Decaying Orbits

[tater]

The only true suborbital trajectory is one that intersects the surface. You can be orbital at 69,999 m in KSP (or 99,999 m on Earth), it's just how many orbits before it decays enough that you reenter finally, to destruction/impact.

Yes, there is decay not based upon atmospheric drag which would require other factors (n-body interactions included), but I think at the very least, atmospheric drag should be accounted for (even if abstracted) for no other reason than housecleaning. 

The idea that the Karman line in KSP might be 70km, and a safe (atmospheric drag = 0) orbit at some other value it not overly complicated. No one expects a 100km Earth orbit to be stable.

 

[regex]

4 minutes ago, Alshain said:

Nothing, it was two different conversations happening at the same time.

No, it wasn't, you were claiming up above that 

10 hours ago, Alshain said:

It was two different concepts of "orbital decay" that were being discussed.  One topic was about unloaded objects having atmospheric drag (technically not orbital decay because it's not orbit) and the other was actual orbital decay (n-body).

In response to me asking about

11 hours ago, regex said:

Also, what does atmospheric drag have to do with N-body orbital calculations?

regarding this statement

14 hours ago, KingDominoIII said:

No! That requires simulation of Lagrange points and N-bodies and would kill all but supercomputers.

and now you're telling me it is apparently in response to you talking to tater earlier about suborbital atmospheric decay?

Maybe you're the one who needs to "keep up". Stop trying to derail the conversation. I am very capable of managing a conversation with one person while you have a conversation with another in a single thread.

[Alshain]

@regex KingDomino was replying to the OP.  That happens on forums.  He wasn't talking about atmosphere.

Edited May 30, 2017 by Alshain

[Brent Kerman]

YES!  This is a great idea!

[tater]

Being orbital has exactly nothing to do with the atmosphere, or some arbitrary altitude considered to be "space." It is the instantaneous condition of having orbital velocity. Functionally, if the craft can no longer complete a full orbit, it is suborbital.

Such a condition only exists in KSP while a craft is in focus, and it's often wrongly labeled "suborbital." Kissing the underside of the karman line, or even the atmosphere is not "suborbital" even though KSP labels it so.

Edited May 30, 2017 by tater

[regex]

1 minute ago, Alshain said:

@regex KingDomino was replying to the OP.  That happens on forums.  The only mention of atmosphere was our earlier conversation so I thought you were reply to that.  Apparently you were talking to the imaginary man in your head.

The OP was about decaying orbits. This is a realistic mechanic based on an actual phenomenon craft experience in LEO. The major force of orbital decay in LEO is atmospheric drag, hence my question about what N-body calculations and lagrange points have to do with atmospheric drag considering that all lagrangian points are far from an atmosphere and orbital perturbation by multiple bodies is an entirely different category of phenomenon.

And yes, the OP did mention atmospheric height.

[Alshain]

Just now, regex said:

The OP was about decaying orbits. This is a realistic mechanic based on an actual phenomenon craft experience in LEO. The major force of orbital decay in LEO is atmospheric drag, hence my question about what N-body calculations and lagrange points have to do with atmospheric drag considering that all lagrangian points are far from an atmosphere and orbital perturbation by multiple bodies is an entirely different category of phenomenon.

And yes, the OP did mention atmospheric height.

It didn't 14 hours ago when he posted that.

Quote

Edited April 29 by Space_taco

When I first read the OP it was only mentioned "orbital decay" in general and had no specifics.

Edited May 30, 2017 by Alshain

[regex]

3 minutes ago, Alshain said:

It didn't 14 hours ago when he posted that.

So what? The problem is that you took my question out of context and focused it on your conversation when it was not at all related.

E: This is what a single-threaded forum looks like, people may have multiple topics related to the OP they are talking about at the same time. That's why quoting is so useful.

Edited May 30, 2017 by regex

[Firemetal]

I think a realism option should be added in the future and this should be part of it. Some won't like it because it makes the game a lot tougher and more tedious. But for those that do, it should be an option.

Fire

[Alshain]

7 minutes ago, regex said:

So what? The problem is that you took my question out of context and focused it on your conversation when it was not at all related.

Well you asked about atmosphere and the last conversation in the thread about atmosphere was ours.

EDIT: Hmm, well I guess you did tag someone.  My mistake I guess, I just missed that.

Edited May 30, 2017 by Alshain

[tater]

There are clearly different regimes involved in this concept. One includes EM effects, particle collisions, perturbations, etc (lunar masscons, for example), the other is the far simpler atmospheric drag issue.

We can put a test craft in KSP in an orbit with a periapsis of 69,999 meters, and see how many orbits it makes before it becomes suborbital. The answer is certainly "many." It would be nice---regardless of what altitude the game considers it to start at---if there was some sort of out of focus solution to this issue, so that craft/debris that kiss an atmosphere eventually deorbit on their own.

[regex]

3 minutes ago, Alshain said:

Well you asked about atmosphere and the last conversation in the thread about atmosphere was ours.  Since you didn't quote or tag anyone the inference was that you were joining that conversation, not making a completely random comment to someone who wasn't discussing atmosphere at all.

I did, in fact, quote the comment I was questioning, which was about langrangian points and N-body calculations, neither of which have anything to do with an atmosphere. I also later asked if you could provide a reference to the ISS' orbit being perturbed by the Moon and that requiring a correction burn since I have read nothing of the sort but would actually love to learn about, at which point you could have considered me joining your conversation.

Please.

Keep.

Up.

[Alshain]

4 minutes ago, regex said:

I did, in fact, quote the comment I was questioning, which was about langrangian points and N-body calculations, neither of which have anything to do with an atmosphere. I also later asked if you could provide a reference to the ISS' orbit being perturbed by the Moon and that requiring a correction burn since I have read nothing of the sort but would actually love to learn about, at which point you could have considered me joining your conversation.

Please.

Keep.

Up.

It's the crappy forum software.  It's not showing the quote on my phone for some reason.  Even right now it's not showing you quoted anyone, even though it's showing other quotes from other people.  I didn't see your quote till I moved over to the PC.  Sorry for the confusion.

[tater]

It's pretty safe to say that the base game is not getting n-body, or other non-atmospheric drag effects as a stock feature, ever.

Atmospheric drag, OTOH, is an entirely reasonable addition, even if not terribly accurate, and merely abstracted within the on-rails system using the worst-case drag (largest cross section for the craft in question). It has the benefit of functioning as a clearing system for debris, outside of setting yourself a low tracked debris number.

[regex]

18 minutes ago, tater said:

It's pretty safe to say that the base game is not getting n-body, or other non-atmospheric drag effects as a stock feature, ever.

Atmospheric drag, OTOH, is an entirely reasonable addition, even if not terribly accurate, and merely abstracted within the on-rails system using the worst-case drag (largest cross section for the craft in question). It has the benefit of functioning as a clearing system for debris, outside of setting yourself a low tracked debris number.

Atmospheric drag based on atmosphere scale height would be the best and, probably, the easiest since the game already performs drag calculations. A packed vessel can have a drag factor added based on whatever facing the designers feel is right using the existing drag cubes and then that can be iterated on every few frames or something. By choosing a single value for a packed vessel this would simply get rolled into the normal orbital altitude check that every vessel undergoes and have a negligent effect on game processing.

Edited May 30, 2017 by regex

[Superfluous J]

If they completely automate dealing with it (just spending drops of fuel to keep an orbit stable) then sure. 

But if they're going to go against every design decision  they've made ever and add automation of anything,  I've a list a mile long and "add orbital decay and then add stationkeeping" isn't as close to the top as you'd probably prefer. 

Edited May 30, 2017 by 5thHorseman

[tater]

They need not automate anything at all about atmospheric drag other than it decaying the orbit.

Simple question: If you leave a spent tank with an apoapsis of 50km above Kerbin, do you think it should remain in orbit forever, yes or no? If you think yes, then they might as well do away with the atmosphere altogether. If you think it should decay and reenter at some point, then we are only quibbling about the details.

Edited May 30, 2017 by tater

[MultiFrapser]

This could be a fun thing for hardcore players, maybe make it possible to enable and disable ''Decaying orbits'' ? Or make at least a mod out of it or smthing.

[tater]

26 minutes ago, MultiFrapser said:

This could be a fun thing for hardcore players, maybe make it possible to enable and disable ''Decaying orbits'' ? Or make at least a mod out of it or smthing.

 

Given that the only version of thins likely to be considered is atmospheric drag, why would this be "hardcore?" Do you expect the craft that KSP already labels as "suborbital" to in fact be orbital forever as long as the periapsis > 0?

[Superfluous J]

19 hours ago, tater said:

Simple question: If you leave a spent tank with an apoapsis of 50km above Kerbin, do you think it should remain in orbit forever, yes or no? If you think yes, then they might as well do away with the atmosphere altogether. If you think it should decay and reenter at some point, then we are only quibbling about the details.

Simple answer: No. Now for my simple question: Do you feel the same if the periapsis is 70001m?

Edited May 31, 2017 by 5thHorseman
Holy cow that's the problem with simple answers. I originally incorrectly answered yes.

[tater]

7 minutes ago, 5thHorseman said:

Simple answer: Yes. Now for my simple question: Do you feel the same if the periapsis is 70001m?

 In reference to your simple answer (since the forum will not let me split the $$#@! quote): So the atmosphere is meaningless, and "orbit"  is wrongly taught as having periapsis and apoapsis as above the karman line (which is not a definition of orbit).

 

For 70001m? I would have the atmosphere have a gradient, and eventually reach a value where it is "safe" and has 0 drag. I am open to whatever number they decide as long as anything that is in the "unsafe" zone decays on it's own (out of focus) until suborbital. If that arbitrary value is 70km, so be it, and 70,001m would be entirely safe.

Edited May 31, 2017 by tater

[tater]

When I first started KSP (0.23-0.24 transition) I didn't read the forums at first. As a result, I read the part descriptions, and assumed they reflected the way the game modeled reality. I wondered how I would ever get a landing can into orbit, as it was listed as incapable of surviving atmospheric flight. I put nosecones on everything, because aerodynamics (not realizing that this was in fact making my craft less, not more efficient).

I also assumed that if a craft was suborbital, it would fail to make another complete orbit (since that what suborbital, you know, means).

If we assume that 70km denotes the safe altitude, then it is not unreasonable to have anything below that decay. Anyone who has misjudged propellant in KSP who has managed to get their periapsis just below 70km knows that this decay is very slow, indeed, at that altitude, and that many, many orbits will occur before the craft is headed home (actually suborbital, which in KSP is after the sub-70km periapsis and apoapsis swap, and the spacecraft will reenter). We will ignore the pilot getting out and pushing with RCS  .

Anyone expecting a craft below 70km to not decay has been taught that by KSP not behaving as you would expect. They would not expect that by default.

Edited May 31, 2017 by tater

[Superfluous J]

I totally agree that any orbit under 70km should decay. I accept that they don't but don't agree with it or utilize it in any way.

My problem is with making all orbits slowly decay just to be a tiny bit realistic, when all it does is add annoyance.

Not saying you said that, but it's been proposed.

[tater]

Yeah, the impact of solar wind, magnetic fields, tidal forces, etc, seems out of focus for stock KSP. Atmospheric drag I can totally get behind. Stock atmosphere heights in KSP are simultaneously too high, and too low I think. Spacecraft in LEO are not really considered safe from atmospheric drag until what, a couple thousand km? 

I'm not wed to any particular altitude for such drag to reach, but it certainly adds value in terms of clearing junk away (it's ridiculous that in KSP to be "clean" WRT spent stages we have to either maintain focus for many, many orbits, explicitly delete them as roleplaying, or put probe cores and leave propellant to deorbit them, when leaving them in a low orbit should do it alone. If the drag altitude were to be increased above the Karman line (as it clearly in in RL) to some altitude, then all it does is make the "safe" orbit somewhat higher. In stock KSP this basically makes no difference since it's trivial to get virtually anything to orbit with dv to spare.

[KingDominoIII]

On 5/30/2017 at 0:54 AM, regex said:

Principia and my laptop would like a word with you.

Also, what does atmospheric drag have to do with N-body orbital calculations?

I like this idea for the base game, especially if there is a cap on the altitude where it can happen, maybe based on scale height. Two or three scale heights max, drag increasing based on "depth", nothing too severe, just enough that you'll notice when your "Sputnik" degrades after a year but not enough to touch anything that serves the solar system. The drag would be pretty minimal but would necessitate higher parking orbits for interplanetary vessels that would hang around for more than a week or so.

Because every object pulls others towards it with its gravity, an N-body cakcuoation must be used to accurately simulate orbital decay. Orbital decay can occur due to other forces outside the sphere of influence.