In the final launch attempt available this year, Discovery and its seven astronauts blasted off tonight on the last human space flight of the 20th century to refurbish the Hubble Space Telescope.

Under clear and starry skies at the Kennedy Space Center, Discovery lifted off on time at 6:50 p.m. Central time, lighting up the Central Florida coastline, to send Commander Curt Brown, Pilot Scott Kelly, and Mission Specialists Steve Smith, Jean-Francois Clervoy, John Grunsfeld, Mike Foale and Claude Nicollier on a two-day chase to catch up to and retrieve the 12 and a half ton telescope. Hubble was sailing over Eastern Africa at the time of launch.

Eight and a half minutes after the third and final shuttle launch of the year, Discovery was in orbit as its crew members began to configure shuttle systems for the planned 8-day mission. One rendezvous burn of the reaction control system jets is planned before the crew goes to sleep early Monday to fine tune Discovery's path to catch up to Hubble.

Technically, Hubble has been in hibernation since the loss of a fourth gyroscope on November 13 designed to enable the telescope to point precisely at distant astronomical targets for scientific observations. Hubble is in what is known as "safe mode", a state of dormancy in which the telescope aims itself constantly at the sun to provide electrical power to its systems. Hubble is scheduled to be captured by Discovery's robot arm around 6:40 p.m. Central time Tuesday.

Once the crew retrieves Hubble, it will be parked at the rear of Discovery's cargo bay so that two teams of space-walking astronauts can perform repairs and upgrades to its systems during three nights of space walks. The most vital of the space walks will occur on Wednesday night, when Smith and Grunsfeld replace all six of Hubble's gyroscopes and install devices to improve voltage regulation to the telescope's systems. Only three space walks are planned because the mission was shortened. Smith and Grunsfeld will conduct the first and third space walks, while the second will be conducted by Foale and Nicollier.

If all goes as planned, Hubble will be released back into orbit on Christmas Day around 5 p.m. Central time, with landing planned on Dec. 27 at 4:24 p.m.. Central time at the Kennedy Space Center.

The astronauts are scheduled to begin an eight-hour sleep period at 1:50 a.m. Central time Monday and will be awakened at 9:50 a.m. Central time to begin their first full day in orbit.

Discovery is orbiting the Earth at an altitude of about 300 nautical miles, completing one orbit of the Earth every 90 minutes.

The next STS-103 mission status report will be issued shortly after crew wakeup Monday morning.