Tuesday, April 22, 2008

Questions linger on Soyuz "Ballistic" re-entry

The Space Shuttle would
not have survived
a similar re-entry

Expedition 16 Commander Dr. Peggy Whitson waves to a crowd of well wishers from the top of the airplane steps as she arrives at Chkalovsky Airport near Star City, along with Flight Engineer and Soyuz Commander Yuri Malenchenko and So-yeon Yi of South Korea. Whitson, Malechenko and Yi landed their Soyuz TMA-11 spacecraft on April 19, 2008 in central Kazakhstan to complete 192 days in space for Whitson and Malenchenko and 11 days in orbit for Yi. Photo Credit: (NASA/Bill Ingalls)

Joel Raupe - The Soyuz TMA spacecraft has proven to be an amazingly dependable support vehicle, first for MIR and now for ISS. Roscosmos, the Russian Federal Space Agency, plans to replace the vehicle soon, and if NASA's solidifying status quo timeline is upheld through the winds of politics until the Constellation's Orion Block One and Ares I booster is available, the United States will be depending on some version of the Soyuz for a half decade.

The advent of ESA's ATV and American commercial ISS servicing spacecraft will help, but lingering questions Roscosmos and a respectful NASA seem reticent to discuss should be answered. Sources in the Astronaut Corp agree, though they also confirm NASA's hierarchy agrees also, and are committed to allowing the Russians to clear up an embarrassing third and second in a row failure of the primary hyperbolic re-entry burn on a Soyuz TMA that had been parked for half a year docked and powered down on the International Space Station.

The back-up secondary re-entry system kicks-in a second or so after the primary system's failure is confirmed, and those few seconds take the vehicle kilometers further along it's path, widening the available angle of atmospheric contact needed to bring the Soyuz down anywhere near the desired landing site. The re-entry that follows is "shallow" and hotter, it is also hairy with two command officers carrying a rookie through many gees rather than a few, after months of weightlessness.

Still, before silence fell over the re-entry's story, Roscosmos was either mistranslated or translated correctly when quoted as saying that "the crew" (meaning Malenchenko) "made a decision," a conscious choice to return to Earth in the most dangerous way available, presumably for the thrill?

If you are wondering why Malenchenko would make such a decision, you can count on that decision being necessary and spontaneous. Soyuz is not built for long-term independent space travel and is not equipped with much more fuel when lined up for re-entry than a Mercury capsule. At the high inclination of the ISS orbital plain, the window for re-entry was unlikely to be as precise for many hours or days, and having just enough fuel to slow the spacecraft and change
periapsis slightly below 60 kilometers and the atmosphere left nothing close to what might be needed for changing the plain for its orbit more favorably, or the kind of waive off regularly experienced by the Shuttle may not be possible for the Soyuz design.

The failure has brought a design flaw to light that may or may not be intrenzic to Soyuz being parked at ISS for six months, or aging parts used to assembly "new" TMA's - but perhaps more importantly it has shown the fragility of the Soyuz in the context of its robust mission experience but minimalist design.

The Space Shuttle would not have survived a similar re-entry protocol, but the decades-old design also keeps fuel that is dumped after the OMS re-entry burn, available for slight changes in its future orbital plain should they be needed for a true and modern "orbital re-entry," and a kind of protocol that allows days to pass before it must return, and to to a wider range of options available for lower latitude landings.

Whether such questions are foolish, or whether they are finally being tossed about behind closed doors or Emailed to contractors and heeded as a red-flag warning in need of answers, at NASA for Orion or Roscosmos for the next Soyuz remains to be seen.

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