While NASA managers await the results of a Russian engineering analysis to determine what went wrong during a returning Soyuz capsule's steep, off-course descent from the international space station Saturday, space experts around the world are discussing what may have been a much more serious problem than initially believed.
The Russian Soyuz TMA-11 spacecraft that carried two space station crew members and aback to Earth apparently suffered a failure, possibly involving explosive bolts, that prevented one of two sections connected to the central crew capsule from separating properly before re-entry, sources say.
The capsule apparently entered the discernible atmosphere in an unusual orientation and was subjected to relatively violent buffeting until the attached section finally broke away, as planned in such scenarios, allowing the descent module to settle into a normal heat- shield-down orientation. The failure of the lower propulsion module to cleanly separate is believed to have forced the craft into a steep, so-called ballistic re-entry.
The timing of major entry events is not yet known, but the spacecraft landed some 295 miles short of its target. The final moments of the descent occurred out of sight and out of contact with Russian recovery forces and mission control near Moscow. Smoke apparently entered the capsule at one point, but it's not clear what might have caused it.
Instead of being met by flight surgeons and engineers, Soyuz commander Yuri Malenchenko, outgoing space station commander Peggy Whitson and guest flier So-Yeon Yi initially were assisted by local residents who were astonished to find the charred spacecraft resting on its side in their fields. Recovery crews eventually arrived and flew the crew back to Star City near Moscow. All three were reported to be in good health, although Malenchenko and Whitson face weeks of physical therapy to help them re-adapt to Earth's gravity after six months in weightlessness.
Russian space agency officials have not confirmed any problems with the separation of the Soyuz spacecraft's three modules, saying only that the spacecraft followed a ballistic, or unguided, trajectory because of an unspecified problem and that the system is designed to safely fly such trajectories without putting the crew in jeopardy.
This was the second flight in a row to end with a ballistic descent, which can subject the crew to 10 times the normal force of Earth's gravity.
Interviewed shortly after landing, Malenchenko, speaking through an interpreter in footage carried on NASA television, was asked about the experience.
"Well, it was interesting. Interesting is a good description," he said.
"Did it feel like a merry-go-round?" the interviewer asked.
"Well, pretty much so."
He did not say anything about a problem with the module separation system.
Because the Soyuz is a Russian spacecraft, U.S. space officials have not officially addressed the issue one way or the other, saying only that Russian engineers have barely started a detailed engineering analysis. With the descent module available for study, agency officials have said they are confident their Russian counterparts will eventually figure out what went wrong and do whatever is required to fix it.
But several U.S. observers privately expressed concern. With U.S. astronaut Michael Fincke scheduled to blast off aboard the next Soyuz in October as commander of space station Expedition 18, NASA managers will be particularly interested in the progress of the Russian probe.
"They've got a good track record with the Soyuz," said one official.
But he said this was a "serious" issue that will require conclusive results to restore confidence in the system. After the ballistic entry on the previous flight last year, Russian engineers determined the cause was a one-time manufacturing defect. As such, that should not have affected the TMA-11 spacecraft, a U.S. source said. Given what happened Saturday, that issue will have to be re-examined.
"This has been a remarkably robust system for lots of years," said John Logsdon, a space policy analyst at George Washington University and a member of the Columbia Accident Investigation Board. "What's a little worrisome is apparently there were some similarities with the one before this one. They had a ballistic entry. You don't want that happening on every mission, especially with people coming back from long-duration stays. They're feeling bad enough anyway without going through this.
"Could you compare it to what the CAIB said about the need for laser focus on quality for every mission, every time? Have the people doing Soyuz over and over again lost some of that? I think it's a legitimate concern."
It is a potentially critical issue for both Russia and the United States. NASA plans to retire the space shuttle in 2010 and rely on the Soyuz to ferry U.S. astronauts to and from the space station until a replacement spacecraft debuts in the 2015 timeframe.
Malenchenko and Whitson were completing a 192-day mission as members of space station Expecdition 16 while Yi, who rode into orbit with Expedition 17 commander Sergei Volkov and Oleg Kononenko on April 8, was wrapping up an 11-day voyage.
Volkov, Kononenko and Yi were launched aboard the Soyuz TMA-12 spacecraft, which remains docked at the international space station. It is scheduled to carry Volkov, Kononenko and U.S. space tourist Richard Garriott back to Earth this fall. Given the TMA-11 incident, the health of TMA-12 is open to question.
Malenchenko and Whitson rode into orbit last October aboard the same Soyuz TMA-11 spacecraft they returned in Saturday. Undocking from the space station went normally and the Soyuz's braking rockets fired as planned to drop the ship out of orbit for a landing near Arkalyk in Kazakhstan.
The Soyuz TMA spacecraft is made up of a lower propulsion, or service, module equipped with two solar panels, fuel tanks, rocket engines and other systems; a central crew module with the spacecraft's control systems; and an upper orbital module that includes rendezvous equipment and a docking system. Astronauts and cosmonauts ride to and from space strapped into cushioned seats in the central module, the only one of the three equipped with a heat shield. The cramped descent module weighs about 6,400 pounds and has a habitable volume of just 141 cubic feet.
Just before reaching the discernible atmosphere during re-entry, at an altitude of some 400,000 feet, commands are sent to fire explosive bolts to separate the connections holding the spacecraft's three modules together. Only the central descent module is built to withstand the rigors of re-entry. The other two modules burn up in the atmosphere.
In a normal, guided re-entry, the descent module is oriented to modify its lift slightly, permitting a shallower, less severe trajectory. In a ballistic entry, the capsule's unguided descent is steeper, subjecting the crew to more extreme deceleration.
What happened Saturday is not yet clear. Sources say the propulsion module apparently did not immediately separate from the descent module just prior to entry, possibly because an explosive bolt failed to fire. As a result, the crew cabin apparently did not enter the atmosphere in the proper orientation. The attached module broke free at some point, allowing the crew cabin to right itself and continue the descent in the proper orientation. Sources said smoke was present in the crew cabin during or just after the descent, but it's not clear what might have caused it or when it occurred.
Descriptions of the Soyuz TMA-11 re-entry brought to mind an early Soyuz entry problem that almost ended in disaster. On Jan. 18, 1969, six months before the Apollo 11 landing on the moon, cosmonaut Boris Volynov faced a particularly dire situation.
"The service module of the Soyuz failed to separate after retrofire," according to Encyclopedia Astronautica, a respected European web site that tracks international space activity. "Once the Soyuz started reaching the tendrils of the atmosphere, the combined spacecraft sought the most aerodynamically stable position - nose forward, with the heavy descent module with its light metal entry hatch at the front, the less dense service module with its flared base to the back.
Luckily the struts between the descent and service modules broke off or burned through before the hatch melted through and the descent module righted itself, with the heat shield to the rear, before being consumed. Due to a failure of the soft-landing rockets the landing was harder than usual and Volynov broke his teeth."
Details about the Soyuz entry were not revealed until many years later.
Malenchenko, Whitson and Yi have not yet provided any detailed descriptions of their descent, or mentioned any problem with the module separation system. During a news conference in Star City, Russia, Monday, The Associated Press reported that Yi said "during descent I saw some kind of fire outside as we were going through the atmosphere. At first, I was really scared because it looked really, really hot and I thought we could burn."
But she quickly realized the fire was outside the spacecraft. "I looked at the others and I pretended to be OK," she said.
Malenchenko said only that the Soyuz switched to a ballistic trajectory and that "there was no action of the crew that led to this. Time will tell what went wrong."