5 ms·

I'm curious why did you think it was impossible?

Cthulhu_ 6y ago
KSP takes some liberties with physics, simplifying things so that e.g. the N-body does not apply (that is, your craft are only affected by one body at once). Other challenges are the scale and number precision. It doesn't get it exactly right either, especially when you use the time accelleration, things can go a bit... weird. See https://wiki.kerbalspaceprogram.com/wiki/Deep_Space_Kraken https://wiki.kerbalspaceprogram.com/wiki/Deep_Space_Kraken
- NikolaeVarius 6y ago
  We don't really know the scope of the original pitch, so hard to make a determination of feasibility. But yes, a fully modeled spacecraft simulator would have been effectively impossible.
  - TeMPOraL 6y ago
    Goes to show that you don't need a fully modeled simulator, you need modeled enough, and then to iterate on it. (And let the community do some of the hard work for you. With appropriate mods, KSP can have a very realistic aerodynamics model (that handles supersonic speeds as well), and - as others mentioned - n-body physics simulation.)
- mrfredward 6y ago
  There may not be an analytic solution, but solving the n-body problem numerically with newtonian physics isn't a difficult thing to do...it's simple enough that it has been used as a benchmark for doing computations: https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/nbody.html https://benchmarksgame-team.pages.debian.net/benchmarksgame/...
  - ben-schaaf 6y ago
    I'm sure they know this. The problem is that n-body simulations don't scale well with simulation speed. In KSP you can speed up time by up to 100,000x, which is essential for gameplay. If you want the same accuracy for n-body at that speed, you'll also need to do 100,000x the calculations. Whereas with KSPs simplified model you can calculate the position in orbit at arbitrary points in time, making 100,000x just as computationally expensive as 10x.
    - bkanber 6y ago
      I don't know which integrators they're using but an algorithm like RKF45 should handle time acceleration with adaptive step sizes no problem. As grandparent said, n-body is very well-known. Regardless, KSP's workaround of using SOIs is simple and quite effective.
    - mrfredward 6y ago
      The top entry in my link above simulates 50 million years in 6 seconds for an n=6 system. That's 11,000,000,000,000X running on a normal PC.
    - e_y_ 6y ago
      From a gameplay perspective, there isn't much sense in a full N-body simulation. Players only care about their spacecraft, which is a restricted three-body problem (small spacecraft, massive gravitational bodies) outside of special cases like gravity tractors. And the simplified two-body SOI worked pretty well in practice. In any case, the bigger gameplay problem tends to be the vehicle physics simulation, where you have hundreds+ parts interacting and not in the most stable fashion especially above 2x time warp. That's the part that seemed amazing when KSP first came out, moreso than the orbital simulation (although the solar system exploration clinched the overall experience).
      - philwelch 6y ago
        From a gameplay perspective, I would love to put some propellant depots at Lagrangian points.
- garaetjjte 6y ago
  KSP community implemented n-body physics: https://github.com/mockingbirdnest/Principia https://github.com/mockingbirdnest/Principia
  - sq_ 6y ago
    > Principia is released on every new moon with whatever features and bug fixes are ready at the time. This ensures relatively timely improvements and bug fixes. This may be the funniest/best way to say "we have a roughly monthly release cadence" that I've ever seen.
  - afterburner 6y ago
    Any idea how well it works? Are there trade offs, or is it all upside, physics-fidelity-wise?
    - cydonian_monk 6y ago
      It worked really well when I used it. It replaces a bunch of the stock navigation tools, and takes a bit of learning, but really seemed to be a good n-body simulation engine. It's been well over a year since I touched KSP though, so I can't speak for the current versions of either Principia or the base game.
speeder 6y ago
The aerodynamics, he was then a flight simulator modder, and said his dream was to make a game where you could use parts to build an arbitrarily shaped airplane and it would calculate automatically the aerodynamics, because the manual setup of aerodynamics for flight simulator was really bad and annoying. Granted wasn't him that implemented airplane aerodynamics on KSP (it was a modder of KSP, his mod being considered "mandatory" with how much it changed the game physics)
- shadowgovt 6y ago
  You had the right instinct---what he's describing is done by X-Plane, but X-Plane started as an aerodynamics sim tool that became a flight simulator, so they had to swallow the hard-part elephant before getting to the game part of it. (On the other hand, someone should note that maybe both our instincts are flawed, because you could also see the X-Plane story and say "Why can't he do it? It's been done before!" ;) )

KSP takes some liberties with physics, simplifying things so that e.g. the N-body does not apply (that is, your craft are only affected by one body at once). Other challenges are the scale and number precision. It doesn't get it exactly right either, especially when you use the time accelleration, things can go a bit... weird. See https://wiki.kerbalspaceprogram.com/wiki/Deep_Space_Kraken https://wiki.kerbalspaceprogram.com/wiki/Deep_Space_Kraken

NikolaeVarius 6y ago
We don't really know the scope of the original pitch, so hard to make a determination of feasibility. But yes, a fully modeled spacecraft simulator would have been effectively impossible.
- TeMPOraL 6y ago
  Goes to show that you don't need a fully modeled simulator, you need modeled enough, and then to iterate on it. (And let the community do some of the hard work for you. With appropriate mods, KSP can have a very realistic aerodynamics model (that handles supersonic speeds as well), and - as others mentioned - n-body physics simulation.)
mrfredward 6y ago
There may not be an analytic solution, but solving the n-body problem numerically with newtonian physics isn't a difficult thing to do...it's simple enough that it has been used as a benchmark for doing computations: https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/nbody.html https://benchmarksgame-team.pages.debian.net/benchmarksgame/...
- ben-schaaf 6y ago
  I'm sure they know this. The problem is that n-body simulations don't scale well with simulation speed. In KSP you can speed up time by up to 100,000x, which is essential for gameplay. If you want the same accuracy for n-body at that speed, you'll also need to do 100,000x the calculations. Whereas with KSPs simplified model you can calculate the position in orbit at arbitrary points in time, making 100,000x just as computationally expensive as 10x.
  - bkanber 6y ago
    I don't know which integrators they're using but an algorithm like RKF45 should handle time acceleration with adaptive step sizes no problem. As grandparent said, n-body is very well-known. Regardless, KSP's workaround of using SOIs is simple and quite effective.
  - mrfredward 6y ago
    The top entry in my link above simulates 50 million years in 6 seconds for an n=6 system. That's 11,000,000,000,000X running on a normal PC.
  - e_y_ 6y ago
    From a gameplay perspective, there isn't much sense in a full N-body simulation. Players only care about their spacecraft, which is a restricted three-body problem (small spacecraft, massive gravitational bodies) outside of special cases like gravity tractors. And the simplified two-body SOI worked pretty well in practice. In any case, the bigger gameplay problem tends to be the vehicle physics simulation, where you have hundreds+ parts interacting and not in the most stable fashion especially above 2x time warp. That's the part that seemed amazing when KSP first came out, moreso than the orbital simulation (although the solar system exploration clinched the overall experience).
    - philwelch 6y ago
      From a gameplay perspective, I would love to put some propellant depots at Lagrangian points.
garaetjjte 6y ago
KSP community implemented n-body physics: https://github.com/mockingbirdnest/Principia https://github.com/mockingbirdnest/Principia
- sq_ 6y ago
  > Principia is released on every new moon with whatever features and bug fixes are ready at the time. This ensures relatively timely improvements and bug fixes. This may be the funniest/best way to say "we have a roughly monthly release cadence" that I've ever seen.
- afterburner 6y ago
  Any idea how well it works? Are there trade offs, or is it all upside, physics-fidelity-wise?
  - cydonian_monk 6y ago
    It worked really well when I used it. It replaces a bunch of the stock navigation tools, and takes a bit of learning, but really seemed to be a good n-body simulation engine. It's been well over a year since I touched KSP though, so I can't speak for the current versions of either Principia or the base game.

speeder 6y ago

The aerodynamics, he was then a flight simulator modder, and said his dream was to make a game where you could use parts to build an arbitrarily shaped airplane and it would calculate automatically the aerodynamics, because the manual setup of aerodynamics for flight simulator was really bad and annoying. Granted wasn't him that implemented airplane aerodynamics on KSP (it was a modder of KSP, his mod being considered "mandatory" with how much it changed the game physics)

shadowgovt 6y ago
You had the right instinct---what he's describing is done by X-Plane, but X-Plane started as an aerodynamics sim tool that became a flight simulator, so they had to swallow the hard-part elephant before getting to the game part of it. (On the other hand, someone should note that maybe both our instincts are flawed, because you could also see the X-Plane story and say "Why can't he do it? It's been done before!" ;) )