Are KSP's physics, at this stage, a good approximation of this universe's physics?

[rodion_herrera]

I was wondering if you think (or maybe one of the devs can answer this question) KSP's physics (Newtonian/Galilean?), at this stage (v0.20.1), a good approximation of this universe's physics? By this universe, I refer to this same one we human beings inhabit? The reason I ask is, like some forum members here who are either members of the academe, or somehow teach physics or related subjects in schools, I am interested in using KSP as a "visual guide" or "visual basic introduction" to space exploration or sciences related to it, to introduced to kids in the elementary and high school level.

So is it safe to assume that yes, the current physics or "laws of nature" in KSP, behave more or less like the physics we know, only that the Kerbol system (and the Kerbals themselves) is somewhat "scaled-down" in terms of physical size? Or, are there deliberate "tweaks" in the KSP physics we know, that the devs introduced, as to make activities within KSP more "interesting" or "fun"? Because if the latter is true, then I would have apprehensions on my plan on using it to demonstrate some basic principles in spaceflight.

Any thoughts you can share are welcome, and thanks.

EDIT: so the units of mass (kg) and dimensions (meters) in KSP, equivalent to how we use them in this real universe?

[OUScooby]

As I understand it the scale of the planets is reduced for the purpose of gameplay, but to compensate for this and produce a closer real world analog, the density of the planets is increased. For instance, the diameter of Kerbin is smaller than Earth, but by making it denser its gravitational force and thus the amount force needed to launch from it and get orbit (or escape orbit) is similar to that of the real Earth. Someone correct me if I'm wrong here.

[Specula]

It's a 'somewhat decent' analog. Right now, the biggest difference is that your rocket can only be in the gravitational influence of one thing at a time. IE, if you're in Kerbin Orbit, you're only affected by the gravity of Kerbin, not Mun, Minmus, Kerbol, etc.

[lobsterbark]

As I understand it the scale of the planets is reduced for the purpose of gameplay, but to compensate for this and produce a closer real world analog, the density of the planets is increased. For instance, the diameter of Kerbin is smaller than Earth, but by making it denser its gravitational force and thus the amount force needed to launch from it and get orbit (or escape orbit) is similar to that of the real Earth. Someone correct me if I'm wrong here.

Actually, it take about the same amount of force to get into orbit from Eve as it does to get into Earth orbit. The rockets are scaled down as well, to prevent the game from being too easy.

[Good_Apollo]

No Lagrange Points, no simulation of multiple gravitational forces between two or more bodies. KSP currently just 'switches' you to the nearest 'sphere of influence' at certain points.

I really do hate the scale down. The huge shots of the Earth as the I.S.S 'just skims' over the atmosphere at 400+KM altitude and 7,000 m/s are epic and orbiting Kerbin just isn't the same.

Edited May 30, 2013 by Good_Apollo

[Michael Kim]

As far as I can tell, the physics in the game is pretty much what is used for human space explorations. Well maybe the aerodynamics needs some improvement.

if you're in Kerbin Orbit, you're only affected by the gravity of Kerbin, not Mun, Minmus, Kerbol, etc.

You are by Kerbol, lol

[DevoidLight]

You are by Kerbol, lol

Kerbin and Kerbol are two different things.

[SargeRho]

Orbital mechanics are fairly accurate, but gravity is very inaccurate, but good enough.

[haltux]

Or, are there deliberate "tweaks" in the KSP physics we know, that the devs introduced, as to make activities within KSP more "interesting" or "fun"?

The most obvious I can think of is the lack of proper drag model. It can be seen as a technical issue, and it has been clearly stated that it will change in the future.

However, I guess it is also a gameplay issue. With a vaguely realistic drag model, the silly, fat, cathedral-like rockets that you can send now in orbit would become useless. Basically, rockets would have to look like rockets, and I am not sure most people would like that. I really wonder how squad will handle that.

About the fact that only one body attract your ship at one given instant, my guess is that it does not change trajectory as much as you would think. The main difference it makes is that with this model, any trajectory is entirely predictable with extreme precision, which is not true in reality. If a multi-body gravity model were implemented, predicted trajectories would not exactly match with actual trajectories, which could be interesting. However, I think that devs said that it would not happen.

[Good_Apollo]

The most obvious I can think of is the lack of proper drag model. It can be seen as a technical issue, and it has been clearly stated that it will change in the future.

However, I guess it is also a gameplay issue. With a vaguely realistic drag model, the silly, fat, cathedral-like rockets that you can send now in orbit would become useless. Basically, rockets would have to look like rockets, and I am not sure most people would like that. I really wonder how squad will handle that.

About the fact that only one body attract your ship at one given instant, my guess is that it does not change trajectory as much as you would think. The main difference it makes is that with this model, any trajectory is entirely predictable with extreme precision, which is not true in reality. If a multi-body gravity model were implemented, predicted trajectories would not exactly match with actual trajectories, which could be interesting. However, I think that devs said that it would not happen.

It's too complex, but really the real loss are Lagrange Points. Those things are useful...

[Michael Kim]

Kerbin and Kerbol are two different things.

Of course I know

When you are in orbit of Kerbin, you are attracted by Kerbol. It's just you don't feel it

[Splode]

The FAR mod provides an excellent drag model, however, the current part catalogue is not adequate for building aerodynamic rockets. until fairings, larger engines, wider parts etc are introduced, realistic drag just makes everything a nightmare. There are plenty of part pack mods, but you end up requiring loads and loads of mods, which has its own set of problems. The placeholder drag model is good enough for teaching gravity turns and efficient staging without requiring a degree in aerospace engineering.

[Michael Kim]

Orbital mechanics are fairly accurate, but gravity is very inaccurate, but good enough.

This doesn't make sense... orbit is all about gravity

[comham]

However, I guess it is also a gameplay issue. With a vaguely realistic drag model, the silly, fat, cathedral-like rockets that you can send now in orbit would become useless. Basically, rockets would have to look like rockets, and I am not sure most people would like that. I really wonder how squad will handle that.

I would hope that squad doesn't gimp the final game just for the sake of some people who have been playing the alpha to death and have got used to the weird idiosyncrasies of an unfinished game.

I really do hate the scale down. The huge shots of the Earth as the I.S.S 'just skims' over the atmosphere at 400+KM altitude and 7,000 m/s are epic and orbiting Kerbin just isn't the same.

Scale doesn't matter, only detail and graphics does. If Kerbin had more detail viewable from orbit (more terrain types, more detailed lighting, clouds, etc) it would be just as impressive.

Think about it, all that matters is how close you are to a sphere, not how big it is.

[MockKnizzle]

As far as I know, all fundamental physical laws and constants are true to reality. A meter in-game is a real-life meter, a kilogram is a real-life kilogram, gravity is still proportional to 1/r^2, etc.

The only unrealistic thing (besides aerodynamic model) is the density of the planets, which are cooked in such a way that a 600km-radius Kerbin has a gravitational acceleration of 9.8m/s^2 at the surface. The engine powers and fuel/dry-mass ratios are considerably less than their real-world analogues as well, but they're still consistent with conventional physics and it's entirely reasonable that Kerbal engineers (bless their little hearts) just haven't quite figured out the most efficient designs yet.

[rodion_herrera]

Your input is enriching, guys, keep them coming. I'm planning to create a sort of table/matrix so that I can have a kind of birds-eye-view on which physics are "fair-to-excellent" and which ones are "poor-to-terrible". By doing this, someone who has aims of using KSP as an educational tool, can then use it as reference so that he/she can try out examples that cover the "fair-to-excellent" envelope in terms of real-world physics. Thanks again.

[EleSigma]

The planet and moon scales are done in a way so that it is easier on performance, does not take as long to create a planet, and is a convience for the player during flight to prevent extremely long flight times. Everything is scaled by a factor of 10, so Kerbin is 10x smaller than it should be and distances between moons and planets are 10 times shorter.

[Michael Kim]

Just thought of this: KSP is much better in physics than those space flight/combat games where you throttle up to move faster and throttle down to move slower. Sir Issac Newton won't like them

[rodion_herrera]

Just thought of this: KSP is much better in physics than those space flight/combat games where you throttle up to move faster and throttle down to move slower. Sir Issac Newton won't like them

Don't worry, I'm totally aware of that. I've been using Orbiter: Space Flight Simulator since 2001 (and have been creating addons/mods for it too), and before that, Microsoft's Space Flight Simulator. So I'm pretty familiar with more realistic space flight simulators.

Thing is, everytime I let kids see Orbiter, I think they get overwhelmed with the interface (i.e. even my adult friends stare blankly whenever they see the MFDs and the HUD with all those numbers hehe). But KSP has this "cuteness" appeal that might just get kids to become interested in space exploration, astronomy, and science in general. That is my goal.

[SargeRho]

This doesn't make sense... orbit is all about gravity

Yes, it does make sense. Orbits generally work just like they do IRL. But gravity doesn't. Gravity here only comes from the body the Sphere of Influence you currently are in belongs to. So there are no langragian points for example.

[Neomatt]

Apart from the scales, N-body problem, and some oddities like Minmus, KSP is rather good at physics approximations.

Maybe if you go into non-Newtonian physics (relativity, etc), that's where some inconsistencies are visible.

[rodion_herrera]

To Michael Kim and SargeRho, I think the best way to "see" this issue is by thinking about the classic "dimple-in-space" or "dimple in a rubber mat" example for gravity.

So basically what Sarge here is saying, is that in KSP, once a craft/vessel reaches the influence of a specific body (that say, it's about to do a flyby or perhaps, plan to orbit), the "dimple" of any other body is NEGLECTED or cancelled out--meaning if we see KSP gravity as dimples around its planets, the dimple for say, Kerbin, disappears once you reach Mun, and thus you cannot have Lagrange points, because you still need Kerbin's "dimple" for that.

I hope this makes sense.

[Michael Kim]

Orbits generally work just like they do IRL. But gravity doesn't.

These two sentences don't go together. Orbit is the path of an object, which is determined by gravity.

Since you mentioned L points, then orbits there certainly don't work like they do IRL

[rodion_herrera]

These two sentences don't go together. Orbit is the path of an object, which is determined by gravity.

Since you mentioned L points, then orbits there certainly don't work like they do IRL

Michael, please refer to my explanation above--I don't think Sarge meant it that way.

[Michael Kim]

Michael, please refer to my explanation above--I don't think Sarge meant it that way.

Sorry, just saw it. But still gravity determines orbits.

BTW, Patched Conic Approximation works pretty well IRL except for L points. I believe it is widely used in real space programs