Problem Precision Needed to Get to Moon

Alexrey

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Hi guys,

I've been using Tex's Earth to Moon TransX tutorial but am having some problems. I can set the flight plan up fine and align our orbital planes, but when it comes to actually applying the thrust in the required direction I seem to mess it up. I make sure the green x is in the centre of the compass until just before delta-v cutoff where it understandably goes a little haywire, but I can never reach the Moon. What's more frustrating is that when watching Tex, he just lets the green x wander off centre near the end of the burn and still manages to get to the Moon! What am I missing? Are there any techniques to more precise flying (currently I make fine adjustments using Ctrl + linear or rotational RCS).
 

ADSWNJ

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Lots of reasons why this may not be working, but there will be a simple answer in the end and you WILL get there :).

Can you post a scenario file coming up to your burn and then right after? To do this ... hit Ctrl-S to do a quicksave, then find the .SCN file in the Quicksave folder. Insert it into your reply between a CODE /CODE block (i.e. type CODE inside square brackets, then paste the quicksave, then /CODE in square brackets).

My guess is you are burning at the wrong time, or the plan is wrong, but we shall see!!
 

Alexrey

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Since writing the post I've managed to get to the Moon, but I still mess it up most of the time. I have noticed though, that the delta-v given by TransX was not enough to get me to the Moon and I had to add some more to make it there. Here are the before and after quicksaves.
 

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  • DG Mk4 in orbit 1.scn
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  • DG Mk4 in orbit 2.scn
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garyw

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One MFD I still use all the time for fine tuning my approach to a planet or moon is [ame="http://orbithangar.com/searchid.php?ID=1823"]Encounter MFD[/ame] it's an old MFD but still works with 2010 and is invaluable to see how even small burns affect the approach to the target.
 

Alexrey

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I've done a few more practice runs to the Moon and have found that using linear RCS is FAR better than using rotational RCS when trying to keep the green x centred, but I still have to add between 5-10 m/s of delta-v onto the value given by TransX to be able to reach the Moon otherwise it always falls short.

As an aside, does anyone else have the problem whereby the videnie mod doesn't work when using the orbiter_ng exe (I'm using the 110912 version of videnie)?
 

T.Neo

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Apologies for being off topic here, but howzit! Welcome to the forum from SA! :)
 

ADSWNJ

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The inaccuracy is due to the two-body calculation model of TransX (i.e. your ship plus the dominant body - e.g. Earth). It ignores the effects of the Moon. For Earth-Moon trips, you'll find LunarTransferMFD is much more precise.
 

Alexrey

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Apologies for being off topic here, but howzit! Welcome to the forum from SA! :)
Thanks buddy, great to finally find out about Orbiter!

The inaccuracy is due to the two-body calculation model of TransX (i.e. your ship plus the dominant body - e.g. Earth). It ignores the effects of the Moon. For Earth-Moon trips, you'll find LunarTransferMFD is much more precise.

Aha, okay so I wasn't going crazy, great. I'm assuming then that Orbiter uses an N-body simulation to recreate the Solar System? If so it's very impressive that it runs so smoothly!

Are there any other tips that users here might have that will make transfers to the Moon, or any other celestial body for that matter, easier to achieve?
 
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ADSWNJ

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Check out this video using LTMFD:

[ame="http://www.youtube.com/watch?v=APgUMa2ei-4"]http://www.youtube.com/watch?v=APgUMa2ei-4[/ame]

Outside of Earth's influence, it gets religious between TransX and IMFD. Both cool for different things!
 

blixel

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Thanks for mentioning my video, but I kinda hate that example of using LTMFD. Also, from what I'm reading, he's trying to work out how to go from the Earth to the Moon at this point, not the other way around.

If you're looking for some non-tutorials :) - I have a few Earth to Moon using TransX examples on my youtube channel you can watch.



And more recently, dgatsoulis took the time to get onto TeamViewer with me to help me learn how to use IMFD. In this first example, we're going from the earth to the moon using a simplified method. (Dimitris shows me a better method in part 3 of this series.)

[ame="http://www.youtube.com/watch?v=btiYvWy-QeM"]Orbiter 2010 - [Part 1] IMFD Training with Dimitris - Earth to Moon - YouTube[/ame]
 

statickid

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The only thing I can think to add is this:

If you're cutting it that close it sounds like you're doing a really minimal trip. Perhaps you just need to plan a higher overall DV. My guess is that your taking more than three days to get there is this true? I typically aim for about 1.1-1.15 lunar orbit radii (eyeball it).

My general advice for reaching your goals is just remember space flight is rarely a fire-and-forget missel. you should be watching your instrument panel and trajectory predictions very closely. If you're going to be missing the moon there should be no surprise. It will notice at the end of your burn or before you're half way there. Then adjust with mid course corrections. Navigate the spacecraft, not just fling it and hope for the best :thumbup:
 

meson800

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I'm assuming then that Orbiter uses an N-body simulation to recreate the Solar System? If so it's very impressive that it runs so smoothly!

Not exactly.

It [the sun] uses the VSOP87 solution, which contains power series expansions of the orbits, fitted over a couple of millenia. The same approach as the major planets. This is _not_ a dynamic state propagation, but hardcoded for our solar system and time.

Basically, the Sun and the planets propagate along pre-determined paths, but these paths have been created so they coincide with the N-body solution for the solar system for the next couple million years. This means that the orbits of the planets are just as accurate as an N-body solution.

As to the vessels, I believe that all of the vessel states are calculated with an N-body solution.

This, of course, doesn't take away from the impressiveness of Orbiter you mentioned :hailprobe:
 

flytandem

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I loaded the original scenario and even though the setup for the maneuver looked good it sure didn't execute how it was shown. I would ask how far in advance the planned maneuver had been set up? If I am planning a burn many orbits ahead I will use that planned maneuver just to know which orbit I will be doing the burn then on that orbit I will turn off the maneuver and set up the burn again. I did this on your scenario and it then worked fine. In order to have enough time to set it up, since it was only 90 seconds away, I reduce the time by warping to 1/10th real time. In a couple of minutes I had the burn all set up, returned to real time and it executed just fine with resulting trip to the moon. Rule of thumb is to set up these burns in the hour or maybe couple of hours before the actual burn not days.
 
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