It occurs to me that, for the Ice Gun, I could use this little trick I know called "maths". Namely: how long can the barrel go?
Earth is an ellipsoid whose radius at the poles is 6356 km. The initial proposal for the gunbarrel there was 1000 km; straight at first but pointing diagonal-upward at the end. The first half is the straight half, so about the middle would be the deepest point.
These people could not literally mean that it's straight, much less concave against the Earth. Its least distance from the core is Pythagorean: square root of (63562 - 250000). That's 6336 km: in depth from the top a nice even twenty kilometers. Nowhere in Antarctica is the ice-sheet 20 km thick. It's a continent, so we are probably not hitting asthenosphere; but we are deeper into bedrock than the Mponeng. By a factor of five.
I concede: a straight line has some advantage in starting acceleration, inasmuch as it's using the Earth's pull to help out. We want something more like root [63562 - 63552] especially if we are worried about the sheet melting to less than a kilometer. 112.74 km straight to the middle of the barrel and deepest under ice, which (for simplicity) we double for the total: 225 km.
The authors of that page perhaps should have started with that. Better: they should have ended with that; nobody wants 10 G, given that classical G-LOC starts 5.4 G.
For the 1000 km option I must assume that by "straight" they mean in the Mercator sense. This barrel will be skating the circumference, fighting gravity all the way. Anyway it's never going to happen, so whatever.
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