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Dangling strap to blame for scary space leak?

The Soyuz TMA-6 spacecraft leaves the international space station on Oct. 11, as seen through a station porthole. The craft consists of three modules: from left, the service module with solar arrays, the descent capsule and the spherical orbital module.
The Soyuz TMA-6 spacecraft leaves the international space station on Oct. 11, as seen through a station porthole. The craft consists of three modules: from left, the service module with solar arrays, the descent capsule and the spherical orbital module.NASA

Russian space officials are unofficially blaming the alarming pressure drop during last month's landing of the Soyuz TMA-6 spacecraft on a dangling strap and crew error, has learned. The Russian space agency's draft report on the matter remains unsigned, however, according to the NASA safety official who provided with a copy of the report.

The NASA official, who asked his name not be revealed, said that "disagreements between the specialists and crew" still had to be resolved, but that the Russians had shared the draft report in an e-mail to their NASA counterparts.

The pressure drop during the Oct. 11 landing is not a secret — both Soyuz commander Sergey Krikalev and passenger Gregory Olsen have publicly made reference to the unusual event. But neither the U.S. or Russian space agencies have offered any comment. The third man aboard the Soyuz as it returned to Earth from the international space station, NASA astronaut John Phillips, has not referred to the matter, either.

While the incident was not life-threatening — all passengers aboard Soyuz spacecraft have worn pressure suits during such mission-critical phases since a similar failure killed three cosmonauts in 1971 — the secrecy around its cause has inflamed private speculation about a possible design flaw or possible flaws in decision-making. A similar Soyuz is currently docked to the space station and with the U.S. shuttles grounded, the Soyuz is the station's lifeline.

“We had certain problems with pressurization before undocking,” Krikalev stated during a post-flight news conference. He added that there had been additional problems with the craft’s airtightness during the descent: “In principle this was an anomalous situation of medium complexity,” he added. “In fact, it was a fairly serious situation.”

During the three-hour coast from undocking to actually firing the craft’s braking engine for the descent into the atmosphere, Soyuz cabin pressure fell from the normal 765 mmHG (equivalent to sea level) to below 660 mmHg (equivalent to air density in Taos, New Mexico), another source said shortly after the incident. The crew was instructed to pump the pressure back up by releasing bottled oxygen, and there was some improvement.

What may have happened
Two hatches must be sealed off before the Soyuz can leave the space station: one from the forward orbital module to the station, and one from the descent module — where the crew actually rides. It is the descent module that actually lands on Earth; the other parts of the spacecraft separate from it before landing.

A post-landing inspection of the descent module hatch found "an impression in the seal ... which resembled the buckle of a strap," according to the Russian draft report. Such straps are used to hold insulation blankets in place against the insides of the exterior walls of the spacecraft in order to prevent moisture condensation.

Normally, steps are taken to make sure there are no foreign objects trapped in the hatches when they are closed for departure. But this time, the report suggests, the crew was careless.

“Before departure, the crew performed the hatch seal inspection and cleaning before hatch closure and a visual inspection to ensure the mated surface area was clear of any objects,” the report states. Representatives of the spacecraft manufacturer “believe the crew was more pressed on time and may have been hurried,” and hence overlooked the strap, which could have been sucked into the gap by air flow just as the hatch was being closed and locked.

The crew was more hurried than usual, these experts speculate, due to pressure from specialists back on Earth. “Scientists have become more interested in the biology-type payloads,” the report continues, “which are stored in the ISS freezer until one hour before departure.” But then they must be brought to the landing capsule in insulated packages.

“The more of these payloads you have the more you are rushed at the last minute to complete Soyuz packing and departure preparations,” the experts concluded. The crew was bringing back scientific samples that originally were to have ridden back to Earth aboard a space shuttle mission, but were stranded in orbit when problems on the shuttle flight in July delayed the next flight from September until sometime next spring at the earliest.

As a check on hatch airtightness prior to undocking, air is bled out of the forward (unoccupied) orbital module, and pressure inside the crew cabin in the descent module is monitored. “The hatch leak test results were inconclusive,” the report states, with a “somewhat off-nominal reading, but this did not really indicate a leak.” After a delay of at least six minutes, permission was given to undock, even though Mission Control in Moscow wasn’t sure of the cause of the unusual pressure readings.

But after undocking the pressure drop became more obvious as air from the descent module leaked into the orbital module. This went on for several hours.

However, once the orbital module was jettisoned, the leak — which might then have gotten much worse — instead stopped entirely. The experts interpreted this to mean that the much higher pressure difference across the hatch — now facing the pure vacuum of space — actually compressed the flexible rubber seal and strangled the leak off.

The chance of the alternate possibility — physical rupture of the damaged seal and a considerably increased leak rate leading to total cabin depressurization — remains uncalculated, but in that event the crew’s spacesuits would have saved their lives.

While the experts cited in the report insist that no changes in crew procedures were needed as long as future crews properly perform the hatch seal inspections, the report itself remains preliminary. And the two space professionals aboard the Soyuz that day, Krikalev and Phillips, returned to Houston from Moscow last week without signing off on the version that holds them responsible for the space scare.