Alright,
So today I had launched the SimpleBeast to determine the minimum altitude possible to be definable as an orbit (meaning orbital decay can occur but it must be above the point where atmospheric parameters are measurable). I achieved orbit at 85km w/low eccentricity before dropping the orbit to 60.5km w/low eccentricity (eccentricity was 0).

I believed that in the region between 59-57km an orbit would attain too much decay to be able to sustain, and thus would quickly lose velocity and deorbit. I also believed that below 60km time acceleration to 10x would not be allowed.

The first thing that surprised me was that in the orbit I was in to start, the altitude of the Periapsis and Apoapsis began flickering down to lower altitudes over a course of 3 hours. Falling through 60km I was surprised to be able to continue using time acceleration to reorient the spacecraft which turned onwards toward prograde. Below 59km the time acceleration continued to work, that is until roughly 58.3. At that altitude temperature (-270C to be exact) and Mach number (mach 9.8) were measurable and immediately the spacecraft began to lose velocity and altitude.

After reentry and landing I ended the flight to find a time of 4:15:??. About three and a half hours in atmospheric slowdown. What I also found was a maximum possible orbital velocity in a circular orbit of 3455 m/s. With that velocity any program using a function of altitude to orbital velocity for circular orbit can use that and 59km to determine orbital velocity for any altitude.

Note: the function for relating altitude to orbital velocity will be nonlinear. I plotted points which showed a curve occurring. If you want any pictures of that I will need to know how to get pictures posted on this site.


15 Comments

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    Only that much???

    2.6 years ago
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    @TopSecret2 60km. Orbiting at even 59.5 km for me produced drag and I began to lose altitude.

    3.1 years ago
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    @HorizonsTechnologies Even a year later, it is not; atmosphere starts between 58-59km now. This comment section might as well be outdated but I checked the current version.

    3.1 years ago
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    Droodian karman line is 60km

    3.1 years ago
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    @crowxe Long time coming for this reply: the issue was not the part of the perigee and apogee switching but the fact that they were doing it entirely while self-decaying below the Droodian Karman Line, despite the atmosphere clearly cutting off below it (at least during that version of this game we were discussing at the time.)

    4.5 years ago
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    8,458 crowxe

    @TopSecret2 we still didn't try having the command chip right on the CG , I believe this will stop the swaying , but as for the almost perfect circular orbit I wouldn't worry if my perigee switched with apogee when it's couple of 100 m difference, I don't think it matters even in real space travel

    4.9 years ago
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    @crowxe This conversation was very interesting, but as for taking several hours for orbital decay to occur, that’s exactly what I did from a 60.2-60.8km orbit. If the flickering does in fact originate from a glitch, it might also be an inaccuracy in the precision which might be related to the glitch as a result of the inability of the orbital mechanics to interpret perfect circles (which you would think would have been considered in the game engine’s design).

    +1 4.9 years ago
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    8,458 crowxe

    @NoIDontWanna oh ok i got it, well i said the rotation "feeds in" velocity to the calculation, the orbit itself doesn't change. it the display because the speed feed comes from the capsule , if a rocket has command chip exactly in the center of mass then rotation will not affect the displayed orbit. and regarding minimum orbit i think it's not more than 58.25 km , never decayed above that unless it require several hours/days which i never done

    4.9 years ago
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    8,458 crowxe

    @NoIDontWanna can't understand fragmented phrases

    4.9 years ago
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    8,458 crowxe

    @NoIDontWanna not sure which point are you referring to !

    4.9 years ago
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    Dev Pedro

    @NoIDontWanna Not only circles but most curves, the smaller a orbit gets the easiest it is to notice the issue. If you play ESS and try to orbit Ilithos you can get really weird behaviours like the craft being locked around the planet in position

    4.9 years ago
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    1,155 huuminberd

    Would it be relating to air density? Anything above zero is going to start creating drag. I don't remember what the exact boundary is though I'm guessing about 58Km. Certainly drag doesn't become particularly effective at slowing anything down much above 55Km but that may be down to lack of patience...

    4.9 years ago
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    8,458 crowxe

    I think the lowest orbit is between 58 exactly and 58.25 , I'm sure it was 58.25 but recently I think it no decay happened above 58 . The orbit nodes flickering can happen (even in less perfect circular orbits) when the RCS is on or when you change orientation even by gyro as it tends to swivel the command pod/chip around thus feeds in increase/decrease in velocity and its vector into the calculations that displays the orbit. That's my hypothesis. Not sure if it's correct.

    4.9 years ago
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    235 bspawn

    I get a decay of about 100m every ~5 minutes or so at 100km Droo orbit, but that may be a bug - https://www.simplerockets.com/Feedback/View/N81KwK/Orbital-Decay-Below-20km-Without-Atmosphere

    4.9 years ago
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    Ive gotten into a 79k orbit once

    4.9 years ago

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