[SPACE 4e] System Design help? (star systems that is...)
 

Alright I bought GURPS:SPACE 4/e and I am looking for a little bit of advice or at least someone to point me in the right direction.

For a player in my campaign I need to concoct a star system that has THREE planets within the life zone. Thats right 3 (!!) planets in some kind of tolerable and believable orbit bands and such ...all of them plausibly habitable for humans. And is VERY "okay" if one of the 3 turns out to be a mostly "Desert World" . I also own INTERSTELLER WARS ....but I figure might as well use the more detailed system.

Any advice on this? Should I just roll dice until I get "close" to what we want? Has someone already got parameters close to this in a Playtest exercise? (and please don't send me a link to a PYRAMID article - am not a subscriber....can't afford it ..YET)

So, any planetary system designing versions of "Gearheads" out there...That can give me some tips or suggestions?

- Edmund W. Charlton

Re: [SPACE] System Design help? (star systems that is...)
 

I don't have GURPs Space yet, but I am interested in astronomy in a general way (read books and articles). I suggest that you roll up a system and then adjust it so that three planets are habitable. For example, Mars might very well be habitable today if the planet had greater mass and hence gravity. This would have allowed it to hold on to more of it's original atmosphere. Venus would have much more habitable (though very hot, perhaps too hot for humans) in the early history of the solar system (it started out with water which, ironically, made the greenhouse effect it suffered later that much worse). In the outer solar system, a large enough gas giant could possibly warm it's moon enough for human inhabitation to be possible (maybe a ocean world similar, but warmer, than Europa).

Re: [SPACE] System Design help? (star systems that is...)
 

It should be possible, especially if you wave your hands real hard. Mumbling something about terraforming will help a lot too, if that fits your conception of the system. I tried to run some numbers, but couldn't quite get it, but I got pretty close. You'll end up with one hot world, one "goldilocks" world, and one that's actually a Standard(Ice) type rather than Standard(Ocean), but it's really close.

With the Basic Worldbuilding chapter, you can generate as many habitable planets as you want and put them wherever you want, so I assume you're asking about the Advanced Worldbuilding chapter. One problem that may develop is that you'll need a fairly bright star -- I'd go something like an F6 V, although you could probably get away with a G class star. This is only a problem if you want the planet to have native life, as bright stars will have shorter lifespans, and any aliens won't have long to evolve.

I would not roll dice until you get close, because you'll be rolling dice for a long time. I'd just use the rules to guide your decisions.

Let's just start with an F6 luminosity, main sequence star, on page 103. We'll also assume it's a single star, although you can add a distant companion later if you really want. Set the age to something you like (or roll dice), but it should not go over the main sequence age. For arguments sake, I'll go with 2.3 billion years for age. With an F5V star, this gives a luminosity of 3.2. The orbital zones (p. 106) are going to be: Inner Limit = .13 AU, Outer Limit = 52 AU, and a Snow Line Distance of ~8.67 AU. So your three garden planets will be within 8.6 AU of the star, and probably quite a bit closer.

Generating gas giants next, if you want three habitable planets, you'll probably want either no gas giants or a conventional gas giant arrangement. I'd go with gas giants in the conventional arrangement, but it really doesn't matter for the most part.

Now this is the tricky part -- setting up orbits to give three planets in the Standard or Large Garden Range (241-320 Kelvin). Using the formula on p. 108, we see that a temperature of 241 Kelvin give us an orbital radius of 2.3 AU, while 320 gives us a radius of 1.3 AU. Now it's possible for us to get one planet at 1.3 AU, one at 1.82 AU, and one at 2.5 AU, given the minimum ratio between orbits of 1.4. The other orbits aren't important for the moment, so we can generate those later. We'll put a standard planet in each of the three orbits, and do moons later.

What's really important is the blackbody temperature. For our luminosity (3.2) we get blackbody temperatures of 320 Kelvin at 1.35 AU, 275 Kelvin at 1.82 AU, and 235 Kelvin at 2.5 AU. Your outermost planet is technically a standard (Ice) planet in the inner most one will be uncomfortable in the summer, but it's pretty dang close. You can work out the rest of the details to fit your own setting, or fiddle with it to get it close to what you want.

Hope that helps.

Re: [SPACE] System Design help? (star systems that is...)
 

Id,

That Is VERY helpful .
Funny thing is ..I used to be better at this number-crunching stuff when I was a teenager ......nowadays my brain starts rebelling and just wants to do characters and plots.

Anyone else have advice about this ? Who knows - this might help out some other GURPS GM or player out there.

- E.W. Charlton

Re: [SPACE] System Design help? (star systems that is...)
 

I'd go for three very large moons around a very large gas giant that's in the habitable zone.

Re: [SPACE] System Design help? (star systems that is...)
 

Not speaking for the rules in Space (I've read Space 4e, but not really digested the info), but it's going to be mostly impossible to place more than two worlds within a habitable zone of a single star without one of three unlikely things happening:

• 1) Two of the planets will share the same orbit, rotating around each other. For two Earth-sized planets they will be tide-locked towards each other revolving around a common axis. This will likely result in a day length measured in weeks (much like our Moon, which is tide-locked to the Earth and orbits once every 28 days). The third planet may end up at another orbital position within the habitable zone.

• 2) Some serious Terraforming on at least one of the worlds. Remember that Mars probably once had water, but it was not stable over billions of years. It would be possible to Terraform worlds to be Earthlike but which would be unstable without maintenence. Perhaps the campaign is set some 100,000 years after the "Ancients" left, and their Terraformed worlds are starting to become unstable.

• 3) An outer planet is a Brown Dwarf, radiating enough heat to warm one of it's moons. The world will be rather dim, and likely subject to severe tidal effects making it geologically unstable.
  3a) A Large Gas Giant or Brown Dwarf is located in the habitable zone and has a large host of moons, several of which may be habitable.

And, of course, there's a variation on #1 in which two planets share the same orbit, but orbit on opposite sides of the sun, or (maybe) residing in each others' Lagrangian Points relative to the Sun. This kind of configuration is likely to be unstable since slight variations in orbital velocity would eventually draw the two planets closer to each other. Again, though, this is another chance to draw "Ancients" into the background, and any Ancient Race capable of moving or building entire worlds is kind of scarry.

There is also a fourth possibility: Two stars orbit each other at a distance of some dozens or hundreds of AU. Each star can sustain it's own planetary system, including habitable worlds. One may have two worlds in the habitable zone while the other has one, but on an interstellar scale these stars are definately a binary star system.

In fact, for the space campaign I've been cooking up I planned on having the capital world located in just such a binary system, figuring that any Solar system which has 3 habitable worlds would be so valuable it would quickly grow to become the center of the region economically and politically. At any rate, any system with 3 habitable worlds is going to be so rare (possibly once in a campaign) that there's no good way to randomly generate it; you really need to design such a system.

Re: [SPACE] System Design help? (star systems that is...)
 

I think that Space mentions a rossette, whereby your three planets share an orbital distance. This is ridiculously unlikely to form on its own, BUT will be dynamically stable once finished.
Really funny if archaeologists keep scouring them for the evidence of alien intervention they KNOW is there.... when it really is a one in a trillion shot.

Re: [SPACE] System Design help? (star systems that is...)
 

I'm not sure how likely this is; but consider the Trojan points. It seems reasonable that if you get stable enough L4 and L5 points in the orbit of a brown dwarf, and enough mass accumulating there, you might get terrestial planets to form. Place one in each Trojan Point and one in orbit around the brown dwarf, and place the brown dwarf in the primary's habitable zone, and you can get three habitable worlds.

Note that this may not be feasable: it depends on the amount of matter that's likely to pool in the Trojan Points. I suspect that the more massive the brown dwarf, the more mass is likely to pool - except that the more massive the brown dwarf, the less stable its Trojan Points will be (maximum mass for satellite with stable trojan points = 4% of primary's mass). This option may be no more likely than a natural Rosetta (or it may be far more likely; I don't know); but it is an option that has the virtue of being unique: I have never seen anyone try it.

I'd design the terrestrial worlds according to the Basic Worldbuilding rules; I'd then place all three in the same orbit: one orbiting the brown dwarf, and one in each of the two Trojan Points. The main sticking point will be the worlds' climates: hold off on determining the worlds' atmospheric masses in Step 3. Instead, determine the blackbody temperature for the orbit that all three worlds will be in; divide each world's average surface temperature by this common blackbody temperature to get its Blackbody Correction Factor; then reverse-engineer the atmospheric mass from that:

atmospheric mass = (blackbody correction factor / world's absorption factor - 1) / world's greenhouse factor.

This can then be used to finish establishing the world's atmospheric properties.

Note also that the world orbiting the brown dwarf has the potential to see vast changes in climate, depending on how far out it orbits the brown dwarf: get it far enough away, and it will be swinging from the inner edge of the primary's habitable zone to the outer edge. Depending on how warm the brown dwarf is, you might even get additional heating from it, possibly enough to render the inner surface's climate Infernal while the outer surface fluctuates between Hot (during the day) and Cold (at night), or Warm and Cool.

Re: [SPACE] System Design help? (star systems that is...)
 

Or fifth: a trinary like Alpha/Proxima Centauri. You can have a habitable world for each star.

Re: [SPACE] System Design help? (star systems that is...)
 

Possible, but probably less likely. Trinary systems have all sorts of problems of their own; getting 3 stable stars which are Sol-like is rather unlikely. The Alpha Centauri system consists of a G, a K, and an M class Star, only the former two are likely to privide Earthlike planets; M stars probably can't have Earthlike planets, and Proxima Centauri is a Flare Star (which is fairly common of M class), and makes it even less likely to have liveable planets.

Further, most Tinary systems have two stars which are in close orbit (meaning they may interfere with the formation of planets around the other) and a third that orbits at some distance. In the case of Proxima Centauri it's some ~13,000 AU (roughly ~0.06 parsecs) distance from the Binary pair of Alpha Centauri A/B (which orbit each other at ~11 AU at their closest).

Stellar Age can be a problem; in a Trinary system the wider orbiting star is likely to be of a vastly different age than the closer Binary pair of the system. In the case of the Alpha Centauri system at only 1 Billion years Proxima is *MUCH* younger than Alpha Centauri A/B, at 5-6 Billion years. Sol, for comparison, is about 5 Billion years old.

The arrangement of the Alpha Centauri system actually makes it possible for all three stars to have planetary systems, but the instability of Proxima Centauri makes it unlikely that all three could have Earthlike planets. It's age means even if Proxima did have a planet in the habitable zone the planet would look more like primordial Earth than modern Earth.

Re: [SPACE] System Design help? (star systems that is...)
 

No problem. It was kinda fun to fiddle with the design constraints to make a specific system. Usually I just go by the dice rolls and work from the "dirt up" rather than from the "story down".

The three planets will all be fairly different, and I think you should be able to easily fudge the outermost one into an Earthlike world that's perpetually glaciated, but has enough photosynthetic life to create a marginal, but breathable atmosphere (a thick atmosphere will help warm it, too.)

Personally, I want to see how the system turns out once you get it the way you like it.

Re: [SPACE] System Design help? (star systems that is...)
 

that Inner planet, 'Hot in the summer.' Easy solution, give it an almost spherical orbit, same temperature all year round, probably like a semi-tropical rainforest or something like that. outer planet, thick atmosphere. Done and done.

I'm not much of a number cruncher, don't have the books, and definitly don't know my astronomy so scuse any blatant stupidity.

Re: [SPACE] System Design help? (star systems that is...)
 

Unfortunately, that's not what causes summers to be warmer than winters. Witness the fact that our world has summers at opposite times of the year depending on whether you are in the northern or southern hemisphere. This would be impossible if it was caused by proximity to the sun, because you can be closest to the sun at two times during the year no matter what your orbit looks like.

However... he's got the right concept. Give your innermost planet an axial tilt of 0. Then you won't have any seasonal effects. Technically this only shifts the problem from a seasonal one to a latitude one. The equator would be too hot. But, the temperate and polar zones might just be ok.

Re: [SPACE] System Design help? (star systems that is...)
 

Well, usually eccentricity doesn't cause the seasonal changes. However, if a planet had an extremely eccentric orbit it could cause climatic changes similar to those caused by axial tilt (though the whole planet would have summer and winter at the same time, rather than opposite in the two hemispheres). Combined with an axial tilt this could cause some extremely different climate conditions between the Northern and Southern hemispheres.

If the eccentricity works to enhance the seasonal variations (perigee and apogee lining up with axial tilt) you might wind up with a Northern climate which has a warm summer but bitter cold winter while the Southern hemisphere would have blistering hot summers but mild winters. Or, if the eccentricity works to mitigate the seasonal variations (perigee and apogee being at right angles to axial tilt) you'de have mild summers and winters in farther reaches of the the Northern and Southern hemispheres, but the equatorial region would swing between very hot and very cool spring and fall seasons. Further, axial tilt tends to wobble over thousands of years, meaning you'de have long climate cycles where eccentricity enhances seasonal variances, followed by periods where it mitigates seasonal variances.

Re: [SPACE] System Design help? (star systems that is...)
 

Doing some quick checking for Space 3e, the only stars that appear to be able to have two worlds in the habitable zone are G-V and G-VI, and that puts one planet on each edge of the habitable zone.

Re: [SPACE] System Design help? (star systems that is...)
 

That may be...but I need UP-To -DATE 4th edition references. That is what I and the rest of us are using.

Thanks for checking tho...

- E.W. Charlton
(4th edition books are really good...)

Re: [SPACE] System Design help? (star systems that is...)
 

Brandon, I realize (and fully respect) that you feel 3e is superior to 4e, but that doesn't make the 10 year old science in 3e superior to the current astrophysical models.

Re: [SPACE] System Design help? (star systems that is...)
 

My post had nothing to do with what I thought was superior. It was about using the most recent RPG astrophysical model I have to help the OP.

And, that being the case, I should have used the data from GURPS Traveller: First In, instead; while it came out the same year as Space 3e, it uses more recent science. It looks like it probably isn't possible to have two planets in different orbits both fall in the life zone.

Re: [SPACE] System Design help? (star systems that is...)
 

Brandon,
The Astrophysics and science in SPACE 4/e - is based on what was in FIRST IN. BUT it is even more "up-to-Date". Thats a big chunk of the reason that I bought it. This is one case where the more RECENT the edition and book is the better .

Thanks for trying to be helpful tho.

- E.W. Charlton

Re: [SPACE] System Design help? (star systems that is...)
 

I really don't use the system generation rules from First In (which is why I didn't think of it initially). They may be more realistic than Space 3e, but I don't think all the added complexity is worth it.Then again, I was pretty satisfied with the pre-Book 6 CT way of rolling up worlds and systems.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

I'd go with a wide binary star system, in which both stars are about the same mass and age, and are reasonably Sol-like. It's unlikely but feasible to get two worlds in the habitable zone of a single star. Three is really stretching it, but the third one can orbit the companion star.

This is, oddly enough, exactly the arrangement of the Manticore system from David Weber's "Honor Harrington" novels. If I remember correctly, Manticore (the planet) and Sphinx orbit the star Manticore-A, while Gryphon orbits Manticore-B. Manticore is pleasantly Earthlike, Sphinx is further out and has very severe winters, and Gryphon has high axial tilt yielding very strong seasonal variations. Weber may have borrowed a little too enthusiastically from Napoleonic history, but his worldbuilding is fairly plausible.

Re: [SPACE] System Design help? (star systems that is...)
 

I've used that model, it's a valid idea, and its unlikeliness can be waved off with enough possibilities.


The other model I've used, though possibly even less likely, is a double planet* along with a third planet within the habitable zone.



*The double planet setup simply requires the equivalent of an Earth-Moon system on a greater scale, the planets would be further apart, but the tides would still be greater than ours.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Holy *BLEEP*!,
The Author of the book himself replied. Wow!! Well, I will have to give your advice and suggestion a little more weight.

Looks like time to get out out the notepaper pad, a few pens and work all this out. I'm meeting with the player in question this Saturday afternoon.
If anyone has any more suggestions - I will look forward to reading them.

- Edmund W. Charlton

Re: [SPACE] System Design help? (star systems that is...)
 

And conveniently you could have the two poles being near centers to two supercontinents so most of the living space on the planet is away from the equator.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Had lunch with the player in question. She gave me more parameters - but does not actually care how "perfect" the Astrophysics winds up being.

So I can fudge it if I have to .

As she described it to me ...none of the three are "HellHoles" or variations of "Hell-like".

There are 3 planets in this system. We'll refer to them by number(letter) combinations - okay?

1(Bt)
The closest in to the system's star is 1(B) That planet is the "capital" in this system. It has quite a bit of trade, High-tech, ARTS & Literature, Museums, parklands and such. The Weather there is closest to that of Central Italy - Mild winters and such. There IS a little bit of Ice and Snow at the poles.

2(Gl)
The "middle" planet for placement purposes is 2(G) . This planet's climate and weather is mostly like that of the Mediterranean in the Northern part of the world...but more Desert-like in the southern plart of the planet . (Think of an Israel-like "Desert")

3(Sh)
Third planet out from the Main Star that is habitable we'll refer to as 3(Sh) That one is the "home planet" of the player's character. Its terrain is dominated by a Red Desert, stony - some sandy areas...evidence of volcanic activity in the past (i.e. colored sand; multi-color rocks) The culture there is mostly Fighters, Shepherds; agriculture. Only recently have they started to go "high-Tech" (within the past 60 years before the game starts. )
This planet's Poles only get as cold as the Mediterranean at its coldest.

So with all that in mind - what orbits, and other things could or would accomodate the above?

- E.W. Charlton

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Does this mean that the several stars of a multiple star system can have different ages, notwithstanding the rules stating that age is determined per system? Or should there be one age for the system but possibly a different age for Distant companions (drawing from the Proxima Centauri example)?

While we're at it, in a system with the Eccentric Gas Giant arrangement, should there be a roll for the eccentricity, and would it sweep out a forbidden zone much like a companion star (but smaller, presumably)? Or instead would the next orbit in/next orbit out be determined from the initial gas giant's periastron/apastron instead of its mean orbital radius?

For that matter, should there be a roll on the Eccentricity table for regular planets, and what would be the mod?

[Side idea: What would you think of a generation system whereby the planets were generated as for a Main Sequence star of the star's original mass, and then evolved (read: mostly destroyed) if the star were old enough to be a subgiant, giant, or white dwarf? I'm aware that most inner planets would be swallowed and destroyed in a star's giant phase, but would gas giants have their atmospheres reduced (blown away) and ice planets melted either in the giant phase or in the stellar shell ejection?]

(I'm writing a php script and eventually an Astrosynthesis plugin to generate systems, so saying "pick it yourself to taste" won't actually be helpful. :-)

Thanks,

Re: [SPACE 4e] System Design help? (star systems that is...)
 

I would love to see that. I just started to do it for a subgiant system. I first rolled up the original system, and then I redid all planetary classifications based on the new blackbody temperature.
In my case, the GGs kept their atmospheres (but look probably a lot larger), but some terrestrials were changed a lot.

Another thing I would be interested in is temperature variations for eccentrity.
I believe that planets warm and cool quite slowly, so even noticable eccentrity wouldn´t necessarily create seasons of its own. But I have no idea
how much eccentrity I can safely ignore, and where it might become an issue.
And also no idea how important atmospheres or oceans are for this.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Don't read too much into my slip of the tongue :-). Yes, in general, you can assume that all of the components of a multiple star system formed at the same time and are the same age, hence the rule as written. I could see a Distant companion being of a different age, as you suggest, if it were formed at a different time but was eventually captured into the system (or if it just happens to be wandering by).

Both of those would be reasonable extensions - I considered adding them to the original rules set, but eventually decided they would add too much complication for a special case. One could also make the case that an epistellar gas giant would prevent the formation of planets anywhere between its final position and the snow line . . . eating the protoplanets for breakfast as it spiraled inward to its final position.

Hmmm? Not quite understanding your question here.

Again, that's a reasonable extension to the system.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Makes sense. Would an eccentric GG do the same?
Well, planetary orbits in the Sol system arent' circular -- I was wondering if you'd contemplated generating this on the Eccentricity table. No worries -- I'll just make something up.
Cool. I'll give it a shot, once I do a little more research.

Thanks!

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Probably. The model seems to be the same for both, except that the physical processes that cause the epistellar gas giant to spiral all the way inward don't work as effectively (or as completely) for the eccentric gas giant.

Hmmm. I don't have my author's copy in front of me, but I could have sworn I had some provision for the eccentricity of planetary orbits in there. Let me get back to you after I've had a chance to review the text.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

The last 2 or 3 comments are interesting guys - but does that have any effect on my three potential planets?

Just wondering.

- E.W. Charlton

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Qoltar -- sorry for the thread hijack; I thought your question had been answered and I took the opportunity to quiz Mr. Zeigler.

Jon -- never mind, now that I have my book before me I see there is a planetary eccentricity table.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

"Back" to this star system ... hhmm... this sort of a TRAVELLER questiuon now but here goes:

Would planetary masking be an issue for a starship jumping in from either JumpSpace or Hyperspace??

Also what are the likely travel times between the 3 planets??

- E.W. Charlton

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Those two questions are so campaign dependent as to be nearly impossible to answer.

First, by "planetary masking" I take it you mean that the star gets in the way of the incoming ships route so it is forced to drop from Jump Space at a location away from the planet?? That's always a problem with a Traveller style Jump drive, and if you go with a binary pair of stars it's double the problems, since either star has a chance of blocking access to planets around the other depending on the direction the ships are coming from and the distance between the two stars (two stars at 20AU are going to block more of each other's space than two stars at 20,000AU).

For the second question it is necessary to know what technology is available for FTL and STL drives, what speed they go, and what distance the 3 planets are from one another (which can vary at different times of the year). It takes, what, 8 months for us to go from Earth to Mars using current technology? But then we don't have Reactionless Drives as in Traveller; with a 1G constant acceleration (easy in Traveller) that same trip to Mars would take between 2-4.5 days, depending on the exact positions of the two planets in their orbit. With a Grav drive which can do 100G or more that trip could be cut down to less than 12 hours.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

I just got Space this week.

Back when I was using GURPS Traveller: First In, I found that, instead of one bright star (which doesn't have enough time to form a decent ecosystem), if you had two semi-bright stars (say, a Sol and a red dwarf), their combined luminosity gave you enough energy to get three planets into the life zone.

I found that you couldn't get a habitable world in the first sixth-ish of the life zone (too hot), nor the last third-ish (too cold). But it's possible to fit in a hot garden, a decent garden, and a cold garden in that distance.

As for just three worlds, how about five? Have a trinary system: A green/yellow sun (our sun is green with lighter shades of yellow; we just can't see green as well as yellow) with a close red companion, and a distant green/yellow companion with two worlds in its life zone.

Toss in a couple of asteroid belts, and a couple of gas giants, and it's a neat little system.

(Note: pulling this idea from On Death Ground/Shiva Option books...)

I'm SO looking forward to someone designing a spreadsheet to help with this. :)

Re: [SPACE 4e] System Design help? (star systems that is...)
 

How did you calculate combined luminosity and blackbody tempreratures ?

IIRC one first adds (all stars luminosity divided by the square of distance) before taking the fourt root and multiplying with 278. So a close companian red dwarf would add very little to the blackbody temperatures of planets.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Per Traveller: First In, pg 53 (Step 6: Locate Orbital Zones), if two stars have Very Close separation, simply add the masses and luminosities together and treat them as one star. This allows you to get the larger Life Zone of a brighter star, but with a longer lifespan.

As for red dwarfs, you should know it's been about a year since I've done this, so I don't remember how I did it. The idea is the same, though: a second, not-as-bright close companion that adds mass (to determine the Outer Limit) and luminosity (to determine the range of the Life Zone and the Snow Line and the black-body radiation of the planets).

I generally toss in a third star at such a point as to wipe out the last three or four orbitals.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Okay, I've looked at the data. It's impossible, under the rules as written, to have 3 garden worlds for one star. Within the inner rings, the minimum separation from orbits must be 0.15 AU, and the minimum separation ratio is 1.4.

The range of black-body temperatures for garden worlds is 241K to 320K (page 113). Using the formula for placing pre-designed worlds, the radius of the orbit is 77300 / B^2 x sqrt(L). Using the range of black-body temps, above, the orbital radii would be 1.330 x sqrt(L) and 0.755 x sqrt(L), respectively. That means the geometric-average separation ratio would be 1.33, well below the mininum separation ratio of 1.40.

So pretty much nothing even remotely human-habitable can be fit in a third orbit. :( As I've previously stated, the first sixth-ish of the "Life Zone" (GURPS 3E Traveller: First In concept not brought in to 4E) is too hot and the last third-ish is too cold.

Too bad they don't have detailed star system generation any more. As it is, a lot of the numbers have changed. :shrug:

Re: [SPACE 4e] System Design help? (star systems that is...)
 

What about the double planet suggestion I made, along with a third world in a separate orbit?

And what discounts the idea of three habitable large moons around a gas giant?

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Those have some serious problems because of the high levels of radiation (the gas giants magnetic field funnels stellar radiation right into the moons) and extreme tidal effects. On the up side, the extreme tidal effects means lots of volcanism, which means a strong magnetic field for the moon, which means possible protection from the radiation. On the down side, lots of volcanism means lots of, well, volcanos - lots of ash in the atmosphere and lots of volcanic gasses such as CO2, and pleanty of places you don't want to live unless you want your village to be incinerated once every couple generations. Not likely to be a nice place to live.

Not that it's impossible, but they're far less likely to be habitable.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

In Traveller you have two choices. Normal ballistic travel between planets and FTL. If ships can continuously do 1 gee out turn over and 1 gee decelerate it'll vary depending on current planetary distances, but in general: Not take very long.

If you're using a more orbital mechanical travel, the general answer is 'longer than that'.

If you're using Traveller's jump drive to cross a system the answer is 1 week plus time spent getting through planet diameter distance etc.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

I was only approaching it from the perspective of three planets in a row. There are other solutions (double-planets, rosettes, and so on) that have a possibility.

I wish there were a way of getting three planets in a row, but as I've show, even using one extreme (ice age) to the other (it's a dry heat), you'll not get three gardens in a row.

What you can do is tinker with hydrographics and atmospheric mass to get the black-body temperature within the range, and end up with two planets in a row with reasonable temperature ranges (cold and hot, for instance). All you have to do is set the orbits at 1.4 ratio, with a minimum separation of 0.15 AU.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

What about by putting in a Brown Dwarf in the outer region?

Re: [SPACE 4e] System Design help? (star systems that is...)
 

But you're going on the assumption of close in moons to take advantage of the gas giants' temperature radiation, right?

If we have planets/moons further out in orbit of the gas giant so that they aren't too close to the gas giant's magnetic fields, but all of them within the star's livable band, then while possibly experiencing a more rapid seasonal shift, the planets/moons could be livable.

(Especially if the moons' orbits were perpendicular to the gas giant's elliptic, but we don't need to go there.)

Re: [SPACE 4e] System Design help? (star systems that is...)
 

I dunno. I haven't gone that far in the system design paperwork. :) I keep trying for three. (And I'm SO upset at Chalker for his Warden Diamond configuration, because I'd LOVE to have four planets in a row. :) )

It might be interesting to have a brown dwarf in the system I'm trying to create... I'm trying to create a trinary system (two very close, and the third
distant), with three or more decent habitable planets close together-ish. (Plus a couple of asteroid belts and a gas giant or three--I have a fondness for Jupiter and Saturn. :) )

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Well, you could always follow the John Norman, Gor route, and put them in the same orbits, just offset. *innocent look*

Re: [SPACE 4e] System Design help? (star systems that is...)
 

What I decided to go with was TWO planets in the True "Life zone" ...with the third outer livable planet as one that is orbiting a Gas Giant.

For the un-informed : John F. Ziegler is the one who wrote G;T FIRST IN He also wrote the recently released GURPS:SPACE 4/e ...so any references to "First In" are sort of out-of-date by comparison.

I will figure out a way that the moon/planet has adequate magnetic fields and such of its own - so that radiation from the Gas Giant is NOt an issue. Also, that world should be "habitable" - but barely so . Its the "Desert worlds" of the three planets being created - and the last to be settled.

Thanks for all the advice! ,

- E.W. Charlton

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Why not try a "double planet" in one orbit and the third in the second orbit.
It's not that hard if you make a standard garden the moon of a smallish large garden planet with a low density.

I made Ekeetra with a 0.8 G and 1.2 atm. "orbiting" a low density planet Silosia with 1.0 G and 2.7 atm. made breathable by Ekeetrans from a low O2 content. Tidal locking pushed them into having 13.5 day long days leading to unique circadian rhthyms, but hey that just makes them "special". :)

Made even busier by a mars-sized second moon that still has some volcanism. Nice first extraplanetary base for my little space explorers.

Sorry, I had to brag about my babies. My space campaign has them as the progenitors of intersteller travel.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Could you do a "trial run" through these scenarios?

That is, I'm interested, and would like to see how it's done by the rules, so that I can apply it to my own star-building. :) So if you can provide examples of how you'd go through the rules and achieve these, I'd appreciate it. Even broad instructions would be helpful.

Thanks!

Re: [SPACE 4e] System Design help? (star systems that is...)
 

For the moons around a GG you simply put a GG in the life zone and give it 3 standard size terrestrial moons (unlikely to be rolled randomly, but possible). Then you develop the moons like any other Terrestrial. The GG is only there to anchor them in a single orbit. They may well be tidelocked to the GG, but as they still orbit the GG, they will not be tidelocked relatively to the star, so tidelocking will not make them uninhabitable. So the GG may also provide protection against tidelocking.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

For the double planet, I prefer doing one bigger, usually about 0.2-0.4G bigger, this makes the sattelite "planet" almost a moon, except the two planets actually both orbit around a center of mass which then orbits around the star, so only one orbit around the star is taken up.

The two planets are likely tidally locked to each other and at least 1-2 million miles apart, but there's no reason they wouldn't rotate around their center of mass in a stable orbit, while the center of mass orbits the sun.

This then allows you to have the third planet in the life zone some 100 million miles or so away from the center of mass of the double planet.

For other effects on the system, just consider the total mass of the two planets as if it were one larger planet in the center of mass orbit.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

The Moon orbits the Earth at 30 Earth-diameters. You're talking about something that's in the range of 100- to 200+ Main-Planet-diameters. Is there a reason you chose that distance? I'm guessing the effects on tidal force. So we're not talking about a Rocheworld, are we? That is, two planets close enough together that they bulge towards each other?

Going back to life-zone gas giants, how do I generate heating effects for major moons of gas giants? I've got a gas giant that's generating (through, again, some fudgery) a Standard Ice moon. I'd like to find out how to get that extra black-body temp to push it into a warmer temperature, and thus manage to get a Standard Garden possibly further out in the life-zone.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

I would think that tidal effects of two planets tide locked together wouldn't be that bad, actually. The main reason the tidal effects of the moon are so noticable is because they act differently upon different areas of the earth's surface at different times. With two tide locked worlds they will reach a point of equilibrium in which the tidal effects should't cause problems anymore.


Any two bodies orbiting around each other will bulge towards the other; that's the nature of gravity pulling on them. The Earth's surface bulges slightly towards the moon in it's orbit, however the bulge is relatively small. Of course, the bulge of the liquid oceans with the moons orbit is much more noticible to us on Earth. The closer together the two bodies are the more noticible the bulge will be. On tide locked worlds the bulge will be in one place, and thus will be more noticible still.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

a) Forget for regular Gas Giants.
b) Brown Dwarfs have Luminosity. We discussed this long ago on the Delphi board, and IIRC Constantine said that for multiple heat sources one should add all (L/R^²) for the individual sources before drawing the fourth root from the sum and multiplying with 278.

Three life-zone Garden planets IS possible.
 

I hope this doesn't screw up the formatting. The first column is Hydrographic percentage. For Garden worlds, there are three ranges: 21-50% (represented by 050), 51-90% (represented by 070), and 91-100% (represented by 100). The second column is Atmospheric mass, which ranges from 0.5 to 1.5 (or, if rolled randomly, 0.3 to 1.8), but 0.7 to 1.3 will cover most situations. Then across the top of the data is the mid-range of Cold, Chilly, Cool, Normal, Warm, Tropical, and Hot climate ranges.

By playing with hydrographic percentage and atmospheric mass, it's possible to get three life-zone planets without having to resort to double-worlds, life-zone gas giants, or brown dwarfs.

The numbers above are multiplied by the SQRT of luminosity to get the orbital radius.

I have to get ready for work, so I haven't tested these numbers through the world creation system. I don't know what the atmospheric pressures will turn out to be, for instance. I was only trying to get average world temps within specified ranges. By varying atmMass, you should be able to adjust the temperature to suit, while keeping the atmospheric pressure under control.

Edit: Took out example, which wasn't accurate. Went back and checked the numbers. The following constraints apply: No multiplier greater than 1.342 (blackbody temp = 240K) and no multiplier less than 0.755 (blackbody temp = 320K). So it looks like you can't get three life-zone planets without resorting to doubles or gas-giant moons. The third planet will always end up a Greenhouse or an Ice planet.

Dang it. :(

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Pragmatic,
Thank you for trying...and that chart.

Okay lets say I can get TWO of my desired planets within the standard lifezone.
The Third planet is actually a "moon" orbiting the Gas Giant closest to the "LifeZone" . Does that make any sense??

Could that Moon/Planet have enough properties to sustain human life if it got enough light from both the local star and the Gas Giant? Would a Gas Giant rafdiate or reflect enough warmth? (thinking harsh mostly-livable Desert Planet.) Imagine said planet to be halfway between Earth and Mawrs in living quality - with possible terraforming assistance/modification sometime in its recent past - less than 300 years ago.

- Ed Charlton

Re: [SPACE 4e] System Design help? (star systems that is...)
 

You can't get a gas giant in the life zone if you have two terrestrial planets in the life zone, and the gas giant not in the life zone won't add enough heat to make a world orbiting it habitable. Assuming you don't want a binary system, I'd go with the trojan point suggestion from page 1 -- you have a gas giant in the life zone, with a terrestrial planet its 4th and 5th trojan points, and another terrestrial planet orbiting the GG. This is grossly unlikely but not forbidden by orbital mechanics.

Re: [SPACE 4e] System Design help? (star systems that is...)
 

Thanks "A" , thats pretty helpful.

My players may not make it to that Star System for a while still.

But at least you have pointed me in the right direction.

The planet with the "desert-like" environment should be mostly like either Israel or Lebanon in the general climate and terrain of the livable areas. My player was also wanting that one to be the furthest out from the system's star ...or at least the first planet that incoming Travelers have a chance of landing on.

- Ed Charlton