>>14106964>>14106957In KSP, take the Centaur III upperstage and increase the number of engines from 2 to 4. Put Orion on top of it, get it to the Karman line like Below Orbit does, and then try to land back on Kerbin propulsively using the 4-engine Centaur III upperstage with landing legs while carrying big bertha Orion. You'll find quickly, that even with 4 engines, the kN output relative to the fuel/mass ratio of the entire vehicle is so utterly shit, you'll pancake into the ground rather than actually land.
The Delta IV heavy has 3 RS-68s, each of them have a 3,137kN. So to get 31 tons (D4HV) to LEO, you need 9,375kN of thrust. Orion BY ITSELF weighs 22.7 metric tons. 73% of the D4HV payload to LEO capability is taken up by Orion. Doing linear approximation you need 6,864kN of thrust to get Orion to orbit OR to land Orion from orbit propulsively back onto Kerbin. But if you're landing, you want like 5% margin on fuel in case something goes wrong, so the actual kN value is greater closer to 7,332kN (I know fuel/mass/exhaust velocity doesn't work like this, but we're doing this relative to KSP, so deal with it).
The 2-engine Centaur III upperstage is powered by a pair of
https://en.wikipedia.org/wiki/RL10 engines. Each of them have a thrust profile of 110kN. You put four of them together on the same tank, and assuming plumbing and flow works for magically, you'd get a combined thrust profile of 440kN. You need 16x MORE thrust to handle Orion in a gravity well during landing on Earth. Kerbin is like ~40% the size of Earth and Mun is 1/2 that. Assuming napkin approximations (and at this point this math is super sketch, but for the purpose of this example, its probably good enough), 40% of Earth @ 7332kN = 2,932.9kN. Mun is half that, so 1,466kN.
Kerbin landing thrust requirement with Orion = 2,932.9kN approximate
Mun landing requirement with Orion = 1,466kN approximate
4-engine Centaur III stage w/ landing legs w/ Orion = 440kN actual. Fucking lol dude.
