[/caption]Back in April, the world was captivated by what happened to the crew of Soyuz TMA-11. It was supposed to be a routine trip from the International Space Station to the Kazakhstan landing site, but the crew return capsule endured a ballistic re-entry (i.e. an uncontrolled re-entry occurring steeper than planned) and a hard landing 400 km off-target. Fortunately cosmonaut Yuri Malenchenko, US astronaut Peggy Whitson and South Korean spaceflight participant Yi So-yeon survived the landing, but endured significant stress (plus Yi So-yeon had to receive medical attention to her back). Several days of media confusion ensued as misinformation was circulated by Russian officials, accusations of incompetence were directed at the crew (by the Russian space agency), and then (my personal favourite) a senior space agency manager put forward his theory on what had gone wrong: Having more women than men on board the spaceship was a bad omen.
So, what really happened above the atmosphere of Russia? It appears Russian engineers are beginning to understand what initiated the ballistic re-entry (without an omen in sight)…
While the rest of the world tried to work out who was to blame for the April 19th hard landing, engineers were busy trying to figure out what actually went wrong with Soyuz TMA-11. For a while now there has been a focus on the explosive bolts that possibly failed to fully separate the service module from the descent module as the craft began to enter the upper atmosphere. A rather heroic spacewalk was even carried out to remove one of the bolts from Soyuz TMA-12 whilst attached to the space station in July 2008. It was placed (carefully) in a blast-proof container and brought back to Earth for analysis.
Russian space officials have said the problem with the explosive bolts (or “pyrobolts”) has been solved and re-entries can go on as normal. However, an instrument will be attached to the outside of the space station, near to where the Soyuz vehicles dock. The installation is scheduled for a December 23rd spacewalk. If the problem has been solved, why investigate the issue further? The reality is that Russian scientists are still trying to understand what causes the Soyuz pyrobolts to misfire; after all, the ballistic re-entry is not exclusive to the April 2008 descent, it also happened in October 2007 during the re-entry of Soyuz TMA-10.
According to Bill Gerstenmaier, NASA’s associate administrator for the Space Operations Mission Directorate, scientists in the Russian space agency have converged on a common theory, the electromagnetic interference (EMI) hypothesis. EMI is thought to be caused by the flow of space plasma around the hull of the station, causing interference with the pyrobolts in the docked Soyuz vehicles. One effect could be the hardening of the explosives igniter wire, meaning a higher electrical current is needed to trigger the small explosives. Another effect of EMI could cause “the slurry of combustible material around the wire [to] migrate away from the wire, so there’s a gap between the slurry and the wire,” Gerstenmaier said.
Therefore, the hull-mounted instrument (called a Langmuir probe) will be used to measure the electric potential of the plasma flowing around the station near the Soyuz dock. This will help the scientist on the ground gauge the significance of the two space plasma EMI hypotheses, while they continue to study the pyrobolt brought back from TMA-12. It will be interesting to hear what they find out…