I'm playing a campaign presently where the GM (*waves hi*) has progressed the timeline to late AF 12/early AF 13. I'm just a player (not GM), but I offer a lot of worldbuilding advice (particularly in STEM-y sorta areas, since I have a lot of training in those areas). Anyway, the Titanian space elevator would be completed by AF 12, if all goes according to plan (and, in our campaign, it does).
So. This might be nitpicky and somewhat irrelevant--for one, I get that the setting was initially being built in the 2000s, when Titan was even more unknown than it is now; for two, in campaigns set in canonical AF 10, the space elevator would still be being built; for three, I get that this level of technical accuracy *just isn't* important to a lot of gamers.
However, why is the space elevator placed where it is (in the Xanadu region near Nyhavn)?
One thing to remember about Titan is (like Luna) it is tidally locked to the body it orbits--the Titanian "day" is 15 Earth days long. This obviously make an elevator extending to geostationary orbit unfeasible. In the Lunar space elevator, this is solved by actually having it have a mobile base. *However* ([url=https://en.wikipedia.org/wiki/Space_elevator#Extraterrestrial_elevators]... to Wikipedia[/url]), you could still have a space elevator on such bodies by extending it through the L1 Lagrange point (that is, the Lagrange point between the two bodies). But, look at these maps, and remember that the prime meridian (0 longitude) on Titan is the Saturn-facing line:
[url=https://saturn.jpl.nasa.gov/system/resources/detail_files/7492_PIA20713_...
[url=http://i.imgur.com/RhcNzPd.png][img]http://i.imgur.com/RhcNzPd.png[/img]...
If the elevator were to extend to L1, wouldn't placing it in the vicinity of New Quebec make more sense? Or is there something about space elevator physics I am missing?
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questions about Titanian space elevator
Mon, 2017-02-27 01:12
#1
boomzilla
questions about Titanian space elevator
Mon, 2017-02-27 01:20
#2
boomzilla
wait--is it trying to extend
wait--is it trying to extend to the L4? Wow, that would be ambitious!
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Mon, 2017-02-27 07:52
#3
boomzilla
"synchronous orbit"
Okay, I think I spotted the problem:
"Titan’s main space port maintains a synchronous orbit above the capital, Nyhavn." --Rimward page 109
That (synchronous orbit) is not possible with a tidally-locked body.
FWIW, I *do* totally appreciate the general attention to small technical details for astronomy stuff. Yeah, I get that errors will crop up (and, again, Titan is still very much an unexplored body even as of 2017!)
This can just be retconned in our campaign, I guess (I get that EP encourages gaming groups to do their own world-building/deviation from canon).
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Mon, 2017-02-27 09:39
#4
ORCACommander
well if L4 is more ambitious
well if L4 is more ambitious and therefore more awesome then have them reaching for the L4 :P
Guess we can have PS+ fix this in a follow up printing or a pdf update
Mon, 2017-02-27 13:03
#5
Trappedinwikipedia
L4 could actually make more
L4 could actually make more sense than L1 for a lagrange anchored point, as L1 isn't stable while L4 is. It's extremely difficult to put an object in L1 and have it stay there without active thrust control, which is harder to to with a huge string attached, and expensive for a large counterweight.
That said, a space elevator to L4 would probably be a different kind of megastructure than a space elevator, because that's insanely long, might be beyond AF10 materials science and is probably not worth the massive extra cost to run a string 1/6th of the way around Titan's orbital path around Saturn.
More to the point, Space Elevators don't need to be straight lines, there's nothing preventing one from being strung from the moon's south pole to Earth-Moon L1 for example. That means that running it from anywhere on the inner hemisphere to L1 is fine (and anywhere on the outer hemisphere to L2). That means that the locations was probably chosen to make it closer to the supply lines and spaceports which it would be working with.
https://en.wikipedia.org/wiki/Lunar_space_elevator#/media/File:Lunar_spa...
Tue, 2017-02-28 05:41
#6
puke
stability?
Does a counterweight at L1 need to be "stable"?
Could it not be just a touch beyond the L1 point, creating a slight tension on the tether? That might have the practical result of making it even more "stable" in the sense that it will self-correct.
If your counterweight in synchronous orbit or at L4/5 gets out of position, you need to spend effort to re-position it. A counterweight on a tether just beyond L1 will always be pulling its self into true. This could even offset the need to always move as much mass down the elevator as up it, the weight could remain in position regardless of traffic.
Maybe trickier to build, though?
Tue, 2017-02-28 11:09
#7
ThatWhichNeverWas
Very quickly...
I don't have time do the math, but could the Endcap actually be under power, using a plasma sail or other magnetodynamic propulsion system?
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Tue, 2017-02-28 11:45
#8
puke
instead or in which circumstance?
Like, instead of being at a lagrange point? It would probably need to have an absurd level of power available to it.
Or did you mean to "hold station" at one of the points? Maybe you could have massive solar arrays at stations along the length of the cable, all generating enormous power. Then use that to power an ion drive, or somesuch. Photon pressure from a solar sail is probably not sufficient by its self, especially at Saturn's distance.
Wed, 2017-03-01 06:49
#9
ThatWhichNeverWas
Sort of.
More the former. I was pondering a moderate reduction in cable length, but using engines to make up the loss in centripetal force.
Power wouldn't be an insurmountable problem; Saturn has a fairly hefty radiological environment, and the cable itself could be used as a hardline from fusion groundstations.
...
I've just realised what I'm picturing is basically an Orbital Ring.
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Wed, 2017-03-01 08:26
#10
puke
except de-orbited
That would be something. Build an orbital ring in low planetary orbit, and then spin it down.
Just like the elevator: Since the body is tidally locked, the ring will have to be not-orbiting in order to stay in position.
I feel like that would be insanely dangerous, though. If broke, or if it got nudged the wrong way, the whole thing comes crashing down onto the surface. For safety, you'd probably want a bunch of elevator tethers like spokes on a wheel. But if it broke, those would just become part of the problem.
Now, if you spun up the planetoid a bit...
Wed, 2017-03-01 09:54
#11
ShadowDragon8685
I've always just reckoned
I've always just reckoned that with Titan's insane atmospheric density compared to its gravitational density, it would probably be simplest to do orbital ferrying around Titan with spaceplanes. Yes, there's no oxygen in that air, but if you use electricity to spin a turbine - or hell, a prop! - fast enough, you can get a lot of height and velocity. Then switch to the main thrusters for the last push up. Getting down is, theoretically, even simpler if you have a big enough station; you can use a magnetic accelerator to launch craft heading down "backwards," IE, canceling much of their orbital momentum. If they can get into the atmosphere, they can deploy flaps and bring themselves down.
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Wed, 2017-03-01 12:25
#12
puke
Balloon Launch!
as title.
Maybe the "ground" side of the tether is on a balloon :)
Or "stratospheric boat"... I don't remember which piece of sci-fi that was stolen from, but it basically sits in the upper atmosphere with a top open to vacuum.
Tue, 2017-03-07 20:41
#13
Chernoborg
Chiming in!
Anytime they bring up a station parked above a moon I assume it's at either L1 or L2. The same thing happens at Ganymede with Liberty City and Liberty Station. As both locations happen to be on the side opposite their Planet, the L2 is the point used.
Keep in mind for Titan that the Commonwealth has placed defense stations at L1 (Phoebe!), L4(Skathi), and L5(Abramsen) so there's also a reason not to poke around those locations.
True, L2 isn't stable but that would really only be a problem for relatively immature spacefaring civilizations. Right now, it would be a huge expense to maintain a station just at our Moon's L2. In Eclipse Phase scheduling a fuel run would be pretty trivial.
My guess is that when the elevator is built, it would incorporate the existing Commonwealth Hub as a spaceport at the actual L2 zone while the counterweight sits much further out (this has to do with keeping tension in the cable and the relative mass of the weight). The extra length could then be used the same way the Martian elevator is - to fling cargo and ships off into the solar system.
Personally, I kind of liked the idea of the Titan end of the tether not going all the way down and having a port complex held just above the ground. Much like Zalem from the Gunm manga but quite a bit smaller! Unfortunately, with the anchor not being directly under the L2 point that probably wouldn't work -or it would look REALLY weird!
Now if you were to ask how the Large Collider is in orbit ...I have NO idea!
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Wed, 2017-03-08 10:20
#14
boomzilla
Excellent. Thanks, all, for
Excellent. Thanks, all, for the input!
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