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Old 03-15-2019, 08:38 AM   #16

I've checked it in Orbiler, and it works.
There is a "lodestar" (for the green trajectory) that can be used to target LOP-G from Brighton-Beach:
  STATUS Orbiting Moon
  RPOS -3111927.892 -26616079.085 -14832641.036
  RVEL 8.0341 435.9435 99.7092

Last edited by Ajaja; 03-15-2019 at 08:43 AM.
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Old 03-17-2019, 01:45 AM   #17

The green line is the trajectory to the LOP-G from a low circular orbit above Brighton-Beach and the yellow is the return trajectory. The most interesting fact is that we need less than 200 m/s at the apoapsis to align speed with LOP-G, dock, and then to make a burn to return back.
dV = 2343 m/s + 86 m/s + 99 m/s + 2344 m/s
I'm really quite impressed with what you've managed to achieve here with GMAT.

The dV numbers that you quote make intuitive sense: if one thinks of a NRHO as glorified highly eccentric Keplerian orbit (albeit one subject to string tidal forces from the Earth), the periapsis speed needed to achieve an apoapsis of about LOP-G's orbital apoapsis is around 2330 to 2340 m/s. Moreover, apoapis speed is going to be around 45 m/s so, taking into account the possibility of an up to 90 degree plane change to align planes with LOP-G, means that the maximum rendezvous speed is going to be approximately \sqrt{2} of that or approximately 65 m/s. And although this is 'back of the envelope' stuff, it aligns pretty well with your considerably more accurate GMAT results.

There are a couple of takeaways from this:

* GMAT seems to be a useful adjunct to working with three body orbits in Orbiter. In the absence of tools developed specifically for Orbiter, trajectory planing using third party tools such as GMAT is clearly advantageous.

* In a fuel efficiency sense, targeting an arbitrary point on the lunar surface with a lunar lander is beset achieved at LOP-G orbital apoapsis for both departure and return.

* However, this fuel efficient strategy comes at the price of having the crew of a lunar lander being fully dependent on that vehicle for 3-4 days of the descent to the Moon's surface from LOP-G; up to two weeks on the lunar surface; and another 3-4 days for the return ascent back to LOP-G. The lunar lander is going ti have to provide food, water and oxygen (and radiation shielding) for two or more people for at least three weeks. That, I would imagine, is quite a design challenge.

Ajaja, many thanks for your contribution on this subject.
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