Where will we build the first Space Elevator?

[SargeRho]

2 hours ago, K^2 said:

None of these, because it's a dumb concept for every single one of these objects? I'm not sure why that's not an option, given that it's an obvious one. Except for Earth, all of the other bodies don't have enough atmosphere/gravity to interfere with direct magrail to orbit launches. Mars will require some rocket propulsion, but it will still be way cheaper than building a space elevator.

And for Earth, there are way better options. like launch loop. If we don't want to build a full size launch loop, we can get away with using a smaller one for suborbital launches, and assist with a space teather.Again, way cheaper and more efficient than space elevator could ever be.

What about orbit to surface transport? If LiftPort's estimate of 100 tons for a lunar space elevator is correct, then might it not make sense to set one up, before a colony, so that you can transport more material per launch to the Moon, and less fuel needed for the descent to the surface, since it would likely take a while before a lunar colony would be in a position where it could export materials?

[kunok]

1 hour ago, SargeRho said:

What about orbit to surface transport? If LiftPort's estimate of 100 tons for a lunar space elevator is correct, then might it not make sense to set one up, before a colony, so that you can transport more material per launch to the Moon, and less fuel needed for the descent to the surface, since it would likely take a while before a lunar colony would be in a position where it could export materials?

Yeah, controlled non-rocket landing could be a good point for a space elevator. It's one of the advantages of a space elevator, it can be used in both ways, most of the other non-rocket launch systems can't be used for landing, or at least easily.

2 hours ago, K^2 said:

Titan came to mind, but its orbit makes it tricky. It's tidally locked to Saturn, with orbital period of 15 days. Which means the counterweight would have to be suspended above L₂. Unfortunately, it's quite a bit out given the orbital period and mass of Titan, and Hyperion's orbit is going to pass close by. While odds of actual collision between elevator and Hyperion are negligible, it can pass close enough to the tether to provide considerable lateral forces, which would be all kinds of bad.

I totally forgotten about the other moons influence. What about the L1 point? Rea it's not that close but it's bigger, n-body physics can be a lot trickier than 3 body so I'm not sure. When 1.1 it's out, hoping it will improve performance,  I plan to try principia and try lot's of weird concepts of n-body physics.

 

Maybe instead of disputing which known object is a good candidate for a space elevator we should try to define which parameters an object (planet, dwarf planet or moon) should have to be a good candidate.

-Gravity. Huge gravities makes the tether absurdly long (and more massive) and requires stronger materials. In very little gravity ones, it wont have much sense but they would be cheap.

-Density of an atmosphere. If there it's not atmosphere at all or it's a little one, doesn't make sense for launching things to space. Maybe it has sense for controlled landing?

-Rotation period. Stationary orbits are defined by the rotation of the object itself, the lower rotation period better, because it will make the stationary orbit closer to the surface. In moons maybe it's not a decisive parameter because the Lagrange points.

-Materials available. Lighter, cheaper and stronger materials could make the other requisites less strict. I think we should only consider currently used materials

Are this assumptions correct? If they are, we can star thinking about values, I hope we can at least estimate at least the order of magnitude.

Edited February 15, 2016 by kunok
gramar

[tater]

You don't build something, then look for a use. You have a need, then design something to fill that need. Short of a lunar infrastructure that needs an elevator, there is no reason to build one on the moon. The same can be said for every other choice except Earth right now. Having done that, it's an engineering issue, and assuming it is even possible, then a cost-benefit analysis is required.

For Earth there are substantial engineering issues, and even if solved, they are costly. Does the need exceed the cost such that an elevator, even assuming it is possible, is the best solution?

[HopDavid]

On February 13, 2016 at 10:54 AM, Tex_NL said:

Building an elevator on a low gravity body is a waste as it is already easy to get to orbit.

Getting off a body's surface isn't the only elevator use. If the elevator is long enough and angular velocity (ω) is high, the tether can sling payloads at high velocity. Speed is ωr, where ω is angular velocity in radians over time and r is distance from center of rotation.

Thus a Ceres elevator could not only get stuff off Ceres' surface, it could provide some of the delta V needed for a heliocentric transfer orbit to another destination in the solar system.

Another benefit of a Ceres elevator: it could dock with ion driven spacecraft. Ion engines have fantastic ISP but very poor thrust. Even with Ceres' very low gravity, thrust to weight ratio would be less than 1. So an ion engine couldn't take off from Ceres, nor could it soft land.

A Phobos tether of relatively modest length could sling stuff earthward, Ceresward as well as lower stuff almost to Mars' surface. See Phobos, Panama Canal of The Inner Solar System.

 

 

[Rakaydos]

On 2/14/2016 at 10:35 PM, SargeRho said:

What about orbit to surface transport? If LiftPort's estimate of 100 tons for a lunar space elevator is correct, then might it not make sense to set one up, before a colony, so that you can transport more material per launch to the Moon, and less fuel needed for the descent to the surface, since it would likely take a while before a lunar colony would be in a position where it could export materials?

I think it's actually a bit more than 100 tonnes, but it was less than 150 tonnes. But that's for a single cable, you need at least 2 for regular maintinance.

[YNM]

Some space stations ? I believe when we figure out how to have artificial gravity, flight of stairs would be a problem, so there goes elevator in space...

[lugge]

On 15.2.2016 at 4:16 PM, tater said:

You don't build something, then look for a use. You have a need, then design something to fill that need.

What about SLS?

SCNR ;-)

[YNM]

1 hour ago, lugge said:

What about SLS?

SCNR ;-)

That's driven by the need to keep people working at most...

[RainDreamer]

So ignoring why we need to build such a thing...maybe at the poles? I imagine it would have to deal less with the earth's rotation there.

[Hary R]

8 minutes ago, RainDreamer said:

So ignoring why we need to build such a thing...maybe at the poles? I imagine it would have to deal less with the earth's rotation there.

do you imply that the station should be in a polar orbit?

[eberkain]

I used to love the concept of a space elevator, the more I have learned about physics, I think SSTOs are where our future is going to be.   Basically the equivalent of today's 767 that can go to space and carry either cargo or passengers, then return home, gas up, swap pilots, and make another trip.  Just imagine how much we could do in space if all we had to pay for was the fuel to get you there and routine maintenance on the ship. 

[SuperFastJellyfish]

2 hours ago, RainDreamer said:

So ignoring why we need to build such a thing...maybe at the poles? I imagine it would have to deal less with the earth's rotation there.

If you're talking about a space elevator then no.  Space elevators need the rotation of the body to provide the centripetal force to keep it from crumpling back to the source of gravity.  It's like swinging a ball tied to a string around with your hand.  The string stays taught because of the rotation.  If you try to have the ball just stay up vertically above your head without any swinging force then it will just fall down and bonk you on the head.

[HopDavid]

Sorry for the thread necromancy but I've added elevator stuff to my blogs. I came across a spread sheet that gives an estimate of tether mass needed for a given payload mass. Here's an explanation of the spreadsheet as well as links to various tether scenarios. I assume Zylon tethers throughout.

I am not that enthusiastic about a lunar elevator. I am more excited about a Phobos elevator, both extending towards Mars as well as extending away from Mars.

[kunok]

17 hours ago, HopDavid said:

Sorry for the thread necromancy but I've added elevator stuff to my blogs. I came across a spread sheet that gives an estimate of tether mass needed for a given payload mass. Here's an explanation of the spreadsheet as well as links to various tether scenarios. I assume Zylon tethers throughout.

I am not that enthusiastic about a lunar elevator. I am more excited about a Phobos elevator, both extending towards Mars as well as extending away from Mars.

You are a everyday hero, you are crazy that spreadsheet, you really did a iterative calculation in excel!!! Very impressive.

Your blog is interesting, and the fobos post is very aclaratory. But the thing is atmosphereless bodies launching is easier with a maglev or other launch system. Landing or transporting delicate cargo may be the places for a Space elevator.

Edited May 8, 2016 by kunok
I will totally fail my english level test...

[HopDavid]

1 hour ago, kunok said:

Your a everyday hero, you are crazy that spreadsheet, you really did a iterative calculation in excel!!! Very impressive.

Your blog is interesting, and the fobos post is very aclaratory. But the thing is atmosphereless bodies launching is easier with a maglev or other launch system. Landing or transporting delicate cargo may be the places for a Space elevator.

One of the biggest launch constraints is volume and mass. Especially true in the early stages when everything comes from the bottom of earth's gravity well. So an important metric is ratio of launch infra structure mass to payload mass. You can see that's what I'm looking at with the tether spreadsheets.

A mag lev needs a lot of juice, it goes up with the square of the velocity needed. To send stuff into orbit requires massive rails as well as a stud hoss power source. Mag lev launches on airless worlds are another technology that would be much more doable with a better alpha.

And as you mention, rail guns are little help for a soft landing. One of the things that excite me most about a Ceres elevator is it would enable coming and going from Ceres with ion engines. As you probably know, ion has fantastic ISP but weak thrust. Ceres has a shallow gravity well but still deep enough that thrust to weight ratio prevents soft landing on Ceres with ion engines.

The solar acceleration at 3 A.U. is around .7 mm/sec (if I did my arithmetic right). So an ion craft with 1 mm/sec^2 acceleration could do impulsive burns for injection to elliptical transfers between Main Belt asteroids (unlike deep in earth's gravity well where an ion path would be long, slow spiral). A ion craft could dock with a Ceres or Vesta elevator. A Ceres or Vesta elevator might also lend a hand sending an ion ship on it's way with a .5 to 1 km/s toss. Not much of a propellent saver with ion's great ISP, but it would save some time.

Ion craft and elevators would make travel about the Main Belt much less difficult.

[wumpus]

Do you realize that a lunar elevator has to lift a body to an orbit such that it has a one (lunar) month orbit?  And that the energy required to use a maglev or other rail-driven system requires exactly the same energy (well the same if it puts it into lunar-stationary orbit, it could always use less and go to low lunar orbit).  I have no idea what rate Ceres orbits at, but it should be a consideration.  From what I've heard, Venus is a no-go (you aren't going to construct anything down to the surface anyway).

If you think SSTOs are a solution, might I introduce you to the rocket equation?  Don't try to build a SSTO with current ISPs.

[HopDavid]

3 hours ago, wumpus said:

Do you realize that a lunar elevator has to lift a body to an orbit such that it has a one (lunar) month orbit? And that the energy required to use a maglev or other rail-driven system requires exactly the same energy (well the same if it puts it into lunar-stationary orbit, it could always use less and go to low lunar orbit).  I have no idea what rate Ceres orbits at, but it should be a consideration.  From what I've heard, Venus is a no-go (you aren't going to construct anything down to the surface anyway).

If you think SSTOs are a solution, might I introduce you to the rocket equation?  Don't try to build a SSTO with current ISPs.

Did you read my post on a lunar elevators through L1? I don't like the idea.

Much of what you say is incorrect. When climbing an elevator, horizontal velocity is imparted to the climber from the elevator. So no, energy requirements are not exactly the same as a surface maglev.

If you don't know anything about Ceres, why do you mention it?

Venus? I posted to the wrong thread recently. Did you do the same?

And who's talking about SSTOs? Although they are possible from the Lunar surface. I know the rocket equation but I'm not sure you do.

[lobe]

The answer to this question would also apply to building spaceports that the rest of you are going to need for your 767-like SSTO. 

It would probably be built in either Brazil or Ecuador. Looking at where the equator runs these seem to be the stablest regions with the best relations to the people who would fund the elevator. The others are Colombia, Gabon, Congo, Uganda, Rwanda, and Indonesia. Considering altitude will also be a factor in the construction I think this really limits the choices down to Ecuador, because the Andes runs through it.

[kerbiloid]

Lunar orbital speed is just 1.6 km/s.  It's just a gun shot speed, rather than the terrestrial 7.8 km/s, and there's no air drag.

So, no need in a Lunar spacelift, just a V-1-style railway ramp is required. And a tiny engine for the apoapsis burn.

 

Orbital speeds of puny ice moons and cereses are ~100-300 m/s. It's a problem not to launch from their surface, but not to launch too fast,
So, instead of a spacelift - a sportcar is in order.

 

 

Edited May 9, 2016 by kerbiloid

[James Kerman]

I believe the first space elevator will be built on Earth by Obayashi, although not by 2050 as they claim.  They have actively been doing tests.

[HopDavid]

10 hours ago, kerbiloid said:

Lunar orbital speed is just 1.6 km/s.  It's just a gun shot speed, rather than the terrestrial 7.8 km/s, and there's no air drag.

So, no need in a Lunar spacelift, just a V-1-style railway ramp is required. And a tiny engine for the apoapsis burn.

1.6 km/s is kinetic energy of 1.28e10 joules per kilogram.

Let's say you wanted to launch a 10 tonne payload each week. That would be 604800 seconds to charge up the maglev's capacitors. Looks like you'd need a 21 kilowatt power source. If your PV panels crank out 250 watts per kilogram, the panels need only mass 85 kg if you're on a plateau of eternal light, 170 kg for lower latitudes. That's more doable than I expected!

However the track is a problem. For easy arithmetic I'm approximating a g as 10 m/s^2. 5 g's would take 32 seconds to reach 1.6 km/s and the track would need to be about 26 kilometers long. Clearing a straight 26 kilometer runway on the moon is not an easy exercise. And what is the mass of the 26 km long rails?

And as already mentioned, these rails are no help for a soft landing. A lunar soft landing takes about 3 km/s if coming from LEO. For Ceres a soft landing is not doable with ion craft.

10 hours ago, kerbiloid said:

Orbital speeds of puny ice moons and cereses are ~100-300 m/s. It's a problem not to launch from their surface, but not to launch too fast,
So, instead of a spacelift - a sportcar is in order.

Yup -- a sportscar can leave a small body. (Yawn). It's tedious repeating myself. The object of such an elevator is not getting off the surface. It's flinging or dropping payloads.

Phobos, for example. It is extremely easy to leave Phobos, no sports car needed. A Ford Focus or maybe even a bicycle could do it.

But it's not so easy to drop payloads into Mars atmosphere at .6 km/s. Or fling payloads From Mars orbit to earth transfer orbits or even Ceres transfer orbits. A 14,000 km Phobos elevator could do all these things.

Edited May 9, 2016 by HopDavid

[kerbiloid]

45 minutes ago, HopDavid said:

and the track would need to be about 26 kilometers long. Clearing a straight 26 kilometer runway on the moon is not an easy exercise. And what is the mass of the 26 km long rails?

Still much more easy than build a 26 km high tower. And a spacelift requires more than 26 km height.

48 minutes ago, HopDavid said:

And as already mentioned, these rails are no help for a soft landing. A lunar soft landing takes about 3 km/s if coming from LEO.

The building of a lunar spacetower presumes that a construction industry is already built on the Moon surface, just because 1.6 << 7.8, and its easier to build a metallurgical plant in place than to deliver every truss from the Earth.

So, when the spacelift will appear in agenda, the "heavy" traffic will be mostly upwards (from Moon to space) or sideways (along the Moon surface).
And will require more launches than landings.

Passengers and auxilliary movement of course will be bidirectional, but the "up" is covered by the launch ramp,
"Down" - yes, ramp is useless.


 

[HopDavid]

1 hour ago, kerbiloid said:

Still much more easy than build a 26 km high tower. And a spacelift requires more than 26 km height.

Towers and elevators are different animals. A tower needs compressive strength, an elevator tensile strength.

A hair thin Zylon tether can support a lot of newtons. Again, here's a description of the model I'm using to determine tether mass.

Which is less massive? Tens or hundreds km of railroad tracks or thousands km of fish line? Much of a zylon tether might be even thinner than fish line.

1 hour ago, kerbiloid said:

The building of a lunar spacetower presumes that a construction industry is already built on the Moon surface, just because 1.6 << 7.8, and its easier to build a metallurgical plant in place than to deliver every truss from the Earth.

Nope. A lunar elevator or orbital tether doesn't presume a lunar construction industry. Zylon tethers don't come from metallurgical plants either lunar or on earth. Trusses aren't relevant.

Edited May 9, 2016 by HopDavid