Real/Kerbal Physics

[Shna_na]

Hi! I love physics, but am only really a part-time/hobbyist follower of it, so to speak. I'd love to learn more and understand it as well as possible, but that would entail either taking a formal education course on it or trusting internet answers. So I came up with a solution: This.

In this thread, I would like for people to discuss all things physics that relate to Kerbal Space Program (going off on a tangential conversation that is related to anything said here is fine though). For example: The units used, what they are, how they are used, why they are used, etc. Basically, just explain any part of the game/real physics that you want down the the point. I would really love to find out more about the units used in the game, how to read the symbols in physics equations, how to calculate some related things, and all the things. I think this would be beneficial for the community and teach people in general more about physics and how it works, hopefully drawing more people into the matter.

I've struggled with my words a little here, but I hope I've made it clear and easy enough to understand. This is essentially a discussion topic. Please, do ramble.

Thanks

[Streetwind]

KSP uses real physics in most places, but often chooses simplified models that are "good enough" for the application at hand.

For example, gravity interactions in space are usually a n-body problem, which can get very complicated in a hurry. But KSP uses an approach called patched conics in which only one body affects your spacecraft with gravity at any one time. The simplification is possible because there is one body (Kerbol) which overpowers all other bodies by gigantic proportions. Therefore, you know that any object in KSP is always in orbit around Kerbol, no matter where it is and what it does (even when landed on a planet). Because that is always true, you don't have to bother calculating it; you just focus on the thing that applies the most changes to your Kerbol orbit - in other words, the closest celestial object. The result is accurate to within a couple of percent, which is not always accurate enough IRL but is all but indistinguishable from the real thing for gameplay purposes. We don't have Lagrange points, but that's about it.

Units for ingame numbers are a thing that I missed as well when I started, because I didn't know how to interpretate the numbers in the part stats. But you can very quickly figure it out empirically. KSP uses the metric system, and the units for common numbers are: weight in tons, thrust in kilonewtons, specific impulse in seconds, distance in meters, speed in meters per second, acceleration (including gravity) in meters per second squared.

Other numbers are completely arbitrary, such as electric charge or the number of fuel units in a tank.