Thisstory was updated at 6:39 p.m. EDT.
The spaceshuttle Atlantis and a crew of seven astronauts are officially set for aplanned May 11 launch to give the Hubble Space Telescope one last upgrade, NASAannounced Thursday.
After morethan half a year of delays, top shuttle mission managers found that Atlantisand its crew are ready to overhaulthe 19-year-old Hubble for the final time. Liftoff is set for 2:01 p.m. EDT(1801 GMT) on launch day at NASA?s Kennedy Space Center in Cape Canaveral, Fla.
?We?rereally looking forward to launchingon May 11,? said John Shannon, NASA?s shuttle program manager, in abriefing at the Florida spaceport.
NASA announcedthe official launch date after a day-long meeting at the agency?s Kennedy SpaceCenter launch site in Florida to review the shuttle?s readiness for flight. Ina NASA first, the space agency announced the shuttle launch decision via themicro-blogging Web site Twitter.
Lastflight to Hubble
Commandedby veteran spaceflyer Scott Altman, Atlantis and its crew are slated to launchon an 11-day mission to Hubble. Five back-to-back spacewalks are scheduled toadd new instruments, replace broken gyroscopes and old batteries, as well asattach a docking mechanism for a future robotic vehicle. The astronauts willalso attempt unprecedented repairs on equipment never designed to be fixed inspace.
If all goeswell, the mission will extendHubble?s mission life through at least 2014, mission managers said. Astronautshave not visited Hubble since 2002 and Atlantis? mission is NASA?s first since addingroutine heat shield inspections following the 2003 Columbia tragedy.
?This is notyour average shuttle flight,? Shannon said. ?This is a different Hubble flightthan the previous Hubble repair missions.?
Initiallyslated to launch in October 2008, the Hubble servicing mission has been delayedfor months after a data handling unit aboard the space telescope failedunexpectedly last year. The added chore of fixing that broken part was added tothe flight.
Missionmanagers initially targeted a May 12 launch for Atlantis, but decided last weekto target an earlier liftoff in order to get at least three chances to lift offbefore standing down due to launch range traffic.
NASA launchedthe Hubble Space Telescope in April 1990 and has sent astronauts to repair orupgrade the observatory four times. With the space shuttle fleet set to retirein 2010, Atlantis? mission will be the fifth and last service call, NASA hassaid.
MikeLeinbach, NASA?s shuttle launch director, said engineers plan to fix a minor radiatording in one of Atlantis? payload bay doors caused by a dropped tool part lastweek. But the repair should not hinder the shuttle?s launch plans.
?It?s awell understood repair,? Leinbach said, adding that the fix should be completethis weekend.
Rescue shuttleon standby
NASA isalso prepared if the mission goes substantially awry. While Atlantis is inorbit, a second space shuttle - the Endeavour orbiter - will be on standby tolaunch a rescue mission in case of an emergency.
Unlikerecent shuttle missions to the International Space Station, where astronautscan seek refuge if their orbiter suffers critical damage, Atlantis astronautshave no such safe haven. They cannot reach the station from Hubble because thespace telescope flies in higher orbit than the orbiting lab and in a differentorbital inclination, or tilt relative to Earth?s equator.
The missionalso has a slightly higher risk of damage from space debris, about a 1-in-229chance of a critical strike. Missions to the space station have about a1-in-300 chance of being struck, NASA officials have said. The space agency'sbenchmark for space debris risk is a 1-in-200 chance of a serious hit, theyadded.
Since Atlantiscannot reach the space station from Hubble?s position, Endeavour is primed tolaunch within a week of a declared emergency with a sparse crew of fourastronauts.
Accordingto the plan, Endeavour would rendezvous with Atlantis, where thestricken shuttle?s astronauts would perform three spacewalks to abandonship and return home. Atlantis would then be disposed of during re-entry overthe Pacific Ocean, NASA officials have said.
Shannonsaid Thursday that there?s ?a very low probability? that Atlantis would sufferany damage just after launch or during the mission that would warrant launchinga rescue flight.
Atlantis iscurrently scheduled to land on Friday, May 22 at the end of the Hubble mission.Once the shuttle returns, NASA would begin preparing Endeavour for a plannedJune mission to continue construction of the International Space Station.
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