The Space Shuttle's Lessons For The Future
By Frank Morring, Jr.
The second flight of the space shuttle Atlantis was almost its last.
What was then NASA’s newest orbiter sustained severe damage to its fragile thermal protection system when it lifted off from Kennedy Space Center’s Launch Complex 39B on Dec. 2, 1988. But through a combination of military secrecy and plain old human misunderstanding, the problem went unaddressed until Atlantis returned to Earth four days later.
The STS-27 mission was the second shuttle flight after the fatal Challenger mission, an urgent “black” mission to orbit the Lacrosse-1 radar-reconnaissance satellite for the National Reconnaissance Office (AW&ST July 9, 2007, p. 28). The military space program was backing away from the shuttle as fast as it could in the wake of the accident (see p. 59), but it had built payloads like the first of the billion-dollar Lacrosse satellites that could only be launched on the shuttle.
Liftoff seemed normal to the crew and the launch team, but engineers at Johnson Space Center reviewing imagery of the ascent later saw something break away from the nose of the right-hand solid rocket booster and hit the orbiter. As a precaution, the Atlantis crew unlimbered the robotic arm and used its video camera to inspect the fragile tiles in the apparent impact zone on the starboard side.
“[W]e could see that at least one tile had been completely blasted from the fuselage,” writes arm-operator Mike Mullane in his memoir, Riding Rockets. “The white streaking [indicating tile damage] grew thicker and faded aft beyond the view of the camera. It appeared that hundreds of tiles had been damaged and the scars extended outboard toward the carbon-composite panels on the leading edge of the wing.”
A crack in one of those same panels would destroy Columbia 14 years later, and the Atlantis crew understood the danger as they watched the video with growing apprehension. But heat-shield experts in Houston did not think it was that bad, and they quickly decided nothing needed to be done.
The crew argued that it looked pretty bad to them, but Houston held firm and the mission proceeded as planned. Mullane deployed the satellite—a task that won him and his crewmates medals they were not allowed to wear in public—and Atlantis returned to land at Edwards AFB in the California desert.
It turned out that the crew was right about the tile damage. “There was already a knot of engineers gathered at the right forward fuselage shaking their heads in disbelief,” Mullane writes of the scene that awaited the crew as they exited the orbiter. “The damage was much worse than any of us had expected.”
Some 700 tiles had been gouged by what turned out to have been the nose cap from the booster rocket. The aluminum beneath the missing tile had started to melt, and Mullane says probably the only thing that prevented a burn-through was an antenna mount that required a thicker structure than elsewhere on the fuselage.
Robert “Hoot” Gibson, the STS-27 commander who told controllers from space that they did not seem to understand how serious the damage appeared, later found out that was exactly the case. Because it was a classified mission, the video downlink was encrypted, and as a result engineers on the ground were seeing Mullane’s robotic arm videos at lower resolution than the crew.
Had the reinforced carbon-carbon nose cap or starboard wing leading edge been penetrated by the debris that fell 85 sec. into the flight, or had the damaged tiles “unzipped” during reentry, Atlantis would have been destroyed. And because the mission’s 57-deg. inclination brought it back into the atmosphere over the Northern Pacific, the root cause of the loss might never have been discovered because the wreckage would have been lost at sea.
Coming on the second flight after the Challenger disaster, “that probably would have been the end of the program,” Gibson says.
That near-miss underscores a lesson that the Columbia Accident Investigation Board (CAIB) put very succinctly in its August 2003 report: “Building rockets is hard.” Today, as NASA scrambles to find a new way to get humans into space, there is a danger that lesson has again been forgotten.
At NASA’s Marshall Space Flight Center, the roots of both accidents—and the near-accident on STS-27—can be traced back to shuttle components managed there. Challenger fell victim to a poorly designed field joint between two segments of one of its solid-fueled booster rockets, and Columbia was fatally damaged by a piece of foam insulation that dropped from the external tank onto one of the wing leading edges that the solid-boost tip narrowly missed on Atlantis. As a result, veterans of the shuttle projects run at Marshall have some very hard-won lessons on how to “cheat gravity,” as they like to say.
“You don’t become a spaceship until you’re going 17,500 mph.,” says John Chapman, who took over as manager of the external tank project after the Columbia accident and retired this year. “In order to do that, the laws of physics say you’re going to be operating on the margins. You’ve got to get the weight way down. You’re going to be dealing with pressures and temperatures that somewhat boggle the mind, and so you’re going to be challenging the performance capability of materials throughout the whole thing. The more you can know about the environment which you’re flying in and what those materials do in those environments, . . . the more you are liable to be able to make design adjustments and fabrication adjustments to cope with the fact that you actually are operating on the ragged edge.”
In the wake of the Columbia accident, Sean O’Keefe, the NASA administrator in charge at the time, made fun of the amateur “foamologists” in the media trying to understand the dawning realization that a flimsy piece of insulation from the shuttle’s external tank could crack the heat shield on a wing’s leading edge. Myron Pessin is a professional “foamologist” whose white paper on the subject was used by the CAIB (and is available in the web special at
Aviation, Defense and Space News, Jobs, Conferences by AVIATION WEEK that accompanies this special report).
One lesson Pessin learned in working on the tank for 25 years is the difficulty of maintaining control of non-metallic materials like the foam and the adhesives that keep it attached to the tank. Sometimes nothing stands between specifications and an imperfect supply chain but the skill of a single worker, he says. On one occasion, the sampling program allowed an out-of-spec commercial primer to reach the factory floor at the Michoud Assembly Facility where the tanks are made.
“The technician who sprayed a 1,000-sq.-ft. dome said, ‘this isn’t the same material I’ve been spraying,’” Pessin says. “So we went back and discovered the vendor had put the wrong solvent reducer in the can. It was labeled properly. Everything was right, except the wrong material was in the can . . . . We had to hand-sand a 1,000-sq.-ft. dome to get the primer off.”
The expensive rework led to a new inspection program to ensure the chemicals used in preparing tanks meet specifications. A similar issue arose with the solid rocket boosters in 1996, when managers decided to destack STS-79 and replace its boosters because post-recovery inspection of the boosters from the previous flight showed hot gas had penetrated the field joints in an ominous echo of the failure that had destroyed Challenger a decade earlier.
The problem, says Deputy Shuttle Program Manager Steve Cash, was traced to a new water-based adhesive used to meet environmental regulations. The new adhesive had worked well in a hot-fire motor test in Utah, but the higher humidity in Florida changed its chemical characteristics. A divided management team decided to opt for caution and replace the boosters, says Cash, who was working the solid-fuel booster project at the time. The project switched back to the old adhesive under an Environmental Protection Agency waiver.
The approach—maintaining sharp vigilance over the systems and proceeding with caution when they do not act as expected—goes back to the earliest days of spaceflight. “We had von Braun,” says Alex McCool, an engineer and manager who started working for Wernher von Braun on the Redstone rocket in 1954 and who joined the shuttle program in 1972. “What he did, with his ‘board of directors,’ he instilled in us this idea of working together, checking, double-checking, testing components, subsystems, systems. Some things you can’t do, and you do the best you can.”
Perhaps nowhere has that lesson been applied with more rigor than in the space shuttle main engine (SSME) project. Despite its almost unbelievable operating parameters of -423-6,000F, 7,250 psi., 23,700 rpm., the reusable cryogenic engine has never caused an accident. Otto Goetz, the retired SSME chief engineer, attributes that to a continuous process of testing, research and upgrades.
“In the SSME program, we had principle that you never fly what you haven’t tested on the ground,” he says. “You never fly a configuration unless you have tested it on the ground, and on the ground we had the principle of fleet leader.”
That means the engines hot-fired in the test stands at Stennis Space Center are pushed harder than the engines that fly, leaving a performance margin that enhances robustness. “We didn’t compromise,” Goetz says.
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The Space Shuttle's Lessons For The Future
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