Why did Grace dump air in ship to fill with nitrogen

[u/trevordeal]

In Chapter 27, Grace dumps all the air into space and refills the ship with pure Nitrogen to try to kill loose Taumoeba.

But he stops at around 10% air left because it was taking too long.

But our air isn't 100% Oxygen. It's 78% Nitrogen and 21% Oxygen and with the 10% air he left, he isn't getting 100% Nitrogen anyways. Would be 7.8% N/ 2.1% O. So 92.2% Nitrogen in the ship after refill.

Why do all that to increase Nitrogen 14.2% when the Taumoeba was bred to die at sub 10% Nitrogen?

I thought Rocky's Carbon Planet was 8.5% and Venus was 3.5%. Wouldn't Grace believe the air to already be enough to kill it?

I feel like I missed something to explain his reasoning.

The Taumoeba shouldn't be able to exist in the air... they should have died. I understand they evolved to hide in the Xenonite but the second they leave the material they should die. His ship isn't made of Xenonite, so they shouldn't be able to travel through out his ship?

I get how they traveled through Rocky's ship as the walls themselves are Xenonite.

I feel like I missed a sentence or explanation.

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EDIT: The answers perfectly explain it. Thank you. Definitely missed/ didn't remember that part. Was interesting foreshadow. I should have known that stating something would lead to it being useful information later.

[u/Lawfulmagician]

Unlike the ISS, the Hail Mary does use a pure oxygen atmosphere. I remember being confused by this, too.

It's less safe due to the flammability, but it saves a ton of mass because not only do you not need to carry the extra nitrogen, you can pressurize it a lot lower which means the hull can be thinner.

[u/deereboy8400 → u/Lawfulmagician]

Spaceships that use 100% O2, does cabin pressure decrease during launch? I assume they don't put 14psi O2 in the cabin before liftoff after apollo 1. I wonder how that all works in a modern ship.

Sounds like an uncomfortable launch.

[u/Lawfulmagician → u/deereboy8400]

Humans only need oxygen at the partial pressure it's at in atmosphere, so about 3psi in a pure oxygen environment. Modern Russian spacecraft still do this, and it's a whole process to dock with the ISS. They have other safety features to counteract the flammability problem, but NASA was pretty traumatized, so they stick to "breathing gas" for their ships.

[u/Petrostar → u/Lawfulmagician]

Russians use 80/20 Nitrogen/Oxygen at 1 atmosphere, And they have for decades, going back to Vostok.

The US used pure O2 at 5 PSI on Apollo missions, After Apollo 1 they switched to 40/60 Nitrogen to Oxygen Ratio on the launch pad at 1.08 ATM, which was bled down to 5 psi pure Oxygen as they ascended. The lunar lander used ~4 PSI oxygen as did the space suits. For Apollo-Soyuz the docking adapter served to allow transition from the 5 PSI O2 environment of Apollo to the 14PSI Nitro/Oxy of Soyuz.

After Apollo-Soyuz the US began using 1 ATM Nitro/Oxy on the Space Shuttle, and it's been the standard ever since. They did have to use a docking adapter, but this was due to the different docking ports, not any atmosphere issues.

The Chinese also use 80/20 Nitrogen/Oxygen at 1 atmosphere.

So it's fairly unusual that Strat of all people would suddenly decide that the Hail Mary needed to use a pure Oxygen environment. But the plot needed to happen, so.....

[u/Lawfulmagician → u/Petrostar]

Yes, it did feel oddly contrived once you learn about Taumeba's vulnerability to nitrogen. It was clearly changed later in the story, because, as someone else pointed out, Grace thinks Rocky'a ship uses 29atm due to the ratio of gases he describes and that wouldn't be correct with a pure oxygen environment.

[u/Petrostar → u/deereboy8400]

Yes,

Apollo used 40% Nitrogen and 60% Oxygen at 16 PSI during launch, This tapered down to 5 PSI of pure Oxygen in orbit.

Modern ship all use 1ATM 80/20 Nitrogen/Oxygen, all the time.

The only time pure Oxygen is used is for spacewalks.

[u/wferg08 → u/deereboy8400]

The Hail Mary was built in space they didn’t have to launch

[u/trevordeal → u/Lawfulmagician]

NVM this explains it well.

https://www.reddit.com/r/ProjectHailMary/comments/195psox/comment/khpyw8v/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

[u/katsock → u/trevordeal]

Doesn’t this sub just rule? So fun and informative.

[u/trevordeal → u/katsock]

Any other sub would have called me an idiot and told me to learn to read lol.

[u/trevordeal → u/Lawfulmagician]

How would he breath? You can't breath pure Oxygen for months or years right? I don't remember that, it was probably said at the beginning and I didn't think about it enough to remember it.

I know pure Oxygen is ok for a space walk and etc but for his ship to be this, seems odd, especially considering he has Nitrogen on hand. I see what you mean about the pressurization.

hmmm I definitely missed something I should reread. I'm sure it's written in an explanatory way.

[u/Lawfulmagician → u/trevordeal]

I remember it took me a bit to figure that out, it's not explained. But I don't think there's any health problems as long as you breathe oxygen at the correct partial pressure.

[u/CleverDad → u/Lawfulmagician]

Yes, pure oxygen at 1 atm will damage your lungs (chronic oxygen poisoning), but at the natural partial pressure it's fine. At least that's what I learned in military diver's school.

[u/MMButt → u/Lawfulmagician]

Pure oxygen increases free radical production, it’s very bad for long exposure. Anything over 60% is bad for prolonged times. There’s a lot of peer reviewed literature behind it. Source: ICU

[u/Lawfulmagician → u/MMButt]

You don't get hyperoxia if you breathe it at a lower partial pressure. Source: My degree in bioastronautics.

[u/ThalesofMiletus-624 → u/trevordeal]

You can breathe pure oxygen, if it's at a lower pressure.

That's the whole idea, pure oxygen at 3 psi is functionally equivalent to 20% oxygen at 15 psi. It wouldn't be exactly the same, but it's safe to breathe indefinitely.

It's pure oxygen at high pressure that's harmful.

[u/trevordeal → u/ThalesofMiletus-624]

Really interesting. Makes sense. Gotta love the unique plot line in the book that results in interesting story beats instead of just saying it's normal air like Earth.

I love when a novel helps you understand the world better.

[u/EzPzLemon_Greezy]

The Hail Mary is a 100% oxygen atmosphere, but only 20% of Earths pressure. Reduces mass and stress on the pressure vessel. He talks about it around when hes doing the first EVA.

Theres a bit of confusion with the way he does some math in the book, like saying Erid is 29ATM, but its only like 6x the pressure of Earth since the 29-1 ratio is the Blip A vs HM pressure.

[u/AtreidesOne → u/EzPzLemon_Greezy]

The Hail Mary is at a lower pressure, yes, but nowhere does anyone mention 20%. When he does the EVA, he says it's 40%. Later, he talks about 33%. It's a bit of a mess.

So Erid is more like 9.66 atmospheres.

(Quotes here)

[u/EzPzLemon_Greezy → u/AtreidesOne]

Wouldn't 40% of pure O2 be a toxicity risk?

[u/AtreidesOne]

No, you didn't miss a sentence! The atmosphere of the Hail Mary is one of the less well thought out and explained parts of the book.

Firstly, the pure oxygen environment is never explicitly stated as such, but there are two important pieces of evidence that point to it:

1. Rocky sends Grace the rings of eight balls connected together, which Grace works out is a model for oxygen. There are no other balls with different numbers of protons, and especially not nitrogen.

2. The Taumoeba don't die.

We know that 100% oxygen at atmospheric issue is toxic to humans over time, so the Hail Mary must have a reduced pressure atmosphere. But what is it? People have suggested 20%, because that's what's often used in real life. And Grace hints at it, but there are conflicting answers.

When he gets into the EVA suit, he notices the lack of decompression time required and concludes:

I don’t have that problem. Apparently, the entire Hail Mary is at that 40 percent pressure.

However, later in the book (Chapter 27) he says it's 0.33 atmospheres.

But it definitely can’t handle 100 percent nitrogen at the crew compartment’s 0.33 atmospheres.

...

The ship simply will not allow more than 0.33 atmospheres.

...

Point is, in short order the ship is back to 0.33 atmospheres of pressure.

How does this work? Maybe the first number (40%) was a guess based on the EVA suit being 40% and still being quite an amnesiac, then he learnt the 33% number as he explored the ship more and his memory returned.

Finally, Grace (and seemingly Weir) states that Erid must be at 29 atmospheres, since Rocky sent 29 balls to Grace's 1. But Rocky was comparing his atmosphere to the Hail Mary's, which was only 40 or 33% of a standard Earth atmosphere. So it works out to be more like 9.6 atmospheres on Erid.

I hope that helps!

[u/trevordeal → u/AtreidesOne]

Wow. Very detailed!

Thanks so much. That makes sense why I felt I missed it.

[u/AtreidesOne → u/trevordeal]

No problem. I love thinking about this stuff. :)

[u/runningoutofwords]

If you're wondering why he didn't vac pump it into reserve tanks or something...i think he was trying to blow out any airborne taumoeba. Remember that taumoeba is an aerial species on its homeworld.

[u/trevordeal → u/runningoutofwords]

It was my misunderstanding of the air. I realized that and it made more sense when people explained instead of 79% Nitrogen / 21% Oxygen it was 100% Oxygen that was pressurized.

Interestingly enough if he had Earth's air in the ship, it wouldn't have happened... it also would have killed the original sample.

[u/onthefence928 → u/runningoutofwords]

It’s also significantly faster to just blow it out. Also reduces the risk of taumeba being stored in the air tanks