Suggestion: Non-spherical gravitational bodies

[The_Rocketeer]

Seen a few posts recently about possible new content for KSP that's more interesting than just 'more of the same'. It occurred to me that having planets or moons that were far-from spherical would be a really interesting and unique places to visit. Even Gilly, for all it's lumps and bumps, is still more-or-less round. How about an hourglass shaped moon, or a world with a flattish top, or a donut?

Now I realise that the way KSP uses SOIs doesn't make for brilliant gravitational realism here, but is that really a big deal? Landing on some of these things could be an incredible challenge, and EVAs once you got there could be really trippy...

Just food for thought. Perhaps someone already had this idea.

Edited May 14, 2016 by The_Rocketeer

[thereaverofdarkness2]

It would be difficult, but it's not impossible. The big hurdle is that each world is an altitude map made from virtual splines sticking straight out from the center of the world, and its center of mass is the same as the center of the splines. They are also procedurally generated using fractal seeds to generate the majority of the terrain including the general style of the terrain. For example Minmus' flats are probably created by having the terrain generator pop the lowlands up to a specific altitude, then another factor smooths out the edge of the flats so there isn't a sharp corner there. Only specific features such as the obelisks or the Kraken corpse were actually constructed entirely by hand.

A person could easily make a rough 3D sketch of the lopsided world they want, and then determine the position of its center of mass using volume calculations on the computer. But then making the procedurally generated altitude map cooperate to give you a world with roughly that shape is going to be difficult.

I, for one, would love to see a lopsided world added to KSP, so I hope the wonderful artists at Squad decide to show us what they're capable of!

[Alshain]

 

28 minutes ago, thereaverofdarkness2 said:

It would be difficult, but it's not impossible. The big hurdle is that each world is an altitude map made from virtual splines sticking straight out from the center of the world, and its center of mass is the same as the center of the splines. They are also procedurally generated using fractal seeds to generate the majority of the terrain including the general style of the terrain. For example Minmus' flats are probably created by having the terrain generator pop the lowlands up to a specific altitude, then another factor smooths out the edge of the flats so there isn't a sharp corner there. Only specific features such as the obelisks or the Kraken corpse were actually constructed entirely by hand.

A person could easily make a rough 3D sketch of the lopsided world they want, and then determine the position of its center of mass using volume calculations on the computer. But then making the procedurally generated altitude map cooperate to give you a world with roughly that shape is going to be difficult.

I, for one, would love to see a lopsided world added to KSP, so I hope the wonderful artists at Squad decide to show us what they're capable of!

The only thing procedural are the Mun's minor impact craters and the scatter detail, which isn't even physical.  Minmus along with every other planet and moon are static. 

As far as difficulty of accomplishing the task, it's not that difficult.  There is an egg shaped moon in the Outer Planets Mod.  I don't think they went to that much difficulty to make it. EDIT (Don't get me wrong though, a lot of hard work went into that mod)

Edited May 15, 2016 by Alshain

[Snark]

19 hours ago, The_Rocketeer said:

Seen a few posts recently about possible new content for KSP that's more interesting than just 'more of the same'. It occurred to me that having planets or moons that were far-from spherical would be a really interesting and unique places to visit. Even Gilly, for all it's lumps and bumps, is still more-or-less round. How about an hourglass shaped moon, or a world with a flattish top, or a donut?

Now I realise that the way KSP uses SOIs doesn't make for brilliant gravitational realism here, but is that really a big deal? Landing on some of these things could be an incredible challenge, and EVAs once you got there could be really trippy...

I'd say that this is a non-starter, based on my understanding of what you really want.  I'd put it firmly in the "ain't gonna happen" category.

Certainly it's possible to be somewhat aspherical.  For example,

13 hours ago, Alshain said:

There is an egg shaped moon in the Outer Planets Mod.

...and I saw another mod with a cubical moon.

However, both of those were really just spherical moons that have creatively-designed height maps.  For example, Ovok, the moon that Alshain's referring to, just has a really tall hemisphere-sized mountain on one side to give it the egg shape.

Makes it interesting to fly around, yes!    However, the gravity is still very much just the gravity of a spherical world.

There are two important limitations of KSP that you're going to run up against:

First, in KSP, all worlds are spherical and the topology is just a height-map.  So you can kinda get lots of different shapes, but they have to be "radially convex".  (Maybe not quite the right term for it; certainly you can have concave craters and such.  But the normal vector of the ground always has to point radially outward from the planet's CoM.) Also, if they're very non-spherical (like a pancake shape or something) you'll get some counterintuitive behavior since they'll still have the gravity of a spherical world.  However, it's simply not possible to model an hourglass or a torus without a serious overhaul to KSP internals, which would be a huge work item for Squad, and I seriously doubt they'd do it.

Which brings us to the second (and bigger) problem, which is math.

A spherically symmetric body is very easy to model, gravitationally.  The gravity field is just a simple radial one following an inverse-square law:  it acts as if all of the body's mass is concentrated in a point in the center.  This vastly simplifies the math that the program has to handle.  In particular, it means that orbits are deterministic conic sections and don't have to be calculated iteratively.

If you have a spherically asymmetric mass distribution IRL, you're going to get an oddly-shaped gravity field.  I gather that that's actually what you want (thus your comment about trippy EVAs).  However, you can't have that in KSP.  Modeling that kind of field would require the program to do a lot more math, trajectories wouldn't be analytically solvable, ships couldn't run "on rails".  Aside from the (large) workload of programming it, the sheer computational horsepower required would bring the game to its knees.

So no, I don't think this can happen in KSP, ever.

[The_Rocketeer]

@Snark, I observed in the OP that KSP's SOI-based gravity wouldn't conform non-spherical RL gravity fields, so no, that isn't what I'm talking about or want (however awesome it may be, I realise that it's basically not happening). Sorry I didn't make that clearer.

I'm talking only about worlds that do have ordinary SOI gravity (however unrealistically), but significantly deviate from the 'ball in space' norm. Traveling on the surface of such planets would mean that journeys along a straight flat surface would actually be more like driving down one side of a bowl and up the other side due to the changing relative direction of gravity.

This is an example of a unique experience in KSP, one which cannot currently be experienced anywhere (except perhaps in a tiny way on the KSC runway), and that is different from the general 'let's add more planets' approach to new content.

Edited May 15, 2016 by The_Rocketeer

[thereaverofdarkness2]

On 5/15/2016 at 10:19 PM, Alshain said:

 

The only thing procedural are the Mun's minor impact craters and the scatter detail, which isn't even physical.  Minmus along with every other planet and moon are static.

Static and procedurally generated are not mutually exclusive. All of the terrain is static and most of it is procedurally generated. Given the number of polygons in the larger craters on the Mün, I'd wager they are, to some extent, procedurally generated.

13 hours ago, Snark said:

Also, if they're very non-spherical (like a pancake shape or something) you'll get some counterintuitive behavior since they'll still have the gravity of a spherical world.

If you have a spherically asymmetric mass distribution IRL, you're going to get an oddly-shaped gravity field.

If they are reasonably ovoid or potato-shaped, the gravity modeling inaccuracy won't be that strong and won't hugely impact the quality of the world. Its higher altitudes will have noticeably less gravity than the lower areas and this is what you'd usually get in real life. The main difference between reality and simulation in this case is that in the simulation, the gravity variance by altitude is greater than in real life.

[Red Iron Crown]

Kopernicus/RSS seems to manage this, Saturn is now oblate. Not sure how accurate the gravitation is near the surface, though. Is it not similar to a point mass at the planet's center?

[The_Rocketeer]

8 hours ago, Red Iron Crown said:

Kopernicus/RSS seems to manage this, Saturn is now oblate. Not sure how accurate the gravitation is near the surface, though. Is it not similar to a point mass at the planet's center?

That's my understanding of how all KSP gravity works, so gravity's force is only determined by a given point mass and it's distance from you/your altitude above it. This is why gravity isn't part of what I'm suggesting, since it would mean a total conversion to a much more sophisticated gravitational model, with the necessary system resource demands and potential game engine inadequacies (the latter being something I am merely vaguely aware of, not familiar with).

At the same time, there are a lot of ways to make surface gravity more interesting to explore and try out just by changing the shape of a planet. I was partly inspired by A Slower Speed of Light in suggesting this - it can't just show you what really happens at the speed of light, so it instead shows you what would happen if the speed of light was slower.

Edited May 16, 2016 by The_Rocketeer

[Red Iron Crown]

I suspect the gravity system would handle it just fine, honestly. Gravity already changes with distance from the point mass, an oblate world would have more gravity at the poles and less at the equator (I think is what would happen in a real oblate world, but I'm no physicist).

[FleshJeb]

1 hour ago, Red Iron Crown said:

I suspect the gravity system would handle it just fine, honestly. Gravity already changes with distance from the point mass, an oblate world would have more gravity at the poles and less at the equator (I think is what would happen in a real oblate world, but I'm no physicist).

https://en.wikipedia.org/wiki/Gravity_of_Earth#Latitude

Correct. Although when it's oblate, you can't really model gravity as a point mass, per the last paragraph of that section.

(I'm just a surveyor with a casual interest in geodesy.)

[The_Rocketeer]

1 hour ago, Red Iron Crown said:

I suspect the gravity system would handle it just fine, honestly. Gravity already changes with distance from the point mass, an oblate world would have more gravity at the poles and less at the equator (I think is what would happen in a real oblate world, but I'm no physicist).

 

44 minutes ago, FleshJeb said:

Correct. Although when it's oblate, you can't really model gravity as a point mass, per the last paragraph of that section.

Yeh, this is it. Imagine standing on a planet the shape of an egg. The pointy end is further from the centre of mass, so you would expect it to experience lower gravity. However, because all the mass of the planet is more nearly directly beneath you (rather than just in various directions on the same general side of you), gravity ends up being stronger than you would expect if you were orbiting at the same altitude around a spherical planet of the same mass.

Am I making any sense?

Awesome new thought (well I think so): a spherical planet could have an off-centre SOI compared with it's surface, indicating a 'denser half'. Orbiting would be so counter-intuitive...!

Edited May 16, 2016 by The_Rocketeer

[SpaceplaneAddict]

On 5/15/2016 at 11:01 PM, thereaverofdarkness2 said:

It would be difficult, but it's not impossible. The big hurdle is that each world is an altitude map made from virtual splines sticking straight out from the center of the world, and its center of mass is the same as the center of the splines. They are also procedurally generated using fractal seeds to generate the majority of the terrain including the general style of the terrain. For example Minmus' flats are probably created by having the terrain generator pop the lowlands up to a specific altitude, then another factor smooths out the edge of the flats so there isn't a sharp corner there. Only specific features such as the obelisks or the Kraken corpse were actually constructed entirely by hand.

A person could easily make a rough 3D sketch of the lopsided world they want, and then determine the position of its center of mass using volume calculations on the computer. But then making the procedurally generated altitude map cooperate to give you a world with roughly that shape is going to be difficult.

I, for one, would love to see a lopsided world added to KSP, so I hope the wonderful artists at Squad decide to show us what they're capable of!

Can't snip, sorry. Though I've dabbled in Minmus's PQS code, and it seems that the terrain is really procedurally generated though PQS mods for height. Same goes for other celestial bodies as well, I believe. I can't tag people ATM, but if someone brought over NathanKell, I'm sure he could accurately explain something. Also, I looked through Minmus's stuff with Kittopia, so that may say something.

*Determination.

Edited May 17, 2016 by SpaceplaneAddict