Video: Fifty years ago today was the first Apollo mission to carry a crew to space

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Less than a year from first crewed mission to landing on the moon!


Saturn 1b! I’ve got one of those!
I took that picture 4 years ago. I have yet to paint on the black trim and apply the decals. But hey, I bought the kit in 1974, and only got around to turning the rubble into a flyable rocket after 29 years or so.


Jeebus, they used pure oxygen in Apollo 1? I’m no rocket scientist, but that seems to me to be an obviously horrible idea.

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They used pure oxygen on all space capsules until the space shuttle.

No. That’s completely false.


It’s amazing and profoundly sad what this nation had the capability to do when we had the political will. Nowadays we can’t even approve funding to keep rush hour traffic bridges from collapsing. People born in the 80’s and onward will never know the United States I knew when I was growing up. We truly were a shining light on the hill to the rest of the world and I fear the world will never again see a nation that had the ideals this nation had at that time. I’ll be long dead, but at least I have those memories the young folk will never have. That’s depressing to me.


I envy your political will. :yum:

For some reason I’m picturing you running around the room making rocket sounds. Fireball XL-5!


At the time it seemed like a really good engineering solution to some issues they were having. Then, suddenly, in retrospect, it was a horrible idea.

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Bah, I let actual motors make the WOOSH! sound!


Looking back at it today, the Mercury/Gemini/Apollo program was almost recklessly ambitious, but damn if it wasn’t also incredibly impressive. Basically every single mission was pushing a new brand boundary of space flight. It’s really a testament to the skill and competence of everyone from the welders to the (human!) computers to the pilots that everything went off with as few hitches as it did.


Yes, the same as In every Mercury, Gemini, and Apollo mission. The extra tanks and pipes to create a mixed oxygen-nitrogen atmosphere weighed too much, so NASA went with 5psi pure O2. At 5psi, the fire risk of pure oxygen isn’t much greater than the fire risk in ordinary Earth atmosphere at 15psi.

The Apollo 1 crew died because they were testing the capsule on the ground at 15 psi of pure oxygen - a very stupid decision, since at 15psi, pure oxygen does present a huge fire risk.

@MarcVader, sorry but you are incorrect. The Space Shuttle did have normal oxy-nitrogen mix, but all space capsules prior to it used pure O2.


hell, we can’t even agree that it’s a bad idea for law enforcement officers to kill unarmed black people.

edited to add–on camera, live on social media.

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The Soviets switched to standard atmosphere quite early on. They too had a deadly accident with a pure oxygen capsule atmosphere a few weeks before Gagarin’s flight. After that Soyuz and Mir used a nitrogen/oxygen mixture. I stand corrected however in that NASA continued to use Oxygen throughout the Apollo program. I was under the impression that they changed that after the Apollo 1 pad fire. The Skylab capsule air apparently was 75% oxygen, 25% nitrogen.

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Correction, the US used pure oxygen on all space capsules until the space shuttle.

One of the main reasons to use pure oxygen is space suits. It is quite difficult to to design a space suit that is flexible when it is inflated. That task is made much easier by inflating them to a much lower pressure. To ensure that the astronaut gets enough oxygen at a lower pressure, they are filled with pure oxygen. Just as the oxygen masks on aircraft for high altitude use use pure oxygen. But if you do your space walks at a lower pressure than the spacecraft you run the risk of getting the bends, the same as divers who come up to quickly from depths. So on the ISS, astronauts have to pre-breath pure oxygen for hours before a spacewalk. Which works, but is operationally complicated. That is also why the Apollo Astronauts were already in their space suits, carrying an oxygen supply as they walked to the spaceship. They had purged their bloodstream of nitrogen to avoid the bends. The real danger with using regular air at atmospheric pressure though is that if there is a catastrophic loss of cabin pressure, the astronauts have not purged the nitrogen from their bloodstream beforehand so there is a real danger that they would get the bends when they rapidly switched to pure oxygen at the lower pressure used in spacesuits. This isn’t as much of a hazard for aircraft which rapidly descend to lower altitude in the event of a loss of cabin pressure. But if you’re half-way to the Moon, you’re stuck. The risk is more acceptable in the ISS where any section with a catastrophic hole can be isolated by sealing it off from the rest of the station.

So pure oxygen at low pressure makes a lot of sense, even the spacecraft itself can be built a bit lighter since it is inflated to a lower pressure. But pure oxygen at 15psi was a really bad idea.


NASA did make a change as a result of the Apollo 1 fire which was to pressurize the capsule with an oxygen/nitrogen mix while it was on the pad and pressure in the capsule was high at over 15 psi. After launch, during ascent, this mixture would be bled away and replaced with pure oxygen at a low pressure of about 5 psi.

@simonize, Michael Collins later related feeling extreme pain in one of his knees early in his Gemini 10 mission, presumably due to nitrogen bubbles, a fact he concealed from ground control for fear they would cut the mission short.

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Nothing “obviously horrible” about pure oxygen.

Operationally, Apollo’s pure-oxygen atmosphere would run around 5 psi, which gives you an 02 partial pressure similar to Earth’s atmosphere, with 21% 02 at 14.7 psi.

Partial pressure of 02 is what alters flammability.

The Apollo 1 pad accident happened during a plugs-out pressure leakdown test. What matters when checking for seal leaks is differential pressure (the difference in pressure between inner and outer seal surfaces).

To simulate the operational pressure differential (5 psi vs. vacuum) without a huge vacuum chamber, they pressurized the cabin to higher than sea-level ambient.

With pure oxygen.

Now, THAT is a bad idea.

And doing that with a crew inside is a genuinely terrible idea.

But a low-pressure pure-O2 environment is a perfectly reasonable thing for a spacecraft. It’s not any sort of obvious, outrageous fire hazard.

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Build with german know-how.
You´re welcome USA.

Ah, partial pressure, didn’t think of that but it makes sense. Thanks!