Strategos' Risk
Pubber
- Joined
- Jan 25, 2023
- Messages
- 21
- Reaction score
- 10
Any chance that this Let's Read might continue? It's always great to see more reviews of SMAC materials.
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Thank you. I wish GURPS books actually had such explanations!I did the calculations. The book just says the air is unbreathable a few hundred feet up but doesn't really go into details. I had to work out the acclimatisation time, and the specifics of the partial pressures of nitrogen and oxygen in order to see how bad the level of nitrogen narcosis and oxygen deprivation was. It was from prior knowledge, it's not in a GURPS book.
If anybody ever wants to do this for a fictional planet you'll need (if you've no interest in maths, see the 2nd paragraph of point 4 for something that might still be interesting):
- The Barometric equation, to get the pressure at various altitudes. Adjusting it to other planets means changing the gravitational acceleration, the pressure at sea level and the average molar mass of the air. The latter is worked out from the relative mixtures of gases in the atmosphere and requires a bit of chemical knowledge.
- The partial pressure equations to get the partial pressure of each gas. This only takes the absolute pressure (from above) and the relative concentration of that gas
- Aveolar gas equation. This is required only if you want absolute accuracy and models the difference between the partial pressure out in the air versus that in the lungs. For most planets only going to stage 2 should be enough. For Alpha Centauri's planet it isn't because of the presence (1% of atmosphere) of toxic gases and because going to the second stage didn't give a completely clear answer to nitrogen narcosis because it was borderline.
- If you want to be very very accurate (this wasn't necessary for Planet) note that the pressure on most planets usually has "layers" where it suddenly drops rapidly. So for instance on Earth you can't use the pressure at ground level to work out the pressure at 12km up because of a sudden pressure drop at 11km (8.5 km on Planet). Instead you have to use the pressure at 11km as the "new" ground level for the barometric equation.
This doesn't matter on Earth or Planet since nobody would live far up enough for it to be relevant. It might matter on a world with very high pressure as it could mean the pressure is low enough up near the summits of massive mountains to be livable. So you'd have the Valleys between mountains where the pressure is lethal, with cities encircling the summits.
The pressure drop off points on Earth are 11km, 20km and 32km. On Planet 8.5km, 15km and 25km. This changes how airflight works on Planet. Which I'll get to later.