This story was updated at 10:16 am EDT on April 23.
NASA is watching closely as Russian engineers hunt for the source of a malfunction that sent a returning Soyuz spacecraft off-course during a Saturday landing.
Bill Gerstenmaier, NASA?s space operations chief, said Tuesday that it is too early to speculate the root cause of glitch or even how much additional peril, if any, the spacecraft?s three-astronaut crew was in, despite recent Russian news reports.
?They?re concerned about the event, but the relative danger to the crew, we?ve had no discussion on that at all,? Gerstenmaier told reporters in a teleconference, adding that he had not heard of any claims from Russian officials that the crew?s lives were in danger. ?They?ve not conveyed to us or conveyed to me any concerns at this point.?
The Russian-built Soyuz TMA-11 spacecraft successfully returned to Earth on Saturday from the International Space Station (ISS) with Expedition 16 commander Peggy Whitson, flight engineer Yuri Malenchenko and South Korean astronaut So-yeon Yi aboard.
It returned on a ballistic trajectory, a backup landing profile that sends the reentry capsule back to Earth in an unguided spin, as well as on a steeper-than-normal course that subjects the crew to up to eight times the force of gravity before parachutes deploy. Nominal landings hit peak loads of at about six times the force of gravity.
?It was pretty, pretty dramatic,? said Whitson, who completed a six-month spaceflight with Malenchenko, in a post-landing audio recording released late Tuesday. ?Gravity is not really my friend right now and 8 Gs was especially not my friend.?
But sometime during the descent, something went wrong. Instead of hitting its target landing zone on the central Asian steppes of Kazakhstan, the spacecraft landed short some 260 miles (420 km) to the east.
"There was no action of the crew that led to this,'' Malenchenko in a post-landing press conference on Monday, the Associated Press reported. "Time will tell what went wrong.''
Malenchenko, who commanded the Soyuz during launch and landing, contacted Mission Control within an hour after landing - the earliest he could free himself from the capsule - using a satellite phone to relay that he and his crewmates were home and in good health.
Whitson said local Kazakhs were first at the scene, possibly due to a fire nearby the spacecraft. NASA officials said the fire was due to brush burning by nearby farmers and unrelated to the Soyuz landing.
Malenchenko and Whitson reported being shaken about in their seats early in the landing operations, which suggests that the three-segment Soyuz spacecraft?s disposable propulsion module may not have jettisoned as cleanly as designed, Gerstenmaier said.
Another potential culprit is an avionics cable that may have shorted out and directed the Soyuz computers to initiate a ballistic descent, he added.
But Russian and NASA engineers will have a better handle on the anomaly once the Soyuz crew capsule and its flight recorder are retrieved.
?It may be a month of so before we start hearing anything definitive back from the commission,? Gerstenmaier said.
The three-segment Soyuz spacecraft design has long been Russia?s workhorse of manned spaceflight.
They consist of a central 6,393-pound (2,900-kg) crew capsule sandwiched between an orbital module on top and a propulsion module - which includes solar arrays and propellant - on the bottom. The three modules separate during reentry, leaving the bell-shaped crew capsule to return to Earth under parachutes and retrorockets.
Gerstenmaier said officials know the following:
- Malenchenko and Whitson reported unusual buffeting, jarring and shaking before entering the ballistic descent, suggesting the propulsion module may not have detached properly.
- The Soyuz spacecraft lost radio contact with Mission Control during reentry for an as-yet unexplained reason. While some Russian media reports suggest an antenna may have burnt away, there may have been ground and air-based issues, Gerstenmaier added.
- Malenchenko did report some signs of smoke inside the Soyuz spacecraft during reentry and powered down a display panel at times. Whether the smell came from inside the vehicle or through vents from the exterior is undetermined.
- A short-circuit in a faulty cable prompted the ballistic reentry of the space station?s Expedition 15 crew and a Malaysian astronaut last October during a descent that also included a propulsion module separation malfunction. The two glitches were thought to be unrelated and the module later sheared away due to aerodynamic forces.
Reliable, despite glitches
Saturday?s ballistic reentry of a Russian Soyuz marked the second in a row and the third since faulty gyroscope equipment forced the space station?s Expedition 6 crew to make a similar landing in May 2003.
?I don?t see this as a major, major problem, but it is clearly something that should not have occurred,? Gerstenmaier said. ?I think there is inherent reliability in this system.?
They served a pivotal role to continue ferrying astronauts to and from the ISS between 2003 and 2005 while NASA recovered from the tragic Columbia shuttle disaster. The U.S. space agency is also banking on Soyuz vehicles to send NASA astronauts to the ISS during the gap between the 2010 retirement of its space shuttles and the first flights of their Orion capsule successor.
More Soyuz spacecraft will also be needed beginning next year, when the space station?s population is expected to jump from three astronauts to a full six-person complement.
?We?ve been discussing with the Russians their ability to support Soyuz production for next year,? Gerstenmaier said. ?But again we need to watch and understand what the failure mode was.?
After last year?s ballistic return of the Expedition 15 crew, Russia?s Federal Space Agency replaced the faulty cable on new Soyuz vehicles and double checked power connections for the explosive bolts governing module separation.
But the Soyuz TMA-11 spacecraft that launched Whitson and Malenchenko into space was already docked at the space station by then. The astronauts safeguarded the ballistic system cable using additional insulation, but could not check the module separation system from inside.
The only way to check that system in orbit would be in a spacewalk that would require astronauts to don spacesuits, carefully peel back layers of their Soyuz vehicle?s protective thermal blankets and examine connectors for each of the explosive bolts, Gerstenmaier said.
?We determined, along with the Russians, that that was probably more risky to go out and pull those blankets back,? he added. ?We didn?t see any more fixes that didn?t carry more risk associated with them than leaving it as it was.?
Gerstenmaier said he expects NASA and Russian space officials to discuss any new findings from the ongoing investigation prior the planned May flight of the Soyuz TMA-12 spacecraft currently docked at the space station. During that flight, NASA astronaut Garrett Reisman and two Russian cosmonauts will move their Soyuz to a new docking port.
?We really need to get the capsule back to understand what occurred,? Gerstenmaier said. ?I don?t want us to speculate.?
The Associated Press contributed to this report.
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