Orbiter Autopsies- page 2 | Space | Air & Space Magazine
The day Discovery completed its 39th and final flight — March 9, 2011 — a tug pulled the vehicle into an Orbiter Processing Facility at the Kennedy Space Center for a thorough examination. (Scott Andrews)

Orbiter Autopsies

What NASA will learn from dissecting Atlantis, Discovery, and Endeavour

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(Continued from page 1)

Long gone are Endeavour’s main engines. Technicians have plucked them with what looks like a Space Age version of a medieval battering ram. Mounted on a 20-foot-high forklift, the steel probe, its tip sheathed in black padding, had pressed into the nozzle of each engine. It extracted them one at a time, hauling them away for storage in a NASA facility at White Sands, New Mexico. If Endeavour’s engines fly again, it will be on NASA’s new Space Launch System, a Saturn V lookalike now in the planning stages.

The shuttle’s emergency crew escape system featured an extending pole; these will be collected from all three orbiters. “That’s a safety reason” for the collection, says Stephanie Stilson, orbiter transition and retirement flow director. “You have some energy built up in that system, where you could potentially hurt someone” if the pole were left intact.

The airlocks and docking rings through which crews on Endeavour and Atlantis entered the International Space Station will be gathered and stored for possible later use. (Discovery’s airlock and docking ring will remain in place.) And technicians have pulled the robotic arms from all three orbiters. Atlantis’ arm will remain with NASA, while Endeavour’s will be returned to the Canadian Space Agency, which developed the technology. Discovery’s robotic arm will go on exhibit at the Steven F. Udvar-Hazy Center.

Discovery returned from its last mission in March 2011, and just weeks later, crews took out the forward reaction control system. The forensic rhinoplasty began with members of the orbiter processing team fanning out across Discovery’s nose while a winch operator levitated the control system slowly up and away from the shuttle. The thruster assembly, bolted into a steel-beam frame, was placed on a trailer, where technicians scrubbed the forward reaction control system of its toxic fuels and oxidizers before reinserting it into the orbiter. In the aft end of the spacecraft, the holes once filled by Discovery’s main engines will be filled with replica engines built from test components. Any additional cavities created by the removal of orbiter components will be covered by panels to make their absence impossible to detect from the outside.

Four months after NASA ferries Discovery atop a modified Boeing 747 to Dulles International Airport (near the Udvar-Hazy Center), Endeavour is scheduled to move to the California Science Center in Los Angeles. And in February 2013, Atlantis will be rolling toward the visitor’s center at Kennedy Space Center in Florida.

The main reason for examining orbiter pieces left behind—wires, feed lines, tanks, valves, and electronics—is to avoid future failures, says John Shannon, NASA shuttle program manager. NASA engineers already have some ideas about what to look for. During the ascent of Columbia on mission STS-93 in July 1999, an electrical short knocked out the computer-based controllers for two of the three main engines. When the engines switched automatically to backup controllers, the mission was saved. It was later determined that mishandling of a wire damaged its insulation. Vibration during repeated launches had caused further wear until an exposed conductor touched a screw, the contact shorting the controllers five seconds after liftoff.

NASA tried to remedy the problem by giving wires a protective covering, an arduous process that may not have had the desired effect. “So we want to go back and look at the wiring to see if there’s anything to be learned,” says Francisco J. Hernandez, deputy chief engineer for orbiter propulsion and power subsystems. “The wiring methods and design are very similar to what is done in the aircraft world, so this is something that is not only potentially applicable to future space vehicles but also maybe to the aviation community.”

In addition, engineers will examine shuttle avionics for signs of “tin whiskers,” wispy extrusions of tin molecules in circuit-board soldering that expand in zero gravity. Knowing the extent of their growth over time could help operators of satellites that use the same tin soldering predict when the satellites could fail. “Long whiskers are a great way to short out a circuit,” says Shannon. “We had a satellite short out, and we think tin whiskers was the most likely cause.”

Orbiter autopsies may also benefit the space station: Cooling systems there use a highly corrosive type of ammonia that was also used on the shuttle. So engineers are examining orbiter cooling systems for signs of damage. “These kinds of failures sneak up on you, and they are not necessarily easy to find,” says Thomas M. Simon, commercial crew assistant chief engineer. “So even if we find [only] a couple issues, the relative cost of these studies compared with losing a mission or setting up an entire test program is a big savings to the agency.”

Analyzing orbiter elevons could yield dividends as well. Each orbiter has four of these control surfaces, two on the trailing edge of each wing. Elevons roll the spacecraft left and right, and pitch the nose up and down. During a pre-launch test for STS-101, which launched on May 19, 2000, the actuators that controlled Atlantis’ elevons failed. NASA followed up by testing every actuator on every orbiter and discovered that in some cases hydraulic fluid had accumulated in tight spaces instead of flowing freely. The problem was traced to microscopic silt, contaminants in the hydraulic system that impede flow like plaque slows blood in the body.

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