The forces aren't *that* high.

Don't forget that cable has a very high strength/weight ratio, so the load needed to carry some payload in a section is mainly just the weight of the payload. It's actually harder to do with the single looped cable- you're carrying the entire weight of the cable on one big pulley at the top.
 

Here's one way- you can deploy the beanstalk in the normal way, and then start a crawler from the bottom carrying the loop- which you pull though from the bottom. If you gear the crawler properly, pulling *down* on a cable leading from the crawler causes the crawler to go *up* the elevator. You keep paying out more cable from the ground and you will get the bottom loop. Once you have that first loop installed you can use the bottom loop to move materials up for the next loop, and so on.

There are some problems I'm not sure I've solved yet though- the angle that the cable leaves the pulley is very shallow, only about 1 degree. This gives the pulley poor torsional stability, and there's a reasonably high chance that the pulley will twist up the loops against the beanstalk and jam the whole lot up. It might require active stabilisation of the pulley system, attitude jets or reaction wheels or something. A bit messy, but soluble. Alternatively adding a long boom carrying the loop away from the beanstalk helps quite a bit, it adds moment of inertia at the pulley and gives a lever arm to help the small angle point the pulley in the right direction. However the arm would be under fairly heavy compression from the cable forces, so it might be quite weighty.

Also, the weight of the pulley system adds mass to the main beanstalk, I haven't calculated that- but the cost of the extra mass is offset against the cost of not having any lasers or photovoltaics, so it's still probably a win.

And the electricity cost of the laser system represents a minimum cost per kg- a relatively high cost which isn't present with the pulley system.

Split it vertically, and attach an axle horizontally, and spin a pulley literally through it.

Keeping the tether from touching can be achieved in one or all of several ways.

a) coriolis keeps the loops plumped out anyway (they separate at order 1 degree depending on what speed the loop goes at- note that laser climbers are power limited- it's unclear what the optimum speed is for mechanically powered climbers)) provided you keep them spinning. When/if they aren't spinning they would tend to tangle though.

b) if you build elevators 'side by side' you can add rollers that keep the cables *miles* apart, except at the pulley even when stationary.

You have a main cable up the middle, and then have very thin guide beanstalks either side, tens or even hundreds of miles apart at the base, with rollers hanging down at a very shallow angle from the thin guide beanstalks

There's little or no load on the rollers, so secondary cables can be minimal- it takes hardly any force to keep them apart due to the small angle. If you design them carefully they can probably help damp any vibrations on the tether out.

Other perturbations like gravity should hopefully be the same for both sides.

There are probably big issues if a cable breaks due to oscillations on the loops that the breakage would cause,  but that's true of elevators in general, probably a hoytether style of construction stops breakages, so design it not to break.

Fixed beyond GEO exactly the same as normal. Below GEO, tapered fixed cable. Going through the cable thin/fixed width cable loops on pulleys able to take about the combined weight of the payload below that point, mechanically linked- you turn the top- they all turn.

You attach a payload to the bottom- clamp it on- and it climbs to the top (de and reclamping at each join between separate loops). No lasers.

Got it?

Actually, I think they've changed the climbers in the last year or two. I think the original NIAC paper had a pulley. Ignore that bit. :-)

Ok, that reduces the justification for it a little, the introduction was incorrect, but I still think the multiple belt system is a big improvement over the laser-powered concept.

The last para is a bit subtle- the payloads, but *not* (most of) the weight of the thinner cables hangs off of the GEO motor (the thinner cables weight is symmetrical and hence is carried onto the main elevator cable by the pulleys). If you make the motor at ground level then the weight of the payloads goes all the way up to GEO and then back down to ground again; so the ground-level thinner cable has to be thickened. If you pull it up towards you from GEO, then the load path stops at GEO. Clear?

Ok, consider a standard tapered elevator, with say, 3 climbers on it.

Now, notice that the cable gets thicker as you climb so the climbers need pulleys that can deal with progressively thicker cables, this is really awkward. Also, consider that at each climber the cable goes around a pulley or two and then goes on up the elevator. So, effectively, the cable has 3 sets of pulleys on the beanstalk at any one time.

I propose we change this architecture. Let's keep three or so pulleys, but fix them at certain heights and move the cable in loops instead.

i.e. cable from ground up to the first pulley and back down to the ground, and then a second thicker cable loop from the first pulley up to the second and back down to the ground, third thicker loop up etc. etc.

By stepping the cable like that, the cable regains most of the strength of a fully tapered cable, but allows you to move the loops individually (although you would mechanically couple them together so that the torque from one acts on the next).

But, because the pulleys don't move they can be designed for only one thickness of cable, so they actually become *lighter*- the overall mass of the elevator as a whole goes *down* when you do this (and the loops are no thicker than the original solid cable, each half is about half the thickness, ok a little more to deal with the stepping losses).

In addition, the non payload mass of the actual climbers goes down- you don't need the solar panels on the actual payload, only a clamp to grab the cable, since the cable can be powered from the ground or GEO.

And the efficiency of the power transmission goes way, way up- you only have bearing friction and aerodynamic drag in the atmospheric portion which is probably one or a few tens of percent at most, rather than facing laser transmission losses at 98%.

Ok, so that's one idea. Now this is good, much better than a single loop, but I thought of something even better:

Instead of moving the whole cable- it's better to have a proper, stationary, exponentially tapered cable, and hang pulleys off of that (actually, I think you would split the stationary cable lengthwise and spin the pulleys in the middle). That way you can have smaller, lighter pulleys that only take the weight of the *payloads*, rather than carrying the weight of the whole *cable*. So the stress on the pulleys is much lower, and so the pulleys can be made much lighter (actually in passing I note that that trick can be used on a normal fixed elevator too... it is wrong to pass the load from the elevator cable through the pulley- it's much better to have a 'separate' *fixed width* cable that just carries the weight of the car that is hung off the main cable every so often.)

Also, a note on powering it all- you would want to have several payloads lifting simultaneously if at all possible. Therefore, you would want to power it from GEO- the top cable is cheaper to make thicker, so can handle the force much better, otherwise you are lifting all of the climbing mass from the spindly end at the earth end, rather than the thick end at GEO.

Comments?

You must be an American, you need to get out more :-)

The rest of the world just looks at the Shuttle as *A* launcher, a spectacularly expensive, and not especially reliable one. The fact that the Shuttle has flaws does not mean that *rocketry* has flaws, unless you can show that rocketry directly leads to those flaws.

Lots of people have.


Reference?

So, it's a truism, and I'm wrong? :-) LOL


Funny how there doesn't seem to be a market for that either. Incidentally, I wouldn't believe everything that NASA said about the Shuttle back the 70s- they flat out lied so they could get the project funded- they never even *attempted* to install the launch pad facilities to launch 50+ times a year.

What makes you think that there is a market for the Space Elevator either?


Soyuz? Nobody has died in more than 20 years; and the current version has had *no* deaths. Even taking the Soyuz over all the versions, it's currently twice as safe as the Shuttle, and looking better with each launch.


I'm shocked, shocked- SHOCKED that people die in a transportation system.


Governments are *really* bad at marketing technologies; and thirty years ago only governments were able to handle launch technologies. Spaceship One has proven unequivocally that private companies can deal with accessing space; and much of the technology is now public anyway. There have been legal, technological, market advances.

Noteably, the cold war is dead. That alone liberates rocketry to be more than an ICBM related tech.

The shuttle design was screwed up, The main blocks on full reusability are:

a) the tiles (the flimsy ceramic tiles necessitated by return from polar orbit were a big mistake)
b) the main engines are less reusable than the Saturn V F1 engines (if you work out the time between overhauls there's little to choose- other rocket engines have been started 10,000x with no sign of wear- this is not a general feature of rocket engines)
c) the SRBs aren't really reusable; at best they are retreads.

Other than that, the Shuttle design more or less works, it's just they messed up the details.


Never mind the cost, look at the performance? Say what?

Of course it doesn't- the plan is to leave it up there! (Edward's design is a one-way tether!)


Agreed. The chances of 10-100x improvement of performance is low.  Who cares about performance? The chances of improvement of *cost* is extremely high.


Show me a launch system that has launched as many times as a 1950 aircraft during it's *test* program, and I'll eat my shorts.

Why is that? It's lack of market. There just aren't that many things that people want to put up there right now. And the space elevator costs as much to build as a new launch system, has 10x as many potential fatal flaws and the cost of the electricity is *higher* than the cost of the fuel!!
 
That's the point of Spaceship One- they are opening a new market. The market research show potentially hundreds of millions of dollars each year on suborbital, and tens of billions in orbital. And the number of launches would be tens of thousands. *That* is a market, one that will push reliability way up and cost way down.

Incidentally, it's a market that a space elevator can address too- imagine going up in an elevator to 200km.


*Big* mistake. If you don't understand why they have failed, then you probably won't succeed in solving the problem. The problem is *not* the technology. It's the market. And the market is essentially identical between the Space Elevator and the rocket.

Approximately correct. Larger vehicles can use rocket on the way up, but may need jet engines for the first stage to return to the launch site.

But that's not really the point of Spaceship One- it's to get investment and derisk the orbital market rather than being a direct technological precursor for orbital tourism.

No, let's not. What a stupid idea.

The Russians don't seem to think so, they just launched a new model last month, Soyuz M-2, which only needs about 1/3 of the people for launching it. Ultimately the cost of launching is wages. Many ICBMs are only barely suborbital, orbital with reduced payload and IRC some only require about 6 people to launch.


That's the list price; for launching maybe 4 a year. Apparently the cost price of a physical Proton rocket is well under $5 million.

That means the bulk price can be *considerably* lower. And, you've deliberately used the unrealistic GEO destination to make it look even more expensive.

GEO isn't a fun place to be- it's more expensive and the radiation is too high. Besides, we're talking about tourism aren't we? It's not like a beanstalk is good for GEO tourism anyway.

Really? So how come the Space Elevator is supposed to be cheaper in the long run if it is more expensive in the long run?

I do? Thanks for telling me! Actually, no I don't.

Nope. The whole point about Spaceship one is that it is a prototype tourist ship. The X-15 was *not* that.

It doesn't matter. If it launches more often then the cost amortises down. Study after study after study has shown that technology might give you a factor of 2 here or there, but launching more reduces costs *more* than any technology. It's not the technology stupid!

If you think about it, Space Elevators are a technology (if you can call something currently impossible to build, a technology), and in the absence of plenty of payloads to go up it, it's a waste of time, it's too expensive.


Nope, the Russians don't use bleeding edge technology and their vehicles are the cheepest around (by dollar cost, or by person hours).

How can something remain bleeding edge for decades? :-)

Actually, the Channel Tunnel is an example of what could happen. Before the tunnel was built it was assumed it would wipe out the ferries. Except it hasn't. The ferries are slower, but cheaper and you can eat and drink on the way across, they are often more comfortable and you can buy duty free stuff.

It's unclear to me that a space elevator that takes about 2 weeks is going to compete with a rocket launch system which can take 10 minutes; but you never know- it might be treated like a cruise or something.

True, but it's unclear it will achieve it. Noteably, the cost of the electricity for raising something up a beanstalk is the same or higher than the cost of the rocketry fuel; given the current technology.

Rocketry costs really do plummet as the launch rate go up. As does the reliability go up.

It looks like it. And if so, the space elevator isn't ready to go; but rocketry is. If the elevator isn't possible in the next ten years, it may never be built. And note, we don't know that a beanstalk is ever going to be possible. I can probably give you a dozen things that may preclude it; but I don't know anything that will definitely preclude it.

The biggest problem I can see for manned use are the Van Allen belts.

Well, we see greenshoots, we await to see whether they can grow. There are also some mighty impressive rocketry designs out there; noteably Skylon- single stage to orbit with hardly much more than 1g acceleration and with no scramjets. Probably as cheap or cheaper than a space elevator too. Might complement a space elevator nicely though (Skylon can only go to LEO- you could conceivably drop fuel and stuff down to LEO from GEO using an elevator, people could board a transfer vehicle and go places from there).

Skylon seems to be buildable today; elevators aren't.

Yeah. Trouble is that large jet vehicles are expensive and unwieldy. There are issues with how big a rocket you can fit into the cargo bay, and safety issues with the rocket fuel onboard. The amount of fuel saved by launching from a few kilometers higher isn't that much, particularly for large vehicles, even allowing for aerodynamic and gravity losses.

The nearest example to doing this is the Pegasus launch vehicle, it's actually about the most expensive launcher by a very long way.

Actually, the fuel is mostly irrelevant, it's the cheap bit- about 1% of the cost of the launch.

Incidentally, the electricity for a SE is expensive- the beamed power technology is very inefficient (they're hoping to *get* *up* to 2%!), and there's no win there over rocket fuel.


Quite a lot of estimates currently show that there aren't- it's just that the costs to modify them to make them reusable exceed the payback over the life of the launch vehicle type. People just don't launch enough stuff up there to make it worthwhile right now.


Mmm. Van Allen Belt radiation.

Actually, surprisingly the independent estimates I have seen show that the SE is hardly any, if at all cheaper except at the very highest launch rates. The problem is that any system has to pay for the startup costs one way or another, and the interest on that massively raises the costs. Incidentally, rockets are pretty similar- similar or lower R&D costs, surprisingly cheap hardware- and if you are positing a high launch rate, the amortisation works just the same for rockets and SE. It's neck and neck, except that rockets are launching, and SE are still a gleam in the designers eye.

My gut feel is that space tourism is going to raise the launch rate for rocketry long before we ever see a SE.

Slight problem. Any trajectory that only thrusts within the atmosphere reenters the atmosphere "a what goes up must come down" kind of deal- the orbit that leaves the atmosphere reenters the atmosphere. What you have to do is leave the atmosphere and do a 'circularisation burn' using a rocket.

In practice, all current airbreathers (including scramjets) are *way* away from reaching useful orbit anyway; they all need big rocket stages to make LEO. Scramjets are currently only doing about mach 10; orbit is mach 25.