The shuttle Atlantis' countdown is proceeding smoothly toward launch Monday on an $887 million mission to service the Hubble Space Telescope. Forecasters are predicting a 90 percent chance of acceptable weather in Florida and only a slight chance of showers near an emergency runway in Spain.
On Saturday, the shuttle's fuel cell system was loaded with liquid oxygen and hydrogen to power the ship's electrical generators and early Sunday, the main engine avionics system was activated and checked out.
There are no technical problems of any significance at launch complex 39A, and engineers are on track preparing the spacecraft for fueling early Monday.
The three-hour fueling process is scheduled to begin around 4:51 a.m. If all goes well, commander Scott Altman, pilot Gregory C. Johnson, flight engineer and robot arm operator Megan McArthur, and spacewalkers John Grunsfeld, Michael Massimino, Andrew Feustel, and Michael Good will head for the pad around 10 a.m. to strap in for launch at 2:01:49 p.m.
The primary goals of NASA's fifth and final mission to service and upgrade the Hubble Space Telescope are to install two new instruments--the Wide Field Camera 3 and the Cosmic Origins Spectrograph--six fresh batteries, six stabilizing gyroscopes, a replacement science data computer, a refurbished fine guidance sensor, and new insulation panels.
The astronauts also will attempt to repair two other instruments, the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph. Both failed in recent years and neither was designed to be serviced by spacewalking astronauts. While mission managers are optimistic the crew will be successful, there are no guarantees.
"There's not much margin for error," Hubble Program Manager Preston Burch said Sunday. "We'll need flawless execution from our astronaut team and we'll also need flawless performance from all of our hardware. But we have done extensive testing, extensive training and we're highly confident that we're going to have another successful mission like the ones we've had before."
Assuming an on-time launch Monday, McArthur, operating Atlantis' robot arm, will capture Hubble around 1 p.m. Wednesday. The first of five back-to-back spacewalks is scheduled to get under way at 8:16 a.m. Thursday.
"As John Kennedy said, we try these things not because they're easy but because they're difficult," said Project Scientist Dave Lekrone. "Particularly on this mission, we're going for broke. We set the bar extraordinarily high for ourselves. And nobody should consider this mission a failure ... if for some reason we don't get all things done to the hundred percent level. This is still an extraordinary mission if we just get (the primary objectives) done."
NASA only has three days to get Atlantis off the ground this week or the flight will be delayed to May 22 because of a military operation on the Air Force Eastern Range that supports all East Coast launches and because of time needed to recharge new batteries bound for the Hubble Space Telescope.
The Florida forecast for Monday calls for near ideal conditions, but an approaching front could cause problems if Atlantis is delayed to Tuesday or Wednesday.
"We actually decreased the probability of KSC weather prohibiting launch (Monday) down to 10 percent," said shuttle weather officer Kathy Winters. "We have a 90 percent chance of good weather tomorrow for launch. Weather still is problematic if we happen to delay to the following day, Tuesday and Wednesday. It looks like we have a front that comes down into the area and that could cause some concerns if we happen to delay. We (have) a 40 percent chance of KSC weather prohibiting launch for Tuesday and also for Wednesday. So right now, day one does look good."
To reach the Hubble Space Telescope, Atlantis will be launched on an easterly trajectory that will carry it between 28.5 degrees north and south latitude. For launches to the International Space Station, NASA staffs three emergency runways in Europe--two in Spain and one in France--but only the southernmost, at Moron, Spain, is reachable by Atlantis.
Only one European landing site is required for a space station mission, but for Atlantis, the weather at Moron must be acceptable or the flight will be delayed.
"For Moron, our one overseas landing site, we do have just a slight chance of showers within 20 (nautical miles) due to a frontal system up to the north," Winters said. "Most of the activity should be up to the north, so just a slight concern there. So overall, pretty good weather at Moron."
A 10,000-word mission preview is available from the CBS News Space Place Web site, along with a detailed history of the Hubble Space Telescope and an overview of NASA's plans to launch an emergency rescue mission if the Atlantis astronauts encounter any major problems that might prevent a safe re-entry.
The CBS News mission preview package, along with NASA's mission and payload overview, crew bios, and other background are available in the CBS News Space Reporter's Handbook, available on the Space Place Downloads page.