How is Orbiter / TransX MFD calculating orbits?

[Topper]

Hi, i have some quetions about orbit calculating in orbiter.

1., i ask me, how is orbiter calculating the position of vessels / g-bodys?
Does the moons from Jupiter attract the other moons? Or are they calculated like a "2 body system"? (for example, is Io attracting europa??)
I think the Vessel position is calculated by numeric integration right?

2., why has transXMFD always an error on far distances? I nevere come to Mars exactly, when iam starting the jorney from earth (without correction burns). In some cases, Encounter MFD is (a little bit) more exactly.

3., are there other factors witch are distorting the calculations of TransX MFD like time aceleration?

4., this is a "sdk quetion": is there a way with the orbiter api to get the planets/gbody position for a given time? (Even for moons of other planets)

Iam trying to create a MFD wich is calculating the position by numeric integration. I get good results now (in some cases, more exactly than with TransX MFD, but there is much more calculation time needed).

I think for calculating the vessel position, the way is good and ok. But even the calculation of the positions of the g-bodys is numeric now, and i need to find a better way, because over far distances the "error" is exeptional by the way.

 

[jarmonik]

Hi, i have some quetions about orbit calculating in orbiter.

1., i ask me, how is orbiter calculating the position of vessels / g-bodys?
Does the moons from Jupiter attract the other moons? Or are they calculated like a "2 body system"? (for example, is Io attracting europa??)
I think the Vessel position is calculated by numeric integration right?

Positions of a vessels are calculated using a numerical integration method called runge-kutta. All major g-bodys including the moons of the jupiter are calculated using ephemerides. Ephemeris is not a numerical integration but it do have a similar precission/accuracy than a numerical integration have. Some other minor bodies those aren't included in the ephemeris package are approximated as a 2-body system.

The moons of the jupiter do behave like being attracted by other g-bodies. But if you add a new moon into the jupiter system that doesn't exist in reality it won't attract the other moons.

2., why has transXMFD always an error on far distances? I nevere come to Mars exactly, when iam starting the jorney from earth (without correction burns). In some cases, Encounter MFD is (a little bit) more exactly.

Calculations made by TransX are based on a 2-body techniques. They are only a rough approximations of the vessel's trajectory. Errors will increase as the time of prediction is increasing. 2-body calculatios are accurate only when the vessel is deep within the gravitational field of a g-body.

3., are there other factors witch are distorting the calculations of TransX MFD like time aceleration?

Time acceleration is not effecting in a calculations. There aren't any other things causing a significant effects.

4., this is a "sdk quetion": is there a way with the orbiter api to get the planets/gbody position for a given time? (Even for moons of other planets)

Yes, there is. You can use Orbiter's Celbody interface but it will only work for g-bodies those are controlled by ephemerides.

Like this:
CELBODY *cMoon = oapiGetCelbodyInterface(hMoon);
cMoon->clbkEphemeris(MJD, EPHEM_TRUEPOS, &pos_vel_data);

Look more details from the SDK documentation.

 

[Topper]

Ok thx that will help me ;-)

But one more simple quetion:
If i build and compile a vessel with enogh mass, can it attract other vessels?

 

[statisticsnerd]

Can I de-orbit the Moon by strapping on a gajillion boosters to one side and burning retrograde until the thing is in the middle of the Pacific Ocean?? Is that possible in Orbiter? I've never tried.. h:

 

[Tommy]

If i build and compile a vessel with enogh mass, can it attract other vessels?

You could simulate this in the vessel's module - have it check for nearby vessels and apply a force to them based on distance, mass, etc. Otherwise, no, it's not supported by the core AFAIK.

Can I de-orbit the Moon by strapping on a gajillion boosters to one side and burning retrograde until the thing is in the middle of the Pacific Ocean?

Pretty sure that's a no. The Moon is controlled by a module (VSOP97 or whatever) and won't react to the thrust applied to it