Astronaut explains secret of space station’s success

Taking a licking, but still ticking
The dual nature of the space station's design was the reason why the space station was able to take such a licking and keep on ticking.

“It was a major contingency to lose all of your U.S. ISS computers,” she admitted, “but the redundancy from the Russian segment — and its ability to be impervious to the root cause of the problem — kept the situation from becoming life-threatening, and that was the real key,” she said.

“The two attitude control systems also have differences in contingency management,” Helms added, in remarks focuing on the systems engineering behind their paired operation. “If the U.S. segment loses its brains, it needs a state vector [a precise description of its location and velocity] uplinked from the ground to recover. If the Russian segment loses its brains, it goes into a mode of looking for the sun and Earth, and rebuilding autonomously a state vector based on inertial references, in case the ground can't lock on with commanding.”

She was intrigued to examine “the difference in design philosophy on how bad you think things could get,” and she suggested it showed how different design approaches could motivate each side’s engineers to develop more robust systems in the future.

“So we've been fortunate that the Russians and Americans integrated their stations together,” she feels, with one caveat: “But not too much, because the enduring nature of the ISS really lies in its diversity.”

“I for one am glad that the ISS spacecraft is a combination of multiple design philosophies,” she concluded, “because as most engineers know, there is no one perfect design that meets the needs of all situations. Multiple design approaches in one machine can really broaden your ability to manage the unforeseen and the unpredictable.”

Lessons for future spaceships
Helms believes the space station's unexpected but gratifying robustness provides lessons that need to be applied to NASA's next spacecraft for manned voyages, the Crew Exploration Vehicle. “Unless there is another joint U.S./Russian-designed spacecraft, I hope that those who are involved with the design process for the Crew Exploration Vehicle spend a great deal of time studying the qualities of ISS that brought it through adversity,” she said.

She recommended that designers “note the nature of the hardware that failed, and note the nature of the hardware that can easily be recovered. They'll notice a theme of simplicity, designs that are inherently reliable, commonality of components, and easy subcomponent maintenance that doesn't require complex tools.”

In particular she stressed the importance of “redundant ops for critical systems like oxygen and CO2 removal.”

“There are also many lessons from ISS concerning the predictability of failure modes for major systems,” she added, for both large and small problems. “One thing we really can't afford is to be 'off the mark' on this for an exploration mission.”

She summarized what the space station's success has taught her: "It seems to me a lot of effort should go into operation concepts that drive design toward the simple yet robust approach."

More than five years of continuous occupation — with half of it managed by the two-man "skeleton crew" with minimal logistical support from Earth — provide an opportunity to develop "accountability for why predicted versus actual failures have been so diverse in the past," she said.

With these themes, Helms believes future astronauts can confidently venture far beyond low Earth orbit in spacecraft reinforced by the lessons of the international space station.

James Oberg, space analyst for NBC News, spent 22 years at the Johnson Space Center as a Mission Control operator and an orbital designer.

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