I was thinking about the Voyager episode "Rise" today. It's the one where Tuvok and Neelix try to escape the atmosphere in an orbital mining tether with a bunch of locals after an asteroid hit.
Anyway, I've always thought the whole idea of such a machine was quite rediculous, but not being an astrophysics type guy, I'm not sure how far off I am.
I would think that several considerations would make this device impossible:
1) such a structure, with a base no wider than a house, would likely collapse under its own weight long before leaving the atmosphere.
2) From what I gathered, this teher was actually attached to an orbital body as well as to the planet's surface. I can't imagine this working since it would likely pull the body out of orbit. Also, the variation in rotational velocity along the length of the tether would most certainly tear it to bits.
Am I off, or was this idea pretty far fetched? Not that Voyager didn't come up with other far fetched ideas... I just don't remember us ever talking about this one.
Posted by CaptainMike (Member # 709) on :
ive seen a few popular science stories featuring variations of this idea... i think the voyager version was moronic though.. i spernt most of that episode either cringing or laughing, or at times, doing both so hard simultaneously that i wanted to cry. thats on my list of the 10 worst voyager episodes ever.
Posted by Cartman (Member # 256) on :
It's actually quite feasable. Nano-tubes (carbon polymers; an offshoot of buckyballs) possess sufficient strength to withstand the huge rotational and gravitational stress such a surface-to-orbit "cablecar" would be subjected to.
Clarke used this concept in 3001, I believe.
[ July 05, 2002, 11:44: Message edited by: Cartman ]
Posted by Aban Rune (Member # 226) on :
Ok... but wouldn't such a connection (of a planet to a satellite) pull the satellite out of orbit?
Posted by Sol System (Member # 30) on :
Uh, no. The satellite simply has to be in a geosynchronous orbit. This is not unusual or particularly hard. Now, to build your tether/mushroom/skyhook thing, you do need Interesting Materials, as Cartman points out. But not Impossible Materials.
Posted by MinutiaeMan (Member # 444) on :
Not necessarily. For a body to be pulled out of orbit, it would need to have a significant mass compared to the planet.
However, the really cool thing is that the cable need not actually be attached to the planet!
The "orbital tether" concept was also used in Kim Stanley Robinson's "Red Mars" trilogy. They used Phobos (moved into a geosynchronous orbit) as a counterweight/anchor, and lowered the cable from there. They stopped the cable just a few meters short of the surface in the middle of a big crater, and the cable literally hung in midair!
Posted by Sol System (Member # 30) on :
Incidently, while there was indeed such a structure in 3001, Clarke (and others) came up with the idea some 30 or 40 years earlier, and had used it in several other (and much, much better) books.
And why did I say mushroom? I don't think anyone calls them mushrooms. Beanstalks is what I was thinking of.
Posted by Shik (Member # 343) on :
It's not connected to a "satellite" per se, either natural or artificial. There's a destination station that's actually at the midpoint of the tether; on the other side of it is a rotational counterweight. Think of it like a centrifugal sling or a hammer throw--you're constantly throwing out the counterweight & this keeps the tether taut & in place.
Posted by Sol System (Member # 30) on :
I don't mean to drown this thread in dull posts, but I want to say that this sort of idea is such a good one, provided you have the necessary technology, that such tethers should be the rule in Star Trek, and not the exception.
Posted by Aban Rune (Member # 226) on :
Wow. Thanks for the info guys. One other thing, though... explain geo synch orbit. From what I gather, it's an orbit in which the orbiting body remains in the same relative position to the planet. It doesn't go around the planet like the moon goes around the earth... it just stays put, right?
I'm just having trouble understanding the physics of how it works and I figure I'll understand one of your explanations better than a text book's Posted by Sol System (Member # 30) on :
The closer to a body (like the Earth) you are, the faster you have to go to maintain a stable orbit. For instance, Mercury goes around the sun once every 88 days, while it takes Pluto 248 years. Blah blah blah, gravity, etc.
Anyway, let's say we want to get a satellite hanging over downtown Tehran 24 hours a day. The shuttle, orbiting at a usual altitude of about (I think) 150 miles or so, travels at a speed a bit over 17,000 mph. This is fast. Too fast, as it turns out. The shuttle goes all the way around the planet every 90 minutes (or so). We need an orbit in which it will take 24 hours for our satellite to travel all the way around the Earth, so that Tehran, which is also traveling all the way around the planet (so to speak) in 24 hours, is always underneath.
As it happens, our satellite will need to be 22,223 miles up, traveling at a velocity near 7,000 mph.
In geostationary orbit, an object's speed is such that it retains its position above the same point on the surface of a planetary body.
Geosynchronous satellites have an orbital period of 24 hours. We want those orbits to be suitable for communication (and other purposes), which means that a satellite's:
1). radial velocity must be zero 2). tangential velocity must be constant 3). relative location must be fixed
The only way to meet all conditions is to place the satellite at an altitude of approximately 36,000 kilometers. At that height, its orbital velocity causes it to "hover in place" --- the centripetal force that attempts to pull the satellite towards its rotational center is balanced by its momentum. If you're interested, I could attempt to explain Newton's laws which govern these mechanics
Alternatively, a quick visit to howstuffworks.com could tell you exactly the same
[ July 05, 2002, 16:21: Message edited by: Cartman ]
Posted by Mark Nguyen (Member # 469) on :
I don't mean to drown this thread in dull posts, but I want to say that this sort of idea is such a good one, provided you have the necessary technology, that such tethers should be the rule in Star Trek, and not the exception.
I disagree. What with shuttles being so bloody efficient even in the 22nd century, to build and maintain an orbital tether when you can very likely build and maintain a number of shuttlecraft and cargo haulers that can far more work than the tehter ever could in less time - a tether trip may take a few hours, limited by the physical speed of the actual lift, when shuttles can get to orbit in minutes. As with everything else in Trek, environmental damage by their technology is almost never an issue, so this would not be a factor.
What *would* be a factor would be if the tether were ever to fall. KSR's book shows exactly that, and the catastrophe of having something that long hit the planet extremely fast, essentially winding its way around the planet and crushing everything in its path. Anything strong enough to resist shear and weather will be strong enough to survive re-entry, and so something like that falling over Earth would kill a lot of people, and piss off a lot more people. So no, I don't see orbital tethers being s good thing in Trek.
Nor for that matter have I ever seen the logic of placing a massive spacedock in orbit as seen in STIII et. al. Can you imaigne what'd happen if one of THOSE things fell to the surface?
Mark
Posted by Sol System (Member # 30) on :
Well, yeah, and if something ever went wrong with a warp core while a ship is in orbit it would probably sterilize the planet down to the bedrock. This doesn't happen, however, in the fictional stories to which we are a party to, and so we could presume that any Federation beanstalk would be relatively immune to disaster as well.
Your point about incredibly efficient shuttles is well-taken, though, and it was something I thought about several minutes after posting, but I stand by my point for two reasons. One, I suspect a UFP-designed orbital tether would be even more efficient than a UFP-designed shuttle for your usual boring "let's get this stuff into orbit" jobs. And two, I don't necessarily mean that Earth needs one of the things. (At least, not Star Trek's Earth.) Or even any Federation world. But they should be out there. The Borg should be engaged in engineering megaprojects to boggle the mind, for instance, but that's perhaps somewhat beside the point.
Posted by Shik (Member # 343) on :
And t'round out all the hoohah, what's the cover story for the July 2002 issue of Popular Mechanics? You guessed it...
[ July 05, 2002, 19:28: Message edited by: Shik ]
Posted by MinutiaeMan (Member # 444) on :
On the topic of shuttles being more efficient than tethers... I'm not so sure about that. I'm not well-versed in the physics that would be involved, but isn't one of the major benefits of the tether supposed to be that a lift that goes up regains 90% of the energy that it spent rising on the way back down? This would make it extremely energy-efficient.
Consider that when you're on a shuttlecraft, you get your escape velocity from a one-time burn of energy from a fusion reactor. This energy is nonrecoverable, and also requires more fuel.
Now, this certainly wouldn't work for the fast transportation that's often needed, like for sending people up to orbit. Because the elevators WOULD still move relatively slowly. However, for non-urgent cargo transportation, I'd wager that an orbital tether would still have a big advantage.
Posted by Treknophyle (Member # 509) on :
Just a thought...
I'd think that transporter technology would be far more efficient than either shuttle or 'beanstalk'. No energy being lost via friction or moving parts...
BTW: for fiction dealing with beanstalks - read Sheffield.
ABTW: The 'stationary orbit' is also referred to as the 'Clarke Belt' - named after the golden age sci-fi writer who pointed out the usefulness of communications sattelites positioned here.
Posted by Sol System (Member # 30) on :
It seems a sad day when Clarke needs an introduction in a place like this...
And doesn't the TNG technical manual more or less say explicitly that shuttles are more effecient for any extended bit of freight moving you might need done? Not to mention that every time we see an established orbital facility or similar, it's swarming with shuttles, which would appear to be empirical evidence of their value in such conditions.
Posted by MinutiaeMan (Member # 444) on :
Yeah, yeah... but shuttles are so... normal. It'd be cool to have something that's really "farfetched" from our perspective. We already use the Space Shuttle, albeit at a greatly reduced frequency. Something like a space tower would be a really fun thing to actually see in SFX shots. "Rise" didn't do the concept justice, IMO.
Posted by Sol System (Member # 30) on :
Hey, I was the one in favor of them in the first place! Sort of!
But I like shuttles too.
Posted by Timo (Member # 245) on :
Well, like Treknophyle said, the "really farfetched cool-looking thing" that augments/replaces the shuttles in Trek is the transporter. Sure, shuttles may move a few dozen people or a few tons of freight from ground to orbit with relative ease, but what if you have to move ten thousand people per day, or pump imported and exported goods up and down constantly?
A transporter apparently is impervious to the problems of moving stuff in and out of a gravity well, or matching linear and angular velocities, or any other traditional space launcher problems. And it runs on the same AA battery that a hand phaser uses (at least in TNG "The Hunted" it did). Surely it must be the most attractive surface-to-orbit transport system imaginable.
And since Delta quadrant doesn't have much in the way of transporters, it's only natural that our first two beanstalk references come from there...
As for which is the fastest - shuttle, beanstalk, transporter - it probably mainly depends on the terminal logistics. A transporter works more or less instantaneously; a shuttle ascent probably takes a few minutes; and the beanstalk cabin speed depends on how much Trek magic you add to the basically real-world device. But how long does it take to do the preflight checks on a shuttle, or maneuver her through the traffic jam of thousands of other small craft departing and arriving? Will transporters (with potentially a very large number of platforms) present fewer congestion problems than the one or two narrow beanstalks per planet? Will they have "bandwidth" problems?
I'd imagine that UFP civilian surface-to-orbit traffic relies heavily on transporters, explaining why we don't see much in the way of expansive shuttleports or landing-capable starships when we visit Earth. The military is more enamored with the old-fashioned shuttles, since they are more versatile in adverse conditions - plus the military logistics are not quite as demanding.
Timo Saloniemi
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