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Starship STL speeds

Tue 03 Aug 2021, 19:45

Hey all,

It might've been stated somewhere clear as day but I can't find it... How fast does starship travel out of FTL? How long does it take, say... a Conestoga or Bison at STL through a starship? An AUs traveled speed would be cool :)

Awesome if someone can help an idiot out with this.
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I'm deranged".
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Re: Starship STL speeds

Tue 03 Aug 2021, 23:06


it's a good question, as I certainly haven't seen it mentioned explicitly in the main book. There are a few hints in the CM ops manual but I'll leave discussion of that to the GM-only forum, as they might be spoilers for the missions therein.

That said, unlike other sci-fi settings & games like Traveller, there aren't any hard limits on where you can go to FTL or how often, so no limits of having to charge up a jump drive for days or get to the outer system or out of 10x planetary diameters gravity wells or the like before you can go FTL. So I'd assumed in my campaign that one could go to FTL for anything more than a few light seconds travel, hence STL speeds aren't that important. In the movies they use STL thrusters mainly for planetary landings. These would be limited by reaction mass, i.e. how much tons of diamond dust or other bulk matter you can carry, since they have plenty of fusion power. Long distance travel at STL speeds is limited by reaction mass in the real world too, as if your thrusters can lift you off Earth, they can accelerate you to a respectable interplanetary speed in just a few days.

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Re: Starship STL speeds

Wed 04 Aug 2021, 02:10

Taking a cue from Joss Whedon when asked about how fast Serenity flies: "it moves at the speed of plot"

Alien Resurrection takes quite a while for Auriga to make it from Jupiter to Earth - but there's one time for in-system speed with a given number of AUs.

The Nostromo has some on-screen graphics that MIGHT include some gleanable system speeds - but its braking a huge refinery into orbit over a not-very-logical planetoid (1200km, but near-Earth gravity?!?) so its probably going far slower than "system cruise".

But there's a couple of places you might get screen-canon speeds from.
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Re: Starship STL speeds

Wed 04 Aug 2021, 10:47

Thanks guys. Great insights.

I should have clarified that this is explicitly STL for two reasons:
1)The ship currently has no hyperdrive (the Bison took a lot of damage in a recent terrorist attack, and the hyperengine is being overhauled back at dock);
2)The CMs hitching a ride are doing a quick patrol fly-through of the system anyway, looking for signs of terrorist hideouts along the way, so... STL

So, just to think out loud... The speed of light is a bit faster than 7 AUs per hour, but let's keep it nice and round. STL should, of course, be MUCH slower than that.

At current 21st century tech, flying Earth to Mars (1.5 AUs) takes about 7 months; or almost 5 months per AU.

For practical reasons, Alien RPG STL speeds should probably be a LOT faster than that... If we set the STL speed to 1 AU/day, it'll take a ship roughly 40 days to do the Pluto-Sun trip, or a good 4 days from Earth to Jupiter.

I think I like those speeds; thoughts? Of course, various ships would have different STL speeds, so 1 AU/day might be a fast CMC cruiser, while a Bison might take x2 or x3 times longer.
(And yes, I realize there's a lot of other factors going into this, such as relative orbital placement stuff, but I ain't gonna bother with that for the RPG).

Is this completely insane?
"And the rain sets in,
it's the Angelman.
I'm deranged".
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Re: Starship STL speeds

Wed 04 Aug 2021, 18:01

It sounds reasonable. I think you should do what ever makes your game work.

I relate with Exileinparadise. I think easiest it to just feel something out. The 'reasoning' I adapted came from some alien novel hinting that folds are made outside the system and “sub-light” is used within systems (all body gravity fields, rocks, ships and stuff are potentially dangerous).

The sub-light trip I tend to hold for 3-4 days -military drive- [max speed ~0,3-0,4 AU/ hour???] getting close to the objective so players can get some time to plan, get paranoid, not loosing flow and so-on (spending weeks or months in sub-light is too stone-age for the setting IMO). A commercial drive possible a few days extra. Reason is that military can’t hang around for weeks if a strategic window is lost within days [-Hi, great, we needed that ammo last month.], besides they probably have -very- good engines.
But at the same time I do believe in some “speed limits” and navigation dangers pending on system traffic/obstacles so its just as basic as slowing down like exiting from the highway. The closer one get to objective the slower one goes. Any contact with other vessels is expected to take place here.
Players may opt to “sleep” through this interim journey but at least its an option (staying awake) especially if expecting something, or entering a more “trafficked” space.

Oh! My brain just went blank. Did any of the above make sense?
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Re: Starship STL speeds

Tue 10 Aug 2021, 02:32

Thanks for posing this question! I think it's an element of SciFi RPGs which needs more attention, especially in a game like ALIEN.

I'm running an ALIEN-inspired homebrew using the Space Engine program (available on Steam) for interstellar and in-system mapping.

Hundreds of real star systems (and thousands of procedurally generated ones) are mapped in quite a bit of detail, including orbital parameters for planets, moons and asteroids. This provides interanetary distances which are updated automatically over time.

For PC and NPC spacecraft, I assign thrust ratings (in g's) based on the ship's maneuverability rating, and thrust-hours' worth of propellant. I use an Excel spreadsheet to calculate travel times based on planetary distances and the ship's thrust. The spreadsheet does calculations for accelerating to midpoint and decelerating (as in Traveller), for constant acceleration, and for user-defined acceleration and coasting periods.

The result is realistic travel times based on assumed thrust capabilities. Travelling across a star system could take many days or weeks, depending on thrust and fuel limits. (I don't have my spreadsheet handy right now, or I'd give a specific example. It's fairly easy to find examples and calculators online.)

ALIEN, to me, is a bit more hard SF than other settings, so I like space travel to reflect that quality a bit.

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