Polar Lunar Tug Circuit

Using GMAT for specific types of missions.

Polar Lunar Tug Circuit

Postby njb » Thu Feb 21, 2019 5:40 am

I'm trying to put together a set of trajectories for a polar lunar propellant tug; departure LLO @ 90 degrees inclination - TEI - HEEO @ X degrees inclination - circular equatorial - TLI - departure LLO (ideally the same orbit).

I can do all sorts of parts of it:
HHEO@X - Equatorial: easy
Equatorial - LLO@90 by B plane targeting: easy - I think I can hit "clockwise" or anti but haven't tried both,
HEEO - LLO@90: also easy (and indicates there would be an energetically similar trajectory going the other way?)
which is good considering the low base I'm coming off...

But I'm having trouble trying to find a LLO@90 - HEEO - basically getting a low Earth Pe from the TEI, the solver just seems to get stuck jittering between two bad solutions and not really exploring the parameter space (TA for burn, delta-v). Also conceptually how can one find which turn of the corkscrew that is LLO is "the one"?

I've got a bad feeling I'll have to do something like your multi shooting example with two segments? (and repeat for each turn of the screw) a forward TEI and a backward HEEO capture burn and optimize to join them together? Or can I back prop solving for (epoch, deltaV)@(Pe on line of nodes) achieving Luna Pe "at the right place" like reverse B plane targeting?

Thanks - I hope someone can help...
njb
 
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Re: Polar Lunar Tug Circuit

Postby Ajaja » Thu Feb 21, 2019 7:48 am

HEEO - LLO@90: also easy (and indicates there would be an energetically similar trajectory going the other way?)

Yes, but what about orientation of the LLO plane? Maybe solutions for an arbitrary LLO@90 appear only in small windows twice a month?
Ajaja
 
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Re: Polar Lunar Tug Circuit

Postby njb » Thu Feb 21, 2019 11:45 pm

I figured out how to use the back propagation to go from LLO to HEEO - put Pe on earth moon plane line of nodes, vary epoch with Pe at Earth 185 km vary EOI and back propagate to a Lunar RMAG, vary TEI and back propagate to achieve INC, ECC.

I was not able to get arbitrary RAANs - the orientation of the LLO@90 plane - right? Which I can sort of see makes sense. But I found that the LLO inertial RAAN for the LLO-HEEO at lunar ascending node and the GEO-LLO at lunar descending node were within 2 degrees of each other (round 270). I guess this means the tug departs and arrives within a couple degrees, and a propellant depot could be at LLO 90, 270? A tug could make a 2 or 6 week sortie. I didn't run the AN/DN scenarios the other way, I did one and it was different, probably they are a matched pair also - if so depot A and depot B in different RAAN planes could both operate launching on alternate fortnights?
njb
 
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Re: Polar Lunar Tug Circuit

Postby Ajaja » Fri Feb 22, 2019 2:13 pm

I'm not sure, it's hard to understand all of this without scenario.
Obviously, the easiest way to achive any target inclination is to make plane change maneuvre (in N/-N direction) when you are crossing the equatorial plane on the way to Earth. And I don't get why you need some specific HEEO@X. If your goal is a circular equatorial orbit then your should get it as soon as possible (changing orbit planes near Earth needs more fuel).
Ajaja
 
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