General Question Why do Stars Need a Module

[Interstellar Planet]

Why do stars need the line "module = sun" in their configuration files while planets do not need a module? I couldn't seem to find the answer to this anywhere. Thanks.

 

[martins]

Stars whose movement is computed by a module use that line. The same as planets. In the standard installation, the Sun, all major planets and most moons are controlled by modules that implement series expansions to perturbation solutions.

 

[BruceJohnJennerLawso]

Stars whose movement is computed by a module use that line. The same as planets. In the standard installation, the Sun, all major planets and most moons are controlled by modules that implement series expansions to perturbation solutions.

So the difference being that a module coded star will orbit the systems center of mass, as opposed to just sitting at the origin of the Orbiter coordinate system?

 

[N_Molson]

So the difference being that a module coded star will orbit the systems center of mass, as opposed to just sitting at the origin of the Orbiter coordinate system?

I guess that the barycenter of the Solar System isn't exactly the center of the Sun. And while I'm not sure where science is about this, maybe there is an inequal mass distribution, like on Earth. Also the Sun spins on itself, which affects calculations (basically, you sort of slingshot the Sun when you travel from a planet to the other ?).

 

[BruceJohnJennerLawso]

I guess that the barycenter of the Solar System isn't exactly the center of the Sun. And while I'm not sure where science is about this, maybe there is an inequal mass distribution, like on Earth. Also the Sun spins on itself, which affects calculations (basically, you sort of slingshot the Sun when you travel from a planet to the other ?).

Thats an interesting thought... :hmm:

But yes that is the general idea. Any basic two body system cant have the CG at the exact center of any one body if the masses are non zero. It may be really, really, close, but never quite perfectly at the center even if one of the masses is huge, as Sol most definitely is.

But does the Sun module scan the solar system config file for configs to use in its calculations, or is its strictly hardcoded to reflect the basic Orbiter distributions planets?

 

[jedidia]

basically, you sort of slingshot the Sun when you travel from a planet to the other ?

No, you slingshot it when you travel from one time to another :lol:

But does the Sun module scan the solar system config file for configs to use in its calculations, or is its strictly hardcoded to reflect the basic Orbiter distributions planets?

I would assume that it works in a similar way as the planet modules: algorithms that describe its movements as observed in reality, disregarding any other data (i.e. I would expect it to behave the same way even if you remove all the planets).

 

[BruceJohnJennerLawso]

I would assume that it works in a similar way as the planet modules: algorithms that describe its movements as observed in reality, disregarding any other data (i.e. I would expect it to behave the same way even if you remove all the planets).

Yeah, but what does it base the algorithms on? The relative wiggle that our sun has, or is it adjusted for large bodies in a system (ie, does this create small, but real differences in extrasolar systems that use the Sun module?)

 

[Interstellar Planet]

If the sun.dll module just contains info about the movement of a star, then why does orbiter crash if the line "module = sun" is not included in a star's config file? Planets work just fine without a module.:hmm:

 

[jedidia]

That, on the other hand, is a really good question... I didn't even know that this was the case (ironic, since I wrote a procedural system generator for orbiter that outputs config files... probably I have just forgotten about it since then).

 

[N_Molson]

No, you slingshot it when you travel from one time to another

Yes, too, I guess :hmm:

But seriously, if a there is an interaction between a spacecraft (or an object in general) that slingshots a planet (gaining velocity by "taking" a very tiny fraction of the rotation speed of the planet) and the planet itself, why that would not apply to the Sun ? :hmm: :hmm:

Or would it work only for a spacecraft/object that would come from another system, slingshots at our Sun, then escapes to another system ? :hmm: :hmm: :hmm:

 

[martins]

So the difference being that a module coded star will orbit the systems center of mass, as opposed to just sitting at the origin of the Orbiter coordinate system?

Well, the star _should_ orbit the system's centre of mass, otherwise you've got the physics wrong. (unless you are modelling a system without planets).

Thats an interesting thought... :hmm:

But yes that is the general idea. Any basic two body system cant have the CG at the exact center of any one body if the masses are non zero. It may be really, really, close, but never quite perfectly at the center even if one of the masses is huge, as Sol most definitely is.

But does the Sun module scan the solar system config file for configs to use in its calculations, or is its strictly hardcoded to reflect the basic Orbiter distributions planets?

It 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. Trying to use the sun's dll for a different solar system will not work very well.

I would assume that it works in a similar way as the planet modules: algorithms that describe its movements as observed in reality, disregarding any other data (i.e. I would expect it to behave the same way even if you remove all the planets).

Yes.

If the sun.dll module just contains info about the movement of a star, then why does orbiter crash if the line "module = sun" is not included in a star's config file? Planets work just fine without a module.:hmm:

I don't know. I didn't realise that that was the case (The sun in Orbiter has been controlled by module for a long time). Of course, if you don't use a module, you must at least specify the two-body elements in the cfg file. What set of elements did you try?

 

[Interstellar Planet]

Of course, if you don't use a module, you must at least specify the two-body elements in the cfg file. What set of elements did you try?

Sorry, I didn't know that two-body elements could be specified for a star! I just assumed stars didn't need those because the cfg file for the sun did not have any two-body elements. Thanks!

So, how would you write the two-body elements for a star? Is it different than for a planet?