Detailed System Construction Rules

[Synch]

So, I own T20, and I want some rules to generate starsystems with a bit more detail. Heck, a lot more would be great. I once owned a copy of GURPS: Space 2nd edition and the rules in there were pretty good, so I'm considering buying a copy of the 3rd edition, but I'm really interested in getting something with even more detail if that's possible. Does anyone know where I can find something that will let me generate all sorts of different systems with just a roll of the dice?

Also, does anyone have a chart listing the "habitable zone" for planets given the size and color of their stars? That would be, pardon the pun, stellar.

Thanks again guys!

 

[etherflyer]

You have two choices:

Buy GURPS Traveller: First In, which has a detailed system generation system in it. It's more detailed than Space 3e.

Wait until Space is republished for GURPS 4e. The system is even more detailed than that in First In, and updated with more recent science. OTOH, SJG hasn't announced a ship date yet, which means you're looking at sometime past August at the earliest, and I'm going to guess more likely late 2005 or early 2006.

 

[far-trader]

There is the expanded system generation in the T20 book. But I doubt you missed it (p370+) except there is a habitable zone table (p373-4).

 

[Malenfant]

I'm still working on it...

To figure out the habitable zone:

Inner edge distance (in AU) is 0.95 * SQRT (Luminosity of star in Sols)
Outer edge distance (in AU) is 1.30 * SQRT (Luminosity of star in Sols)

Though remember that the surface conditions on the planet also matter - it may for example have a high greenhouse effect or something.

 

[Horatius]

If you're using the First In system, I have an Excel Spreadsheet that does everything for you. All you have to do is input the stellar data.

There is another one that still needs work that does entire sectors and subsectors (stars, systems and all) if anyone wants a copy.

 

[robject]

Originally posted by Malenfant:
I'm still working on it...

To figure out the habitable zone:

Inner edge distance (in AU) is 0.95 * SQRT (Luminosity of star in Sols)
Outer edge distance (in AU) is 1.30 * SQRT (Luminosity of star in Sols)

Though remember that the surface conditions on the planet also matter - it may for example have a high greenhouse effect or something.

Thanks Dr.!

Is there a similar equation for the snowline? Something like

4.5 * SQRT( Luminosity in Sols ) ?

 

[GypsyComet]

Past versions of high detail world building can be found in CT Book 6: Scouts, currently found in The Rules volume of the "big floppy reprints", in DGPs "Grand Survey" for CT and "World Builders Handbook" for MT, and in "World Tamers Guide" for TNE. None of them are precisely simple...

Scouts has the luminosity table, but all of them have the charts for habitable orbits that I recall. These are Trav-standard orbits according to standard solar system construction theories of 20 years ago, mind you. More recent thought has lent less weight to the standard orbital distances, but it's not like we have extensive details on other examples...

 

[Malenfant]

The equation for the Snow Line Distance in First In is wrong - it's too conservative.

A better approximation is

Snowline in AU = 2.5 * SQRT(Luminosity in Sols)

That's the distance at which a blackbody is at 175K, which is roughly where water and other volatiles are condensing out en masse from the nebula - you can get 'snowballing' beyond that distance. First In uses a multiple of 5 instead of 2.5, which corresponds to a MUCH lower temperature.

As an aside, the initial luminosity of the star is about 0.75 of the luminosity shown in the charts in Scouts or FI (which are good enough to use for now). It increases with age, going up to 2 times the stated luminosity in the tables at the end of the main sequence.

This means that you technically should be using the Initial Luminosity to determine the Snow Line distance. As the star ages, the Snow line (and the habitable zone) will move outwards, with interesting effects on the planets around them.

 

[robject]

That is interesting. It sounds useful to know the age of the star. Or is that opening up a can of worms?

 

[Malenfant]

Originally posted by dzibilrobjectaplaketl:
That is interesting. It sounds useful to know the age of the star. Or is that opening up a can of worms?

Yes

I have a huge table derived from the Geneva Stellar Evolution grids - it basically separates stars out by mass, and shows how each star evolves - what it's radius, temperature, and luminosity (and therefore spectral type) are at any given point after its formation, from the start of main sequence all the way up to the end of their last Red Giant phase when they turn into white dwarfs. (see this page for a layman's description of stellar evolution)

The main sequence is usually just a monotonic increase in luminosity (ie, it only increases, it doesn't decrease), but the stages after that are full of rapid jumps and plummets and sometimes the luminosity goes up and down and back up within an evolutionary phase.

And to cap it all, you can't just list the luminosities for a given spectral type on a table like you do in FI or Scouts - a G0V of a given mass is not going to be the same as a G0V of a slightly bigger or smaller mass.

I'll give you an example - here's the table for a star with 1 solar mass, and solar metallicity:

</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">Age/yrs M T/K Ls Ts Rs R/AU Spec Type Frost Line (AU) 100D (AU) Hab Zone (AU)
5.00E+07 1.000 5689 0.74 0.96 0.89 0.0041 G3 V 2.17 0.82 0.86
8.11E+08 1.000 5728 0.79 0.97 0.90 0.0042 G3 V 2.25 0.84 0.89
1.81E+08 1.000 5754 0.85 0.98 0.93 0.0043 G2 V 2.33 0.86 0.92
2.81E+09 1.000 5794 0.92 0.98 0.95 0.0044 G2 V 2.43 0.89 0.96
3.73E+09 1.000 5821 0.99 0.99 0.98 0.0046 G2 V 2.52 0.91 1.00
4.62E+09 1.000 5848 1.07 0.99 1.01 0.0047 G2 V 2.62 0.94 1.04
5.47E+09 1.000 5861 1.16 0.99 1.05 0.0049 G1 V 2.73 0.97 1.08
6.05E+09 1.000 5861 1.23 0.99 1.08 0.0050 G1 V 2.80 1.00 1.11
6.58E+09 1.000 5875 1.29 1.00 1.10 0.0051 G1 V 2.88 1.02 1.14
6.90E+09 1.000 5861 1.33 0.99 1.12 0.0052 G1 V 2.92 1.04 1.15
7.18E+09 1.000 5861 1.37 0.99 1.14 0.0053 G1 V 2.96 1.06 1.17
7.70E+09 1.000 5861 1.47 0.99 1.18 0.0055 G1 V 3.06 1.09 1.21
9.54E+09 1.000 5754 1.98 0.98 1.42 0.0066 G2 V 3.56 1.32 1.41
9.98E+09 1.000 5649 2.17 0.96 1.54 0.0072 G3.5 IV 3.73 1.43 1.47
1.01E+10 1.000 5585 2.24 0.95 1.60 0.0074 G4 IV 3.79 1.49 1.50
1.04E+10 1.000 5470 2.31 0.93 1.69 0.0079 G5 IV 3.84 1.57 1.52
1.05E+10 1.000 5346 2.30 0.91 1.77 0.0082 G6 IV 3.83 1.64 1.52
1.05E+10 1.000 5224 2.27 0.89 1.84 0.0086 G8 IV 3.81 1.71 1.51
1.06E+10 1.000 5140 2.26 0.87 1.90 0.0088 G9 IV 3.80 1.76 1.50
1.07E+10 1.000 5000 2.33 0.85 2.04 0.0095 K0 IV 3.86 1.89 1.53
1.08E+10 1.000 4864 2.88 0.82 2.39 0.0111 K1 IV 4.29 2.22 1.70
1.12E+10 0.997 4345 35.32 0.74 10.50 0.0488 K4 III 15.03 9.75 5.94
1.13E+10 0.964 3581 432.51 0.61 54.12 0.2512 K9 III 52.59 50.24 20.80
1.13E+10 0.876 3281 1517.05 0.56 120.74 0.5604 M1 II 98.49 112.08 38.95
1.13E+10 0.867 4446 46.77 0.75 11.54 0.0536 K4 III 17.29 10.72 6.84
1.13E+10 0.866 4436 47.64 0.75 11.70 0.0543 K4 III 17.45 10.87 6.90
1.13E+10 0.866 4446 47.53 0.75 11.64 0.0540 K4 III 17.43 10.80 6.89
1.13E+10 0.865 4446 47.21 0.75 11.60 0.0538 K4 III 17.37 10.77 6.87
1.13E+10 0.865 4457 46.88 0.76 11.50 0.0534 K4 III 17.31 10.68 6.85
1.13E+10 0.864 4457 46.77 0.76 11.49 0.0533 K4 III 17.29 10.67 6.84
1.13E+10 0.864 4467 46.56 0.76 11.41 0.0530 K4 III 17.25 10.59 6.82
1.13E+10 0.863 4467 46.45 0.76 11.40 0.0529 K4 III 17.23 10.58 6.82
1.13E+10 0.863 4477 46.24 0.76 11.32 0.0525 K3 III 17.20 10.51 6.80
1.13E+10 0.862 4477 46.24 0.76 11.32 0.0525 K3 III 17.20 10.51 6.80
1.13E+10 0.862 4477 46.24 0.76 11.32 0.0525 K3 III 17.20 10.51 6.80
1.13E+10 0.862 4477 46.45 0.76 11.35 0.0527 K3 III 17.23 10.53 6.82
1.13E+10 0.858 4457 51.40 0.76 12.05 0.0559 K3 III 18.13 11.18 7.17
1.13E+10 0.858 4508 46.34 0.76 11.18 0.0519 K3 III 17.22 10.38 6.81
1.13E+10 0.858 4508 46.99 0.76 11.25 0.0522 K3 III 17.33 10.45 6.85
1.13E+10 0.857 4498 47.97 0.76 11.42 0.0530 K3 III 17.52 10.61 6.93
1.13E+10 0.857 4477 49.89 0.76 11.76 0.0546 K3 III 17.86 10.92 7.06
1.13E+10 0.856 4446 52.60 0.75 12.24 0.0568 K4 III 18.34 11.36 7.25
1.14E+10 0.855 4416 59.70 0.75 13.22 0.0614 K4 III 19.54 12.28 7.73
1.14E+10 0.854 4375 66.37 0.74 14.20 0.0659 K4 III 20.60 13.18 8.15
1.14E+10 0.853 4276 84.53 0.72 16.78 0.0779 K5 III 23.25 15.58 9.19
1.14E+10 0.842 4150 121.90 0.70 21.40 0.0993 K6 III 27.92 19.86 11.04
1.14E+10 0.822 4009 185.35 0.68 28.27 0.1312 K7 III 34.43 26.25 13.61
1.14E+10 0.808 3908 251.77 0.66 34.66 0.1609 K7 III 40.12 32.18 15.87
1.14E+10 0.798 3733 380.19 0.63 46.70 0.2168 K8 III 49.31 43.36 19.50
1.14E+10 0.786 3573 559.76 0.61 61.85 0.2871 K9.5 III 59.83 57.42 23.66
1.14E+10 0.771 3443 845.28 0.58 81.82 0.3798 M0 III 73.52 75.95 29.07
1.14E+10 0.765 3334 1205.04 0.57 104.19 0.4836 M1 II 87.78 96.73 34.71
1.14E+10 0.745 3281 1761.98 0.56 130.12 0.6040 M1 II 106.15 120.79 41.98
1.14E+10 0.696 3258 2546.83 0.55 158.61 0.7362 M1.5 II 127.62 147.25 50.47</pre>[/QUOTE]Note that the mass decreases in the red giant stage (and then that final mass decreases as the AGB giant turns into a White Dwarf). Rs, Ts, Ls are Radius, Temperature, Luminosity in Sols. Frost Line is calculated as shown above. 100D is the normal OTU jump limit distance. I've got tables like this for 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.25, 1.5, 1.7, 2, 2.5, 3, 4, 5, 7, and 15 solar masses.

So with all this, you'd have to consider the effects of each evolutionary stage and increase in luminosity on the planets around the star.

And also note, this is based on theoretical modelling. In practise, the radius, temperature, luminosity etc of a star aren't actually bang on these values, there's a good deal of wiggle room. Especially with the spectral types because they depend on the chemistry of the star too.

 

[far-trader]

Apologies in advance if this is taken the wrong way...

The thing is unless your game involves extreme time travel or stasis it seems pretty pointless to me to worry about something that happens on a time scale of hundreds of millions or billions of years.

If you want to put your players through a major stellar event you'll have to pretty much play god and just make it happen to happen in the lifetime of the game.

Or are you just looking at this as a refinement of the stellar data set for the system info? Again what's the point? Not to rain on the parade, and if it's of interest then that's cool, but it just seems to me like more detail than myself or the player's I've gamed with want to know when visiting a system. Mostly what we want to know to do with the local star(s) is what the climate on any planet is and what color the star(s) and sky(s) are. To a lesser degree, and only for myself in my experience, I also want to know about the chance and magnitude of any solar flare activity that I can use to screw with the player's sensors and commo.

The habitable zone and frost line are of interest but again for a game these can be pretty averaged. I don't want to have to have a degree in all the space sciences any more than I want to have to have a degree in interstellar economics or starship engineering or whatever, just to PLAY a game

Of course I'd love for the people with said degrees to be the ones designing the background mechanics and translating them into the easy rules to play said game

 

[Fritz_Brown]

Originally posted by Malenfant:
And also note, this is based on theoretical modelling.

No offense, Mal, but DUH!

But thanks for the detailed info. I (almost) never turn down free information.

Originally posted by far-trader:
Of course I'd love for the people with said degrees to be the ones designing the background mechanics and translating them into the easy rules to play said game

Not if the only techie PhD I ever had as an undergrad were the representative sample.

Guy knew his stuff, but he couldn't communicate worth squat! (And some of the textbooks he chose had the same problem.) Now, if they hired Malenfant to do it, that would be worth a small uptick in the price of the system!

 

[Malenfant]

Just had this over on T5 too...

Me, I want to make a realistic world. I can figure out a system's history and use that to make the system more realistic. I can say whether the world's environment is stable or if it's slowly roasting over time. I can figure out if it's tidal-locked or still rotating relative to the primary, since I know the masses of all the bodies involved and I know how to figure out if tidal forces have locked it over time. And so on.

It's a lot of effort to go through, sure - and in practice it'd probably at most add one or two sentences to a description that you could easily just make up on the spot. But that's not the point of doing it really - the point is that I'd want my universe to be realistic. I don't want habitable worlds orbiting white dwarfs or supergiants, or worlds that are so close to eachother that they'd be shredded by tidal forces. I don't want to PLAY in a game that has those, because my suspenders of disbelief wouldn't last a second.

With scifi, it's important for me to get this background stuff right - it makes the universe more real. And its rather educational to find out how it all works anyway. I can well appreciate that others may not care so much (if at all) - but if you don't, you don't have to use it.

But I know I'd rather have much more information than I actually need and distill what's relevant from that, than have too little and have to guess or fudge at what I'd need.

 

[far-trader]

Originally posted by Fritz88:
</font><blockquote>quote:</font><hr />Originally posted by far-trader:
Of course I'd love for the people with said degrees to be the ones designing the background mechanics and translating them into the easy rules to play said game

Not if the only techie PhD I ever had as an undergrad were the representative sample.

Guy knew his stuff, but he couldn't communicate worth squat! (And some of the textbooks he chose had the same problem.) Now, if they hired Malenfant to do it, that would be worth a small uptick in the price of the system!

</font>[/QUOTE]Quite! My ideal Traveller book would be a textbook of all the sciences written for the layman in a good sci-fi novel form and explain the reality and background behind the rules of the game, said rules being a few pages in the appendix and some sidebars

Hey, I can dream

 

[far-trader]

I agree Mal, and do appreciate the work you do to that end. It's just that in the end it all gets to be too much information (not just the work you do for stellar/planetary data, but all the trade, tech, and such done by others) and I go overload and start looking at the old LBB 1-3 with longing

It would be easier too if players didn't have the habit of entering a detailed system that one's worked some time on to make believable and interesting and planning to have said players investigate only to have them take a quick look at the UWP in their database, ignore the clues that there's something else going on, and just refuel at the GG and jump out

But that's hardly your fault and I'm sure not throwing blame for my or my players shortcomings on anyone who is trying to make the game better by putting more science in my fiction. No, for that I applaud you.

 

[robject]

Dan, this is exactly the kind of information I like, although I would not use it to the degree that Malenfant would... I'd probably boil it down into some number of heuristics and use a first approximation with an average of 1.5 significant digits.

 

[Synch]

I am highly impressed with the volume of information. I too believe that knowing as much about the layout and history of a system's formation can give one clues as to how the residents (if any) of a system should treat it, and consequently, how they should react to a host of other variables. I think I'm going to take the above mentioned table and integrate it into the work I'm already doing. Thanks greatly for that!

As for the other suggestions, I guess it's time for me to start buying sourcebooks.

 

[Malenfant]

Good to know that there are other crazy folk out there who want what I'm doing .

Synch - that's only the one table for a star with one solar mass. As I mentioned, I have lots of others. I'm still puzzling over how to present them... maybe I should put them on a webpage in the same format as I showed here? Or do people think it's too complicated?

 

[TheEngineer]

Hi !

Mal, if You dont mind I would like to incorporate those construction rules bit by bit into my systemview software.
I guess, as you want to keep the design sequence as realistic as possible we might get not away from computer assistance anyway. So I would not care about the amount of data

Maybe we could once convince Stuart Ferris to but it into H&E2, too...

Regards,

Mert

 

[Malenfant]

Well, here's where I am with the realistic system so far.

I've got Size sorted out. I've got a means to determine the orbital zone of the planet, and the size and density of the planet (which ties into the metallicity of the star). World size goes from 0 to C.

Atmosphere: I split atmosphere into Composition and Pressure. It's more complicated now, but I can generate any of the existing atmosphere types, plus a few more - but I can do it realistically so you don't end up with small planets with thick atmospheres of gases that they shouldn't be able to hold onto.

Hydrographics: Bit stuck on this one. I've got a lot of info on the pressures and temperatures that liquids are stable at on planetary surfaces, but when I left it I still had to figure out how to determine how much liquid there is on the surface.

Population: got lots of ideas, but I'm leaving it til after Hydrographics gets sorted out. But basically - Garden worlds = high population, everthing else = low population.


I really should at least get the physical stuff done though...