A Discussion of Gravity

[Serratus]

@willitstimothy OK, I\'ve gotta ask you - why would you want parts to have their own gravity SOI? It\'s just hard for me to find a god reason for it. Maybe if you explain what exactly you want to do with it, someone will come across a good idea on how to do that.

[willitstimothy]

We can't add new celestial bodies currently, and likely won't have any new ones until they release all of them (who knows when?), but for the sake of realism mainly, which is what this game has sought to a degree uncommon in its genre, and for the sake of being able to properly use the over-sized parts, which we are allowed to make and use, for more than just something to look at, it seems like part gravity and SOI for sufficiently large parts would be a must. Otherwise, at what point is this game going to make realistic use of parts that are 2 km across? Especially when everything is scaled down to 1/10th of the realistic size?

In the real world, the Japanese have landed a probe on a clump of rock that was formed by smaller pieces merging together due to micro-gravity, this rock is called 25143 Itokawa, and it measures 535 x 294 x 209 m, and it's g is 0.00001 m/s^2 (it has unusually low density though). Now with a scale of ten factor in KSP this rock would realistically have a g or 0.0001 m/s^2, and with higher density and maximum size one can see that the g would get to the point where one could feasibly treat a very large part as a small 'planet' such that one could land on it and use it to catch a ride to somewhere.

I understand now that there will be such things later on in a different form, and if part gravity is really such an enormous problem that the realism of it is not worth it to the game developers, I'll live with it and still love this game. I want this game to be perfect, and if it can be done it should be done. That's my view and my opinion.

Edited August 18, 2012 by willitstimothy

[C7Studios]

I think everyone has made their arguments on the matter Feel free to start your own thread and continue this discussion elsewhere.

That said, I\'m settling down to work for the night on the landing gear. If I can get the bugs ironed out, I\'ll upload some shiny videos.

Edit: Not a big deal, Just trying to keep things on topic.

[willitstimothy]

Oh my, sorry C7.

[willitstimothy]

@Mr_Orion

(In reference to an earlier comment you made to me)

I talked with C7 about the part gravity thing already, and he mentioned that there would be some sort of problem if a dynamic (movable) ship had parts that were being treated as a celestial object. All pieces of debris are considered ships in the persistent file and that is why (currently) they are saved in their orbits and are cluttering up the sky as we speak. Hence it stands to reason that if one made sure that only static ships were used there should be one less problem.

Well, that is why, as I have said elsewhere, that SOI could be only assigned to certain object that met certain mass and volume requirements so as to make it so that only the largest of objects would have SOI, thereby cutting the processor load enormously.

When they give us the ability to create our own celestial bodies, and give us their own creations as well, I will be very grateful, but it still seems funny that I'll be able to ram a giant asteroid part into one of the future celestial asteroids that are roughly the same size and mass as the part, and have no orbital, or otherwise, effect on it. It will also be funny that I can land on one of them and not on the other.

Edited August 18, 2012 by willitstimothy

[willitstimothy]

@NovaSilisko

So, use a variation of that plugin, make a module named LargeBody or something, input gravitational parameters in the cfg, and you have yourself an asteroid you can land on.

In fact, I might just do that myself.

Please do, and then release it. I'd try it myself, but I am terrible at troubleshooting code, and not much better at writing it.

Edited August 18, 2012 by willitstimothy

[Mr_Orion]

When they give us the ability to create our own celestial bodies, and give us their own creations as well, I will be very grateful, but it still seems funny that I\'ll be able to ram a giant asteroid part into one of the future celestial asteroids that are roughly the same size and mass as the part, and have no orbital, or otherwise, effect on it. It will also be funny that I can land on one of them and not on the other.

When you can create your own celestial bodies, why even try making an asteroid part? That\'s pointless...

Not to mention, a part that big would have a very, very inaccurate physics model if the visual model isn\'t a literally perfect shape with exactly 256 sides, but that looks incredibly ugly.

[willitstimothy]

There already are asteroid parts though:

http://kerbalspaceprogram.com/forum/index.php?topic=7844.0

And if we can make them, why can't we use them?

Edited August 18, 2012 by willitstimothy

[Kryten]

Is there any other situation in which having parts with their own gravity would be useful? Considering having stuff like that as ship parts is a temporary work-around anyway, it doesn\'t seem worth the effort to add this to the game.

[willitstimothy]

If we can make parts that are the size of small towns, and by all rights massive enough to have a detectable gravitational field, we should allow them to have gravity and small SOI.

It seems like realism is to much of a bother, even in this matter (this is a space game, thus it seems to me that a space game should strive to treat all massive objects equally), thus I will just concede that this idea is out there but that I am not going to try to promote it further unless some olive branch of opportunity presents itself.

[sal_vager]

Thats the problem though, we aren\'t supposed to be making stuff the size of small towns, KSP isn\'t set up to handle such things and very likely isn\'t going to be.

Stuff isn\'t even visible beyond 2k meters.

What we will get later is an open system for the planets so we can mod our own, and they will have gravity and SOI\'s.

You\'ll likely be able to make an asteroid size planet, apply custom variables to the gravity, SOI and terrain, and stick it in any orbit you want.

KSP is a game not a realistic simulation of every possible aspect of physics, HarvesteR and the rest can only do so much, and at the end of the day it\'s their vision, not ours.

I\'m afraid if you want real world physics recreated in exquisite detail in a PC desktop space game, you\'re out of luck.

KSP will get better, but it will never be reality, we have to suspend disbelief and put up with it\'s world, not bemoan that this or that aspect is incorrect.

I know you\'re getting bored with the game, you have already said, you\'re welcome to try the challenges others have set (like my StarRally ) or try setting one of your own.

[willitstimothy]

Maybe later versions of KSP will though.

I can hope can't I, I mean the computers most of us use today would have been considered super computers less than a couple of decades ago.

Edited August 18, 2012 by willitstimothy

[sal_vager]

We can all hope friend

Personally, my wish is for KSP to simulate orbital combat (via mods, not as a goal of the game), it\'ll be interesting to see what solutions people come up with when faced with the vast differences between what we know about land and air combat, to the unknown of space.

I see lasers are already made but they are direct line of sight, I believe projectile weapons would be very useful against the necessarily light and flimsy spacecraft.

Imagine shooting a projectile that could hit a target on the other side of a planet? It wouldn\'t move if it didn\'t know the attack was coming.

[Mr_Orion]

If we can make parts that are the size of small towns, and by all rights massive enough to have a detectable gravitational field, we should allow them to have gravity and small SOI.

It seems like realism is to much of a bother, even in this matter (this is a space game, thus it seems to me that a space game should strive to treat all massive objects equally), thus I will just concede that this idea is out there but that I am not going to try to promote it further unless some olive branch of opportunity presents itself.

Something the size of a small town has almost no gravity. A 2km lump of lead would still have almost no detectable gravity, so you wouldn\'t even notice the gravity, let alone be able to land on it.

And as I said, the collision mesh is far too inaccurate to even allow you to land on parts that big without severe inaccuracies.

[willitstimothy]

Something the size of a small town has almost no gravity. A 2km lump of lead would still have almost no detectable gravity, so you wouldn't even notice the gravity, let alone be able to land on it.

A 2 km lump of lead:

R = 1km = 1000 m = 100000 cm

V = 4.1887902*10^15 cm^3

? = 11.34 g/cc

G = 6.67384*10^(-11)

m = ?V = 4.75008809*10^16 grams = 4.75008809*10^13 kg

g_surface = G[m/(R^2)]

= [6.67384*10^(-11)][(4.75008809*10^13)/(1000^2)]

= 0.00317013279 m/s^2 but in KSP there is a scale of 10 increase for size hence:

g_surface = 0.0317013279 m/s^2

Which means that it would only take about 30 seconds to accelerate to 1 m/s.

Way weaker than Mun, but still strong enough to be somewhat usable.

Escape velocity would be about 25 m/s in KSP

Edited August 18, 2012 by willitstimothy

[willitstimothy]

Okay, well the collision mesh could be a problem, and I'm probably wrong. So that's that.

Edited August 18, 2012 by willitstimothy

[Iskierka]

There is nothing officially stating that accelerations are multiplied ten times in KSP: The composition of Kerbin and the Mun are complete mysteries, hence they do not have the same density as their real world counterparts, they are simply ten times denser. Thus, lead would have the same acceleration due to gravity.

To add to that, lead is an extremely rare element, and asteroids are more commonly consisting of iron and iron-based ores. Rerunning the numbers using feldspar, an iron ore that is the most common material in the earth\'s crust, the acceleration is less than half. And this would be assuming the materials consisting an asteroid had had the same forces compacting them as they had on earth, which it is fairly likely they wouldn\'t.

[Thiel]

You\'re also going to run into another limitation inherent to KSP. SoI scale with gravity, so you\'d basically hit your asteroid seconds after it\'s SoI. That\'s going to make intercepting them mighty hard, not to mention landing on them and forget about orbiting them unless they\'re perfect spheres.

[Iskierka]

With accelerations that low, you\'re never going to find the SoI until the asteroid is very, very far from everything else.

[sal_vager]

There is nothing that states that player made asteroids have to be exactly to scale, and though a lead asteroid is not common it\'s not impossible either, it could be a planetary fragment.

But even with negligible gravity, there are other ways to land on them, wasn\'t there plans to have a probe anchor itself with claws and drills at one time?

There is provision for this in tosh\'s cart plugin, it has artificial downforce.

Edit: Found it, it was comets not asteroids but hey, the Rosetta space craft will use harpoons to tether itself to the comet 67P/Churyumov–Gerasimenko.

More info here: http://www.universetoday.com/9447/landing-on-a-comet/

Edit2: Actually it\'ll be the Philae probe released by Rosetta that will land https://en.wikipedia.org/wiki/Philae_lander

[The_Duck]

Hi all--I\'ve just put up a part gravity plugin here that includes (with permission) gravitating versions of JellyCube\'s 500m asteroid and NovaSilisko\'s old Mun part, as well as a black hole. Check it out.

I\'ve ignored considerations of realism in setting the magnitude of the gravitational fields, but you can edit them to be whatever you want with the part.cfg files.

[willitstimothy]

Hi all--I've just put up a part gravity plugin here that includes (with permission) gravitating versions of JellyCube's 500m asteroid and NovaSilisko's old Mun part, as well as a black hole. Check it out.

I've ignored considerations of realism in setting the magnitude of the gravitational fields, but you can edit them to be whatever you want with the part.cfg files.

Oh! Thank you so much.

Edited August 18, 2012 by willitstimothy