posted 06-07-2012 08:40 AM               

To compensate for this, the capsules carried bottles of the gas that included an allowance for this loss as well as the capacity to provide supplies for all other aspects of the mission.

One such documented leak was when a leaking hatch on CM of Apollo 15 was spotted whilst it was in orbit round the Moon. Further, I believe that I read somewhere that Apollo was able to sustain a breathable atmosphere in the capsule for about 10 minutes in the presence of a dime sized hole.

posted 06-07-2012 01:02 PM               

On a shuttle mission EVA, astronaut Jay Apt had a minor cut on one of his gloves and it wasn't detected until they got back in. There was a leak, but it was a very slight one and the EMU's pack was able to compensate for it with no alarm bells ringing in the helmet. EMU suits are maintained at about 4.3 PSI.

As for Soyuz, indeed it was the case with no backup tank in the descent module. The Russian craft are pressurized to about 14.7 PSI with a two gas system. For them, part of the reason was to mitigate the fire danger (partly because they lost a cosmonaut in a pure oxygen fire test, many years before Apollo 1). Russian craft normally use chemical beds (super oxides) to create breathable O2 rather than taking up excess bottled oxygen inside the cabin, also because of a risk of fire I believe (changing an oxygen tank can be a dangerous thing if one isn't careful). Over the years, they have incorporated some bottled oxygen though for their space stations to use in emergencies (such as the Progress collision on Mir).

In theory, the idea is a sound one as it is a pretty simple and robust system. Unfortunately Soyuz 11 revealed a flaw in the thinking. Once the descent module pops loose from the propulsion module on reentry, prior to Soyuz 11 there was no spare oxygen generation equipment onboard. But studies determined that each man would have enough oxygen left for the reentry and descent on the parachutes to landing.

When the parachutes opened, one of two valves on the DM would open up to allow fresh air inside. This was done to keep the cosmonauts breathing if they were unconscious while coming home (a concern mainly with Salyut crews coming back from long duration missions). But, one of those valves was not set right and when the pyro bolts blew to separate the orbital module from the descent one, it dislodged a check ball in the valve and the air leaked out on Soyuz 11. The rest of what happened most of us already know.

posted 06-07-2012 03:27 PM            

quote:

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Originally posted by Jay Chladek:
So the lower pressure differential means that leaks aren't as quick if they are small enough.

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posted 06-09-2012 03:08 AM               

quote:

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Originally posted by Jay Chladek:
But, one of those valves was not set right and when the pyro bolts blew to separate the orbital module from the descent one, it dislodged a check ball in the valve and the air leaked out on Soyuz 11.

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Briefly, depressurization happened when a 'breathing ventilation valve' located in an interface ring between the orbital and descent modules failed. This happened about 723 seconds after retro-fire when the 12 explosive bolts used to separate the modules fired simultaneously rather than in sequence.

The force generated caused a seal to open that under normal circumstances would not be activated until much later when it would be pyrotechnically discarded to adjust cabin pressure. As it was, the valve opened at a height of 168 kilometers with the loss of cabin atmosphere resulting in the death of the crew within 30 seconds. It took 935 seconds after retro-fire for the cabin pressure to reach zero, i.e. some 212 seconds after the valve opened, and 1640 seconds for pressure to begin to increase as the module entered the upper reaches of the atmosphere.

posted 06-10-2012 03:41 AM               

Salyut, the First Space Station by Grujica S. Ivanovich

Soyuz, A Universal Spacecraft by Rex Hall and David Shayler.

Both books were written long after the ASTP report was and had the benefit of research materials that NASA didn't have at the time. Even though NASA was in partnership with the Soviets on ASTP, the Soviets still kept some things secret in spots. Plus, the explainations of what happened on Soyuz 11 to the NASA report's authors came from NASA engineers who made some slightly incorrect assumptions about elements of the Soyuz design. Other things may also have deliberately not been told to the NASA engineers as well. While the Soviet engineering teams were more open about certain things, they weren't open about discussiong EVERYTHING.

According to Ivanovich's book, Viktor Patsayev's wife did a lot of investigation on her own as to what happened as she was an intellectual herself and interviewed many of the engineers and designers of the Soyuz to try and come up with a picture of what happened. Chertok's memoirs also discuss it (and I believe that is in the recently translated "Of Rockets and People" Fourth volume). But other information has been pooled together in the text also. There is a lot of background data to back up the valve discussion.

In any event, the account in the ASTP report made the mistake in assuming that the Soyuz pyro bolt sequence to seperate the orbital module from the descent module was similar to what Apollo used with the bolts blowing in sequence rather than at once. But in reality, the Soyuz bolts were designed to blow at once afterall. They never had a problem on previous missions. Now that doesn't discount the notion that the pyro charges might have been a little more powerful than what was used before, but it was but one link in the chain of events that caused the disaster.

According to what I have read, what caused the automatic shutter on the Soyuz 11 valve to open prematurely is the torque specs on the suspect valve were well below the proper tolerances, so the check ball was dislodged by the pyro bolts firing. When engineers went back and checked the valves on other Soyuz craft, they found out the torque specs on most of the other valves were also not correct either (also too low), but none were as low as the one found on Soyuz 11. If the valves were torqued to the proper settings, the check ball in the valve's automatic shutter would not have dislodged when the pyro bolts fired. I don't believe it has ever happened since then and to my knowledge, even though the crewmembers wear Sokol pressure suits today, the valve design is still used.

posted 06-11-2012 02:03 AM               

Nevertheless, the ASTP account is quite clear that the separation bolts were to have fired in sequence. The basic problem was the torque settings. These were found to be low with the Soyuz 11 capsule having the lowest of those investigated.