Throughout the investigation of the Columbia disaster, the question of why the shuttle astronauts had so little ability to inspect and repair the exterior of their own spacecraft has never gone away. So even as the independent investigation board has been narrowing down the exact cause of the Feb. 1 tragedy, NASA engineers have been working to solve the inspection and repair issues.
The need to solve these questions was identified early on. In a Feb. 10 memo to his still-stunned teammates, shuttle program manager Ron Dittemore directed that work immediately begin on developing techniques to inspect and repair the shuttle’s all-too-delicate thermal protection system while in orbit, said Johnson Space Center spokesman Phil West.
A special “Flight Techniques Panel” has since met half a dozen times. They have reviewed all previous projects over the past quarter century, and examined new technologies made available by the multi-agency partnership behind the International Space Station.
The group “is composed of engineers from multiple disciplines — design, operations, safety and materials experts and astronauts and so forth,” said West, himself a former engineer involved with developing spacewalk tools for the space station.
As a result, NASA engineers are now awash in innovative schemes involving access platforms, extendable booms, quick-curing “goop guns” and sculptable replacement tiles, weird “arm wrestling” maneuvers between the shuttle and the space station to create an “orbital dry-dock,” and other ideas.
“Top options are apparent in all areas, and in many cases the single preferred option stands out,” states an internal NASA report to the Space Shuttle Program Requirements Control Board, which approves all modifications to the program. The report, presented to the board on April 17, was obtained by MSNBC.com.
The main goal for inspections, the report says, is to “resolve inspection images to the critical damage level” — that is, determine how detailed a view would be required to detect serious damage. Some surface areas can be surveyed to a resolution of several inches, while other areas would need resolution of a half an inch.
Space-based and ground-based cameras operated by the Defense Department can provide resolutions good enough for some, but not all, of these requirements. “Local” sensors, be they boom-mounted or free-flying cameras, the eyes of a space-walking astronaut, or views from the nearby space station, are needed for other cases.
Orbit designers have even developed an inspection procedure in which the approaching shuttle performs a slow-motion end-over-end tumble about 600 feet below the space station. Astronauts have told MSNBC.com they find the maneuver easy to perform.
To verify that station-based cameras would be able to see the shuttle’s tiles well enough to detect damage, astronauts observed and photographed the approaching Soyuz TMA vehicle on April 28 using the same lenses and cameras that would be used for shuttle imaging. The pictures will be compared to close-up photographs to determine just how much fine detail can be detected.
As for repair capabilities, the report stresses that the study should “focus on critical and REASONABLE damage — and we are going to define ‘reasonable.’” Only later will the team examine “more complicated, more-perfect solutions.”
Some proposed solutions have been around for a quarter of a century, from before the Columbia’s first flights in 1981.
“Tile repair concepts from [that time] focused on silicone material squirted into a void with a device similar to a caulking gun,” West explained.
The NASA report says that three different formulas for such material are being assessed.
Repairing the Reenforced Carbon-Carbon (RCC) material on the wing leading edge panels is more of a challenge.
“The options are variations of patches with some sort of cure-in-place resin,” the report says. Maximum size of needed patches would be determined by how big a hole could survive entry air pressure loads. But there is “more risk on RCC repair materials since it has much less development to date,” the report cautions.
Accessing the repair site
Three options are being studied to allow an astronaut to access an area needing repair: a free-flying astronaut, an extra boom at the end of the existing robot arm, and the use of the space station.
An astronaut using a jet backpack could reach any part of the shuttle, with adequate fuel. But the NASA report highlights the “greater operational complexity [and] risk” of this approach, as well as the need for “worksite stabilization, potentially some form of adhesive pad with a handrail” to be glued over the area to be repaired.
Another suggestion is to install a 60-foot boom along the right edge of the shuttle’s payload bay, in much the same arrangement as the robot arm installed along the left edge. The arm would grab the end of the boom and its retaining latches would be opened, allowing the arm to maneuver the boom’s other end to any point on the underside of the shuttle.
This option, according to the NASA report, has “the lowest overall operational complexity [and] risk”, and provides “stand-alone access,” that is, access when the shuttle is not docked to the space station. However, the report says, installing a boom has the “highest integration impacts,” meaning it would require the most modifications from existing shuttle hardware.
The last option, use of the space station, is the only one that “is an existing capability,” notes the report. In these preliminary plans, the shuttle’s robot arm would grapple a structure on the station and then turn the shuttle’s belly toward the station. The station’s robot arm would then carry the astronaut and repair tools right up to the damaged area.
“The ISS provides some capabilities we didn’t have before,” West said. ”[It is] a stable work platform, which has been one of the challenges to any inspection and repair effort.”
More analysis work lies ahead, especially in analyzing the mechanical stresses that would be induced on the station structure grappled by the shuttle’s arm. But this idea clearly has emerged as the favored approach.
NASA’s task force expects to make a recommendation of an “end-to-end inspection and repair strategy” by August, and have hardware ready to fly by the beginning of next year. When the next shuttle rockets into orbit to resupply the space station, it may even also carry an additional crewmember or two who will perform test tile repair on spacewalks. The technology, NASA workers expect, will be ready.
James Oberg, space analyst for NBC News, spent 22 years at the Johnson Space Center as a Mission Control operator and an orbital designer.