Realistic planetary generation

General discussion about Celestia that doesn't fit into other forums.
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psCargile
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Realistic planetary generation

Post #1by psCargile » 10.04.2007, 19:48

My main reason for using Celestia is creating fictional planetary systems. I want these planets and moons to have realistic orbits, periods, and rotations. I've made use of programs in the Motherlode utilities section--StarGen and the ssc file creator. Plus I'm using Gravity Simulator to check out the orbits.

Another program I am using is an old QBASIC program I got of the 3D Stars website. This is what I use to generate data on planets and moons I create. Inputing things like ideal temperature, surface gravity, number of moons, their mass and distance relative to the Moon, it will tell me distance from the star, its period and rotation and the period of the moon(s). However, I'm not certain of its accuracy. It asks me "How big the planet is" in relation to the Earth, but I don't know if it wants mass or radius, which of course yield different results leaving me to wonder which is more correct.

I'd like to use something better. Is there a excel spreadsheet, or relevant formulas I can use in a spreadsheet, or some downloadable program or javascripted website that is better than what I'm currently using? For those of you that build planetary systems, how do you do it?

LightTanis
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Hi!

Post #2by LightTanis » 10.04.2007, 20:09

Hello man. I'm 3D designer, and i will love to collaborate with you in any project you may want. :)

bh
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Post #3by bh » 10.04.2007, 20:29

regards...bh.

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psCargile
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Post #4by psCargile » 11.04.2007, 06:51

Thanks bh. The tex files are too large for me to DL--no broadband available out here in the country, and not the fastest dial-up.

LightTanis, I do 3d artwork myself, some of which can be seen here at my board. I consider myself more of a conceptual artist and a lot of my models remain to be finished. Texturing is my weakness, more so because I'm impatient and dont want to deal with doing it. So I end up modeling more detail that I should, increasing the file size and slowing the rendering time.

Now that I have it dowdloaded, I have no idea how to use it. This does more than what I want to do. And since I can't DL the textures. . .

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Cham M
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Post #5by Cham » 11.04.2007, 07:13

psCargile,

I saw your GeoStation on your board. It's a really nice one. Can you share it for Celestia ?
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

bh
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Post #6by bh » 11.04.2007, 09:12

Yes... nice model, looks feasable and similar to ISS with the modules and solar arrays. Also your transport models are very well done... good stuff!

As far as I remember Rass's generator produces two text files, one is a ssc and the other a stc. I haven't used it since Celestia ver 1.3.1 so I think the directory structure has changed a bit. If you can download some of the textures it's definately worth a play with, as you know the sscs are easily editable. I got some great results with it!
regards...bh.

Dracontes
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Post #7by Dracontes » 11.04.2007, 13:33

As you can see by this screenshot I use a spreadsheet with a whole lot of calculations done. In fact, this particular *.xls file is close to 1 MB, may that excite you or not :wink:

If you want it quick and more or less dirty you can go with the generators.

I however can't afford that given the peculiar nature of my stellar system - of the sextuple kind - so I had and have to do research on all the pertinent issues regarding celestial mechanics and planetary matters and to maintain tight editorial control.
My particular favourites being Wikipedia and arXiv.

Things I'd look out for are:
- Units of measurement (the more precise the better)
- Keplerian orbital mechanics
- Interactions between planets (a royal pain)

After that it's toil and travail though I'd think a single star system is nothing compared to what I had to go through: I still have planets and moons to cull from my own.

I hope this was moderately helpful. I could offer to prepare a small digest of the equations and constants I used though it would have to wait for an opening in school work.
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Topic author
psCargile
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Post #8by psCargile » 11.04.2007, 18:08

I have no problem writing the ssc files, and I have Erin Dunn's System maker to make things easier. StarGen does a great job creating solar systems, however it doesn't do moons. I've noticed that Celestia (1.4.1) displays output and doesn't care if your inputs are impossible--I've put the Mir in a high elliptic orbit out to the Moon's orbit and gave it a high rate of speed that by all rights should have flung it out of the Solar system. It's easy to put planets and moons anywhere and Celestia's not going to care.

I've looked at the Wiki pages before and during making these posts, particularly Orbital Period and Kepler's laws of planetary motion, along with one on barycenters and the Hill radius. I'm not certain which of these formulas on these two pages are more relevant to my needs, more likely Kepler's 3rd law. And If I use Kepler's 3rd law and my units are in km and kg is the result going to be in seconds?

The qbasic program I use is called World Builder by Stephen Kimmel and the source code is here. The program runs fine, but it is tedious to use because to experiment to get desirable results you must re-input data, and if you make a mistake you have cycle through negative answers to start over. I don't know enough about this subject to decipher most of the code to uncover the formulas used. I have figured out that he is asking for mass when asking how big the planet should be, so that helps. I have no way of gauging the accuracy of the results this program gives, but I take it in faith that its pretty close, or close enough for fiction. It does calculate planetary rotation based on the moon(s) you give it. I don't know the math he used to figure this. I guess that it's speculation given you have to know the planet's initial angular momentum.
As far as coming up with planetary and satellite rotations, how realistic is it possible to get?
There is lots of stuff in the program that I don't care about that is covered it better generators such as whether the planet will have life and what kinds. If parts of this could be decoded and put in a spreadsheet, that would be great. I can do the spreadsheet portion.
If not, I'll continue to use as is.

As far as the GeoStation goes, I will need to trim it down to size when I get done with it. Slow dial-up limits what I'm wiling to upload as well.

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Cham M
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Post #9by Cham » 11.04.2007, 18:48

psCargile wrote:IAs far as the GeoStation goes, I will need to trim it down to size when I get done with it. Slow dial-up limits what I'm wiling to upload as well.


O please, don't remove any detail ! I prefer a high resolution model. 8)
"Well! I've often seen a cat without a grin", thought Alice; "but a grin without a cat! It's the most curious thing I ever saw in all my life!"

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psCargile
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Post #10by psCargile » 11.04.2007, 19:26

The model has some interior features that aren't needed. Currently the unfinished model is 29.8 MB. I can't upload this at my current and not expected to change anytime soon very slow dial-up internet connection. I download 1 MB in 15 to 20 minutes. It would take me about 8 hours to upload something this big. Sorry.

Okay, plugging formula into Excel I find that these formula from Wiki Image and Image are the same thing.

Using Earth and Moon masses in kg and SMA in km I get 2.35716. I have no idea what this result is telling me. I'm an 38 yrs old dog trying to learn a some new tricks.

Dracontes
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Post #11by Dracontes » 11.04.2007, 20:03

psCargile wrote: It's easy to put planets and moons anywhere and Celestia's not going to care.

That's one of the reasons why I prefer to do the math work myself, educated guessing from fooling around with numbers becomes second nature with time :wink:

psCargile wrote:I'm not certain which of these formulas on these two pages are more relevant to my needs, more likely Kepler's 3rd law. And If I use Kepler's 3rd law and my units are in km and kg is the result going to be in seconds?


This is the formula for orbital period. I'd also advise tidal lock timescale coupled with the notions of orbital resonance. This here thread pertains to multiple stellar systems though I think the formulae presented on the linked paper can be used as well for planets and parent stars with good results, if a bit dismaying.
Hell no! Use base SI, kilograms, metres and seconds always. That's why precision to the metre/kilogram/second is always a good thing :D
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Topic author
psCargile
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With us: 13 years 7 months

Post #12by psCargile » 11.04.2007, 22:09

Meters! Alright, so if I input the semimajor axis in meters I should get results that make sense.

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psCargile
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Post #13by psCargile » 17.04.2007, 08:04

I did have a problem but I figured it out. Now my answers make sense. Thanks for all the help.


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