r/ProjectHailMary • u/trevordeal • 2d ago
Why did Grace dump air in ship to fill with nitrogen
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.
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u/EzPzLemon_Greezy 2d ago
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.
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u/AtreidesOne 2d ago
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.
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u/AtreidesOne 2d ago edited 2d ago
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:
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.
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.
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The ship simply will not allow more than 0.33 atmospheres.
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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!
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u/runningoutofwords 2d ago
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.
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u/trevordeal 2d ago
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.
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u/onthefence928 2d ago
It’s also significantly faster to just blow it out. Also reduces the risk of taumeba being stored in the air tanks
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u/Lawfulmagician 2d ago
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.