Space elevators a fantastic idea that maybe someday could be reality?

[Nibb31]

The vehicle does not need to be a cruise ship sized vehicle, that would certainly be impractical (though imagine watching THAT slowly climb!). My comment about the "cruise ship" was that years ago it wasn't that big of a thing that it would take 10+ days to cross the Atlantic. Pricey to do so in comfort and technically pricey at all. But people did it because it was the best way to do it.

The big difference is that masses of people wanted and needed to cross the Atlantic. There was huge demand and the crossing time was the price to pay. Therefore, it made sense to build a huge transportation infrastructure. Those ocean liners really stretched the technological and engineering limits of their time.

This was only possible because there was already things to do, places to visit, people to meet, friends, family, opportunities, etc... on both sides of the Atlantic. People were lining up to pay the price to start a new life, visit their family, or to meet business partners on the other end. In space, there is no new life, no family, no business trips.

You see, building such a huge infrastructure only makes sense in there is massive demand for transportation. Right now, and until there is some hypothetical breakthrough in space business, there simply isn't any demand for mass transportation.

If the best (cheapest, safest, etc) way to get into space is to take a 3 week journey to get up, then that is what you do.

And as I have already said, the space elevator is not really a mass transportation system. Its payload capacity is poor, with a very limiting bottleneck. It is certainly not cheap either. If you have an elevator run every two weeks, with a limited payload, a large ground infrastructure and huge upfront construction cost, I fail to see how it is magically cheaper than conventional launchers, which will be using the same advanced materials and power technologies that are required to build an elevator.

If there is huge demand, then the 2 week bottleneck will keep it expensive. If there is little demand, then it wont be worth the cost. In the end, individual launch vehicles will always be more flexible, scaleable, and will be required anyway as a backup for when the elevator is down. So why build the elevator in the first place?

For going up and down, you are forgetting something. Getting DOWN from space has always been the cheap and easy part. Getting UP is the expensive side.

Getting down from GEO to LEO requires the exact same amount of dV as from going up from LEO to GEO. That is around 4000m/s of dV.

Once it reaches GEO, an elevator climber will be carrying the same amount of energy as any other GEO satellite. It will have an orbital velocity of 3km/s and will have had to fight gravity just as much as a rocket to get there.

The point is, dollar for dollar, the space elevator will ALWAYS be more economical than shuttle vehicles as long as we don't have antigravity available to us. We just need to learn to accept that going to space may take longer that the 10 minutes it takes astronauts.

That's pure conjecture. We don't even have any idea of the material cost for building one because the material simply doesn't exist. No do we have a power source for the climbers or any idea of the payload capacity or the speed of the climbers. How can you have any idea "dollar for dollar" of what a space elevator would cost compared to a launch vehicle that would use the same superlight superstrong material or the same magical power source?

[hugix]

I like the idea. Maybe we should set up a kickstarter?

[Aethon]

Its that long? I thought that space elevator is fast... Halo tricked me again

An answer from Usenet :

In article <[email protected]> Dani Eder,

>[email protected] writes:

>>Now, how fast is your hoist?

>continuous chain of elevator cars running up and down. You can also be

>clever with the hoist design: I've seen suggestions for using linear

>induction motors to move donut-shaped cars up along the cable... [edit- up cars run 'through' the down cars]

>presuming you've got the power, you can go as fast as you like.

Unfortunately, you cant neglect the power supply for the hoist

(it still takes 31 MJ to raise a kg to GEO), and the power line

running up the space elevator represents a parasitic mass.

A better answer, which lowers the required material strength by 30%,

>>is to build a tower up from the ground and have it meet a cable

>>coming down from GEO.

[Aethon]

And as I have already said, the space elevator is not really a mass transportation system. Its payload capacity is poor, with a very limiting bottleneck. It is certainly not cheap either. If you have an elevator run every two weeks, with a limited payload, a large ground infrastructure and huge upfront construction cost, I fail to see how it is magically cheaper than conventional launchers, which will be using the same advanced materials and power technologies that are required to build an elevator.

If there is huge demand, then the 2 week bottleneck will keep it expensive. If there is little demand, then it wont be worth the cost. In the end, individual launch vehicles will always be more flexible, scaleable, and will be required anyway as a backup for when the elevator is down. So why build the elevator in the first place?

More from Dani Eder on this. Dated January 1997:

For a structure that makes economic sense, you have to

transport enough cargo to pay back your investment. For example,

if you need to earn 10% return to pay off your construction loan,

and you can lift one cargo an hour, you can make some estimates

on the maximum mass of the structure. At 10% return, you have

10 years to earn back your cost. There are 87,660 hours in that

time, so you can lift 87,660 cargoes. Assume that your structure

cost $100/kg, and you also charge $100/kg to deliver cargoes.

Then your structure may mass at most 87660 times the cargo weight.

If we divide the structure into a tower and cable, each may mass

43,830 times the cargo. Taking the natural logarithm, we get a

figure of 10.7 scale lengths for each. The Earth's gravity well

is equivalent to 1 gee x 6375 km. This, given the 40% factor

for compressive structures, means that 6375/1.4=10.7 scale lengths.

Therefore the required scale length is 425 km. Existing carbon

fiber has a theoretical scale length of 382 km. Allowing for a

maximum of 60% of theoretical strength as allowable stress, 25%

overhead structures, and the 4 out of 6 cable damage tolerant

design, we get a useable scale length of 122 km. Therefore we

need a factor of 3.5 increase over current materials (3.5 million

psi vs 1 million psi).

- Finally, a full space elevator is not required. You can build

a structure in Earth orbit that is vertical, but shorter than GEO.

The bottom end will move slower than orbital velocity, reaching

zero velocity as the length gets to the full GEO size. Any reduction

in the job a launch vehicle has to do is very useful, and a partial

elevator can be built with today's materials.

Dani Eder

Edited June 21, 2014 by Aethon

[Redjoker]

Although geostationary orbit is very useful for satellite's, current space stations are in much lower orbits. As long as your counter weight was large enough and in Geostationary orbit, could you build a terminal along the elevator that could be used for humans and cargo for space stations since a trip to 370Km would be much shorter meaning it would carry less risk to the crew and reduce the shielding needed.

[Nibb31]

If you step off of a space elevator at 370km, you fall down because you're going much slower than orbital speed.

Physics.

[Redjoker]

I didn't think about that only the counter weight would be at orbital velocity. You would still need a vehicle to get you to the space station which could also be used to accelerate to orbital velocity. This should be cheaper since the space craft will not need to be able to operate in an atmosphere, it will already have some velocity from the elevator's orbit, and will not experience losses due to athmospheric drag along with less losses due to gravity since it be able to burn directly prograde instead of performing a gravity turn.

[rtxoff]

If you step off of a space elevator at 370km, you fall down because you're going much slower than orbital speed.

Physics.

That's no problem if your name is Felix Baumgartner :-D

[Seret]

This means either very very long wires (36000km worth of the thinnest copper wire would be heavier than a nuclear reactor) or beamed power (laser or MW...).

Beamed power does seem to be the solution they're favouring, hence competitions like the Space Elevator Games.

Now, if you have the technology to beam power over such long distances to a climber vehicle, then that same technology could be used to power a launch vehicle and you wouldn't need to mess with megastructures and nanocarbon tethers in the first place.

Only if you had some kind of propulsion system that could turn that electric power into motive force. For a cable climber that's fairly trivial, we are quite happy making electric motors, whether linear or rotary. A cable climber also has certain advantages over a free-flying vehicle, such as being able to ascend at whatever rate it likes (not that dictated by the need to stay aloft) including the ability to stop safely if power from the beam was degraded or lost, so I don't think you could really say they're interchangeable. It's not hard to imagine a future where we had beamed power technology that could power a cable climber, but not an aircraft or rocket.

[Albert VDS]

Someone once asked Arthur C. Clarke when space elevators would become reality, he answered "Probably about 50 years after everybody quits laughing".

But I think it's something you need to test on de moon first, for the Moon you can use current technology and it's not a huge dissaster if somthing goes wrong.

[Klingon Admiral]

Wouldn't a space elevator require constant, non-stop station keeping as the atmospheric drag slows the cable and thus the entire structure down?

[Awaras]

Wouldn't a space elevator require constant, non-stop station keeping as the atmospheric drag slows the cable and thus the entire structure down?

The cable is stationary relative to the atmosphere. What drag?

[Klingon Admiral]

The cable is stationary relative to the atmosphere. What drag?

In contrast to Kerbin, Earths atmosphere isn't static in relation to the rotation of the planet. Differences in temperature and thus density of different parts of the atmosphere lead to a flow of particles from the high-density areas to the low-density areas, creating what we call wind. And there might be different winds at different heights, and winds that can get very, very fast.

[lajoswinkler]

That's no problem if your name is Felix Baumgartner :-D

If you start falling from 370 km, you'll hit the denser layers at almost 10,000 km/h. It's not enough to cause ionization and ablation, but your suit would heat up to unbearing levels and you'd probably die from overheating.

[Nibb31]

Beamed power does seem to be the solution they're favouring, hence competitions like the Space Elevator Games.

Only if you had some kind of propulsion system that could turn that electric power into motive force. For a cable climber that's fairly trivial, we are quite happy making electric motors, whether linear or rotary. A cable climber also has certain advantages over a free-flying vehicle, such as being able to ascend at whatever rate it likes (not that dictated by the need to stay aloft) including the ability to stop safely if power from the beam was degraded or lost, so I don't think you could really say they're interchangeable. It's not hard to imagine a future where we had beamed power technology that could power a cable climber, but not an aircraft or rocket.

Pinch rollers still aren't very scaleable or safe, especially as the ribbon surface under the rollers is going to be limited to a very small surface. I can't see a cable car being much heavier than 1 or 2 tons for this application really.

In contrast to Kerbin, Earths atmosphere isn't static in relation to the rotation of the planet. Differences in temperature and thus density of different parts of the atmosphere lead to a flow of particles from the high-density areas to the low-density areas, creating what we call wind. And there might be different winds at different heights, and winds that can get very, very fast.

It's supposed to be a very thin ribbon, so barely any drag from wind at all.

Of course, you need a way to prevent the climber from swaying all over the place in the wind, which would flex the ribbon and fragilise it.

[peadar1987]

http://en.wikipedia.org/wiki/Launch_loop anyone?

[Tinyboss]

Also, because elevators cannot cross each other on the same tether, you can only have one vehicle at a time either going up or down, therefore taking 2 weeks (or a month) for the elevator to do a round trip limits the total payload capacity of the system.

Surely we can come up with a way for the tractors to exchange cargoes while remaining coupled to the tether?

My first, barely-considered idea: suppose one tractor has its two symmetrically-placed cargo containers oriented north-south, while the tractor above it has its cargo oriented east-west. When they meet, they can latch onto each other's containers, then release the ones they had originally. You could have as many tractors (thus cargoes) on the tether simultaneously as it can support, alternating orientations: north-south on the way up, east-west on the way down. Each tractor would just go up and down its own little section of the tether.

It would be necessary to switch orientations at each end of the tether, but since that means on Earth or in orbit, it's an easy operation. Come to think of it, you'd need some means of orienting the tractors anyway, so that you wouldn't end up with torsion in the tether as two tractors meet. You could rotate the tractor against the mass of the cargo to eliminate any amount of torsion, but you still might then have to rotate the cargoes by up to 90 degrees for the exchange. A reaction wheel would do the trick, but we want to minimize non-cargo mass, so maybe some small thrusters? Or even better, you could design them with a physical shape that nudged them into alignment as they met.

Have I missed any embarrassing flaws with this scheme?

Edited June 22, 2014 by Tinyboss

[peadar1987]

It doesn't even have to be that complicated, just drop the downward bound cargoes off the ribbon after they get a sufficient distance below geostationary orbit. They will return to earth at a predictable and fairly repeatable point downrange of the decoupling point, and can be easily collected.

[Tinyboss]

It doesn't even have to be that complicated, just drop the downward bound cargoes off the ribbon after they get a sufficient distance below geostationary orbit. They will return to earth at a predictable and fairly repeatable point downrange of the decoupling point, and can be easily collected.

Then they have to be built for reentry. On the other hand, they're not on the tether on the way down, so if that makes them less than twice* as heavy it would be a net gain. I guess they also could be designed to burn up. They really only have to be strong enough to keep the cargo contained and dry, and able to be (de)coupled to the tractors, so that might be the way to go.

*Approximately, depending on how far down they need to go to deorbit.

Edited June 22, 2014 by Tinyboss

[Aethon]

Earthbound cargo could use regenerative braking to help power the elevator, taking advantage of the cargo's potential gravitational energy.

[Xeldrak]

Actually I think one of the coolest and often overlooked aspects of the space elevator is that it can be used to launch deep space probes without rockets.

[Aghanim]

http://en.wikipedia.org/wiki/Launch_loop anyone?

If the inner moving loop touches the outer pipe, say goodbye to your launch loop

[Awaras]

http://en.wikipedia.org/wiki/Launch_loop anyone?

"The design concept was published by Keith Lofstrom and describes an active structure maglev cable transport system that would be around 2,000 km (1,240 mi) long and maintained at an altitude of up to 80 km (50 mi). A launch loop would be held up at this altitude by momentum of a belt that circulates around the structure. [clarification needed]"

So, essentially, it's being held up at the altitude of 80 km by a principle similar to a "Space fountain"?

Couldn't something similar be used to raise the 'bottom' of a space elevator's relatively thin ribbon vulnerable to high speed winds and such above the thickest part of the atmosphere?

[Nibb31]

Not the launch loop again. It is even less realistic than the space elevator. There are so many technical issues that it isn't even pie in the sky.

Couldn't something similar be used to raise the 'bottom' of a space elevator's relatively thin ribbon vulnerable to high speed winds and such above the thickest part of the atmosphere?

The biggest issue of the launch loop is that it's impossible to raise it. It would only be stable in a fully powered state with the cable running at 14000km/s inside the sheath. However, it's impossible to go from 0 to 14000km/s instantaneously. The acceleration would have to be progressive and you would have to mechanically raise the 2000km long structure to 80km without the cable ever touching the sheath and without ever compromising the vacuum inside the sheath.

Edited June 23, 2014 by Nibb31

[magnemoe]

If the inner moving loop touches the outer pipe, say goodbye to your launch loop

yes, the obvious downside of any such systems, be careful about systems who need active control and power or they fail catastrophic and it has to be active 24/7 for years.