HOUSTON — Coming back to Earth from space is never routine, but this week's descent of a Soyuz spacecraft with two Russian cosmonauts and a private space traveler from America will be more closely watched than usual — because of two rough rides that came before.
During the previous two Soyuz descents from the international space station, in October 2007 and April 2008, the spacecraft suffered the same type of major anomaly when explosive bolts failed to separate the crew cabin cleanly from other no-longer-needed sections of the vehicle. As a result, in each case, the ship’s landing guidance system switched to a steering mode that dropped the crews far short of their aim points, and far higher accelerations.
With a little added bad luck, such a landing could have killed everybody on board. But for the past few months, Russian space officials have been assuring NASA and the public — as well as the three men who will be inside the descending Soyuz this week — that everything is now under control.
Russian space officials say they solved the problem going forward by making modifications in the spacecraft, starting with the one that was launched this month and will remain attached to the space station until next spring. As for the Soyuz due to come back this week, the Russians say the problem was fixed when an explosive bolt was removed during an emergency spacewalk in July.
Of course, all this assumes that the problem has been correctly identified. And there's the rub.
The supposedly faulty bolt assembly has not yet even been returned to Earth for disassembly and inspection. It will be coming home on the current return mission, and could provide the first real evidence that the theory behind the previous failures (and the justification for the workarounds and repairs) is correct.
The opposing theory — that the proposed failure mode is wrong and that the cause is something else — could be proved as soon as Thursday night if a similar anomaly occurs. Russian cosmonauts Sergei Volkov and Oleg Kononenko, along with American video-game millionaire Richard Garriott, are due to land at 11:36 p.m. ET Thursday (which is midmorning on the following day in the Kazakh landing zone). NASA TV will carry the entire landing sequence live on the Internet.
It’s not hard to imagine scenarios even worse than the previous two hard landings. In some, the falling spacecraft becomes wrapped in flames before it has correctly aligned its heat shield frontward, leading to fiery penetration of its hull. In other scenarios, critical landing systems such as the parachutes are disabled by thermal stresses and fail to slow the ship for its final touchdown. Such possibilities should be answered with the kinds of solid reassurances that have been lacking. Until now.
A theory you can believe in
A more complete explanation behind the Russian theory came out this week from a NASA space official in Houston. The official requested that his name not be used because he was not authorized to divulge the information. His expertise is well-known, however, and he is highly trustworthy.
The explanation made more sense to me — and relieved a lot more anxiety — than all the public reassurances that have come out over the past six months.
According to this source, the anomalies were caused by a combination of electrical phenomena in space and some hardware features of the Soyuz. It is well-documented that the space station plows through a field of charged particles on the edge of the upper atmosphere as well as Earth’s own magnetic field.
Slideshow: Month in Space The space station is equipped with an ion gun to neutralize any charge buildup, but the metallic insulation blanket over this particular bolt, and the nearby hardware designed to hold the craft’s aerodynamic protective shroud during launch, were not grounded.
The source said this “allowed a low-level current to flow through the pyro bolts over a long period of time.” The electrical current induced heating. Even in zero gravity, the bolt’s powder fused and shriveled away from the "flash wire" that is supposed to ignite it when commanded. As a result, when the command was issued, the powder did not ignite.
Under terrestrial conditions, he said, “the Russians did reproduce this phenomenon with a simulated environment and a ‘training bolt,’” but not with a flight-qualified bolt. That probably was close enough.
Coincidentally, the bolt that was susceptible to the electrical effect was the only one that spacewalking cosmonauts could access last summer using existing transfer equipment. By removing the bolt at that time, they guaranteed that it would not "hang up" even if it failed to fire this time. This hangup had twice jerked the modules into a brief uncontrolled tumble before they tore loose in the rising flames of re-entry and then, just in time, properly turned the heat shield into those flames.
Adding a flurry of fixes
There was not enough timely insight to add any sensors to the returning Soyuz, to tell the crew that the bolts have indeed fired correctly. However, the expected velocity changes from a nominal separation have been calculated, and the crew will be monitoring their own navigation system to report these changes — or their absence — within several seconds of the required time of separation, the source said. All subsequent Soyuz vehicles, including the one just launched, have thermal sensors on the bolts that will tell ground controllers whether or not the bolts have fired properly.
In addition, the Soyuz will have a software patch, not further described, “that will help the vehicle separate due to atmospheric heating if the pyro lock fails to open,” the source said. But as with any such fast fixes for complex applications, there is always some anxiety that the fix itself may introduce new failure modes.
From here on out, the Soyuz craft will have better electrical grounding, sturdier explosive bolts and rerouted circuitry for the bolt-firing mechanism.
And just to make sure, a task has been added to a scheduled spacewalk in December to install instrumentation near the Soyuz parking ports, in order to measure the electrical environment more precisely. By then, the returned bolt will have been inspected and compared to the test bolt that was subjected to similar electrical effects in the laboratory.
If the theory is actually verified, this anomaly can be retired, joining a long list of "spaceflight funnies" that have bedeviled space missions for decades. And the Russian space teams can clear the decks for the next "funny" waiting out there. That these continue to occur is no surprise. The only really scary outcome is if they stop being solved.
Thursday night, we’ll get a new data point.
NBC News space analyst James Oberg spent 22 years at NASA's Johnson Space Center as a Mission Control operator and an orbital designer.
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