[Project] Orbiter Galaxy

[jedidia]

Quote:

The second is that there is an outer limit as far as the gravitational stability of orbits, but I don't think it gives a good boundary for the accretion disk of a forming gas giant.

Well, I can specify the boundary for the accretion disk as well as an outer limit for planets to be formed, so this might come in very handy. Will try it out this evening, thanks.

[tgep]

Quote:

Originally Posted by jedidia

 uff, I'm kind of sick lately, so my activity is a bit reduced.



Problem is, how am I going to do multiple solar systems for Orbiter? it just doesn't seem practical (besides the fact that writing a system generator that produces reasonable results for multiple solar systems would be a major undertaking, and probably quite a bit out of my league...)

No , no ..... not Multiple solar systems ....... multiple STAR systems. I'm talking about double and triple stars in orbit about each other .... planetary formation would be VERY unlikely in star systems such as this

[T.Neo]

Why?

I'd imagine if the stars were close enough or far out enough, planets should form fine.

Barring other planets and/or metallicity issues.

[tgep]

Quote:

Originally Posted by T.Neo

 Why?

I'd imagine if the stars were close enough or far out enough, planets should form fine.

Barring other planets and/or metallicity issues.

Your forgetting about the effects of of the solar wind as well as the blast wave from the innitial ignition of the star itself .... put two or three stars like that in close proxcimity and they will clear out a lot of the remaining gas and dust in a hurry.

[jedidia]

Hmmm, the hill sphere suffers a similiar problem as does soi: it is much bigger for planets that are further away, so taking it as a basis for an outer limit for moons that are formed leads to outer gas giants having much more moons than inner gas giants, a fact that I do not see reflected by our solar system. I guess I'll just play around with a gravity limit until I guet results that I like...

Quote:

I'm talking about double and triple stars in orbit about each other

I understood you correctly, but misformulated. But as I said, Orbiter doesn't seem to a very practical platform for systems with more than one star.

[Nemoricus]

Are you sure that that effect is not present in our solar system? The outer planets are harder to observe and may have many more moons than we currently know of. Especially moons of the barely-more-than-debris kind.

[Linguofreak]

Quote:

Originally Posted by tgep

 Your forgetting about the effects of of the solar wind as well as the blast wave from the innitial ignition of the star itself .... put two or three stars like that in close proxcimity and they will clear out a lot of the remaining gas and dust in a hurry.

There is no "blast wave" per se from the ignition. There is a sharp increase in brightness, but it still occurs over the course of many years (it's sharp compared to the lifetime of the star, which is many, many, many, many, many years). Also, if the stars are of different masses, the ignitions will happen at different times and last for different amounts of time (big stars ignite earlier and faster than little stars).

And any given collection of stars is *less* bright than a single star of the same mass.

The primary obstacle to planetary formation in multiple star systems is the gravitational influence of the stars.

---------- Post added at 01:47 ---------- Previous post was at 01:35 ----------

Quote:

Originally Posted by jedidia

 Hmmm, the hill sphere suffers a similiar problem as does soi: it is much bigger for planets that are further away, so taking it as a basis for an outer limit for moons that are formed leads to outer gas giants having much more moons than inner gas giants, a fact that I do not see reflected by our solar system. I guess I'll just play around with a gravity limit until I guet results that I like...

In fact, the problem is actually worse for the Hill Sphere than for the SOI. It's a good limit for capture moons, but not for co-formed moons, and *certainly* not for impact moons (whose orbital radius will depend on the age and angular momentum of the planet-moon system).

Neptune has a pair of moons (capture moons I think, but am not sure), that have *very* wide orbits (SMa's around a third of an AU, apoapses even further out). The total Hill sphere radius is .775 AU.

[jedidia]

Quote:

Are you sure that that effect is not present in our solar system? The outer planets are harder to observe and may have many more moons than we currently know of. Especially moons of the barely-more-than-debris kind.

That stands to reason, of course, but I don't want to create stupendious numbers of small rocks flying around in orbit. It will just give Orbiter a lot more numbers to crack without giving the player anything he can orbit.

I experimented around a bit more, set the outer limit to a simple gravity-limit (0.002 Gs, a bit less than the influence on the outmost "essential" not-captured moon in our solar system), and am currently playing around with the inner limit, which was set too far out by accrete to be usable for gas giants. However, it turns out that there aren't any relevant masses formed beneath that limit anyways, so reusing the accrete algorithm to simulate the accretion around gas giants might not be such a bright idea after all. I'll have to play around with it a bit more and see what other options I can come up with...

[jedidia]

Did some further research into the matter. Pretty hard to find any material about the topic, there doesn't seem to have been too much research into the topic, at least not enough to produce some decent free documentation. So far I gathered bits of this and that together to improve my algorithms. I found information that the moons around the gas giants seem to take up roughly 0.01 percent of the mass of the planet they're orbiting.
Also, there is the theory of orbital contraction, which might just be what I need to get better results (given that currently most moons are formed much further out than they should be compared with the solar system). According to this theory, forming moons induce a wave into the accretion disk, leading to an orbital contraction, bringing the moons further in. The more mass a moon has, the stronger the contraction, resulting in an actual upper mass limit (since the orbits of more massive objects contract beneath the roche limit).

Now the big problem is that I have found this described in a few words here:
http://www.theregister.co.uk/2006/06...ons/print.html

but have been unable to find any precise data about it. Obviously these guys made a computer simulation of their theory... I want that code!

Meanwhile, I'll be conducting my own little experiments with orbital contraction to see if I get some results that I like...

---------- Post added 11-27-09 at 11:21 AM ---------- Previous post was 11-26-09 at 08:50 PM ----------

Just encountered a very nasty bug, and I'm not yet able to tell which elements of my code get screwed up by it, I'll have some cleaning to do.

the problem was that in C any input that has no . deliminator is automatically handled as an integer, so an operation like 1/3 would return 0, while 1.0/3.0 returns the right result. It's well possible that a lot of my mathematical operations currently return bollocks.

[tgep]

Quote:

Originally Posted by Linguofreak

 There is no "blast wave" per se from the ignition. There is a sharp increase in brightness, but it still occurs over the course of many years (it's sharp compared to the lifetime of the star, which is many, many, many, many, many years). Also, if the stars are of different masses, the ignitions will happen at different times and last for different amounts of time (big stars ignite earlier and faster than little stars).

And any given collection of stars is *less* bright than a single star of the same mass.

The primary obstacle to planetary formation in multiple star systems is the gravitational influence of the stars.

---------- Post added at 01:47 ---------- Previous post was at 01:35 ----------

My mistake ... I was thinking of the preasure from the higher radiation release but didn't express it correctly. The combined effects of the gravity wells and radiation preasure would clear out a wide area around a double star and inhibit planetary formation in the zone close to the stars where you would expect to find habitable worlds ..... but planets ( mostly gas giants and proto stars ) COULD form in the outter zones and get slung into closer or highly eccentric orbits by gravitational interactions with each other. ( the Jupiter effect )

[jedidia]

So, I cleaned out my mess and am finally getting some results I like. Now I have to fix the radius problem... stargen uses the Kothari equations to calculate a planet radius, I'll have to read up on that a bit.

Edit: I just solved the problem by NOT solving it. Instead I went through the mass-diameter relationships of the Galilean moons and noticed that the radius of my generated moons is within 2 decimal points when they have the same mass. It just seems a bit strange when looking at the numbers, but obviously that's just the way it is. Hoorray for the original programers!

Now I'll have to do something to give impact moons a reasonable orbit (since stargen only creates the moons without their orbital elements) and I'm all set to plug it all into my galaxy generator.

[tgep]

Excellent Smithers, excellent !
Soon the Galaxy will be ours. ( rubs dry boney hands together and grins maliciousely )

[jedidia]

I'm finished with the solar system generator for now. The future plan looks as follows:

- Plugging system generator into my galaxy generator (easy)
- providing GUI for displaying system overview (will take a while)
- finishing stellar evolution model and changing systems accordingly (already halfway there)
- finishing touches to the galaxy creator (dunno how long this will take, this will probably involve some unforeseen trouble)
- release of a demo of the galaxy generator (without interface to orbiter) for interested people to go bug-hunting and making suggestions about improvements that will certainly be in order (somewhen in January I guess)
-wrapping up output routines, plugging in texture generator and making an MFD to interface the whole thing to orbiter (absolutely no Idea how long this will take, since the problems I will be facing will be completely new to me...)

So for now, you can look forward to a release of the generator as a stand alone.

[dumbo2007]

This is great !!...1 question....it will not be possible to actually add an extra star to the orbiter model yet right....but you have got a model for stellar evolution and galaxy creation....so how is this data visualized in orbiter....or is the output of the model stored in files ?....by output I mean the positions of the stars etc...

[jedidia]

Quote:

so how is this data visualized in orbiter....or is the output of the model stored in files ?....by output I mean the positions of the stars etc...

Well, the positions are visible in the map, which is a program more or less independant from orbiter and will have to be run in a different task. That programm will provide you with all the information about the stars and the systems therein (see the screenshots earlier in this thread. I'm currently updating the GUI to display information on the systems)

Then of course the systems will be outputable to Orbiter format. The biggest concern here are textures, but I hope to be able to use Artlavs texture generation library (he agreed to that a while ago, and I think it shouldn't be too much hassle to implement them).

Finally, there will be an MFD inside orbiter that will be able to show information on the selected target system and allow you to actually get there (similiar to MSSSmfd).

Quote:

it will not be possible to actually add an extra star to the orbiter model yet right

No, but a switch to another system can be achieved relatively easy by loading a new scenario.

---------- Post added at 05:19 PM ---------- Previous post was at 09:19 AM ----------

System Quick overview implemented:



Pops up whenever you move the mouse on a star. Guess I should put in a pop-up delay too, but that will be easy work later on. Now on to the detailed overview that opens on doubleclick, that will be a bit more work...

---------- Post added at 05:19 PM ---------- Previous post was at 05:19 PM ----------
Dang, I managed to double post...