Tuesday, April 22, 2008
In case you thought visiting Korean Astronaut Yi So-yeon was displaying a lack of personal courage as she described the ordeal of Saturday's return to Earth, don't. Further details on the re-entry problems suggest that the Soyuz crew module came closer to disaster than previously believed:
...and Oberg's analysis and comments, with some additional technical explanations, and implied criticism of the schedule pressures on Soyuz production from the impending Shuttle retirement:
The capsule apparently failed to completely separate from its aft "service" module after firing its retro-rockets. On contacting the detectable upper atmosphere, aerodynamic forces on the combined assembly appear to have swung it around into the wrong attitude, with the thin metal hatch of the crew module facing into the extreme heat of the re-entry plume. The crew survived, probably because whatever was holding the thrust module onto the capsule burned away and allowed the capsule to orient itself by it's inherent aerodynamic properties, with the heat shield first, before the hatch burned through (by some accounts, this hatch-first re-entry happened once before in Soyuz history. ). There are accounts of "significant damage" to the hatch. The same inherent properties---if I understand correctly---would have caused the crew module to enter an "emergency" re-entry after it finally separated. Because the roll control needed to enter with a controlled lift vector wasn't available to moderate the descent angle, the craft fell back to Earth in a "ballistic" re-entry, subjecting the crew to something like 9-10 g's deceleration. This would have been especially hard on the two crew members who were returning from six months in microgravity.
The overall basic design of the Soyuz seems to have brought its crew home safely this time, and it probably still has a better statistical safety record than the Shuttle, but ongoing problems with quality assurance of the spacecraft will have to be addressed. This is the second of these "ballistic" failures of the Soyuz capsules in a row, a significant setback for NASA plans to support the ISS entirely with the Russian spacecraft after the STS retires in 2010.
Post a Comment