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Old 01-20-2018, 12:08 PM   #31
Thorsten
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Heh - I happened to stumble across a treasure-trove (of course I knew in theory of such things, but, well, hands on is always different).

I couldn't resist trying to plan a trajectory to the Moon once it was in-sim, and stumbled upon the whole zoo of low energy trajectory solutions.

If the spacecraft gets just nudged into the L1 Lagrange point region, the future trajectory can be altered with really tiny propellant usage - basically the vessel gets pulled towards the Moon, but by a tiny nudge this or that way, the closest distance can be controlled - which leads to vastly different swing-by scenarios - the craft can be deflected out of the orbital plane by 90 degrees, or set onto a retrograde orbit away from the Moon where it leaves its Hill sphere quickly - or deflected along the lunar orbit, where it gets de-celerated by the Moon following it and relatively easily ends up in a closed orbit via a small deceleration burn (for comparison, a Hohmann arrival burn at lunar orbit takes 590 m/s, my cheapest capture into an elliptic orbit was around 150 m/s (there's probably even cheaper solutions - I didn't run the simulation for too long, so I wanted to see periodicity soon).

At the same time, there's a series of marginal orbits where the craft goes around the Moon a few times, but then the perturbations by Earth grow so much that it leaves lunar orbit again.

I'm still struggling to get a good visualization of what is happening - plotting trajectories in 3d space easily leads to a lot of Spaghetti. But this is terribly good fun to explore.

(Sorry to those who already know this stuff to sound over-excited...)
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Old 04-11-2018, 05:31 PM   #32
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Despite movie making, I've finally managed to bring the next version 0.3 of the software into existence, source code can be found in the usual place.

This allows to specify the gravitational influence of (up to five) other bodies on an orbit around Earth - but you can use it to explore transfer to the Moon if you so desire (an Earth-centered coordinate system is just a bit awkward to specify the state vectors).

I've ran some sanity tests, and the resulting perturbations look qualitatively like I'd expect, the orbital dynamics around the Moon seems okay and the one where I found an analytical benchmark (mean drift of the longitude of ascending node of a geosync orbit due to the Moon) seems to come out okay, but I will honestly say that coding the perturbations in Earth-centered coordinates I have managed to confuse myself no less than three times, so there may be bugs left to discover.

I'll start adding new pages to the tutorial series tomorrow to explain the new functions - have fun!

(Transfers will probably be a bit more user-friendly in the next version...)
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Old 04-12-2018, 08:31 AM   #33
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Windows executable of your 0.3 code: https://snoopie.at/face/beta/leo_targeting.exe

I've tested it with the lunar orbit config, resulting in this zoomed plot of the left-most orbit differences:
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Old 04-12-2018, 09:14 AM   #34
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That's the moon-relative, right?

My suspicion is that gets a lot of perturbation from Earth, but I haven't analyzed in detail.
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Old 04-12-2018, 09:31 AM   #35
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Quote:
Originally Posted by Thorsten View Post
 That's the moon-relative, right?

My suspicion is that gets a lot of perturbation from Earth, but I haven't analyzed in detail.
It is the 2D plot and suffixed with "_rel", so yeah, I guess so. On the grand scale, it looks like a thick line depicting a circular orbit, but zoomed in you get these differences.

No particular interest here, I just wanted to quick-check the binary.
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Old 04-13-2018, 05:36 AM   #36
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Thanks for the Windows work - the executable should now be available (and the first tutorial page is also added).
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