Thermospheres/Exospheres for Atmospheric Planets?

[rodion]

I enjoy both the more realistic parts of KSP as well as the bits that are modeled and simplified to make the game more accessible and playable, but when I can launch a probe or craft into, say, a very low 72 km circular orbit around Kerbin, then time-warp years or decades ahead (on say, some other long interplanetary mission), then come back and find my original vehicle's orbit hasn't changed a wink, it strains my suspension of disbelief. Would it be reasonable or possible to ever add an extension to the current atmosphere models where its drag on spacecraft becomes low enough at high altitudes that one can still complete dozens of orbits on medium- or medium-long- timescale maneuvers, like rendezvous, without any detectable change in orbit, but on the timescale of months or years or more it does begin to cause decay?

[Themohawkninja]

The problem is, is that any time warp above 4x causes everything to be on-rails, so physics would cease, and such orbits would be much more permanent. Secondly, this would make low flying space stations impossible if you went to do a Joolean missions, as the station would require constant altitude boosts from time to time, which if your suggestion is put in, would cause unreasonable amounts of micro-management if you were to have a lot of low flying satellites around various atmospheric bodies.

[Sean Mirrsen]

Not possible with the on-rails system. It is, after all, on rails. Every orbit outside of an atmosphere and that doesn't intersect another SOI, is perfectly stable in KSP.

[tntristan12]

I'm hoping that one day there is a way to model approximate drag effects so we get instances like this to be not as blatantly obvious.

[stupid_chris]

This was already proposed before, you basically want orbital decay. The thing is, most people would just think "well now the atmosphere is raised to *insert altitude where drag reaches zero*, better put all my ships up there now!". This is something really interesting, but would require an insane amount of micromanagement depending on how many crafts you have in low orbit. Really, this would make an amazing mod, but wouldn't fit stock very much in my opinion.

[rodion]

The way I see the "micromangement" issue in my mind is not that it forces players to constantly launch servicing missions to all of their craft, but does something else which should probably be in any good space program sim - makes them set realistic lifespans and schedules for their craft and missions, so that after a certain number of years in the field one can finally declare "mission over" and allow the obsolete hardware to make its exit, instead of magically being able to keep everything available in fresh usable condition permanently. Due to the relatively long and minor timescale of the decay, there would be no rush to make sure absolutely everything was okay. Even warping a barge x100k to Jool shouldn't cause catastrophe, just distortion in the orbit unless the object was really placed unreasonably low.

The thing is, most people would just think "well now the atmosphere is raised to *insert altitude where drag reaches zero*, better put all my ships up there now!".

Sadly I also considered people thinking this way myself. I mostly placed faith in the fact that our dedicated KSP players' community helps everyone understand reasonable parameters and ideas for the game, so this kind of thing should easily be integrated into people's minds so that not everything has to pointlessly be in, say, a 700km orbit. There would be no reason to change the values of recommended parking orbits or anything else important because they would be unaffected by the change for those purposes.

[Sean Mirrsen]

The way I see the "micromangement" issue in my mind is not that it forces players to constantly launch servicing missions to all of their craft, but does something else which should probably be in any good space program sim - makes them set realistic lifespans and schedules for their craft and missions, so that after a certain number of years in the field one can finally declare "mission over" and allow the obsolete hardware to make its exit, instead of magically being able to keep everything available in fresh usable condition permanently. Due to the relatively long and minor timescale of the decay, there would be no rush to make sure absolutely everything was okay. Even warping a barge x100k to Jool shouldn't cause catastrophe, just distortion in the orbit unless the object was really placed unreasonably low.

Sadly I also considered people thinking this way myself. I mostly placed faith in the fact that our dedicated KSP players' community helps everyone understand reasonable parameters and ideas for the game, so this kind of thing should easily be integrated into people's minds so that not everything has to pointlessly be in, say, a 700km orbit. There would be no reason to change the values of recommended parking orbits or anything else important because they would be unaffected by the change for those purposes.

Making equipment decay and fail at a certain rate based on distance from a body with atmosphere is certainly possible. It's the orbital decay - the shifting of the orbit - that isn't. So you can definitely have that element of "this satellite's been up there for 60 years, time for a new one", in game-friendly terms, but actual shifting orbits are unlikely.

[Frederf]

If you can hyperedit 0.001 m/s off a craft every 100 days you can have orbital decay. The trick is to get a mod to do that for you and you're half way there.

[tntristan12]

There is no reason the game can't change the velocity of a craft on rails. The problem is in knowing by *how much* to change it. There is no analytical way to predict the behavior of a craft being influenced by both gravity and atmospheric drag - the problem is fundamentally the same one that prevents KSP from having n-body physics.

Atmospheric drag has some basic models that predict motion given some assumptions of the atmosphere and craft. Considering how blatantly obvious the flaws with the current model are, I think any approximation would be an improvement.

Besides, having orbital decay is important to have if we ever want a fully realized recovery mechanic. There is no reason that boosters dropped into the atmosphere with sufficient parachutes should be "destroyed" by the current model. The solution may just be a simple check to see if the number of parachutes would sufficiently slow each part in order to prevent damage, and then automatically have it recovered, but I think a more comprehensive simulation of drag, even with rails accounted for, is not outside the realm of possibility. Once re-entry heat is properly added, maybe parts could be destroyed on their thermal properties as well.

Oh, and doesn't mechjeb even have an aerobraking simulator on it? If mechjeb can do it, the stock game can too.

TL;DR: n-body physics may not be important enough to add to the game, but this is. Not only is the current behavior unrealistic but it doesn't even follow it's own internal logic! A solution to this problem would have gameplay ramifications for part recovery as well. It's worth looking into.

[hansman1982]

Isn't that what would presently happen if you we the orbit within the atmosphere? We are just blessed that Kerbin doesn't have an overly thick atmosphere.

Making the physics work at warp would get some funky things happening to your ships. I played orbiter prior to KSP and too much warp for too long caused me to lose a great many space flights.

[Frederf]

No, it's not. If you orbit at 23,001m+ then you will continue to do so if you depart the craft. The path is cyclical and permanent unless it intersects a set litho+atmo object. Overheating, aero drag, collisions with other craft, etc. aren't a factor.

Decay factor might be based on overall drag averaged over 360x180 rotation or even in a single orientation. It wouldn't have to be remotely precise for 99% of craft to be believable.

tristian brings up an interesting idea about pre-determined unloaded craft fates that could really enhance unloaded craft modeling. With some cheap one-time calculations some valuable craft behaviors can be realized.

[Ernest3.14]

To prevent micromanagement, spacecraft might have a monopropellant trickle, to simulate boosting maneuvers. And when you run out, you would need to service your spacecraft.

[DrMonte]

It is a very good idea which solves a lot of problems and very easy to implement. I don't understand why it was pushed under "never to be done".

How? - just add velocity decrease over atmosphere (depending on height). Also improve autopilot to be capable to "keep orbit" with rcs. There is no problems with rails either - just consume fuel till zero then change rail to descending spiral.

The other part here is that ships are not updated in background. Which could also be done as multiple CPU cores are not used.

We will get rid of all debree and get some realism. And who is talking about stations near Jool without need to support them for years?

[boomerdog2000]

It sounds incredibly annoying and I feel nearly everyone would put their craft above said height limit, disregarding the lack of physics on inactive craft.

[Taribu]

I've seen that the Interstellar Mod now actually enables acceleration while on-rails, using solar sails. I havn't had a look at the source yet (and didn't try the solar sail yet) , but couldn't the same method be used to add this orbital decay (due drag for example) to the game?

+Edit But i agree that a change like this is not that stockalike.

Edited February 12, 2014 by Taribu

[Nemrav]

just put your satellites in a 68 km orbit instead of 70, other than the game will deny you menu, lack of time warp, problem solved.

well, I personally would simply like a "that stuff is out dated, take it down" contracts in career once x amount of objects are within y - z orbit altitudes.

[David H]

If you can hyperedit 0.001 m/s off a craft every 100 days you can have orbital decay. The trick is to get a mod to do that for you and you're half way there.

I like the mod idea but not for all ships. Such as a station. With the money in career. O want to try and recover everything I can.

However say a mapping satellite in a 90° inclination. I gave it just enough fuel to get into orbit.(cost efficiency) I end up running out of fuel to bring it back.

Sending a ship up to try and push it back would cost more than just leaving it up there. Along with trying to push a ship is difficult.

For other items. My station has a return vessel. That's its sole job. Send a new kerbal up. Bring others down.

Occasional a new part goes up. I also take up extra chutes attached as I know I'm bringing some extra weight down.

My landers n things stay up and get cleaned out for next mission.

So for the mod. Make a new part. When attached to a ship. Only that ship will have orbital decay.

just put your satellites in a 68 km orbit instead of 70, other than the game will deny you menu, lack of time warp, problem solved.

well, I personally would simply like a "that stuff is out dated, take it down" contracts in career once x amount of objects are within y - z orbit altitudes.

Won't work.

You can't change ships while in atmosphere.

As far as others saying to just end mission.

That defeates the purpose of orbital decay "realism"

Edited November 6, 2014 by David H