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Hulks not deorbiting


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I rescued several Kerbals for contracts and to be tidy, I created a grabber that could capture the ship. I then turned retrograde and burned long enough to get the hulk's periapsis under 70k.  

I have since been to the Mun and back and am now aerobraking. I noticed that all the ships I have put in those orbits are staying in those orbits.  They will dip down to 60 k but always back up to an 80k apoapsis that never seems to shrink.  Do these just get put on rails until they are controlled?

I've switched to a few in the tracking station and deorbited them that way, but it does not seem they will just do it on their own unless actively "controlled" (even though all I am doing is riding it down).

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Yes. You have to be "riding" them for aero-frictive effects to be seen. If they get below 20 km, on Kerbin I think the other planets have different magic lines, the sofware will assume that they succussfully burn up. 

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As steuben said, each CB has a different "autodeletion altitude". If your hunk of trash has a Pe below that number, it will get autodeleted when it reaches that altitude. I think the number is 25Km for Kerbin.

Aero effects only apply within the physics bubble, which is a small region around the currently active craft.

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That’s the main reason why I made a single probe that can do both part and Kerbal return missions, it just grabs their pod and brings the whole thing down making it easier and also offsetting the costs a bit by getting the cost of the pod refunded- free money is always good!

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On 7/19/2021 at 4:30 PM, steuben said:

I think the other planets have different magic lines

On 7/19/2021 at 8:56 PM, bewing said:

each CB has a different "autodeletion altitude"

I believe the auto-deletion altitude is defined as 1% of Kerbin sea level pressure.  On Kerbin that happens at around 23 km.  On Eve it would be a lot higher, and on Duna considerably lower.

On 7/19/2021 at 4:09 PM, Klapaucius said:

I've switched to a few in the tracking station and deorbited them that way, but it does not seem they will just do it on their own unless actively "controlled" (even though all I am doing is riding it down)

Correct.  As the others have observed, this is just how the game works.

Craft that you're not piloting and which are outside the "physics bubble" are running "on rails"-- there's no physical simulation at all, they're just following a perfect conic-section orbit according to the laws of mathematics.

The game does that because doing an active physics simulation on a craft is computationally expensive.  Basically, they can only afford to simulate the current ship, and any nearby ones.  Since there are potentially hundreds of ships in the game, all in various orbits and situations, there's just no way the game could simulate them all; it would bring the computer to its knees.  Aerodynamic drag is particularly computationally intense-- for every single part on the vessel, the program has to do a bunch of computations based on its speed (which is changing moment by moment), its orientation (also changing), the atmospheric pressure (also changing), etc.

By putting the craft "on rails" they reduce the computational burden to near zero, thus making it possible to have lots of ships in the game without bogging down the computer.  The fact that it works as well as it does without the player ever noticing (most of the time, anyway) ;) is a testament to the effectiveness of the technique.

It does, however, have its limits, and lack of orbital decay is one of those.  The computational shortcut becomes more apparent in situations like the one you're describing.

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