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  Atmosphere leakage rate of Apollo capsules

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Author Topic:   Atmosphere leakage rate of Apollo capsules
moorouge
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posted 06-07-2012 08:40 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Reading an account of the preparations for the ASTP flight I was surprised to discover that the Apollo capsules were built with an acceptable leakage rate of up to a "tenth of a pound an hour of oxygen".

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.

When it came to planning the ASTP flight, the Americans were concerned to find that the Soyuz craft were built with a zero tolerance to leakage and carried no provision to replenish any loss, perhaps adding a contributory factor to the loss of the Soyuz 11 crew.

Jay Chladek
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posted 06-07-2012 01:02 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
Well, part of the reason for the tolerance is down to the Apollo being pressurized to 5 PSI. So the lower pressure differential means that leaks aren't as quick if they are small enough. Still, a large hole could mean a big problem. I recall reading that an Apollo CM could be pressurized up to 8 PSI, but any more than that and it would pop like a balloon. The pressure differential is the primary reason why the docking module/airlock was developed. One ship (Soyuz) couldn't be modified for pure oxygen at reduced pressure due to the fire danger and the other one (Apollo) couldn't be pressurized any higher.

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.

Now Mishin maintained for years after Soyuz 11 if somebody had stuck their finger on the valve hole, they could have kept the remaining air inside until the valve got closed. But without a backup oxygen tank to repressurize the cabin I doubt that would have done that much good. As soon as that valve popped, the Soyuz 11 crew was in a world of hurt and they lost precious seconds thinking it was a problem with the top hatch before focusing on the valve. By the time they knew it was the valve, there was not much oxygen left and without a way to rapidly repressurize the cabin, their fate was sealed.

Blackarrow
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posted 06-07-2012 03:27 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jay Chladek:
So the lower pressure differential means that leaks aren't as quick if they are small enough.

Digressing slightly, I still remember the interminable wait for "Eagle" to depressurize enough for Armstrong and Aldrin to open the hatch. It seemed to take forever. As the pressure approached zero, it was being "topped up" by the astronauts exhaling. As the minutes dragged on, how many of us were wondering if Armstrong would ever get that ruddy hatch to open? For a 14-year-old it was physically painful, but -boy! - it was worth the wait.

schnappsicle
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posted 06-08-2012 12:08 PM     Click Here to See the Profile for schnappsicle   Click Here to Email schnappsicle     Edit/Delete Message   Reply w/Quote
I read in Cernan's book that when he exited Gemini 9, he felt a burning sensation in his lower back. The zipper had come undone or wasn't closed properly. He received a severe sunburn in that area as a result of his skin being exposed to direct sunlight in space. I'm sure some oxygen escaped through the hole. If it did, it wasn't enough to terminate his EVA. So apparently, a small amount of leakage is acceptable.

Jay Chladek
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posted 06-08-2012 01:24 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
Cernan's burning wasn't caused by a loose zipper from what I remember. The thermal covering in that region was damaged exposing the inside layers to higher heat loads (it wasn't discovered until post flight analysis), so his rear end was getting more exposed to heat than it should have. Technically it was not a sun burn. It was a thermal burn, like what happens when you grab a plate that is too hot. It still results in a first degree burn, like a sun burn. To my knowledge, the suit's pressure integrity was still good.

Gonzo
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posted 06-08-2012 02:47 PM     Click Here to See the Profile for Gonzo   Click Here to Email Gonzo     Edit/Delete Message   Reply w/Quote
Jay - that makes sense. If there was a hole large enough for him to feel the warmth of the sun and eventually a sunburn, there would have been two bigger problems.

First, he wouldn't have felt the sun through a hole that big, he would have felt open space, which is VERY cold. Second, if the hole was large enough for him to get a sunburn through, how could he have maintained any kind of atmosphere in his suit?

RichardH
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posted 06-08-2012 04:31 PM     Click Here to See the Profile for RichardH   Click Here to Email RichardH     Edit/Delete Message   Reply w/Quote
How could he have felt cold? Space is a vacuum, and you need some sort of medium to transfer your bodyheat away from your body. He would have experienced that the parts of his body exposed to the vacuum would swell, and that would probably have been painful, and obviously he'd suffer from his suit decompressing. Correct me if I'm wrong.

moorouge
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posted 06-09-2012 03:08 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
quote:
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.
The exact reason for the Soyuz 11 accident was a bone of contention between the US and Russians for many months whilst they were planning the ASTP mission. It wasn't until the 'Mid-Term Review' that the Russians finally came up with the full details.

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.

A fuller account can be found on page 245 of The Partnership: A History of the Apollo-Soyuz Test Project, NASA reference number SP-4209.

Jay Chladek
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From: Bellevue, NE, USA
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posted 06-10-2012 03:41 AM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
I've got the NASA ASTP report also. It is not quite correct in that matter (I referenced it for my own space station book research since ASTP I consider a "space laboratory" of sorts). The better and more accurate accounts about the Soyuz design and the Soyuz 11 accident come from the following books based on my research (both are available from Springer/Praxis):

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.

Part of what also caused the cosmonauts to lose precious time as the cabin depressurized is the wrong valve's manual shutter was opened to begin with (it had been that way since launch day). So precious seconds were likely lost as a crewmember tried to close an already closed valve before realizing the problem and moving to the other valve. But by that time it was too late.

moorouge
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From: U.K.
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posted 06-11-2012 02:03 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Jay, you always provide a full and detailed reply and this is much appreciated.

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.

Further, I find it difficult to image that Gene Lunney or George Low would have accepted anything less than a full explanation of the accident. As it was NASA engineers had access to all the Russian data and agreed with the conclusions drawn.

All times are CT (US)

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