Astronauts inspect shuttle's heat shield for damage

Astronauts today gave the space shuttle a four-and-a-half hour inspection using cameras on the orbiter’s robotic arm early to see if its heat shield was damaged by a mysterious object that apparently floated off the spacecraft.

Nasa engineers began examining the images to decide whether they needed a more in-depth inspection using a 50ft boom that has sensors and cameras attached to its end. The boom is attached to the shuttle’s 50ft robotic arm and can look at hard-to-reach places.

The object appeared to drift away when landing systems were put through a normal but bumpy trial run early yesterday morning.

Worry about whether it came from a crucial part of Atlantis was enough to make Nasa postpone the shuttle’s landing from today until tomorrow or later.

Nasa officials said their best guess was that the object was a plastic filler placed in between thermal tiles which protect the shuttle from blasting heat.

But after bring unable to determine what the object was yesterday, Nasa managers opted to spend early today making sure the shuttle was in good shape instead of concentrating on solving the mystery.

The engineers’ main concern was the status of the all-important heat shield, because a damaged shuttle skin led to the 2003 demise of the shuttle Columbia.

“We are going to verify that our critical heat shield is in good shape for entry to the best of our ability,” shuttle programme manager Wayne Hale said, adding that that goal should be accomplished by 2pm EDT.

Beginning with the right wing at 12.15am EDT (0515 BST), astronauts slowly swept the shuttle’s robot arm above and along Atlantis’ heat shield. The two cameras on the arm looked for any damage to the heat shield from the mystery object. Nasa doesn’t know how big the object is because there was no frame of reference or distance in the video that captured the dark rectangular shape.

A second mystery object was spotted midday yesterday and photographed by astronaut Dan Burbank. Commander Brent Jett said the object looked like a picture hanging clip. But it may be a rubbish bag, which would unlikely be a damage risk, but the issue will be moot if the heat shield looks good, Hale said.

“So far we do not know the identity of the two things that floated away yesterday,” Houston spacecraft communicator Hans Schlegel told Atlantis last night. “Today we want you to survey the vehicle to make sure it’s ready for entry. Last night we already surveyed from ground.”

The odds were 50-50 chance that Nasa would have to take an extra look with the boom, which would take an hour to set up and three hours to conduct, Hale said. Nasa preferred not to use the boom if it wasn’t necessary.

Mission controllers also used cameras at the end of the robot arm to take pictures around the payload bay while astronauts slept yesterday.

If astronauts are too tired from the shield inspection process today, Nasa could postpone landing until Friday, Hale said.

Mission Control woke Atlantis to “Beautiful Day” by U2 and astronaut Heidemarie Stefanyshyn-Piper responded: “Any day in space is a beautiful day and hopefully tomorrow it’ll be a beautiful day in Florida and we’ll be back home.”

There are two landing opportunities at Kennedy Space Centre tomorrow: one in the darkness at 6.22am EDT (1122BST) and a second in daylight at 7.57am EDT (1257 BST).

Nasa has not worked on a contingency plan of parking the shuttle at the international space station for astronauts’ safe haven, but has not ruled that out if serious damage was found.

Nasa’s handling of the problem is “the prudent thing,” said George Washington University space policy director John Logsdon, who was a member of the board that investigated the Columbia accident.

“The point is having a clean vehicle for re-entry, not figuring out what this piece of whatever-it-is is,” Logsdon said.

There is little downside to taking an extra day to make sure the heat shield is intact, said risk analysis expert Paul Fischbeck, a Carnegie Mellon University engineering professor.

“There doesn’t seem to be much cost in doing it,” Fischbeck said. “It’s almost like a freebie; an extra day in space.”

Hale said Nasa’s attitude has changed since the Columbia accident.

“Clearly we are taking a much closer look than we ever did,” Hale said. “You can call it anxiety. You can call it smart. It’s what we do these days.”