MARCIA DUNN

AP Aerospace Writer

CAPE CANAVERAL, Fla. (AP) With storms threatening to delay their return to Earth, the Atlantis astronauts took a break from landing preparations Thursday to update a Senate panel on their triumphant Hubble Space Telescope repairs.

The astronauts checked their ship's flight systems and monitored the weather at NASA's spaceport, which was pounded by fierce thunderstorms. More bad weather was expected Friday when Atlantis was due to fly back home

The rain did not dampen NASA's jubilation over the astronauts' impressive Hubble repairs, which garnered kudos from the president and members of a U.S. Senate subcommittee that invited the crew to testify at a hearing from space. Such in-orbit testimony was a first.

"When we talk about the Hubble and giving it essentially a new life and a new way of going and seeing the universe, you've touched our hearts and you've also made history," said Sen. Barbara Mikulski, D-Md., chairwoman of the science appropriations subcommittee.

Fresh off a call from President Barack Obama the day before, the seven astronauts recounted their most nail-biting moments of the past 1 weeks.

"You should have seen the action out the back window," said pilot Gregory Johnson. "I was on the edge of my seat."

With all their work completed in orbit, the astronauts aimed for a Friday morning touchdown at Kennedy Space Center, but given the dismal weather reports, they were conserving power in order to remain aloft until Monday, if necessary. Mission Control warned that Friday's weather would be "iffy." The backup landing site in Southern California could be used Saturday, if Florida keeps getting hit by storms.

"We flew over today, saw it looked kind of nasty at the moment, but saw some clearing behind it maybe," commander Scott Altman radioed down. "As long as you think there's a chance, we'll be willing to do whatever it takes."

Atlantis rocketed away on NASA's last visit to Hubble on May 11. In five back-to-back spacewalks beset by stuck bolts and other problems, the astronauts installed two top-of-the-line science instruments and replaced burned-out electronics in two other science scopes. They also gave the 19-year-old observatory a new computer for sending back science data, freshened up the power and pointing systems, and beefed up the exterior with steel foil sheets.

When it came time to let Hubble go Tuesday, chief repairman John Grunsfeld recalled turning to Altman and saying, "You know, we really did it."

The refurbished Hubble is expected to perform better than ever over the next five to 10 years and probe even deeper into the universe, as far back in time as 500 million to 600 million years from creation.

Besides watching the weather, NASA had been keeping shuttle Endeavour ready for liftoff in case a rescue mission were needed. On Thursday morning they canceled the backup plan, put in place long ago to minimize the risk the Hubble repair crew was taking. With the astronauts having only enough air to last until Monday, the rescue ship, Endeavour, at this point could not be launched in time to save them.

The six men and one woman had to launch into a 350-mile-high orbit to get to Hubble and had nowhere to go in the event their ship was damaged seriously by liftoff debris or space junk, a bigger problem than usual so high up. The international space station is in a different orbit and unreachable.

NASA considered this last Hubble mission so dangerous that it was canceled in 2004, a year after the Columbia tragedy. It was reinstated in 2006.

On Wednesday, NASA said an extensive survey of Atlantis' vulnerable wings and nose showed no evidence of worrisome trouble, and managers cleared the shuttle for re-entry.

A hole the size of a dinner plate, in the left wing, brought down Columbia.

On the Net:

NASA: http://www.nasa.gov/mission_pages/hubble/main/index.html

Copyright 2009 The Associated Press.