William Gerstenmaier knows the U.S. space program inside out -- both literally and figuratively. As a 30-plus year veteran of NASA, Gerstenmaier has managed the operational dimensions of the space shuttle, international space station, and other space flight missions. For this AeroAstro talk, he dissects a problem that recently grounded the shuttle, coming at it from the perspective of both an engineer, and a top-level manager with responsibility to the highest levels of government.

Gerstenmaier presents his case “as it unfolded,” for a behind-the-scenes view of how NASA keeps its aging shuttles aloft. His account begins in 2008, after a shuttle flight revealed something wrong with flow control valves essential to the shuttle’s hydrogen system. These valves are connected in a closed loop to the main engines, via a 170-foot length of pipe, through all manner of twists and turns, and frequently subjected to very high pressures. Gerstenmaier describes the series of tests his engineering teams performed, over long days, weekends and holidays, to determine what precisely had gone wrong, and the risks posed by potentially faulty equipment.

NASA engineers ruled out wiring problems, but discovered during an “x-ray of the plumbing” a chunk missing from one of the valves. They examined the problem from a structural dynamics standpoint: could the “flow through the plumbing” have made the valves vibrate violently? The same valves had been in use since 1981, but perhaps a “failure associated with an extremely resonant condition that could occur periodically” was responsible.

Gerstenmaier’s team shot particles through a simulated piping system and then used a scanning electron microscope to detect valve damage. They also analyzed historical failure data, which suggested that valve cracks might be a “high cycle fatigue problem,” and could therefore possibly occur during any flight. Gerstenmaier felt bound to “ground the fleet,” until engineers figured out a way of screening for damage in the valves pre flight.

A flash of unorthodox thinking led engineers (unbeknownst to Gerstenmaier) to buy a common bolt tester, which permitted them to get a comprehensive picture of the valves in working shuttles without removing or damaging them. After running numbers around flight risk, and many discussions with his engineers, Gerstenmaier felt they’d arrived at a rationale to resume flying.

Says Gerstenmaier, “I can tell you, I wasn’t looking out the window in Florida. At the shuttle launch, I was looking at data of the flow control valves and watching the pressures … I knew what I needed to look at in terms of the data. An engineer’s tendency comes through.”