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Old 07-10-2012, 04:04 AM   #1
Summercat
 
Join Date: Jul 2012
Default 3rd Edition GURPS Space system generation question

Hello,

This looks like the right place for this.

Anyhow, I am currently in the process of building a random galaxy generator using the system rules for generation in GURPS Space 3rd Edition, 2nd Printing. The 'behind the scenes' code is fairly much finished, except for gas giant generation information, as well as further details on natural satellites.

The only information the book gives about moons is the Roche Limit (2.5 * planetary diameter for habitable worlds), and that moons of terrestrial worlds tend to be less dense than their center of orbit. However, this doesn't really fit my needs entirely - while for terrestrial worlds I'm willing to do some handwaving and just list the number of each type, for Gas Giant sub-systems, it is another matter entirely.

In the rules, it gives some lovely information about gas giant (and brown dwarf) features, and I can get away with using 4d/10 for the mass of gas giants (Diameters are given as a flat), but that does not help me with figuring out the data of the larger, terrestrial-planet sized moons, especially with information that derives from what they orbit.

This is especially vexing for when trying to figure out the distance, orbital period ('year'), and day (if not tidelocked) of world-sized moons.

Also, while the density for Gas Giants is a nice given (assuming that 4d/10 is an acceptable range, .4 to 2.4, book says .6 to 2.5), there is *no* data on the density (Or mass, for that matter) of Brown Dwarfs.

Using Wikipedia (Groan all you want, I don't feel like going into primary sources), and some probably very bad math, I came out with Brown Dwarfs having an average density 5 times that of Earth, or 27.5 g/cm^3 (Earth is ~5.5g/cm^3, listed in the book at Density 5.5).

However, while the density helps (and from the density we can calculate mass, apparently all brown giants are the same diameter as Jupiter. Just much more dense), the resulting mass in Solar Masses is... a giant mess.

According to my (possibly shakey) math and Wikipedia, Sol is 1.408 * 10^3 kg/m^3, or brought into the same terms -

In the middle of writing the above paragraph, I went to double check my conversion of units, and eventually discovered A) I was <explative delative> off a lot, B) The density of Sol is ~1.4g/cm^3, and C) When my math went even more horribly wrong, I found http://www.scholarpedia.org/article/Brown_dwarfs which gives a mass of less than .075 for Brown Dwarfs.

Even assuming a .07 Solar Mass for Brown Dwarfs (Hey, maybe 1D/100?) still doesn't help *too* much with much less massive Gas Giants and their mass, nor with the GURPS-translation of Bode's Law for their orbitals, where everything is in AU.

So, not seeing any errata covering this, and not being smart enough to figure it out myself, I go to the forums, to see if anyone else has run into this issue and found a solution for it.

Before anyone asks, no, I will not be providing my code at this time - not because I want to keep it secret, but because it's an unfinished ugly mess that has no interface whatsoever. Once it's *done*, that's another matter entirely.

Last edited by Summercat; 07-10-2012 at 04:05 AM. Reason: Sol does not mass 1.4g/cm^3
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Old 07-10-2012, 05:28 AM   #2
Pomphis
 
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Default Re: 3rd Edition GURPS Space system generation question

http://forums.sjgames.com/showthread.php?t=41312

was about Brown Dwarfs.

Brown Dwarfs are apparently between 0.015 and 0.07 solar masses.
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Old 07-10-2012, 05:41 AM   #3
Summercat
 
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Default Re: 3rd Edition GURPS Space system generation question

Quote:
Originally Posted by Pomphis View Post
http://forums.sjgames.com/showthread.php?t=41312

was about Brown Dwarfs.

Brown Dwarfs are apparently between 0.015 and 0.07 solar masses.
Thanks, there's that (Now just need to figure out a table/density for 'em)

Still no clue about the orbital bodies *chuckles*
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Old 07-10-2012, 09:24 AM   #4
ericthered
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Default Re: 3rd Edition GURPS Space system generation question

your real problem is that Brown Dwarfs don't have consistent densities. They start out hot (and inflated) and then slowly cool, shrinking as they cool, and becoming partially degenerate.

also: I'm not yelling at you for using wikipedia, its clear and consise, but if you want numbers (and possibly equations), primary sources are excellent (many of them have too many numbers, as a matter of fact).

this is a pdf with a chart of the relationship between mass and radius at given periods of time. The three times charted are 1, 5, and 10 billion years, which give a starting point.

this is another pdf that claims the radius relationship is R=R0*m^(1/8). This source seams to be much less reliable than the other one though.

Indeed, it seems that the debate on the radii of brown dwarfs is up in the air, they were theoretical until recently (in the timescale astronomy moves at).

As for orbital bodies, I'd make a switch that either treats it as a very small star or a very large planet, and let the user toggle that. (I'm assuming they can toggle brown dwarfs off or on in the first place. If not, certainly add it).
you could even just say "you want brown dwarfs? fine, but set these parameters: frequency, distribution, and planets surrounding it"

By the way, what language are you using, and while you don't want to share it due to the mess its currently in, would you mind sharing it with another programmer?:). Yeah, I read the above, thats why I specified programmer.

good luck, and if you've got that much done already, good work!
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Old 07-10-2012, 11:30 AM   #5
Summercat
 
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Default Re: 3rd Edition GURPS Space system generation question

Quote:
Originally Posted by ericthered View Post
your real problem is that Brown Dwarfs don't have consistent densities. They start out hot (and inflated) and then slowly cool, shrinking as they cool, and becoming partially degenerate.

also: I'm not yelling at you for using wikipedia, its clear and consise, but if you want numbers (and possibly equations), primary sources are excellent (many of them have too many numbers, as a matter of fact).

this is a pdf with a chart of the relationship between mass and radius at given periods of time. The three times charted are 1, 5, and 10 billion years, which give a starting point.

this is another pdf that claims the radius relationship is R=R0*m^(1/8). This source seams to be much less reliable than the other one though.

Indeed, it seems that the debate on the radii of brown dwarfs is up in the air, they were theoretical until recently (in the timescale astronomy moves at).

As for orbital bodies, I'd make a switch that either treats it as a very small star or a very large planet, and let the user toggle that. (I'm assuming they can toggle brown dwarfs off or on in the first place. If not, certainly add it).
you could even just say "you want brown dwarfs? fine, but set these parameters: frequency, distribution, and planets surrounding it"

By the way, what language are you using, and while you don't want to share it due to the mess its currently in, would you mind sharing it with another programmer?:). Yeah, I read the above, thats why I specified programmer.

good luck, and if you've got that much done already, good work!
Ugh. Makes me want to stab science. "I'M STUPID JUST GIMME NUMBERS SO I CAN PLAY MAI GAME!" or something *laugh*

I'm currently using Python 3.x, because Python is all I know. If you want to look at my horrible horrible code, I guess...

Eh. Sure. Why the hell not. It's not like I'm going to be selling this when it's done xD http://dl.dropbox.com/u/17713914/galaxy_generator.rar The main file is galaxy_class, and has *nothing* done for terms of stuff.

In terms of map generation, it makes a square grid where each square is 1 parsec^2. I could, if I was so inclined, make it into a cube. But that would be insane.

Right now, I'm pausing working on the generation code to build some analysis tools (all in galaxy_class.py), and I normally work at this when I'm at work (I get paid 11 an hour to... stay awake. My company encourages me to do my own projects while there xD), and I've the next two days off.

If you know anything to do with Python, I'm more than willing to accept suggestions, but you'd be able to tell from the code that I don't really know what I'm doing.
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Old 07-10-2012, 12:19 PM   #6
Jerander
 
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Default Re: 3rd Edition GURPS Space system generation question

May I ask why you chose 3e over 4e? And, good luck with your project!
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Old 07-10-2012, 01:39 PM   #7
ericthered
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Default Re: 3rd Edition GURPS Space system generation question

I think that a good system generator is a wonderful toy. Unfortunately, the problem isn't getting the numbers, its presenting the numbers and doing the interface. That and the shear number of numbers involved. you have to either format all the info correctly or write a program that can take in the data and do it for you.

As mentioned above, making it 3D is INCREDIBLY hard to display. you can use a 3d animator, but then you have to build everything in the animator. Also, I initially didn't notice the program was 3e and not 4e. I started a 4e version of the project a while ago and got tired of editing massive switch statements. Yes, regex helps, but not much, as each table is different.

as a side comment on the science, the tables used in 4e are very accurate. They certainly got my attention. And yeah, bummer that science doesn't really have brown dwarfs nailed down.

Edit: and looking at the code, I think I know why: 3e might be the easier of the two to make.

Last edited by ericthered; 07-10-2012 at 01:42 PM.
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Old 07-10-2012, 03:05 PM   #8
Summercat
 
Join Date: Jul 2012
Default Re: 3rd Edition GURPS Space system generation question

Quote:
Originally Posted by Jerander View Post
May I ask why you chose 3e over 4e? And, good luck with your project!
Quote:
Originally Posted by ericthered
I think that a good system generator is a wonderful toy. Unfortunately, the problem isn't getting the numbers, its presenting the numbers and doing the interface. That and the shear number of numbers involved. you have to either format all the info correctly or write a program that can take in the data and do it for you.

As mentioned above, making it 3D is INCREDIBLY hard to display. you can use a 3d animator, but then you have to build everything in the animator. Also, I initially didn't notice the program was 3e and not 4e. I started a 4e version of the project a while ago and got tired of editing massive switch statements. Yes, regex helps, but not much, as each table is different.

as a side comment on the science, the tables used in 4e are very accurate. They certainly got my attention. And yeah, bummer that science doesn't really have brown dwarfs nailed down.

Edit: and looking at the code, I think I know why: 3e might be the easier of the two to make.
Answering the 3E v 4E question, it's because.... I don't own 4th Edition Space. I own 2nd Edition and 3rd Revised - I thought about getting the ebook of 4th, but I *hate* electronic formats for reference material. Hate Hate Hate. I much prefer hardcopy, I do not order stuff online, and nobody in my area that A) I can find in my time schedule and B) Want to RPG wants to use GURPS. So... no point in me spending more money on books I'm not likely to use. I've had this one for a few years, when a FLGS shut down and marked everything down 90% >_>;;

As for presentation, I actually have a plan for the generator to, once you've approved the results of the analysis tools (Which I'm still writing), have it export an HTML site. The map will be a grid of images (with alt-text of the star name), click on the star brings you to main/star/index.html, and with links to individual planetary bodies at main/star/orbit#.html, with (once I get to that point with gas giant subsystems, main/star/orbit/subsystem/*.html)

The resulting HTML would be static with CSS, so it'd be relatively easy to do editting in notepad.

I'd want to eventually also export a bunch of variables to a conf.py file, so people can muck about with how many stars, star chances, planet info, etc.

Right now, on a 300x300 parsec grid...

>>> arf = Galaxy(300)
>>> arf.star_count()
24941
>>> arf.planet_count()
159795
>>> arf.colonizable()
198

'Colonizable' being any planet with an Oxy/Nitro or Polluted Oxy/Nitro and at least Plants/Flowers/Ferns level of biosphere.

Which may be low, very low, for some campaigns. Suits me and mine just fine; colonizable worlds are rare, space stations tend to be the norm. But obviously I'd want to add some sort of modifier here in case people want it.

Currently, though, the program has 0 interface. I don't even know how to code for it beyond text menus. And don't bother trying to use the print_map() function for anything larger than a 10x10 grid.

--

Also, I'm willing to bet if I sat down with the 4th rules, I could do something with Python. I am not a great innovator, but I'm a great adapter.
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