With the Hubble Space Telescope securely latched in the payload bay, the astronauts aboard Discovery today will turn their attention to the primary objective of their flight -- restoring the capability of the 12.5-ton telescope to observe the universe.

Astronauts Steve Smith and John Grunsfeld are scheduled to begin the first of three planned maintenance spacewalks today at about 1:40 p.m. The crew was awakened this morning to the song "Hucklebuck" performed by Beau Jocque and the Zydeco Hi-Rollers, a tune that the spacewalkers heard many times while training hundreds of hours for the mission in the 6.5-million gallon water tank at the Johnson Space Center in Houston.

Although not scheduled to begin until 1:40 p.m., Smith and Grunsfeld could begin the planned six-hour spacewalk earlier if they complete preparations ahead of schedule. Once outside Discovery's cabin, the first task they will perform will be to replace the telescope's three Rate Sensor Units, each of which contains two gyrsoscopes. Of the six gyroscopes currently installed in Hubble, four have failed. At least three operable gyroscopes are needed to point the telescope with the accuracy required to track its astronomical targets.

After the rate sensor units have been installed, the two spacewalkers will then open valves on the telescope's Near Infrared Camera and Multi-Object Spectrometer to purge nitrogen coolant from that instrument in preparation for its servicing on the next Shuttle maintenance mission. Next, they will install six Voltage/Temperature Improvement Kits for the Hubble's batteries that will increase the batteries' efficiency and reduce a potential for them to overcharge and overheat. If those tasks are completed and the spacewalkers have extra time, they may perform some additional small jobs such as installing handrail covers and inspecting brackets.

While Smith and Grunsfeld are outside, inside the cabin European astronaut Jean-Francois Clervoy will control Discovery's robotic arm, maneuvering the spacewalkers into position to work on the telescope. Discovery's other spacewalking team, astronaut Mike Foale and European astronaut Claude Nicollier, also will assist from inside the cabin. Foale and Nicollier are scheduled to perform the mission's second spacewalk tomorrow. Smith and Grunsfeld are planned to again venture outside on Friday for the flight's third and final spacewalk.

Discovery remains in near-perfect condition with no mechanical problems of concern to flight controllers, as has been the case since its launch on Sunday. It is orbiting at an altitude of 380 by 365 statute miles. The next Mission Control Center status report will be issued at 10 p.m. or as events warrant.