Realistic gravity in KSP 2

[javiarrebolis]

It will be great that KSP had realistic gravity.

In KSP1, if you calculate TWR in an excel document for a rocket in orbit,is not the same one that the game gives you,because the game use g as a constant of 9,81 m/s2,and the real g decrease with the distance.

[Vortygont]

24 minutes ago, javiarrebolis said:

It will be great that KSP had realistic gravity.

In KSP1, if you calculate TWR in an excel document for a rocket in orbit,is not the same one that the game gives you,because the game use g as a constant of 9,81 m/s2,and the real g decrease with the distance.

?

In the game the acceleration of gravity decreases as you say, maybe you are confused with the value of the constant from the game reference for Kerbin at the surface?

[magnemoe]

48 minutes ago, Vortygont said:

?

In the game the acceleration of gravity decreases as you say, maybe you are confused with the value of the constant from the game reference for Kerbin at the surface?

Yes you can even measure gravity with the
https://wiki.kerbalspaceprogram.com/wiki/GRAVMAX_Negative_Gravioli_Detector
Its an made up instrument, measuring gravity in orbit is non trivial, you can measure changes in orbit around the planet /  body or tides I guess. On the ground its easier, weight an known mass on an accurate scale and you get local gravity.  

[t_v]

6 hours ago, javiarrebolis said:

It will be great that KSP had realistic gravity.

In KSP1, if you calculate TWR in an excel document for a rocket in orbit,is not the same one that the game gives you,because the game use g as a constant of 9,81 m/s2,and the real g decrease with the distance.

When the game shows you TWR, it is always relative to Kerbin g’s, so it won’t decrease on low mass bodies. I’ll admit, sometimes it helps to know what 0.35 TWR means on Minmus, so I’d like to see a total acceleration ability (in m/s^2) divided by the gravity you are experiencing. In orbit though, the effective gravity should just read zero. 

[mikegarrison]

21 minutes ago, Laikanaut said:

Gravity also decreases with distance in KSP, you can check this using the Kerbal Engineer Redux mod.

But the planets are unrealistically heavy, so gravity is higher than it would be on real planets of that size.

I wonder if the gravity could be realistic for the planet sizes, though this might make the game too easy.

The answer is to make planets full size, but that would change a lot of established KSP play, require a complete rebalance of all parts and engines, etc. etc.

KSP2 long ago confirmed that they will have the same planet size and scaling as KSP1, if I am remembering that correctly.

51 minutes ago, t_v said:

When the game shows you TWR, it is always relative to Kerbin g’s, so it won’t decrease on low mass bodies. I’ll admit, sometimes it helps to know what 0.35 TWR means on Minmus, so I’d like to see a total acceleration ability (in m/s^2) divided by the gravity you are experiencing. In orbit though, the effective gravity should just read zero. 

If you are using MechJeb (or probably any of several other mods), it will report TWR according to the local body rather than Kerbin. However, they still report it relative to surface gravity.

The game does do gravity (mostly) correctly, although it does not do "n-body". That is, once you are in the Mun's SOI, the game doesn't calculate the effect on your ship of Kerbin's gravity, the sun's gravity, Minmus's gravity, etc. All that is simplified by the Mun being "on rails".

[Vl3d]

9 hours ago, t_v said:

When the game shows you TWR, it is always relative to Kerbin g’s, so it won’t decrease on low mass bodies.

Are you sure about that? You can change the body frame of reference in the VAB and it updates the DeltaV and TWR values in the staging.

[javiarrebolis]

If you build a rocket with 1900kg of mass,with a Terrier engine,the TWR at Kerbin surface is the one I calculate in the picture below,and its the same one that the game gives you (bottom right of the picture).



But,if you calculate the same in vacum,my TWR and the game are the same if g is also 9,81,but in vacum it should be less.



So if you calculate the same in an orbit of 90km,the game gives you a TWR of 3'21,and it should be more,4'26 as I demonstrate.

So yes,i'm sure that KSP1 physics use g as a constant of 9,81.I imagine that for diferent bodies,its diferent,but it doesnt change with the distance between body and rocket.And thats my suggestion for KSP2,that g changes like in real life with the distance.

Edited November 15, 2022 by Snark
Image links adjusted by moderator

[t_v]

4 hours ago, Vl3d said:

Are you sure about that? You can change the body frame of reference in the VAB and it updates the DeltaV and TWR values in the staging.

Yes, what I meant is that the TWR has a constant point of reference while in flight. I’m not sure that if you set it to a low mass body and launch it, it will display that way. I’m pretty sure I’ve done that and it still reverted to Kerbin gravity. 

[Vl3d]

1 hour ago, t_v said:

Yes, what I meant is that the TWR has a constant point of reference while in flight. I’m not sure that if you set it to a low mass body and launch it, it will display that way. I’m pretty sure I’ve done that and it still reverted to Kerbin gravity. 

What you're saying it's very confusing. AFAIK TWR is set as reference to the SOI you are in and varies according to altitude.

Edited November 15, 2022 by Vl3d

[Dinlink]

On 11/14/2022 at 5:16 PM, javiarrebolis said:

It will be great that KSP had realistic gravity.

In KSP1, if you calculate TWR in an excel document for a rocket in orbit,is not the same one that the game gives you,because the game use g as a constant of 9,81 m/s2,and the real g decrease with the distance.

KSP 1 has realistic gravity... That's the reason behind rockets following elliptical trajectories and following the Kepler equation in general.

What KSP doesn't do is to have the most complete model of N-Body dynamics which takes in account the small effects of gravitational pulls of the rest of the bodies in the kerbolar system... These effects would translate in unstable orbits and special region in space like Largrange Points...

The TWR is shown relative to the reference surface gravitational acceleration of the body in which SOI your ship is flying. This is the right way to report the TWR so you can easily calculate the acceleration of your ship "on the fly"... And have a sense of the capability of the ship to take off from surface. It wouldn't make sense to report the TWR relative to the local gravity field, given that would make more difficult to swiftly calculate the acceleration and would loss it's meaning of giving you the sense of how good is your ship on supporting its own weight on take off/landing.

[MarcAbaddon]

In order of your pictures:

1) the vacuum toggle is about the engine properties, not gravity. This is because gravity isn't less just because you are in a vacuum - it is just that for a planet with an atmosphere you need to get some distance from the planet to go into vacuum and this decreases gravity. But the Mun wouldn't suddenly have more gravity just because it has an atmosphere (assuming same mass).

2) TWR as an indicator is interesting in order to know if you are able to lift-off and land on a body. For this to works you need to calculate it using surface gravity, which is what KSP does. For orbital maneuvers maximum acceleration is more useful. 

3) KPS definitely calculates single-body gravity according to Newton correctly. Both the stock gravity meter and Kerbal Engineer Redux shows you the correct gravity. All the orbits would look very different as well if it was just a constant. 

In short: your starting assumption is wrong.

 

For other people reading this and wondering how orbits would actually look like if gravity did not decrease with distance, I found this discussion which seems interesting, but I have not checked in any detail yet myself:
https://math.stackexchange.com/questions/1345571/what-would-a-planetary-orbit-look-like-if-gravity-had-constant-magnitude

[机械主教71号]

the gravity is not a constant in KSP1.

Edited November 28, 2022 by 机械主教71号

[NexustheNinja19]

Aint no way they add N-Body Physics, Just go get Principia.

Edited February 11, 2023 by NexustheNinja19

[Bej Kerman]

On 11/15/2022 at 11:35 AM, javiarrebolis said:

But,if you calculate the same in vacum,my TWR and the game are the same if g is also 9,81,but in vacum it should be less.

No it shouldn't; if you removed the atmosphere from Kerbin, the TWR would be exactly what the tool is telling you.