I've been playing with lunar retrograde orbits in an orbital simulator. The retrograde lunar orbits with apolunes below 40,000 km altitude are pretty stable. They seem resistant to distortion from earth's gravity or the sun's gravity. So I've been thinking of the ceiling for stable LDROs as around 40,000 kilometers.

What is the floor for stable lunar orbits? I am told that if the orbits are too low, they'll be wrecked by mascons.

By stable I mean an orbit that will last a few centuries without station keeping.

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    $\begingroup$ Does the orbital simulator have any mascon data built in? $\endgroup$ – Nathan Tuggy May 16 '15 at 19:58
  • $\begingroup$ No. I can specify mass, position vector and velocity vector. Each object is treated as a point mass. $\endgroup$ – HopDavid May 16 '15 at 21:06
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    $\begingroup$ OK. I see what was confusing me: it sounded (on my first and second reads) as though you were treating data from the simulator as a starting point to determine where mascons start becoming problematic, and attempting to pin down a presumably somewhat inaccurate result accordingly. But you're actually working on stability from two sides and two unrelated sources of perturbation, one of which you have no data on at all. $\endgroup$ – Nathan Tuggy May 16 '15 at 21:09
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    $\begingroup$ You got it. My sim gives me some notion of the ceiling but tells me nothing of the mascons. $\endgroup$ – HopDavid May 16 '15 at 21:33
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    $\begingroup$ This article talks about frozen orbits that avoid the worst of the mascon perturbations for orbits under 100km: science.nasa.gov/science-news/science-at-nasa/2006/… -- but that's talking about stability measured in years, not centuries. Note that for very small objects, non-gravitational perturbations (solar pressure, outgassing) will also be a significant factor. $\endgroup$ – Russell Borogove May 17 '15 at 0:05

The analytical solution for an orbit around the moon would not help you because mascons are ignored, the theory only works for a hypothetical moon of homogenous density. A numerical simulation of an orbit over the known mascons would require very precise data about the mascons and a lot of computing time for the simulation of a few centuries. How much numerical precision is necessary to simulate such a long time? Finding the floor for stable orbits is try and error. A lot of expensive computing time on large parallel processor might be necessary. If a candidate of a stable orbit is found, it must be tested if it is stable even for small variations of orbit height and plane.

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  • $\begingroup$ "How much numerical precision is necessary to simulate such a long time?" Dan Adamo in the link to his FISO talk in my comment above above, says that one needs a precision of 5 meters/second just for the orbital insertion in order to achieve a stable orbit he found at 70,000 km altitude, at the upper limit. Maybe similar precision is needed at his lower limit of 2,700 km.That sounds like allowing for only a very a small margin of error over many orbits. $\endgroup$ – LocalFluff Nov 15 '16 at 11:09

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