How long would it take to travel up an orbital elevator?

[Galacticdefender]

I'm writing a story in which the main character is taking a trip up an orbital elevator, and realized I had no clue how long it would take to get to an anchor station in Orbit. Does anyone have an idea?

 

[chrispenycate]

If we used minimum time calculations, full acceleration for the first bit then slightly higher deceleration to the counterweight, with some way of flipping the capsule at changeover point, with reasonable comfort you could do the trip in slightly under 12 hours. Unfortunately, there'd be a bit where the atmosphere wasn't thin enough, and the capsule was moving fast enough, that atmospheric friction would not only waste huge quantities of energy but would give serious heating problems. Better would be about 36 hours; don't forget that all tickets include meals and beds; the trans spacial express.

Even slower would be more energy efficient. Still, the more decelleration you can manage as you approach the free-fall point (generating energy for acellerating another capsule( the easier it is to use the in flight toilets, or have a shower.

 

[Lenny]

How far out is the counterweight in your example, Chrispy, and how fast is the capsule moving?

Another possible answer - one of Japan's largest construction companies, Obayashi Corporation, has "plans" to build one that will be operational by 2050. With a counterweight in orbit 96,000km from ground, and a capsule travelling at (what I guess is an average speed of) 200km/h, they estimate seven and a half days in the capsule. I doubt it will ever get built, and the figures are pure speculation, but it's an idea for which paid engineers have done some calculations, so it's probably possible.

https://www.google.co.uk/search?q=Obayashi+Corporation+space+elevator

 

[Ursa major]

Can we assume the elevator is attached to Earth or an Earth-like planet?

The only description I can recall of a journey up such an elevator was in a Charles Stross novel, Saturn's Children, where the elevator is attached to Mars and the counterweight is one of its moons (Deimos, I think, though it may not be in its original condition or orbit).

 

[Galacticdefender]

Contact Harvest (great book, actually) had a great description of an orbital elevator, but it was the trip down so it was much faster.


Would ground-based laser propulsion make it faster? And as for the slowing down part, there are a bunch of magnetic rings leading up to the anchor station.

Is there any possible way that a trip up an orbital elevator (implying the anchor station is in low orbit) could last more like, say, three hours? If not, I'm going to have to rewrite nearly a page worth of material.

 

[MstrTal]

Ok I know its Science Fiction and people a lot smarter than I have worked on this before but I have never understood the whole Orbital Elevator concept. I have seen it in Anime and books before but it has always seemed a ludicrous concept. I know I am horrible at math so the physics of it escape me so it is more than likely possible I just see how.

Wouldn't the earths rotation, winds, gravity, the van allen belts and all sorts of other things let alone the earths rotation around the sun cause it to whip around and crash back into the earth? Like I said the math is beyond me but it just seems like common sense that the taller and thinner something is the less stable it will be. I mean ever see a CB radio antenna? Long thin whip like things that you attach on your back bumper and generally bend over and hook to your front bumper because if you don't it will whip all over the place and slash up your paint or the car behind you.

Anyways like I said I know it's SciFi but it's just never made sense to me.

 

[Galacticdefender]

Actually, its not just "sci-fi", there are several actual proposals to get one built, and I think it will happen if not in my lifetime, then just beyond it.

http://en.wikipedia.org/wiki/Space_elevator

That should answer a few questions though. It isn't a free standing structure, it's anchored by a counterweight (I'm calling it an anchor station) in space.

Also, even if an orbital elevator was only going one tenth the speed of a space shuttle, it would still reach orbit in about 85 minutes. So the above poster's 30 hours seem way off. And with the advancements in different ways to propel something up a strand (my universe is set in 4120 or so), I think 2-3 hours should be a decent time.

 

[MstrTal]

Like I said I am sure the science is sound I just never could wrap my mind around it. That said that article makes it a little more realistic. Still seems a bit of a stretch to me. But that said it's always been a cool concept.

 

[iansales]

In Kim Stanley Robinson's 2312, it takes five days.

 

[Sapheron]

I really think this is one of those things you'd be better just making up. Let it take however long it needs to do whatever your characters are meant to be doing during the journey. If it doesn't really matter, then you don't even have to specify, exactly, which means readings who want it to take an hour or a week can be equally happy.

As an aside thing:

I can't imagine a collossal structure that runs from surface to an orbiting station ever being cheaper and easier than strapping rockets to things. They're a cool idea though.

 

[Venusian Broon]

I can't imagine a collossal structure that runs from surface to an orbiting station ever being cheaper and easier than strapping rockets to things. They're a cool idea though.

The vast proportion of the mass of a rocket is used up to get the tiny bit at the end to escape velocity and into orbit. Hence you end up burning most of your time, effort (and money) just to get a few precious kilograms into orbit.

With a space elevator (and I'm sure chrispenycate or iansales knows this better) I believe you can use earth's gravity to help you form a 'conveyer belt' that can lift orders of magnitude of mass into orbit and, more importantly, more or less continuously. Here nothing is burnt up and the energy cost of operating the elevator is relatively small. Hence I'd think that the space elevator very quickly becomes cheaper per kilogram to get stuff into orbit compared to a rocket. Even if it costs hundreds or thousands of billions!

 

[chrispenycate]

In Kim Stanley Robinson's 2312, it takes five days.

Five days sounds quite comfortable, and not over wasteful. After all, you want to reclaim as much of the kinetic energy as you can,

Contact Harvest (great book, actually) had a great description of an orbital elevator, but it was the trip down so it was much faster.

Actually, since the point of highest velocity is deeper into denser atmosphere the trip down should take longer, not less time. I suppose we could cut the trip shorter by building a tube onto the side of the tower and evacuating the air; it's air friction that's burning us up like a meteorite), but unless the tube itself is diamond, or something like that with an inherently high tensile strength, this is going to complicate construction considerably (and it never looked easy).

Would ground-based laser propulsion make it faster? And as for the slowing down part, there are a bunch of magnetic rings leading up to the anchor station.

It's not the propulsion system that counts; with sufficient available energy (and yes, I suspect lossless superconducting cables will be essential over the tens of thousands of kilometres involved) a Laithwaite linear accelerator will do the job fine. Think of it as a vertical bullet train And I really wouldn't want to aim a laser that close to the tower; can you imagine the disaster if you succeeded in breaking it? (If you think of it as a cable it could wrap itself clear round the equator and eat its own tail, multi-megatonnes coming in at meteorite speed). And laser power can not be recuperated on slowing down, unlike your coilgun equivalent.

Is there any possible way that a trip up an orbital elevator (implying the anchor station is in low orbit) could last more like, say, three hours? If not, I'm going to have to rewrite nearly a page worth of material.

Geostationary is essential ( and I don't think the shuttle goes up that high), otherwise the counterweight is wrapping its tether round the Earth. Of course, you could get off earlier – put a request stop half way up – but this would not be in orbit, and you would start to fall toward the planet unless you added some serious delta v sideways.

How far out is the counterweight in your example, Chrispy, and how fast is the capsule moving?

Another possible answer - one of Japan's largest construction companies, Obayashi Corporation, has "plans" to build one that will be operational by 2050. With a counterweight in orbit 96,000km from ground, and a capsule travelling at (what I guess is an average speed of) 200km/h, they estimate seven and a half days in the capsule. I doubt it will ever get built, and the figures are pure speculation, but it's an idea for which paid engineers have done some calculations, so it's probably possible.

I've used the model with the counterweight in geostationary orbit, and built the tower outward at the same time as inward. Less maximum tension in the structure, and you don't need to fly in an extremely unwieldy structure (though yes, you need a bigger counterweight). This means end structure is ±36,000 km from the surface. If you can average 1,000 km/hr, that's 36 hours, and your maximum speed is twice that; serious energy losses and heating if there is appreciable atmosphere; much better to take it more gently. But acceleration is comfortable, nothing like the ten or twelve gees you get in a rocket.

 

[Bowler1]

I can't imagine a collossal structure that runs from surface to an orbiting station ever being cheaper and easier than strapping rockets to things. They're a cool idea though.

Build costs would be the main problem, after that you can think of it as a railway line to the stars, cheap and easy. Right now, at a guess maybe 20 to 50 people go into space every year, I can't see rockets doing a lot more than this. With a space elevator this number of people could be done every hour or every elevator car. So we could have a years rocket launches done in a morning.

I'm stepping aboard, just imagine the views. I suspect Chrispy would have been camping outside for weeks before hand for his spot!

 

[Ursa major]

It depends on what all those people are going to do when they get to the top, Bowler. If there aren't a lot of destinations, and none of them have an elevator of their own, the bottleneck is still there, simply not here on Earth.



(If there's a need for a significant amount of manufacture in zero gravity, that might require the capacity, but it would have to be something very, very valuable to cover the costs of the elevator.)

 

[iansales]

Rockets are expensive but they're also one-shot. An orbital elevator may cost trillions to build, but the cost per kg carried into orbit will be significantly reduced simply because of the volume of traffic it will be able to carry.

 

[Flugel Meister]

Speed could depend on any form of inertial dampening.

 

[Venusian Broon]

It depends on what all those people are going to do when they get to the top, Bowler. If there aren't a lot of destinations, and none of them have an elevator of their own, the bottleneck is still there, simply not here on Earth.

(If there's a need for a significant amount of manufacture in zero gravity, that might require the capacity, but it would have to be something very, very valuable to cover the costs of the elevator.)

That's a good point Ursa, however by building it and disregarding the capital costs initially and running it on operating costs assuming it will last a very long time it will impact the economics of doing things like asteriod capture, space travel, space craft construction, travel to other parts of the solar system, manufacture and open out possibilities that just were not feasible before because of cost. So it could very well develop a vibrant economy around it (eventually). A case of build it and they will come...

To give a real world example I think the Suez canal company went bust at least once and had to be rescued, so the capital cost was double that expected. But the impact afterwards (and to this day) is still extremely significant and although I don't have the figures I would guess that it's benefited the world tremedously and much, much more than the initial costs of building it.

On the other hand it may not spur any development or appetite for space hence remain a very, very tall extremely expensive tower

 

[Ursa major]

Lots of infrastructure businesses have gone bust. Just look at the US railroads: some of the biggest names (well, until the last few decades of consolidation) went bust over and over again, the (fictional) MidWest & Pacific Railroad, being resurrected as the MidWest & Pacific Railway, being resurrected as the MidWest, Rockies & Pacific Railway, being resurrected as the MidWest, Rockies & Pacific Railroad in the process.

And I think someone (it may have been Irwin Stelzer, who writes a column in the Sunday Times and appears on Newsnight) once said that the US airline business had, in all the time since it was founded, not yet earned as much money as it had spent over the same period (spending which doesn't include the costs of all those airports).

However, there were various non-infrastructure, monetary returns from which the owners of these railways/railroads could benefit - land grants, for instance - whose value probably disappeared from the railroads' books before bankruptcy came knocking at the door.


So who is going to put up all the money? And, perhaps more importantly, who is going to make sure that in the time taken for the elevator to be built and start making a return, all those massive debts are not called in?

 

[Venusian Broon]

Lots of infrastructure businesses have gone bust. ....

Yes I was thinking along those lines. In fact I couldn't off hand think of any longterm infrastructure project that has not either gone bankrupt or experienced major finanicial difficulties that required it to be rescued, or at the very least wildly optimistic initial costings: UK rail network (probably all rail networks over the world to be fair...), various attempts at the panama canal, telecom networks, road building...

Possibly because of their clear importance to our society and health, sewage and water systems and electricity networks seemed to have been developed in the public interest by governments and it's difficult to see if they've failed in a similar way to those infrastructure projects above.

So who is going to put up all the money? And, perhaps more importantly, who is going to make sure that in the time taken for the elevator to be built and start making a return, all those massive debts are not called in?

On balance I think It's definitely far too expensive and too much of a risk with scant little to exploit if it was built at the moment.

Conventional space travel needs to get less expensive, as does the material science that you'll need to construct the structures that'll make the elevator; but the project definitely needs a few more compelling economic or other important reasons for getting up there. It probably also needs humanity in a buoyant optimistic mood and willing to take a bit of a gamble as well - something I think economically we're not going to get for a good few decades minimum anyway

 

[Bowler1]

Funding would be relative I guess. We don’t blink an eye at six lane motorways and fast train links under the channel to France these days. However, if I were a Roman I’d by very impressed by all we have today, as they barely managed roads and sewers. A space elevator is not for today (pity, I’d love a go on one) but for the future. And I agree with, VB, build it and they will come!

When it comes to big massive and silly investments, I’m 100% convinced that the funding can be found. History shows us time and again just how silly we are at losing our cash!