Shuttle Gets a Safety Makeover for Its Return to Flight
When NASA’s Discovery orbiter returns the shuttle fleet to flight status later this year, it will mark the culmination of a series of modifications, redesigns and the development of new tools designed to increase the safety of human spaceflight.
Those changes, more than two years in the making, include the installation of new tools for on-orbit inspection, sensors to detect impacts during launch and a host of new processes to prevent accidents like the one that led to the destruction of the Space Shuttle Columbia and the deaths of its seven-astronaut crew Feb. 1, 2003.
Columbia was damaged during launch by a suitcase-sized chunk of foam insulation, which detached from the external tank and ripped a hole in the leading edge of the orbiter’s left wing. During re-entry, hot gases entered the hole and caused so much damage that Columbia broke up.
NASA engineers have since redesigned the shuttle’s external tank — the first of those will be tested in Discovery’s upcoming flight — to prevent the shedding of such large pieces of foam. The orbiter itself has 88 new sensors inside the leading edge of its wings to measure temperature changes and pick up any impacts during launch.
Discovery’s mission, designated by NASA as STS-114, is currently set for a mid-May launch. The main goals of that mission are shakedown tests of the return-to-flight modifications and the delivery of fresh supplies to the international space station .
Shuttle managers and astronauts alike have said the modifications to the external tank have been the primary focus of NASA’s return-to-flight efforts. In its report to NASA, the Columbia Accident Investigation Board (CAIB) recommended that, before the space agency attempts to launch another shuttle, it take great pains to eliminate the type of tank foam shedding that led to the Columbia’s destruction.
“The modifications we have made address the CAIB recommendations to reduce the risk of falling debris,” Sandy Coleman, NASA’s external tank project manager, said when the tank arrived at Kennedy Space Center, Fla., earlier this year.
Engineers eliminated the use of foam insulation around the external tank’s bipod fitting, which connects the tank to a space shuttle. Instead of the foam, NASA now uses heaters to prevent ice from forming at that spot. The foam that damaged Columbia during launch originated from its tank bipod fitting, investigators found.
Coleman said new methods of applying the foam , which is sprayed on by technicians, also have cut down the size of the chunks that might break off during launches. The largest chunk of foam shed by the tank during future launches should be no larger than a marshmallow, NASA officials said.
“In my view, our major task was to keep foam from falling off the tank,” veteran astronaut Eileen Collins, commander of Discovery’s STS-114 mission, said in an interview. “That was really the most important thing we had to do.”
The redesigned external tanks also will carry a video camera that will transmit live images up to 15 minutes after launch, and a number of new ground-based cameras will track the tank and orbiter during liftoff to give flight controllers the best view of shuttle ascent.
Once in space, STS-114 flight controllers plan to test shuttle repair techniques that, they hope, will eventually help astronauts make on-orbit fixes to damaged thermal protection tiles and reinforced carbon-carbon panels. The tiles and panels shield orbiters from the extreme heat of re-entry.
STS-114 mission specialists Soichi Noguchi and Stephen Robinson, who will conduct all three of the mission’s spacewalks, will each test one repair method.
During their first extravehicular activity , Noguchi will test a tile repair device called an Emittance Wash Applicator designed to squeeze out a gray, heat-resistant material that will be dabbed onto purposely damaged tiles that are not part of the orbiter. Robinson, meanwhile, will test a technique to fill in small cracks in reinforced carbon-carbon panels by applying a black goop called NOAX (short for non-oxide adhesive experimental) with a putty knife.
Ground engineers are anxiously awaiting the results from both tests. After the crew returns to Earth, the tiles will be subjected to extreme heat at NASA’s arc jet facility to determine the effectiveness of their repair.
A boom in orbit
Nestled inside Discovery’s payload bay is an orbital boom that will nearly double the length of the shuttle’s robot arm when attached to the remote manipulator. Equipped with cameras and a laser ranging system, the boom will be used to scan wing edges and shuttle tiles for signs of cracks or holes.
“We’re going to learn a lot about how this system works when it gets into orbit,” said Irene Piatek, NASA’s integration lead for the orbital boom sensor system at Johnson Space Center in Houston.
Piatek told Space News that the orbital boom will scan the shuttle’s underside from a distance of between 1.5 and 4 meters in order to prevent bumping into the orbiter’s surface.
In addition to the spacewalk and orbital boom tests, astronauts aboard both Discovery and the international space station will work together to scan the orbiter’s underside for any signs of damage or trauma.
As Discovery approaches the space station , STS-114 pilot Jim Kelly and Collins will spin the orbiter to face its belly toward the space station. During that maneuver, dubbed the pirouette by flight controllers, the space station Expedition 11 crew — commanded by cosmonaut Sergei Krikalev with NASA astronaut John Phillips serving as flight engineer — will make an extensive photographic map of the orbiter’s surface.
In addition to addressing the recommendations of the Columbia accident investigators, NASA officials have drawn up an emergency plan to shelter Discovery astronauts aboard the space station in the event their orbiter suffers serious damage anytime during the mission.
Dubbed the Contingency Shuttle Crew Support , but better known as safe haven, the plan calls for the STS-114 crew to live alongside the two space station astronauts for a period of about a month or so. If Discovery were found unfit to return to Earth, it would eventually be discarded from its space station docking port.
“We assume that we’d have about 20 docked days with shuttle activities,” Bill Gerstenmaier, NASA’s space station program manager, said during a March 17 space station briefing. “We’d transfer critical elements from the (Multi-purpose Logistics Module) and take full advantages of all the consumables and items aboard.”
Shuttle officials expect to be able to launch a second orbiter — currently Atlantis — with a reduced crew to return stranded astronauts within about 45 days.
“The safe haven contingency is at the bottom of the list, the last thing we worry about,” Collins said . “I don’t think we’ll need to use it.”
While Discovery astronauts maintained that using the space station as a safe haven is a last resort, there would be at least some silver lining to the emergency. Discovery will carry additional food and supplies for its crew to use aboard the space station during an extended stay, and while it would be crowded onboard, the astronauts would have the chance to rack up more time in space.
“It’s a very unlikely probability that we would have to stay on station,” Noguchi said during a break from spacewalk training, adding that if he had to do so, he would look forward to it. “I’d love the chance to stay on the space station as long as I can.”