[Space] GURPS Handbook of the Planets

[Whill]

Thanks for answering my questions. Appreciated.

[Kraken]

Brett I recently downloaded your spreadsheet, and love the amount of detail it has (especially as it means I don't have to deal with generating it). I am planning on using it soon to pregenerate a whole batch of worlds for a sci-fi game.

I had a couple of questions - one about the spreadsheet and one more general I thought some of the readers on this thread may be able to answer.

First, Brett, how does your spreadsheet handle binary (and trinary) systems? I have taken a look at a couple of binary builds and can see all the star details for the companion, but does it generate planets, etc. for the companion star? I haven't been able to figure out if it does this.

Second, for everyone. In a binary (etc) system, does the energy released from the companion star also affect the planets in that system? It seems to me that the blackbody temperature for planets should be generated by some sort of combination of L from the two stars in the system. Of course, there is probably some kind of wild swings in the energy received from the secondary star based on the combination of the two orbital periods.

Thanks for any advise on this.

[Nakawaros]

Originally Posted by Kraken

Second, for everyone. In a binary (etc) system, does the energy released from the companion star also affect the planets in that system? It seems to me that the blackbody temperature for planets should be generated by some sort of combination of L from the two stars in the system. Of course, there is probably some kind of wild swings in the energy received from the secondary star based on the combination of the two orbital periods.

Thanks for any advise on this.

Sort of. The GURPS system averages that, but I'm finding that if you're generating by hand there's little to no point in doing the extended calculations

(T(star) = 278 * (L(star))^(1/4) / sqrt(R)))

(T(eff) = (T(star1)^4 + T(star2)^4) .... + T(starn)^4)^1/4)

unless the second star is within 6 or so AU. This differs a bit, but I wasn't really inclined (at the time) to break down exactly where it might matter (more than .25 K)

[Agemegos]

Originally Posted by Kraken

First, Brett, how does your spreadsheet handle binary (and trinary) systems? I have taken a look at a couple of binary builds and can see all the star details for the companion, but does it generate planets, etc. for the companion star? I haven't been able to figure out if it does this.

It calculates the forbidden orbital zones and leaves them empty, and it lists the companion stars on the system sheet. But it doesn't generate the planets of the companion star.

What you have to do is this: First, you generate a system around the main star with the companion in place. Then swap the masses of the main star and the companion, choose the system age to be the same as what you generated first, provide a new system number (I add 0.1 for the first companion, 0.2 for the second), and it will generate a system around the second star with the forbidden zone in the correct place. Keep only the planets that are closer than the companion, and discard any outer planets in the system of the second star. Use the outer planets that were generated in the first system.

As an exercise, I did the Alpha Centauri system.

Second, for everyone. In a binary (etc) system, does the energy released from the companion star also affect the planets in that system?

Yes. In the case of a planet jointly orbiting two close stars, sum their luminosities and masses and proceed as though they were one star. The system will not work out the range of variation, but it is possible to calculate the extremes using the inverse-square law and the Stefan-Boltzmann law.

In the case of a planet orbiting only one component of a binary you can in theory get variation, which you have to work out using a combination of geometry, the inverse-square law, and the Stefan-Boltzmann law. The periodical variations can get complicated. In practice, though, we find that for plausible systems and habitable planets the range works out rather small.

You'll find this thread some help.

[Nakawaros]

So, before I start this again: if I *were* to get a program out,would anyone be interested in helping me improve it from the base rules? (The program's almost done but it relies very much on pure base rules since the various changes I wasn't sure how to apply.)

[Nemoricus]

I'd be interested in doing so.

[Agemegos]

I would be happy to advise, but I don't have the time or inclination to collaborate.

[Anthony]

Originally Posted by Brett

In the case of a planet orbiting only one component of a binary you can in theory get variation, which you have to work out using a combination of geometry, the inverse-square law, and the Stefan-Boltzmann law. The periodical variations can get complicated. In practice, though, we find that for plausible systems and habitable planets the range works out rather small.

For a planet at the edge of the forbidden zone of its star, where the other star is 9x as bright as the one the planet is orbiting, and the average illumination is 1, the total illumination ranges from 1.625 (at closest approach) to 0.78 (at furthest); that's a very improbable setup, and is about as severe as it can get.

[sir_pudding]

Originally Posted by Nakawaros

So, before I start this again: if I *were* to get a program out,would anyone be interested in helping me improve it from the base rules? (The program's almost done but it relies very much on pure base rules since the various changes I wasn't sure how to apply.)

For reasons of transparency (and adherence to SJGames game aid policy intent, I think) I think you ought to make it exactly adhere to GURPS Space by default and then have any tweaks be switchable options.

[ericthered]

Originally Posted by Nakawaros

So, before I start this again: if I *were* to get a program out,would anyone be interested in helping me improve it from the base rules? (The program's almost done but it relies very much on pure base rules since the various changes I wasn't sure how to apply.)

Improve the rules or improve the programming? With the programming I'm in permitting language contstraints.