Snips, Sensors and Spacewalks

by Chris Bergin

The astronauts on board Discovery may have to cope with a new problem before they can return to Earth. Two short strips of filler material (Gap Filler) have been seen dangling from Discovery’s belly.

NASA has to determine whether the protrusions might endanger the shuttle during re-entry – and whether the crew might need to attempt a repair, which will involve an EVA. On Monday, EVA 2 will be the highlight of Mission Day 7.

The potential trouble has nothing to do with launch debris – a shard of foam fell off the fuel tank during launch, but did not do any damage. The problem centres on the material used to fill the spaces between the thermal tiles – a common problem in the past.

NASA has to decide whether to have the material cut off, pulled out or shoved back in place during a space walk. The extremely thin gap fillers are made of a felt-like material and ceramic, and are held in place with glue and by the tight fit.

A spokesman said it could be perfectly safe for Discovery and its crew of seven to fly back with the two drooping pieces, as shuttles have done on many previous flights, most notably on STS-73.

Flight director Paul Hill said engineers would spend the next day analyzing the situation and decide Monday whether to have the crew’s two spacewalkers cut, pull out or shove back in the hanging material.

“We have a team of folks that are working aggressively on options to go and make that gap filler safe, if we decide it’s an issue,” Hill said.

At the post MMT press conference, manager Wayne Hall added: “They are really operating at the limits of the understanding of aerodynamics, and that is a problem. But the consequence, which is heating, is what we’re interested in.”

The TPS was evaluated using new techniques during the mission. NASA scientists and engineers are using high-tech components aboard the space shuttle Discovery to painstakingly inspect the spacecraft for launch-related damage as concerns linger about a piece of insulating foam that broke away from the craft’s external fuel tank during lift-off.

Two laser sensors, a black-and-white camera and a 50-foot extension boom added to the shuttle’s robotic arm allow NASA engineers to carefully peruse every square inch of the spacecraft’s outer surface for flaws that could endanger its return to Earth after its mission.

One of the first concerns relevant to the TPS was the apparent loss of a 1.5-inch section of one of the shuttle’s thousands of ceramic heat shield tiles. The piece that dislodged is near the craft’s front landing gear door. That area of the spacecraft was also carefully reviewed by engineers back on Earth using the images from the sensors.

Since Tuesday’s launch, the shuttle crew and the astronauts in the International Space Station have been taking photographs and laser images of the shuttle to allow engineers on Earth to evaluate its condition. The new lasers and boom extension were added to the shuttle after the shuttle Columbia was lost on re-entry in February 2003.

On that flight, launch-related damage from a piece of foam that smashed into the leading edge of a wing caused a hole that allowed hot gases to enter and burn the ship from the inside upon re-entry, destroying the vehicle and killing all seven astronauts on board.

The exterior inspections of Discovery are being conducted as part of the mission’s original schedule, said Debbie Rahn, a spokeswoman for the space agency, which is providing updated flight information online. “Obviously, we want to understand the state of the vehicle before the crew returns,” she said. “Images received so far by NASA have been very clear, helping engineers study the condition of the vehicle.”

The boom extension was built by the Brampton, Ontario-based space missions group of Canadian technology vendor MacDonald, Dettwiler and Associates Ltd., using spare parts from the original robotic arm. Herb Goettmann, an engineer at MDA, said the specialized laser sensors and camera positioned at the end of the extension can be operated by the shuttle crew to collect detailed images of tiles and protective panels. The data is then downloaded to engineers on Earth.

The extension doubles the length of the shuttle’s robotic arm, and the camera and sensors each have a particular use. For example, NASA’s Intensified Television Camera includes an adjustable zoom lens and can take black-and-white pictures in lighting conditions ranging from very dim to bright.

Another component is a Laser Dynamic Range Imager (LDRI) that was designed and built at Sandia National Laboratories in Albuquerque. NASA said the LDRI produces 2-D and 3-D image data as the sensor scans the shuttle surfaces. In 3-D mode, the scanner colours the images like a Doppler weather radar image, with each colour representing the depth of surface irregularities.

The third device on the boom is a laser camera from Neptec Design Group Ltd. in Ottawa that scans the shuttle’s surface and records data that can be used to create an image model of the surface. The camera uses the reflection of laser light beamed against the surface to measure the depth and other characteristics of any imperfections, said Iain Christie, Neptec’s director of research and development.

NASA Administrator Michael Griffin pointed to the new technology in a statement on Wednesday announcing that the shuttles won’t fly again until the foam-loss issue is corrected. A large section of the PAL Ramp liberated shortly after SRB sep during assent. It is still being debated by various managers as to the cause – listed from a patch, added after modifications in the crotch area of the intertank on the External Tank, to the section simply not being deemed as a potential foam lose area, and thus never modified.

“As with any unexpected occurrence, we will closely and thoroughly evaluate this event and make any needed modifications to the shuttle before we launch again,” Griffin said. “This is a test flight. Among the things we are testing are the integrity of the foam insulation and the performance of new camera equipment installed to detect problems. The cameras worked well. The foam did not.”

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