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An expected engine burn on board the Soyuz capsule taking three astronauts to ISS did not take place as scheduled, forcing at minimum a two day delay in the rendezvous and docking.
[NASA spokesman Rob] Navias said the engine burn was aborted due to a problem with the Soyuz’s attitude control system, but further details were not immediately available. “Right now we don’t understand exactly what happened,” a mission manager at Russian Mission Control told the Soyuz crew late Thursday. Ground controllers planned to download data from the Soyuz and determine whether the glitch was due to a hardware or software problem. [emphasis mine]
Though the astronauts are not in any immediate danger, this is very worrisome. Indications from various other news stories suggest the problem was software related, which in a sense is a good thing. They would still have the option to manually fire their engines to do a manual rendezvous and docking. However, if it isn’t a software issue, and the vagueness of the reports so far makes me wonder about this, they might instead be stranded. Let us hope not.
Update: This report gives a little more information. It appears the capsule itself was not in the right orientation at burn time, and the computer software, sensing this, canceled the burn. If so, the problem might be software (incorrectly gauging the position of the spacecraft) or mechanical (something failing so that the capsule is not oriented correctly). Engineers need to find out which.