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Old 04-05-2017, 12:32 AM   #1
David Johnston2
 
Join Date: Dec 2007
Default Stardivers [Space]

Assume a hyperdrive that can let you make jumps with a maximum range based on the mass of the sun you are leaving. What do you think I should multiply the sun's mass by to get the length of the jump? I'm assuming that it is possible to mount more than stardrive on a ship for increased range but the the only ships that do it are message boat and smugglers.
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Old 04-05-2017, 03:19 AM   #2
Whyte
 
Join Date: Oct 2008
Default Re: Stardivers [Space]

It depends on the hows:
1. How big is your setting?
2. How quickly do you want the PCs to be able to get from planet X to planet Y?
3. How much time does the jump (or recharge afterwards) take?
4. How often do you want them to travel?
5. How important is travelling to the campaign: is it an adventure on its own, or will it be simply skipped?

Since you wish to tie it to the star mass, it implies to me that you do want the travelled distance to matter. Stellar masses are roughly from 0.1 Msol to 100 Msol, with the massive stars very very very very very rare. In practice, most of the stars that the PCs would ever visit would be in the 0.1 - 1 Msol bracket (earth-like planet's host star would probably be even closer to something like 0.7 - 1.3 Msol, so you get very very small range if you focus on 'typical' space opera planets), with stars more massive than 3 Msol or so being so rare as to not really matter for campaign planning (save perhaps as a military base, see below). Since the more massive stars are very unlikely to host habitable planets and they are so rare, any benefit you might gain from a longer jump is negated by the need to travel there, first.

One way to make the big stars matter would be to make it jump-time always a fixed length, regardless of the distance jumped, and make the distance x*(Msol)**2 (factor times mass squared). This means a star of 10 Msol would have a jump distance 100 times more than a normal sun-like star, which would definitely make them more desirable, almost like wormholes in other scifi (Honor Harrington comes to mind). The squared mass also means that the smallest red dwarfs might stay uninhabited or even unexplored, since they might be too far from another star to get back to it with a jumpdrive: say 0.1 squared is 0.01, and if the distance to the nearest other star is about 1 parsec, you need x = 100, or that star becomes a dead end for FTL.

So, lets say that the jump takes a day, your setting is 1000 parsecs across, and you want your PCs able to travel that in a month. In other words, you want 30 jumps to cover that 1000 parsec distance, which means each jump should be about 33.3 parsecs. Since you probably have suitable 1 Msol stars within that 33.3 radius that are more or less along a straight line, that would imply to me that something like x = 50 parsecs would be fine, allowing for a slight fudge factor. Note that if you use the squared mass, this means if you have a 5 Msol star somewhere in your setting, they can reach any point of your setting in one jump: 50*5**2 = 50*25 = 1250 parsecs. Makes for a very nice place to have a fleet presence at, so that you can reinforce any part of your empire in a day (from when you hear that something is wrong, which might take longer). Such higher mass stars would become nexi for high-speed interstellar travel, funneling trade through them. Which has a nice 'geographical' result for trade patterns, meaning you have more 'neglected' systems farther away from the high mass stars, where tramp freighters might ply their trade.

Last edited by Whyte; 04-05-2017 at 03:32 AM.
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Old 04-05-2017, 09:31 AM   #3
Fred Brackin
 
Join Date: Aug 2007
Default Re: Stardivers [Space]

Quote:
Originally Posted by David Johnston2 View Post
Assume a hyperdrive that can let you make jumps with a maximum range based on the mass of the sun you are leaving. What do you think I should multiply the sun's mass by to get the length of the jump? I'm assuming that it is possible to mount more than stardrive on a ship for increased range but the the only ships that do it are message boat and smugglers.
I did this (without the multiple stardrives thing) and I picked 3.3x (in parsecs) the combined mass in Sols of the stars involved. no jumps into empty space possible.

Using the stellar distribution from (probably) First In it gave me interesting results.

G-class stars usually connected to something though direct links between inhabited systems would probably be rare. 3 to 5 jumps in a zig-zag for what would have been a straight line separation of 20-30 parsecs was the norm.

M-class dwarves seldom connected to anything except the other stars in a multiple star system. Most of the time they could be ignored.

A-class stars usually did connect to at least 1 more A-class and these links could form the backbone of a network. In my setting long trips were referred to as "taking the A train".
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Old 04-05-2017, 12:10 PM   #4
David Johnston2
 
Join Date: Dec 2007
Default Re: Stardivers [Space]

Quote:
Originally Posted by Whyte View Post
It depends on the hows:
1. How big is your setting?
2. How quickly do you want the PCs to be able to get from planet X to planet Y?
3. How much time does the jump (or recharge afterwards) take?
4. How often do you want them to travel?
5. How important is travelling to the campaign: is it an adventure on its own, or will it be simply skipped?

Since you wish to tie it to the star mass, it implies to me that you do want the travelled distance to matter. Stellar masses are roughly from 0.1 Msol to 100 Msol, with the massive stars very very very very very rare. In practice, most of the stars that the PCs would ever visit would be in the 0.1 - 1 Msol bracket (earth-like planet's host star would probably be even closer to something like 0.7 - 1.3 Msol, so you get very very small range if you focus on 'typical' space opera planets), with stars more massive than 3 Msol or so being so rare as to not really matter for campaign planning (save perhaps as a military base, see below). Since the more massive stars are very unlikely to host habitable planets and they are so rare, any benefit you might gain from a longer jump is negated by the need to travel there, first.

One way to make the big stars matter would be to make it jump-time always a fixed length, regardless of the distance jumped, and make the distance x*(Msol)**2 (factor times mass squared). This means a star of 10 Msol would have a jump distance 100 times more than a normal sun-like star, which would definitely make them more desirable, almost like wormholes in other scifi (Honor Harrington comes to mind). The squared mass also means that the smallest red dwarfs might stay uninhabited or even unexplored, since they might be too far from another star to get back to it with a jumpdrive: say 0.1 squared is 0.01, and if the distance to the nearest other star is about 1 parsec, you need x = 100, or that star becomes a dead end for FTL.

So, lets say that the jump takes a day, your setting is 1000 parsecs across, and you want your PCs able to travel that in a month. In other words, you want 30 jumps to cover that 1000 parsec distance, which means each jump should be about 33.3 parsecs. Since you probably have suitable 1 Msol stars within that 33.3 radius that are more or less along a straight line, that would imply to me that something like x = 50 parsecs would be fine, allowing for a slight fudge factor. Note that if you use the squared mass, this means if you have a 5 Msol star somewhere in your setting, they can reach any point of your setting in one jump: 50*5**2 = 50*25 = 1250 parsecs. Makes for a very nice place to have a fleet presence at, so that you can reinforce any part of your empire in a day (from when you hear that something is wrong, which might take longer). Such higher mass stars would become nexi for high-speed interstellar travel, funneling trade through them. Which has a nice 'geographical' result for trade patterns, meaning you have more 'neglected' systems farther away from the high mass stars, where tramp freighters might ply their trade.
The jump is instantaneous inside and out (except in the case of rare malfunctions) but the transit time is affected by the fact that you can only jump from the corona of a star and you don't arrive in the corona of the next star (unless you want to do go kaboom since the direction you are moving as you approach the star controls both the direction you are jumping and your vector on emergence and it doesn't correct for the relative velocities of the two stars). The corona doesn't usually damage your ship because you jump as soon as soon you hit it and you're moving at very high speed when that happens to minimize your time of exposure. Hence the name of the setting.

I like the idea of squaring the mass. It will help magnify the strategic importance of larger (named) stars even though they're largely worthless for more than military bases and transhipment points as a place of habitation while isolating the annoyingly common smallest red dwarfs. It's impossible to leave an M7 dwarf by normal means so I can just leave them off the map. So if x=12, let's say, then anything smaller than a M4 dwarf doesn't exist as anything except a one way trip.
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Old 04-05-2017, 12:22 PM   #5
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Stardivers [Space]

Quote:
Originally Posted by David Johnston2 View Post
I like the idea of squaring the mass.
It's not really necessary, even linear in mass means star importance maps pretty well to star brightness.
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Old 04-06-2017, 03:48 AM   #6
Whyte
 
Join Date: Oct 2008
Default Re: Stardivers [Space]

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Originally Posted by Anthony View Post
It's not really necessary, even linear in mass means star importance maps pretty well to star brightness.
The number density of those big stars goes down like 10**-2.35 in the initial mass function, and it gets even worse once you take into account that the massive star lifespans are measured in millions of years rather than billions. I don't have an easy reference at hand for the number of observed stars per stellar mass, but lets assume the exponent is -3 as a test case?

This means that a star of 10 solar masses is 1000 times less likely to be found in the same volume than a 1 solar mass star. Granted, the volume that the 10 solar mass star jump would encompass is also jump_distance**3, so you might actually still gain a small benefit from re-routing via the more massive star, depending where you start in that sphere and where the target is.

If you use squared mass, though, you accomplish dropping the low-mass stars like the red dwarfs, and you make the high mass stars REALLY useful. This, like David points out, has some cartographic advantages for the setting.
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Old 04-06-2017, 11:44 AM   #7
Fred Brackin
 
Join Date: Aug 2007
Default Re: Stardivers [Space]

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Originally Posted by Whyte View Post
This means that a star of 10 solar masses is 1000 times less likely to be found in the same volume than a 1 solar mass star.
Gurps Space normally assumes that anything over an A is too rare to be worth putting on a random table. You'd hardly go over 2 solar masses with those.

Yet A's are common enough. Earth has at least 2 decently close. Sirius at 8.3 ly and Vega at 25. You'd probably need to go 400-500 ly to find a giant star that'll end up in a core-collapse supernova. I think Antares is the closest.

So the size of stars you need to consider is actually fairly limited.
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Old 04-06-2017, 11:58 AM   #8
Anthony
 
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Default Re: Stardivers [Space]

Quote:
Originally Posted by Whyte View Post
The number density of those big stars goes down like 10**-2.35 in the initial mass function, and it gets even worse once you take into account that the massive star lifespans are measured in millions of years rather than billions.
That actually has a kind of useful effect, though, in that it means your routing will actually be dominated by G-class stars (the initial mass function seems to flatten out somewhat below 1 stellar mass, and even if it didn't, lifespan pretty much ceases to be a factor for anything smaller than a G-class star).
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Old 04-07-2017, 03:55 AM   #9
Whyte
 
Join Date: Oct 2008
Default Re: Stardivers [Space]

Quote:
Originally Posted by Fred Brackin View Post
So the size of stars you need to consider is actually fairly limited.
Yep, like I said in my first response. However, if it is mass squared, then those massive stars, while very rare, become very very useful.

If you use just mass, I wouldn't actually bother with it. The most common (i.e. habitable) planets you'd even bother to visit would likely be around K & G stars (M dwarf flares would make habitability an issue and the liquid water zone planets would likely be tidally locked, too), so the difference in masses is so small that it is not worth adding as a complication, IMHO. If you want to discriminate against the ubiquitous red dwarfs, you could easily put in a cutoff at 0.5 solar mass or so and claim that any star smaller than that doesn't allow the stardiver jump drive to work because of reasons.

If the jump distance is small (less than a few parsec), then you might get a Traveller like situation, where you have jump routes, which is nice for some campaign purposes, but also requires you to map the routes (Traveller flinched and did it just in 2D). If the distance is long (10+ parsecs), the you can pretty much assume that you will find a suitable star more or less on the direct line, and there are no more 'routes'; it just adds to the travel time, making it more akin to hyperdrive, with the requirement of a star just being a campaign tweak.

EDIT: Actually, now that I think about it... if the jump is connected to the surface gravity of the star (i.e. the gravity at the stellar atmosphere, the photosphere), then that would actually discriminate against the biggest stars since they are more 'puffed up' than our Sun, and favor red dwarfs! You would feel more of a gravitational force in a corona of a red dwarf, since you would be so much closer to its center! The jump points of choice would become the white dwarfs, which are even more compact.

Last edited by Whyte; 04-07-2017 at 04:35 AM.
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Old 04-07-2017, 07:09 AM   #10
Fred Brackin
 
Join Date: Aug 2007
Default Re: Stardivers [Space]

Quote:
Originally Posted by Whyte View Post
Yep, like I said in my first response. However, if it is mass squared, then those massive stars, while very rare, become very very useful.
.
They're probably too rare.

http://astronomy.stackexchange.com/q...nt-stars/18562

....has a calculation that of the 7000-odd stars within 50 parsecs in the Hipparchos catalog there are _no_ type O's and only 2 or 3 M-class giants. There were 29 B's and he didn't bother to count the A's like Sirius or Vega. This is why Gurps Space doesn't randomly place stars above A.
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