ApolloHoax.net
Apollo Discussions => The Reality of Apollo => Topic started by: Luke Pemberton on February 21, 2015, 02:32:41 PM
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I've posted this in this discussion section out of symbolism that the Apollo 1 accident was just that, an accident.
I understand the cause of the Apollo 1 fire and the recommendations that followed, but I have never really understood the hoax argument (other than Grissom et al. were going to whistleblow and needed removing).
The argument as I understand:
- Pure oxygen above atmospheric pressure was used test the CM.
- The use of pure oxygen was exploited in a 'tragic accident' to remove the astronauts.
- At the inquiry various people stated that they did not understand the dangers of pure oxygen.
- The CTs claim that NASA must have known about the dangers as it was obvious what oxygen does when it oxidises a fuel and there had been incidents with the USAF before.
Is this a correct interpretation of the CT argument? The natural connect would be that it was common practice to use pure oxygen and Apollo was a tragic accident.
Why was pure oxygen used, I have never properly understood the reason. I've read some arguments about N2/02 mixes being better from the point of view of decompression, and that N2/02 mixes are easier to scrub. I've also read that pure O2 can be dangerous to the body when used at the pressures in the Apollo 1 CM test. I've tried to digest the information but it's a bit of a minefield with various people pitching in their view point.
Note: Sorry if this has been discussed somewhere else.
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I've read some arguments about N2/02 mixes being better from the point of view of decompression
That sounds backwards to me. Decompression sickness occurs when dissolved nitrogen in the bloodstream comes out of solution and forms bubbles. Breathing pure oxygen would purge the nitrogen from the bloodstream and prevent decompression sickness. Apollo astronauts could easily decompress the cabin and lower the pressure in their spacesuits without worrying about decompression sickness. The Space Shuttle, on the other hand, used a N2/O2 environment, which resulted in the astronauts having to go through a lengthy pre-EVA decompression process, including breathing pure oxygen for about an hour before starting a spacewalk.
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I've read some arguments about N2/02 mixes being better from the point of view of decompression
That sounds backwards to me. Decompression sickness occurs when dissolved nitrogen in the bloodstream comes out of solution and forms bubbles. Breathing pure oxygen would purge the nitrogen from the bloodstream and prevent decompression sickness.
That is what I thought. When wading through the arguments and debates from both sides of the fence I was found I wasn't getting far. Scuba diving sprung to mind in this case.
The Space Shuttle, on the other hand, used a N2/O2 environment, which resulted in the astronauts having to go through a lengthy pre-EVA decompression process, including breathing pure oxygen for about an hour before starting a spacewalk.
That's an interesting snippet of information. A certain CT argues that the physiological dangers of breathing pure oxygen would have been known to NASA, and that filling the CM with a pure oxygen environment would have been harmful. Therefore, the use of pure oxygen in the test was part of the conspiracy to kill the astronauts. ???
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O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.
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O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.
Ps this is what limits compressed air diving to 40meters, after that depth other gas mixes have to be used, at 40 meters the pressure of O2 reaches one bar
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That's an interesting snippet of information.
A normal air mix can't be used in an EVA suit because the required pressure would result in the suit being too stiff. To obtain the necessary mobility, the pressure inside the suit must be kept low. This requires the use of pure oxygen because the partial pressure of oxygen in air wouldn't be enough to breath. The Space Shuttle cabin used a mix of 21% O2 and 79% N2 at one atmosphere pressure. However, starting about 24 hours prior to an EVA, the entire cabin underwent a pressure decrease of about 30% with a slight increase in O2 percentage. Starting about an hour before the EVA, the spacewalking astronauts would have to wear a mask and breath pure oxygen.
Apollo got around the decompression problem by using low-pressure 100% oxygen at all times in both the cabin and spacesuits. The health and fire risks were lessened by the low pressure. Of course, on the launch pad the cabin had to be pressurized to over one atmosphere to provide positive pressure inside the spacecraft. Since Apollo used a single gas system, it was pressurized using pure oxygen (as had been done on both Mercury and Gemini). This was a fire hazard that probably should have been recognized but wasn't, and it sadly resulted in the Apollo 1 tragedy.
After Apollo 1 the procedure was changed. On the launch pad Apollo was pressurized using a mixture of 60% O2 and 40% N2. During ascent the pressure was vented down to 5 psi, and, while in orbit, the atmosphere was eventually replaced with pure oxygen. Although 60% O2 was much higher than normal air, the introduction of N2 greatly reduced the fire hazard. 60% O2 was needed because as the pressure vented down to 5 psi, the partial pressure of oxygen remained high enough (3 psi) for the astronauts to breath normally after removing their helmets.
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After Apollo 1 the procedure was changed. On the launch pad Apollo was pressurized using a mixture of 60% O2 and 40% N2. During ascent the pressure was vented down to 5 psi, and, while in orbit, the atmosphere was eventually replaced with pure oxygen. Although 60% O2 was much higher than normal air, the introduction of N2 greatly reduced the fire hazard. 60% O2 was needed because as the pressure vented down to 5 psi, the partial pressure of oxygen remained high enough (3 psi) for the astronauts to breath normally after removing their helmets.
Thanks Bob. That has helped a lot. Sometimes a question can save a lot of digging to find the pertinent detail. Thanks for taking time to explain.
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Apollo on the launch pad - didn't they use ambient air until liftoff? Since the astronauts were in full spacesuits, hooked up to the lifesupport system inside the capsule, the capsule could be vented to space, plugged up, and then pressurized with oxygen.
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It was part of the test. It wasn't just pure oxygen at one bar, I believe, a terrifying enough idea in retrospect, it was oxygen at pressure enough to simulate the internal stresses on the spacecraft as a pressure vessel equal to what it was in the vacuum of space, I am guessing part of it being a 'plug out test' to see how the spacecraft handled under full internal power.
Here's my problems with the whole 'whistleblower quash' claim.
For one, there are other ways to kill people that aren't nearly so public and damning. Other astronauts died in training as well, but do CT mention people like Clifton C. Williams or Edward G. Givens, Jr? Oh hell no, those people are, typical knowledgwise, non-entities in comparison. Two, as part of being very public, you are going to have a lot people not part of your organization crawling over everything. What if someone finds an invoice for several hundred tons of 'Lunar grey sifted sand'? ;)
I know I am preaching to the choir here, but the whole thing is damn screwy, like CT claims generally are.
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It wasn't just pure oxygen at one bar, I believe, a terrifying enough idea in retrospect, it was oxygen at pressure enough to simulate the internal stresses on the spacecraft as a pressure vessel equal to what it was in the vacuum of space
From what I've read, it was pressurized to 16.7 psi, or 2 psi over atmospheric pressure.
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It wasn't just pure oxygen at one bar, I believe, a terrifying enough idea in retrospect, it was oxygen at pressure enough to simulate the internal stresses on the spacecraft as a pressure vessel equal to what it was in the vacuum of space
From what I've read, it was pressurized to 16.7 psi, or 2 psi over atmospheric pressure.
If that's true, then I was wrong about it being over pressured enough to exactly test the strain, but it was still over pressured with *shudder* pure freaking oxygen. Valentin Bondarenko (http://en.wikipedia.org/wiki/Valentin_Bondarenko) died from burns suffered during a fire in a test chamber. Some have speculated that if the former USSR had being more public about this failure, it might have awoken NASA to the dangers of pure oxygen.
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From what I've read, it was pressurized to 16.7 psi, or 2 psi over atmospheric pressure.
This much I did know. ;D The positive cabin pressure sealed the plug door hatch cover and purged the cabin space of nitrogen containing air.
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Apollo on the launch pad - didn't they use ambient air until liftoff? Since the astronauts were in full spacesuits, hooked up to the lifesupport system inside the capsule, the capsule could be vented to space, plugged up, and then pressurized with oxygen.
After the hatch was sealed, the CM was pressurized using a 60-40 oxygen-nitrogen mixture supply by equipment on the ground. There were no hardware changes made to the spacecraft's single gas system. Only the cabin used the 60-40 mixture, the spacesuit loop remained 100% oxygen. During ascent the gas was vented down to 5 psi, which left a partial pressure of oxygen high enough to be breathable. As the spacecraft experienced normal leakage during flight, the loss was replaced with oxygen. Thus, by the end of the flight the atmosphere was nearly pure oxygen.
(ETA) Of course in cases where an EVA was done, the atmosphere would be completely evacuated and replaced with 100% oxygen.
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After the hatch was sealed, the CM was pressurized using a 60-40 oxygen-nitrogen mixture supply by equipment on the ground. There were no hardware changes made to the spacecraft's single gas system. Only the cabin used the 60-40 mixture, the spacesuit loop remained 100% oxygen. During ascent the gas was vented down to 5 psi, which left a partial pressure of oxygen high enough to be breathable. As the spacecraft experienced normal leakage during flight, the loss was replaced with oxygen. Thus, by the end of the flight the atmosphere was nearly pure oxygen.
So during the Apollo 1 plugs out test, the astronauts were hooked up to the life support system and weren't breathing oxygen at 2 psi over atmosphere?
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So during the Apollo 1 plugs out test, the astronauts were hooked up to the life support system and weren't breathing oxygen at 2 psi over atmosphere?
From what I've been able to gather, it appears they were breathing high-pressure oxygen. Since the suits were flexible, they had to be pressurized to at least the 16.7 psi cabin pressure. And everything I've read leads me to believe the suit circuit was using 100% oxygen.
Here's a basic description of the system:
The spacecraft used an oxygen only system. The oxygen was supplied from tanks in the SM and passed through high-pressure regulators that lowered the pressure to 100 psi. From there the system split, providing oxygen to the suit circuit demand regulator and the cabin pressure regulator. Under normal operating conditions, the cabin pressure regulator maintained the cabin at a nominal pressure of 5 psi.
The suit subsystem provided the crew with continuously conditioned atmosphere. It automatically controlled suit oxygen circulation, pressure and temperature. It removed debris, excess moisture, and carbon dioxide. When a crew member's face mask was closed, the circuit was isolated from the cabin environment. The suit regulator maintained a pressure of at least 3.5 psi pressure whenever the CM was depressurized. During shirtsleeve operation, the suit system remained in operation, even though the crew was out of their suits, to remove carbon dioxide and moisture from the cabin.
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I think Bob's details are completely correct, so there's not much to add on how Apollo actually worked.
I can add some thoughts on their design choices. Apollo's single-gas design has been much criticized, but I still think it was the right choice once the post-Apollo 1 pad safeguards were added.
Most of the Apollo missions involved a lot of EVAs, and all but two carried a LM. It would have been completely impractical to operate the LM with an air-like mixture. It would have to be much heavier to withstand the increased pressure, the life support system would be more complex and heavier, and the astronauts would have to decompress before every EVA as they do on Shuttle and ISS. And as everybody knows, weight constraints on the LM were extreme. Since the LM was docked with the CSM on the trip out, this forced the CM to use a single gas atmosphere as well. (Apollo did eventually mate with a spacecraft using air during ASTP. It carried a complex "docking module" airlock and gas supply system to make the two compatible.)
The only part of the post-Apollo 1 design I might change is the choice of gas mixture on the pad. As Bob explained, they used 60% O2, 40% N2 to maintain a sufficient ppO2 once they reached orbit at a cabin pressure of 5 psia. A 60% O2 atmosphere is a lot safer than 100% O2, but it's still obviously worse than air. So one idea I had is to launch with ordinary air (at +2 psig to keep the cabin pressurized) and instead of bleeding down to 5 psia and holding during ascent, bleed all the way down to a vacuum. The astronauts' pressure suits, which always contain pure O2, are simultaneously bled down to their nominal 3.75 psia and held there. Then the cabin is repressurized with pure O2 and you're done. No need to slowly purge N2 from the cabin over a few days, which undoubtedly wasted a lot of O2.
I mentioned this idea to Owen Garriott a few years ago and he couldn't see anything wrong with it. Then I saw two possible problems. As flown, suit pressure decreased from about 17 psia (+2 psig at sea level) to about 5 psia rather quickly during ascent. All the N2 had already been purged from the astronauts' bodies before launch, so this evidently did not risk decompression illness. My plan would bleed them down from 17 psia to only 3.75 psia, and this greater change would have to be studied to ensure no decompression problems. A second problem would be that the suits would become stiff once the cabin bled below 3.75 psia during ascent, and this might interfere with their ability to operate the controls. This could be avoided by holding the cabin at 5 psia during ascent, delaying the vacuum purge until they were in orbit.
Owen didn't think it was possible to get the bends on pure O2, but I'm not so sure. It is even more soluble in blood than N2, although the fact you can metabolize it means you can get rid of it without having to breathe it back out.
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O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.
O2 at 1 bar is not acutely toxic, as shown by the fact that every Mercury, Gemini and Apollo astronaut breathed it starting hours before launch when they suited up. It may have some subtle effects when breathed for a long period of time, e.g., several weeks.
The pressure is dropped mainly to reduce the stresses on the spacecraft hull (remember how the LM was built). At 5 psia, the ppO2 is still well above that of sea level air on earth.
Pure O2 does become acutely toxic above pressures of 2-3 bar. Convulsions occur, which are usually fatal in a diver. This severely limits the use of pure O2 in diving, although it's useful as a final mix to help flush out N2 at shallow depth during decompression.
"Technical" mixtures for deep sea diving must limit the partial pressures of both N2 (to avoid narcosis) and O2 (to avoid toxicity). This is almost always done by adding helium. I was surprised to find that on especially deep dives hydrogen is also used. It turns out that it's safe to mix with oxygen provided the O2 percentage is kept below about 4%; that keeps it outside the flammability range. These small O2 percentages are used only at great depths.
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Yeah, it made sense, which was why it was done. Plus, Mercury and Gemini also used pure oxygen, for example, so NASA had a rather good precedent for pure oxygen being safe and reliable. In hindsight, we know different, thanks to all the other problems with the Block 1 CSM, but that's hindsight for you.
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As Bob explained, they used 60% O2, 40% N2 to maintain a sufficient ppO2 once they reached orbit at a cabin pressure of 5 psia. A 60% O2 atmosphere is a lot safer than 100% O2, but it's still obviously worse than air.
NASA performed a series of flammability tests and found that the fire hazard in a 16.2-psia 60% O2/40% N2 atmosphere was essentially equivalent to a 6.2-psia 100% O2 atmosphere. Therefore the fire risk was about the same on the pad as in orbit. Also the Block II CM had a redesigned hatch that could be quickly opened to facilitate rapid egress in the case of a fire on the pad. During the boost phase the crew was suited, so it was possible to vent the cabin to extinguish a fire if one were to occur.
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Most of the Apollo missions involved a lot of EVAs, and all but two carried a LM. It would have been completely impractical to operate the LM with an air-like mixture. It would have to be much heavier to withstand the increased pressure, the life support system would be more complex and heavier, and the astronauts would have to decompress before every EVA as they do on Shuttle and ISS. And as everybody knows, weight constraints on the LM were extreme. Since the LM was docked with the CSM on the trip out, this forced the CM to use a single gas atmosphere as well. (Apollo did eventually mate with a spacecraft using air during ASTP. It carried a complex "docking module" airlock and gas supply system to make the two compatible.)
Thanks for the reply. Picking through the breadcrumbs on the internet regarding the Apollo fire, this tallies with my reading and adds a little more to my understanding. It appears that the rational for a single gas system was linked to weight and system integration. Perfect sense to be found and no conspiracy.
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NASA performed a series of flammability tests and found that the fire hazard in a 16.2-psia 60% O2/40% N2 atmosphere was essentially equivalent to a 6.2-psia 100% O2 atmosphere. Therefore the fire risk was about the same on the pad as in orbit.
Still a little higher, since the orbital cabin pressure was 5 psi.
Flammability is a complex subject. It doesn't depend merely on ppO2, as breathability does. The diluent gases actively carry heat away.
Also the Block II CM had a redesigned hatch that could be quickly opened to facilitate rapid egress in the case of a fire on the pad. During the boost phase the crew was suited, so it was possible to vent the cabin to extinguish a fire if one were to occur.
The Apollo 1 review board found that Grissom had tried and failed to vent the cabin, but it would not have made a difference because the cabin pressure rose so quickly that it would still have ruptured. Was the Block II vent redesigned? Or did the combination of lower O2 concentration and reduced fuel loading make it more likely that venting would extinguish a fire?
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Pure oxygen at 1 bar may not be toxic, but it sure is fun! As students we had to breathe it for a few minutes to compare exercise physiology under normal air and pure O2 conditions. There was a lot of giggling.
I've found many HBs who don't get the fact that while it was pure O2, the pressure was so much lower (particularly important for their 'the suit would have been too stiff' line). If I remember my student biology correctly, what matters is the gradient between partial pressures on either side of the alveolar membrane that allows exchange to occur between lungs and bloodstream. The engineering and medical benefits of a low pressure pure oxygen environment seem like a very happy marriage!
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Pure O2 at 1 bar should have been indistinguishable from ordinary air unless you were exercising so vigorously that you would otherwise have been limited by lung capacity. Once your saO2 (arterial oxygen saturation) reaches 100%, extra oxygen is useless.
I recently underwent a stem cell (aka "bone marrow") transplant. One of the side effects is temporary but severe anemia; my red blood cell count fell to nearly half normal. I had expected it to feel like altitude sickness, which I'd experienced, but it was completely different. I was not short of breath but my muscles ached with even minor exertion. Insufficient oxygen reached my muscles to complete aerobic respiration, so lactic acid built up causing the pain. It faded during rest.
My resting heart rate was elevated, just as you'd expect; with fewer red blood cells in the system, my heart had to pump them that much faster around the loop.
Yet my measured saO2 was always normal, in the mid-high 90s, because my lungs were still working normally; what RBCs passed through them were still leaving fully oxygenated. This meant that breathing pure O2 would not have helped, and so it was never offered. Even though I understood this intellectually, I still felt like trying the experiment just to prove it to myself. Funny how your mind works when you're under stress.
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One of the main objections of the CTs is that pure oxygen can cause irritation of the mucous membranes rather than toxicity in the blood stream. I trawled for some information on using compressed O2. This link:
http://www.iecoguam.com/main/gases_oxygen_compressed.pdf
It would appear that this waves away their arguments quite nicely. Not that I understand their line, as others here have explained, a similar approach was followed for Mercury and Gemini. As the pre-cursors to Apollo I would imagine that scientists and engineers had a rational for a single gas system and learned a lot from Gemini and Mercury discussed above. Sadly they learned much more from Apollo 1.
Thank you for the discussion and replies. It has been appreciated.
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I recently underwent a stem cell (aka "bone marrow") transplant.
Hope your procedure went well. I donated stem cells for the Anthony Nolan Trust. Before making the donation I was injected with HGH for 5 days to stimulate the production of stem cells. My sternum felt like it was about to rupture with the pain. It was explained to me that the pain was due to the stem cell production causing my sternum to swell.
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I was my own donor, so I also had the injections prior to harvest. I didn't have that much pain, though occasionally my hip bone felt like it was in a vise. The nurses said that for some reason donors to others tend to experience more pain than those undergoing autologous transplants. I surmise that may be because my bone marrow was already somewhat suppressed by chemotherapy.
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Flammability is a complex subject. It doesn't depend merely on ppO2, as breathability does. The diluent gases actively carry heat away.
Yes, this was the key finding. Even small percentages of diluents have a pronounced effect on fire propagation -- as you say, for heat-transfer reasons more than chemistry reasons.
I recently underwent a stem cell (aka "bone marrow") transplant. One of the side effects is temporary but severe anemia; my red blood cell count fell to nearly half normal.
My father underwent two, and yes I also remember carefully monitoring his hematocrit. I also remember the size of the needle, and I'm pleased you didn't feel much pain.
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Was the Block II vent redesigned? Or did the combination of lower O2 concentration and reduced fuel loading make it more likely that venting would extinguish a fire?
I don't know if there were design changes or not. Of course, in the Apollo I case the fire was much more aggressive then one would be in a 60% O2, 40% N2 atmosphere. Also note that as the rocket ascended, the external pressure decreased and the pressure differential increased. This would have allowed the CM to vent more rapidly and all the way down to the lower ambient pressure.
Here is the report on the CM flammability tests if your are interested:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700015953.pdf
Strangely this report is dated 1970, though the tests were obviously done earlier than that. The following announcement appeared in the March 1968 Aviation Week & Space Technology:
"Washington - Decision to use a two-gas atmosphere (60% oxygen, 40% nitrogen) during manned Apollo on-the-pad preparations and in pre-orbital flight reflects a basic inability to make the spacecraft flameproof after 14 months of redesign that cost more than $100 million and added about 2,000 lb. to the system."
So during the Apollo 1 plugs out test, the astronauts were hooked up to the life support system and weren't breathing oxygen at 2 psi over atmosphere?
The above referenced report confirms that the astronauts were indeed breathing high-pressure 100% oxygen in their suits. On page 2 it reads,
"After careful and extensive evaluation, it was determined that a 60-percent-oxygen/40-percent nitrogen mixture would satisfy both physiological and flammability requirements for the cabin atmosphere during the launch phase. To avoid redesigning the suit-loop system, the suit loop would contain 16.5 psia 100 percent oxygen while on the launch pad, and the pressure would be reduced to 6.2 psia in space after the cabin pressure had dropped and the cabin atmosphere had phased into a 100-percent-oxygen condition."
The report keeps referring to the use of a 6.2-psia atmosphere in space but, from all other sources I've seen, the cabin pressure was actually 5-psia.
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I don't know if there were design changes or not.
I'm not sure either, but in general you want passive flow control on those kinds of devices for safety reasons.
The report keeps referring to the use of a 6.2-psia atmosphere in space but, from all other sources I've seen, the cabin pressure was actually 5-psia.
It's 5 psia +/- a pound or so. The hysteresis was broad.
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"After careful and extensive evaluation, it was determined that a 60-percent-oxygen/40-percent nitrogen mixture would satisfy both physiological and flammability requirements for the cabin atmosphere during the launch phase. To avoid redesigning the suit-loop system, the suit loop would contain 16.5 psia 100 percent oxygen while on the launch pad, and the pressure would be reduced to 6.2 psia in space after the cabin pressure had dropped and the cabin atmosphere had phased into a 100-percent-oxygen condition."
Thanks for this Bob. It really has given me a lot to go on with. (Thanks to everyone else too.)
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It's 5 psia +/- a pound or so. The hysteresis was broad.
In the concluding remarks, the report does say that 6.2 psia is "the maximum pressure that will be used in space flight."
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The following announcement appeared in the March 1968 Aviation Week & Space Technology:
"Washington - Decision to use a two-gas atmosphere (60% oxygen, 40% nitrogen) during manned Apollo on-the-pad preparations and in pre-orbital flight reflects a basic inability to make the spacecraft flameproof after 14 months of redesign that cost more than $100 million and added about 2,000 lb. to the system."
One thing that caught my eye in this quote is the part about adding 2,000 lb. to the system. I know that the Block II CSM incorporated weight reduction improvements that made it considerably lighter than the Block I CSM. Of course, even though the Block II was lighter overall, it still could have ended up 2,000 lb. heavier than would have otherwise been. I'm unaware of any post-Apollo I design changes that would have added that much weight. Does anyone have any details about this?
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One thing that caught my eye in this quote is the part about adding 2,000 lb. to the system. I know that the Block II CSM incorporated weight reduction improvements that made it considerably lighter than the Block I CSM. Of course, even though the Block II was lighter overall, it still could have ended up 2,000 lb. heavier than would have otherwise been. I'm unaware of any post-Apollo I design changes that would have added that much weight. Does anyone have any details about this?
This space.com article:
http://www.space.com/14379-apollo1-fire-space-capsule-safety-improvements.html
It describes that the walls would have been made thicker.
Maybe marginal, but it would be interesting to know how much the whole rewire job would add to the weight. All the wires were coated with a fireproof insulation, and from what I can understand the wiring was so well insulated that it was possibly a contributing factor in saving the Apollo 13 crew from condensation shorting the CM switches. I defer to the experts, but I would imagine that such a wiring refit would add to the weight too. Not 2000 lbs, clearly.
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No, electrical insulation alone would probably not add 900 kg to the vehicle mass. My understanding was that some additional plumbing had to be added to the SM to accommodate the mixed-gas atmosphere prior to launch, but now some of the postings Bob and Ka9q have offered make me question that. I've seen the difference in the hatches firsthand, and the Block II hatch is considerably more massive.
Kapton (Block I) is a wonderful electrical insulator. Compared to Teflon (Block II), it's as much as half the mass density and has better insulating capacity per unit thickness. Switching from Kapton to Teflon requires thicker insulation sheaths, and the material is heavier per unit mass. But you have to do it -- Kapton has horrible performance in a fire. Teflon is self-extinguishing. Kapton is self-sustaining: once ignited it will produce its own fuel. If I could find the specifics on the cable harness lengths I could work out fairly quickly how much heavier the Block II harnesses were.
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Switching from Kapton to Teflon requires thicker insulation sheaths, and the material is heavier per unit mass.
Heavier per unit mass? That doesn't make sense.
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I've seen the difference in the hatches firsthand, and the Block II hatch is considerably more massive.
This link (+253 pounds)
http://www.space1.com/pdf/news1296.pdf
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Switching from Kapton to Teflon requires thicker insulation sheaths, and the material is heavier per unit mass thickness.
Heavier per unit mass? That doesn't make sense.
...per unit thickness (see inline correction). I originally just wrote that it was "denser" but that sounded dorky. Then I decided "unit thickness" was confusing. Then I forgot what I was writing.
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...per unit thickness (see inline correction). I originally just wrote that it was "denser" but that sounded dorky. Then I decided "unit thickness" was confusing.
In context of what you were writing about, unit thickness was least confusing (IMHO).
Then I forgot what I was writing.
Do you ever walk into a room to get something and then forget what you went in for? I do that at work quite a lot. My clients find it hilarious. But then it is like working at a chimps tea party at times ;)
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I <sarc>love</sarc> when I am writing, get distracted, then write the last word I wrote again before continuing the paragraph, leading to a lot of doubled words.
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Do you ever walk into a room to get something and then forget what you went in for? I do that at work quite a lot. My clients find it hilarious. But then it is like working at a chimps tea party at times ;)
My particular vice is to put something down right beside me than not be able to find it two minutes later. I'd like to be able to say it is a symptom of being over fifty, but alas, it is a symptom of my life.
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I <sarc>love</sarc> when I am writing, get distracted, then write the last word I wrote again before continuing the paragraph, leading to a lot of doubled words.
I've hung my work pass around my neck and then 2 minutes later gone on a 20 minute hunt for it - several times may I add. :-[
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I <sarc>love</sarc> when I am writing, get distracted, then write the last word I wrote again before continuing the paragraph, leading to a lot of doubled words.
I've hung my work pass around my neck and then 2 minutes later gone on a 20 minute hunt for it - several times may I add. :-[
I admit, I laughed, but I could so do that.
I once spent a whole day frantically looking for my Core Rulebook for the Pathfinder RPG, not so much because I needed it for itself, I got the core rules mostly memorized, but because it had my character sheet in it. It should be noted I have a huge stack of RPG books (it reaches up to mid chest height, and I am 5'8'') beside my kitchen table because I literally have no other space for them. I looked in the stack, but I didn't find it. Finally, my friends came to pick me up, and I had to leave without it, recreating my character sheet with reasonable accuracy. The fact we were level 3 helped.
Anyway, got home after having a good time, looked a bit more, didn't find it, and went to bed,
The next day, I looked again, and, bless my soul and whiskers, there it was in that bloody stack of books.
My head got into a beautiful relationship with the desk. At the very least, they were very close.
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Do you ever walk into a room to get something and then forget what you went in for?
I've done that plenty of times. Very often if you return to the location where you first had the thought about what it was you wanted to do, the memory will come right back to you. It's just something quirky in the way the brain works.
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The report keeps referring to the use of a 6.2-psia atmosphere in space but, from all other sources I've seen, the cabin pressure was actually 5-psia.
They might be referring to the pressure in the suit, which was slightly greater than cabin pressure. Most of the references give the relative suit pressure in inches of water rather than psig or kPa, and I didn't convert them.
I really wish we'd just go SI...
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They might be referring to the pressure in the suit, which was slightly greater than cabin pressure.
Although the report mentions 6.2 psia in reference to the suit loop, it seems pretty clear that they are also talking about the cabin pressure. For instance, the report states the following:
"A pressure of 6.2 psia was chosen for the spacecraft while in the vacuum of space for several reasons: (1) the spacecraft structure would be lighter because of the small pressure differential; (2) for lower pressures, less oxygen would have to be stored on board the spacecraft; and (3) at a pressure of 6.2 psia, sufficient oxygen would be available to sustain human life with no adverse physiological effects."
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My father underwent two, and yes I also remember carefully monitoring his hematocrit. I also remember the size of the needle, and I'm pleased you didn't feel much pain.
I don't think I had a single needle during the whole procedure because I had a special 3-lumen catheter installed that emptied in the superior vena cava, the heart's "return port". Drawing blood and administering IVs was then a simple matter of connecting to the external ports. When I first had blood drawn through them I suddenly felt like a cow being milked, so after that I referred to them as my "udders".
Catheters are not only easier for the nurses and less painful for the patient, but whatever you put into them is quickly diluted in a large volume of blood. This is good for some of the more toxic chemo agents.
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I've hung my work pass around my neck and then 2 minutes later gone on a 20 minute hunt for it - several times may I add. :-[
Or looking for my glasses when they're already on my head.
I've found that one of the best ways to find something is to stop looking for it. I'm serious; it'll invariably turn up shortly afterwards.
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Or looking for my glasses when they're already on my head.
I once looked for my car keys when they were in my hand. 5 minutes. I've done the glasses one too.
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I once looked for my car keys when they were in my hand. 5 minutes. I've done the glasses one too.
My current car (2011 Nissan Leaf) is my first with keyless entry, and I love it. It also has Bluetooth connectivity. So I just leave both my keys and my phone in my pants pocket and everything just works. Until I change pants and have to go looking for them in the clothes hamper before they get dumped in the washing machine...
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O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.
Actually O2 is considered potentially toxic above 2 atmospheres partial pressures, which is why oxygen rebreathers were not used below 10 m.
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O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.
Ps this is what limits compressed air diving to 40meters, after that depth other gas mixes have to be used, at 40 meters the pressure of O2 reaches one bar
Again no. Compressed air is generally avoided below 40 m because of nitrogen narcosis. One bar partial pressure is not reached until 50 m, and the two bar limit is thus not reached until 100 m.
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I read through those test results, and it was rather striking how many fires still occurred in the 100% O2 6.2 psi and 60% O2 40% N2 16.2 psi cases. Though they were certainly much less severe than the 100% O2 16.2 psi case, it shows that the Apollo CM was never made fireproof, only fire resistant.
I wonder if helium might be a good diluent gas in a spacecraft. Its heat conductivity is significantly higher than air, so it ought to suppress fire better than an equal percentage of nitrogen. Helium speech used to be a real problem in diving, but I believe it's now possible to use special vocoders to correct it.
I saw a documentary on Sealab showing some guys trying to light matches. It was impossible.
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I also wonder why Apollo used such a high cabin pressure. Maintaining the same ppO2 as sea level air requires only about 3 psi of 100% O2.
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I also wonder why Apollo used such a high cabin pressure. Maintaining the same ppO2 as sea level air requires only about 3 psi of 100% O2.
Two reasons: reserve pressure in case of a puncture, and the general precision of pressure regulators for that volume of gas at that pressure. For the latter, putting the pressure at or above 5 psia makes the gas-handling equipment more reliable.
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I wonder if helium might be a good diluent gas in a spacecraft.
That would stuff up the 'film was slowed down' claims ;)
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Thanks, guys. Now all I'm hearing in my head is a Porky Pig voice saying, "The Ea-ga-ba-eag-- The Eag-aga-ba-- The Eagle has landed!"
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"That's one small squeak for a man..."
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Thanks, guys. Now all I'm hearing in my head is a Porky Pig voice saying, "The Ea-ga-ba-eag-- The Eag-aga-ba-- The Eagle has landed!"
More like Donald Duck in my mind.
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I wonder if helium might be a good diluent gas in a spacecraft. Its heat conductivity is significantly higher than air, so it ought to suppress fire better than an equal percentage of nitrogen. Helium speech used to be a real problem in diving, but I believe it's now possible to use special vocoders to correct it.
My guess is that the heat capacity of the gas is much more significant than the conductivity - lowering the flame temperature would be a function of concentration and heat capacity of the mixed smoke/gas. Helium also has storability problems because it is so difficult to keep liquid.
What about SF6? It is inert, its high molecular weight should give it good heat capacity, it is easy to store as a liquid, it is a stellar dielectric thus reducing the likelihood of electrical fires in the first place, and it would give the astronauts a resounding bass register so Jay can imagine James Earl Jones instead of Porky Pig.
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...and it would give the astronauts a resounding bass register so Jay can imagine James Earl Jones instead of Porky Pig.
So now we have Darth Armstrong exclaiming 'micrometeorites do not concern me Aldrin' as he steps down from the LM.
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I went back to check the Apollo 204 Review Board -- spacecraft 012 indeed had Teflon insulation, not Kapton. The change happened before the Block II. But I do think Block II had thicker insulation to combat damage from abrasion.
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I wonder if helium might be a good diluent gas in a spacecraft. Its heat conductivity is significantly higher than air, so it ought to suppress fire better than an equal percentage of nitrogen. Helium speech used to be a real problem in diving, but I believe it's now possible to use special vocoders to correct it.
This link:
http://history.nasa.gov/Apollo204/invest.html
SPACECRAFT ATMOSPHERE
The use of pure oxygen in American spacecraft has been the subject of much consideration. The use of a diluent gas, either nitrogen or helium, in large proportions would undoubtedly reduce the risk of fire to a significant degree. At the same time it would introduce other operational problems and risks. There is no obvious advantage of one diluent over the other, although much progress has been made in developing the complex technology required for controlling gas concentrations to maintain a proper mixture reliably. This technology is still far from being fully developed. Furthermore, there are many difficult operational problems that must be solved in a reliable manner in order to decrease rather than increase the risks before undertaking the use of a two-gas system.
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Well, all the newer NASA spacecraft are using air. We switched to it with the Shuttle. The ISS contains air, which makes working with the Russians a lot easier as they've always used it.
And I'm sure the fire hazard of a high O2 concentration (regardless of pressure) had a lot to do with it.
To see what it takes to mate spacecraft with different atmospheres, look at the docking module flown on ASTP.
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I wonder if helium might be a good diluent gas in a spacecraft. Its heat conductivity is significantly higher than air, so it ought to suppress fire better than an equal percentage of nitrogen. Helium speech used to be a real problem in diving, but I believe it's now possible to use special vocoders to correct it.
I saw a documentary on Sealab showing some guys trying to light matches. It was impossible.
Helium was considered for MOL, I think. the inability to strike matches on Sealab might have been as much due to the low O2 concentration as to heat conductivity.
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My guess is that the heat capacity of the gas is much more significant than the conductivity
I suspect conductivity plays the major role because it is much higher for helium than any other gaseous element than hydrogen.
He has a heat capacity at constant volume of 12.5 J/mol-K (same for all the noble gases, which are near-ideal). Thermal conductivity is 0.1513 W/m-K.
For N2, a diatomic gas, heat capacity at constant volume is higher than He: 19.9 J/mol-K, but its molar mass is considerably higher (28 vs 4). OTOH, the number of moles would be the same regardless of gas for the same temperature, pressure and volume: PV = nRT. But conductivity is 25.83 mW/m-K, considerably less than He.
I know that some divers inflate their suits with argon because it has an even lower thermal conductivity than air. The tanks are hardwired and/or carefully marked so they can't accidentally breathe it; it's even more narcotic than nitrogen. Double-pane windows are often argon-filled.
SF6 would be a poor choice: thermal conductivity is 11.627 mW/m-K, less than half that of nitrogen. Also, it is almost as narcotic as nitrous oxide. (I'm not sure those inhaling it for comic effect know this). And finally, while chemically almost inert, electric arcs can generate disulfur decafluoride, which is so toxic it was considered as a war gas.
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Well, all the newer NASA spacecraft are using air. We switched to it with the Shuttle. The ISS contains air, which makes working with the Russians a lot easier as they've always used it.
Skylab also used an oxygen-nitrogen atmosphere, those it wasn't a normal Earthlike mixture. It was 74% oxygen, 26% nitrogen at 5 psia.
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I had a chemistry professor once explain to me that electron configuration has a bearing on heat conductivity, hence the behavior of the noble gases. But it was at a party so I wasn't really paying attention.
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I suspect it's molecular weight more than anything else, since there's a strong inverse correlation between it and thermal conductivity. It's probably for the same reason that the average molecular speed and the speed of sound are greater in lighter gases at the same temperature.
Per-mole heat capacity on the other hand is the same for all monatomic gases (the noble gases, which are close to ideal). Diatomic gases have more degrees of freedom and can store more energy, so they have higher heat capacity, and more complex gas molecules have more still.
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O2 at one bar (atmospheric pressure) is toxic, therefore in a pure O2 environment the pressure is reduced to 1/5th atmospheric normal. There would be advantages in decompressing and recompressing a craft. Using an air mix does introduce the problems of narcosis, but reduces the problems of fire in a pure O2 system.
O2 at 1 bar is not acutely toxic, as shown by the fact that every Mercury, Gemini and Apollo astronaut breathed it starting hours before launch when they suited up. It may have some subtle effects when breathed for a long period of time, e.g., several weeks.
The pressure is dropped mainly to reduce the stresses on the spacecraft hull (remember how the LM was built). At 5 psia, the ppO2 is still well above that of sea level air on earth.
Pure O2 does become acutely toxic above pressures of 2-3 bar. Convulsions occur, which are usually fatal in a diver. This severely limits the use of pure O2 in diving, although it's useful as a final mix to help flush out N2 at shallow depth during decompression.
"Technical" mixtures for deep sea diving must limit the partial pressures of both N2 (to avoid narcosis) and O2 (to avoid toxicity). This is almost always done by adding helium. I was surprised to find that on especially deep dives hydrogen is also used. It turns out that it's safe to mix with oxygen provided the O2 percentage is kept below about 4%; that keeps it outside the flammability range. These small O2 percentages are used only at great depths.
I've just started re-reading Chaikin's "A Man on the Moon", and I've just read his description of the Apollo 1 fire.
One of the things the book mentions is that, in response to Grissom's grumble that the comms were misbehaving, both Joe Shea and Deke Slayton considered joining the crew in the CM on the day of the fire. But they didn't follow through because of difficulties with including them in the spacecraft comms.
As I read I wondered whether the CM's atmosphere would've been a problem for whoever sat in there. What I'm reading here suggests it wouldn't have been. Is that the case, or would the interloper have had to wear breathing equipment of some sort?
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Until the fire another person would have been fine in the cabin since it was filled with pure oxygen at a few tenths of a bar above ambient. The astronauts themselves were breathing oxygen at a pressure slightly above that in the cabin.
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One of the things the book mentions is that, in response to Grissom's grumble that the comms were misbehaving, both Joe Shea and Deke Slayton considered joining the crew in the CM on the day of the fire. But they didn't follow through because of difficulties with including them in the spacecraft comms.
Oh, if only to beat the Blunder here and show how easy it is to make rubbish up.
<bs conspiracy mode>
Yeah, right. More likely NASA briefed them not to go in the CM because they wanted to bump off the crew. Slayton and Shea were also in on the conspiracy so NASA had to call them off entering the CM.
</bs conspiracy mode>
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One of the things the book mentions is that, in response to Grissom's grumble that the comms were misbehaving, both Joe Shea and Deke Slayton considered joining the crew in the CM on the day of the fire. But they didn't follow through because of difficulties with including them in the spacecraft comms.
Oh, if only to beat the Blunder here and show how easy it is to make rubbish up.
<bs conspiracy mode>
Yeah, right. More likely NASA briefed them not to go in the CM because they wanted to bump off the crew. Slayton and Shea were also in on the conspiracy so NASA had to call them off entering the CM.
</bs conspiracy mode>
Of course, the only way to include them would be to have a separate cable running through the hatch which would have meant the pressure test could not happen and therefore the incident would have never occurred.
Those facts would never enter the 'Worsty Westy' thinking.