far as I know, one glitch in the whole process," said David Lorenz, a satellite manager.
The astronauts are working nights and going to sleep at dawn because of the need to place the observatory in just the right spot late Saturday.
Shuttle commander John O. Creighton and pilot Kenneth S. Reightler planned to maneuver Discovery late Friday from an altitude of 336 miles to an unusually high 354 miles. Tiny thrusters will boost the satellite an additional 18 miles next week.
After awaking Friday afternoon, crew members Mark N. Brown and James F. Buchli began setting up liquid-filled cylinders that will be shaken to see how fluids react in the absence of gravity. The results will be applied to space station design.
Also scheduled for the second day of the flight was an examination of the spacesuits that Buchli and Charles D. Gemar will don if they have to go into the cargo bay to make emergency satellite repairs.
The astronauts activated the observatory's systems shortly after reaching orbit Thursday. They worked into the morning Friday, checking the satellite and the shuttle's mechanical arm, which will be used to free the spacecraft.
The Upper Atmosphere Research Satellite is the first in a series of spacecraft to be launched in NASA's Mission to Planet Earth, a campaign to better understand and protect the environment.
The observatory is to study Earth's endangered ozone layer, believed to be the victim of man-made pollutants, as well as to gather data on stratospheric winds, atmospheric chemicals and particles of energy.