Atlantis returns to launch pad for Hubble mission
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 31, 2009
The space shuttle Atlantis, bolted to a mobile launch platform atop an Apollo-era crawler-transporter, was hauled to launch pad 39A at the Kennedy Space Center Tuesday for work to ready the ship for blastoff May 12 on a fifth and final mission to service the Hubble Space Telescope.
But testing a spare ground unit at the Goddard Space Flight Center in Greenbelt, Md., getting it certified for flight and working the mission back into NASA's shuttle manifest ended up delaying Atlantis and Hubble Servicing Mission 4 - SM-4 - for seven months.
The replacement SI/C&DH was delivered to the Kennedy Space Center Monday and Atlantis, attached to an external fuel tank and two solid-fuel boosters, took its first step toward space with a six-and-a-half-hour, 3.2-mile trip from the Vehicle Assembly Building to pad 39A Tuesday.
Shuttle commander Scott Altman, pilot Gregory C. Johnson, flight engineer Megan McArthur and spacewalkers John Grunsfeld, Michael Massimino, Andrew Feustel and Michael Good plan to fly to Kennedy late this week to inspect the replacement computer unit before it is moved to the pad April 18, along with the rest of the Hubble payload, for installation in Atlantis' cargo bay.
Hubble SM-4 is the fifth and final planned shuttle mission to the space telescope (SM-3 was spread across two flights). During five back-to-back spacewalks, the Atlantis astronauts plan to install a new camera, called the Wide Field Camera 3, the Cosmic Origins Spectrograph, a full set of batteries, six new stabilizing gyroscopes, a new fine guidance sensor, new insulation and to carry out repairs on two other science instruments that are currently out of action.
The new 135-pound science instrument command and data handling unit will be wired into Hubble's electrical system during the first spacewalk, after the Wide Field Camera 3 is installed.
As it now stands, no major mission objectives have been deleted despite the late addition of the SI/C&DH installation. But to get everything done, the astronauts must be able to complete a complex repair of the Advanced Camera for Surveys during a single spacewalk. The original flight plan broke that task into two parts.
If it turns out the astronauts need more time for the repair work, the fine guidance sensor replacement could be deleted.
There are no technical problems of any significance with Atlantis or its payload, but analysts are still evaluating the threat posed by orbital debris at Hubble's 350-mile-high altitude. Because of a satellite collision in February, the debris environment is somewhat worse at Hubble's altitude and as of this writing the mean chance of a catastrophic impact during the shuttle visit is believed to be around 1-in-185.
Odds worse than 1-in-200 require an executive-level decision on whether the additional risk is acceptable. Engineers say additional analysis, possible changes to the shuttle's orientation in space and other factors are expected to improve those odds and senior managers appear confident Atlantis ultimately will be cleared for flight.
Shuttle program managers plan to meet April 20 and 21 to review launch processing, followed by an executive-level flight readiness review April 30 at the Kennedy Space Center to formally clear the ship for launch. If no problems develop, Atlantis' countdown will begin May 9 for a launch attempt the afternoon of May 12.
The last published launch time was 1:31 p.m. EDT, about 20 minutes into the Hubble launch window. But flight planners may adjust that pending additional analysis of payload weight and ascent performance margin.
Here is a brief overview of the crew's flight plan (assumes a launch at 1:31 p.m. on May 12; spacewalks, or EVAs, would begin around 6:46 a.m. each day):
Because the Hubble Space Telescope is in a different orbit than the international space station, the Atlantis astronauts cannot seek safe haven aboard the lab complex if a major problem develops that might prevent a safe re-entry.
As a result, NASA plans to move the shuttle Endeavour to launch pad 39B on April 17 to ready the ship for a quick-response blastoff on an emergency rescue mission if needed. If not, Endeavour will be moved to pad 39A after Atlantis lands for normal processing and launch around June 13 on the next space station assembly mission.