NASA's experts are drawing up detailed plans for a spacewalk to repair a gouge in the shuttle Endeavour's tiles, even though mission managers may ultimately decide against using those plans, officials said Tuesday.
The gouge is relatively small — 3.5 by 2 inches (9 by 5 centimeters) — and NASA says the damage is benign enough for Endeavour to fly safely home. In fact, experts were "cautiously optimistic" that no orbital repairs will be needed, said John Shannon, chairman of the mission management team.
Endeavour commander Scott Kelly said he wasn't worried about the damage from the standpoint of crew safety. “My understanding is this tile damage is not an issue of the safety of the crew. It’s more of an issue of the ability to reuse the orbiter and damaging the orbiter,” Kelly told journalists. “We still have analysis ongoing. We still might choose to repair it.”
Part of the gouge penetrates through the protective thermal tiles, leaving just a thin layer of coated felt over the space shuttle's aluminum frame to keep out the heat of re-entry. NASA is conducting tests to determine just how much damage could be done to the shuttle during re-entry.
The thermal analyses conducted so far have indicated that Endeavour would not suffer significant damage during re-entry, even if the gouge was left as is, Shannon told reporters. However, he cautioned that experts still had to finish arc-jet tests on mock-ups of the damaged tiles.
Mission managers are due to meet Wednesday to go over the complete test results, and a decision is expected late in the day or early Thursday.
In the meantime, engineers, astronauts and spacewalk gurus are getting a head start on the logistics that would be required for the repair operation. The spacewalk would take place on Friday, or on Saturday if more time is needed for the preparations. NASA managers are also considering extending the mission beyond its currently scheduled 14 days to complete the repairs, if needed.
Endeavour astronaut Richard Mastracchio has been tapped as the lead spacewalker for the repairs, managers told NBC News. Canadian astronaut Dave Williams, Mastracchio's crewmate on the shuttle, would be the other spacewalker. This is the second shuttle mission for both astronauts, and they have trained extensively on the ground using the material for filling in the gouge. The astronauts’ last tile-repair class was just three or four weeks before launch.
How the repair would be done
To patch the gouge, the spacewalkers would perch on the end of the shuttle’s 100-foot (30-meter) robotic arm and extension boom, be maneuvered under the spacecraft, apply protective black paint and then squirt in a caulklike goop. An alternate repair technique, involving a protective plate that could be screwed over the damage, has been ruled out because it's more suited for larger gaps, mission managers said.
All three techniques were developed following Columbia’s catastrophic re-entry in 2003, and NASA has never tried using the goop on an orbiting shuttle. Only the black paint has been tested in space.
Covering the exposed white coated felt with black protective paint would keep heat from building up in the cavity. Squirting in the goop from a tank attached to the astronauts’ spacesuit backpack would provide extra protection. The spacewalkers would apply the paint first to make sure the goop stuck.
As part of the preparations, astronauts on the ground will practice repairing a replica of the gouge underwater so they can create precise instructions for the spacewalkers and their crewmates.
The repair itself would be relatively simple, but the astronauts would be wearing 300-pound (136-kilogram) spacesuits and carrying 150 pounds (68 kilograms) of tools that could bang into the shuttle and cause even more damage. All spacewalks are hazardous, Shannon noted, and so NASA would not want to add more outside work unless it was absolutely necessary.
Mastracchio and Williams have already completed two spacewalks in three days. On Monday, they replaced a 600-plus-pound (300-kilogram) gyroscope on the space station’s exterior. On Wednesday, Mastracchio is scheduled to go out with space station astronaut Clay Anderson for the mission's third spacewalk, to move an antenna and other equipment on the station's exterior.
Even if NASA decides against repairing the gouge, mission planners might still go ahead with a fourth spacewalk. Before the damage came to light, NASA's mission plan called for Williams and Anderson to install some additional antennas and perform other maintenance tasks on Friday.
‘We’re prepared to do it’
During a series of interviews on Tuesday, Kelly told journalists that his crew was ready to deal with the tile gouge, one way or another. "If the data indicate that we need to repair it to protect the orbiter from damage, we're prepared to do it," Kelly said.
Educator-astronaut Barbara Morgan — who is making her first spaceflight 21 years after the first space teacher, Christa McAuliffe, was killed in the Challenger explosion — seconded Kelly's remarks. "We know everything's going to work out just fine," she said.
Later Tuesday, Morgan conducted her first space-to-Earth educational event.
Another task on the mission agenda, installing a new storage platform on the space station, was completed Tuesday morning. Morgan and her crewmates used Endeavour’s robotic arm to pull the platform from the ship’s cargo bay. Astronauts then passed it off to the station’s robotic arm for installation.
A choir of children belted out Tuesday’s wake-up music: A slightly out-of-synch but audibly enthusiastic rendition of “Happy Birthday” for astronaut Tracy Caldwell. She turned 38.
In the to-do list NASA sent up to the astronauts was a note instructing them: “Wish Tracy a very Happy Birthday!” In honor of her birthday, the document said, the international space station is scheduled to pass a notable milestone on Tuesday: Its 50,000th orbit.
This report includes information from MSNBC.com, The Associated Press and Reuters.