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It could be done, if we could drain the radiation belts first. They're not radioactive (in the fission sense), they're just full of high-energy particles that are trapped by the magnetic field. But we haven't even tried it on Earth yet, and Jupiter and its field are a lot larger.

I actually disagree.

What a surprise.

You can use existing fiber.

I didn't say you couldn't. So actually, you agree.

Supposed that the heavy lift capability to the Lagrange point is 100 tons.

We don't have that. Not even the beast envisioned heavy lift vehicle could do that. We wont have that until propellant depots have been deployed.

If you dedicated one flight just to lifting your cable, you could build an elevator capable of ferrying a ~50 kg payload with two flights (one for the cable, one for equipment for the cable).

Do you actually have a study to back this up or are you just pulling these numbers from your ass? This paper is the most practical lunar rotavator concept that has ever been studied. It sounds nothing like your fantasy.

Now, it is reasonable to expect the next decade or so we will produce better fibers, but assume we don't.

Lets.

With one flight, we could build this micro-elevator, send down a small rover or two, and bring up some soil samples. That would I think be worth it, all by itself.

Why? Develop the biggest launch vehicle ever to do a sample return mission? That makes Apollo look good.

If carbon nanofibers earn their promise, we might be able to send up and down a 500 km payload, again with one flight dedicated to carrying cable. That's potentially big enough to carry a person

Facepalm. Read the paper I linked above ok?

but, no matter what the payload, we would start gaining information about how to use space elevators. If they prove their worth on the Moon, that will really spur getting the R&D required for a terrestrial one, and I think we would find the resources to make the Lunar cable human capable.

A plan for risk retirement of space tethers is indeed a sensible thing for NASA to be pursuing.. but the way to do that is to fly some unmanned tether missions in LEO. After they have successfully demonstrated some basic tether concepts we can talk about scaling up to some catch-and-throw experiments. Then we can figure out how to deliver 20t to LLO and do some effective-zero-velocity ops at low lunar elevations. At that point you could actually have something practical that can take cargo both ways from LLO to the lunar surface, and you could even use that mass to increase the counterweight and bootstrap the system. From there you can start speculating on what a bigger system would entail.. would a static tether that vehicles mechanically drive along be sensible? Or would a conveyor belt type system work better? Or are static tethers just too damn inefficient?

A million paper studies can not retire the risk of space tether system.. you need to fly hardware, and so long as people are advocating grandiose "elevator" concepts, NASA won't touch it.
 

Instead of atmospheric drag a conductive tether moving through the Earth's magnetic current generates a current and radiates the heat from tether resistance. The dissipated energy will eventually bring the satellite down. The technique has been developed by Tethers Unlimited and the late Dr. Robert Forward

http://www.tethers.com/TT.html

http://www.tethers.com/TT.html

I saw Robert L Forward talk about this at a con years ago.

I'm trying to picture the "vertically oscillating cables." How about a rotating-tether skyhook?

Most claims made about space elevators can be seen at the Wikipedia article, which includes detailed info about building one from steel and why it is impractical (but not impossible). I'll conceed that it's barely possible that the entire article is a plant by LiftPort, however there are a lot of links to other companies that are doing independent research. Of particular interest is Gizmonic Inc., who seem to have adopted space elevators as a corporate hobby, doing lots of spare time R&D and provided lots of calculators so you can check the math yourself. Hans Morovec wrote a research paper in 1978 investigating the feasibility of using Kelvar. Not related to your question but also interesting, Tethers Unlimited, Inc., aren't working on space elevators but are working on lots of related technology.

I fished around a little and found a link for the actual research paper the article is based on. The paper itself requires a subscription, but here's the abstract:

The atmospheric implications of radiation belt remediation

C. J. Rodger, M. A. Clilverd, Th. Ulich, P. T. Verronen, E. Turunen, N. R. Thomson

Abstract: High altitude nuclear explosions (HANEs) and geomagnetic storms can produce large scale injections of relativistic particles into the inner radiation belts. It is recognised that these large increases in >1 MeV trapped electron fluxes can shorten the operational lifetime of low Earth orbiting satellites, threatening a large, valuable population. Therefore, studies are being undertaken to bring about practical human control of the radiation belts, termed "Radiation Belt Remediation" (RBR). Here we consider the upper atmospheric consequences of an RBR system operating over either 1 or 10 days. The RBR-forced neutral chemistry changes, leading to NOx enhancements and Ox depletions, are significant during the timescale of the precipitation but are generally not long-lasting. The magnitudes, time-scales, and altitudes of these changes are no more significant than those observed during large solar proton events. In contrast, RBR-operation will lead to unusually intense HF blackouts for about the first half of the operation time, producing large scale disruptions to radio communication and navigation systems. While the neutral atmosphere changes are not particularly important, HF disruptions could be an important area for policy makers to consider, particularly for the remediation of natural injections.

I'd never heard of the "radiation belt remediation" procedure that was mentioned in the article, so I dug around some more and located the following paper:

Remediation of radiation belts using electrostatic tether structures

Abstract: Scattering of energetic charged particles by high-voltage electrostatic tether structures may present a technically and economically viable method of rapidly remediating radiation belts caused by both natural processes and manmade events. In this paper, we describe a concept for a system of electrostatic tether structures designed to rapidly remediate an artificial radiation belt caused by a high altitude nuclear detonation. We then investigate the scaling of the system size and power requirements with the tether voltage and other design parameters. These scaling analyses indicate that a conventional single-line tether design cannot provide sufficient performance to achieve a system design that is viable. We then propose innovative multiwire tether geometry and show that this tether design can significantly improve the overall performance of the electrostatic system, enabling the requirements for total power and number of satellite systems to be reduced to levels that are both technically and economically viable.


The slashdot submission and popular press-article (but not the research paper) engages in some fear-mongering about how the US is supposedly planning on deploying RBR, but I haven't found any sources which confirm this to actually be the case. It should probably be mentioned that DARPA funds almost everything under the sun, usually without much expectation of it actually being of practical use. I mean, this is the same DARPA that funded psychic telepathy research and mechanical elephants for the jungles of Vietnam.

Regardless of whether or not it's practical, radiation belt remediation still seems like interesting research. It'd be a shame if fear-mongering about this being a "US plot to disrupt worldwide communications" or something resulted in funding for this research being cut off.

For a start, rewrite the space treaty so governments are not responsible for everything their citizens launch into space. Next, hold the corporations responsible for their own mess. For every year they fail to deorbit their space junk (or boost it into a safe parking orbit) charge them a fine. If the fine is just twice as high as a terminator tether they'll soon take care of their space junk.

check out http://www.tethers.com/ They have a net thingie for grabbing space debris, and tethers for dragging debris out of orbit!

Thanks for the great explanation Moofie. ;)

The problem is that the tethers get damaged by micrometeors. A small comparison graph of the degradation rate of single and interlinked tethers can be seen near the bottom of http://www.tethers.com/Hoytether.html. IMHO, this means that other (non-tethered) means of magnetic propulsion may be worth investigating, as there is nothing unique about the tethered geometry which makes it advantageous for magnetic propusion.

It's got nothing to do with materials! We have the materials to build all sorts of tether based space access systems. It's all about where the pork will go. As such, about the only company that has a chance of building anything involving tethers is Boeing with their HASTOL concept.

Yah. More please. Virgin Galactic? Get up there already. Elon Musk, Steve Bozzos? We're routin' for ya guys, get those payload boosters up to human safety levels and strap on a space ship. John Carmack? Dude, you show so much promise, good luck, and I hope you make it.

Oh, and before anyone replies to this post saying that SpaceShipOne isn't scalable.. who the hell says you have to have a powered ascent to orbit? There are alternatives to rockets.

Tethers are cheaper, don't have to be at the equator, and can be used elsewhere in the system for orbital transfers. It's probably also harder to crash a plane into them, since they don't reach the ground (you rendezvous with the end via aircraft). They don't even need carbon nanotubes. You can make them out of nylon (IIRC, see papers at link).

why not shoot for something a little smaller scale than a full blown elevator: Momentum-Exchange Tethers? This would make gettings things into higher orbit or out of orbit much easier, allowing the use of smaller rockets. It could also be used to very easily get things on and off the moon.

Then, a moon based elevator would be the next step...

Or, leaving aside Analog hard sci-fi, we can go for the real deal: a tether-powered station to pitch smaller rockets from LEO to GEO (or higher). Tethers Unlimited, Inc. already has a plan, called MXER ( Momentum-Exchange / Electrodynamic-Reboost ), for a simple slingshot system that would be capable of lifting satellites into geostationary or -synchronous orbit... or launching manned ships into a
lunar orbit. The best part is they've already tested their system in space and have tethers in operation on commercial satellites right now.

Or, leaving aside Analog hard sci-fi, we can go for the real deal: a tether-powered station to pitch smaller rockets from LEO to GEO (or higher). Tethers Unlimited, Inc. already has a plan, called MXER ( Momentum-Exchange / Electrodynamic-Reboost ), for a simple slingshot system that would be capable of lifting satellites into geostationary or -synchronous orbit... or launching manned ships into a
lunar orbit. The best part is they've already tested their system in space and have tethers in operation on commercial satellites right now.

Or, leaving aside Analog hard sci-fi, we can go for the real deal: a tether-powered station to pitch smaller rockets from LEO to GEO (or higher). Tethers Unlimited, Inc. already has a plan, called MXER ( Momentum-Exchange / Electrodynamic-Reboost ), for a simple slingshot system that would be capable of lifting satellites into geostationary or -synchronous orbit... or launching manned ships into a
lunar orbit. The best part is they've already tested their system in space and have tethers in operation on commercial satellites right now.

Or, leaving aside Analog hard sci-fi, we can go for the real deal: a tether-powered station to pitch smaller rockets from LEO to GEO (or higher). Tethers Unlimited, Inc. already has a plan, called MXER ( Momentum-Exchange / Electrodynamic-Reboost ), for a simple slingshot system that would be capable of lifting satellites into geostationary or -synchronous orbit... or launching manned ships into a
lunar orbit. The best part is they've already tested their system in space and have tethers in operation on commercial satellites right now.

Or, leaving aside Analog hard sci-fi, we can go for the real deal: a tether-powered station to pitch smaller rockets from LEO to GEO (or higher). Tethers Unlimited, Inc. already has a plan, called MXER ( Momentum-Exchange / Electrodynamic-Reboost ), for a simple slingshot system that would be capable of lifting satellites into geostationary or -synchronous orbit... or launching manned ships into a
lunar orbit. The best part is they've already tested their system in space and have tethers in operation on commercial satellites right now.

Secondly, if you want to be rational about space elevators you have to face the fact that nanotube fibers don't yet exist but fibers like Dyneema or Spectra do. So what? Here's what:

With existing fibers you can build Hans Moravec's Rotovator(tm) which picks up hypersonic (near mach 12) payloads from an altitude of 100km and slings them to orbit.

Current proposals for implementation of the Moravec's design rely on a hypersonic air-breather of advanced aerodynamic design like the Boeing DF-9 (that exists only on paper).

Is there anything likely come along in the near future that could take paylods to 100km and mach 12?

Probably the same thing that is driving the technosocialist pundits to make all this noise about space elevators now:

The prospect that centralized space programs will be left behind by the emergence of a competitive suborbital launch industry with the emergence of suborbital space tourism and prizes like the Ansari X-Prize.

A key to the Rotovator(tm) is getting hub mass in place to keep it out of the atmosphere while it picks up mass from 100km@mach12 -- but that mass can be any old space junk (what is the dry weight of the International Space Station?) -- at least at the hub where it counts the most for high strength materials like carbon nanotubes. However, you can do a Rotovator(tm) with off-the-shelf commercially available fibers and still have a factor of 2.

Nice thing about Rotovators(tm) is that they can be built with much lower capitaliztion over a much shorter period of time using existing commercial materials. All you need is a bunch of mass orbiting near earth, some quite-doable tethers, and sufficient manuverability and speed in the atmospheric leg to hook up with the tether as it reaches the nadir.

Modest prize awards toward early milestones of a space elevator could end up enabling the Rotovator(tm) as well.

http://www.tethers.com/TT.html

It uses magnetic drag to slow the spacecraft.
Unfortunatly, you fall out of orbit before shedding enough speed to reduce the amount of thermal protection needed.

Radiation in the Van Allen belts is a potentially solvable problem. Here is a design for a space tether that would take most of the punch out of particles in the belts in about six months. If we ever become serious about deep space travel a tether to defang the betls is almost certainly a good first step.

Its the cosmic radiation thats hard. Shielding against that takes a lot of mass.

"I think they'd also have to go through the Van Allen radiation belts which could also be a concern."

There are proposals out there to use high voltage tethers that would scatter most of the particles out of the belts and reduce the energy in them 1% of their current level in about a half a year. If you are transporting a lot of people, on a regular basic, from LEO to GEO and beyond you would probably want to do it.

How would you use a motor to reposition an object in space?

So what's your opinion on tethers? (IAASE (Systems Engineer), NSS Member, no I don't work for Tethers unlimited) A scaled-up horizontally launched platform (like the successor to SS-1) can reach the minimum altitude for a tether and transfer a crew module into LEO, or possibly MEO. From there you can just about go anywhere (L1 or L2). (Overview on Lagrange Points here)

You know, with the Space Tether and a few thousand watts of solar-panel provided juice backed by a pair or two of flywheels, , the station could possibly be self-lofting. Maybe tack on a few more solar arrays, make the damn thing useful as a solar power satellite testbed.

It's not an issue of power.... It's an issue of propellant.

Damping torsional vibrations is relatively easy; you've got a magnetic field you can torque against, and passive coils will damp out rotation just fine (they're used to de-spin some passively-stabilized LEO satellites). East-west vibrations can be damped using current through the tether (additional plasma contactors will be required to allow the current to vary in different segments). Not sure how you'd handle north-south vibrations, but I have neither given it thought nor done research.

If you need to provide make-up thrust of 1 N through the segment between 120 km and 400 km, which is moving at an average forward velocity of ~1400 m/sec (figuring 10 m/sec/km), that is 1400 watts plus losses. Compared to the tens or hundreds of KW you'll need to reboost in compensation for net upward traffic, drag comp is nothing.

Even the relatively tiny tethers we've tried in space have had big problems with severing, accumulating currents, the works.

1e-5 tesla field times 1400 m/sec is 14 millivolts per meter; over the 280 km segment that dips below 400 km, that's only about 4 kV. I doubt that this is going to be a big headache, especially if the tether is segmented and charge pumps used to keep each segment at close to the ambient voltage level (each charge pump would be in an insulated segment). For each difficulty there are probably several ways to address it; we should be flying a few so that we can get engineering experience.

We're a creative species. I'm absolutely certain we could come up with something that would work.

Or tethers, which are cheaper, and don't have to be geosynchronous. You do need a suborbital vehicle to reach the near end, though.

Plus, you know their ads will eventually feature bondage. :)

Current proposals for implementation of the Moravec's design rely on a hypersonic air-breather of advanced aerodynamic design like the Boeing DF-9 (that exists only on paper).

Is there anything likely come along in the near future that could take paylods to 100km and mach 12?

Clue: Someone just went 100km this morning.

A key to the Rotovator(tm) is getting hub mass in place to keep it out of the atmosphere while it picks up mass -- but that mass can be any old space junk for the hub where it counts the most for high strength materials like carbon nanotubes.

Can you think of anything really massive that is likely to end up as space junk soon?

Clue: This /. article concerns such a hunk of junk.

Nice thing about Rotovators(tm) is that they can be built with much lower capitaliztion over a much shorter period of time using existing commercial materials. All you need is a bunch of mass orbiting near earth, some quite-doable tethers, and sufficient manuverability and speed in the atmospheric leg to hook up with the tether as it reaches the nadir.

Hans Moravec's Rotovator(tm) picks up hypersonic (near mach 12) payloads from an altitude of 100km and slings them to orbit.

Current proposals for implementation of the Moravec's design rely on a hypersonic air-breather of advanced aerodynamic design like the Boeing DF-9 (that exists only on paper).

Is there anything likely come along in the near future that could take paylods to 100km and mach 12?

Probably the same thing that is driving the bureaucrats to make all this noise about space elevators now:

The prospect that centralized space programs will be left behind by the emergence of a competitive suborbital launch industry with the emergence of suborbital space tourism and prizes like the Ansari X-Prize.

A key to the Rotovator(tm) is getting hub mass in place to keep it out of the atmosphere while it picks up mass from 100km@mach12 -- but that mass can be any old space junk (what is the dry weight of the International Space Station?) -- at least at the hub where it counts the most for high strength materials like carbon nanotubes. However, you can do a Rotovator(tm) with off-the-shelf commercially available fibers and still have a factor of 2.

Nice thing about Rotovators(tm) is that they can be built with much lower capitaliztion over a much shorter period of time using existing commercial materials. All you need is a bunch of mass orbiting near earth, some quite-doable tethers, and sufficient manuverability and speed in the atmospheric leg to hook up with the tether as it reaches the nadir.

Modest prize awards toward early milestones of a space elevator could end up enabling the Rotovator(tm) as well.

The tether can get energy back from tourists returning to Earth. So if your main traffic is tourists going up and down, the tether energy is easy. Another fun trick is that if you had a series of tether in LEO, GEO, and Lunar orbit you could send stuff to the moon and send moon rocks (or other stuff) back to the Earth without needed to add energy. You just keep the total mass going each way balanced.

Because of this, orbital or lunar tourism will not take much more energy than suborbital rocket rides. So we should see it within the next 20 years.

I have a site, spacetethers.com that has info and a Java applet tether simulator. There is also lots of info at tethers.com

I wish I had modpoints. Rotovators are indeed much more practical than space elevators. They do not require exotic new materials such as carbon nanotubes. They can be built with cheap materials like spectra or zylon fiber. They are also much shorter (100km instead of 36000km) and more flexible.

This system could double the payload capacity of launchers to geosynchronous transfer orbit or pick up small payloads from suborbital trajectories.

This could be built today. Rotovators are also a very good addition to suborbital space transports such as SpaceShipOne.

Current proposals for implementation of the Hans Moravec's original design rely on a hypersonic air-breather of advanced aerodynamic design like the Boeing DF-9 (that exists only on paper).

Can /. readers think of anything likely come along in the near future that could take paylods to 100km and mach 12?

Probably the same thing that is driving the bureaucrats to make all this noise about space elevators now.

A key to the Rotovator(tm) is getting hub mass in place to keep it out of the atmosphere while it picks up mass from 100km@mach12 -- but that mass can be any old space junk -- at least at the hub where it counts the most for high strength materials like carbon nanotubes. However, you can do a Rotovator(tm) with off-the-shelf commercially available fibers and still have a factor of 2.

Nice thing about Rotovators(tm) is that they can be built with much lower capitaliztion over a much shorter period of time using existing commercial materials. All you need is a bunch of mass orbiting near earth, some quite-doable tethers, and sufficient manuverability and speed in the atmospheric leg to hook up with the tether as it reaches the nadir.

Wow, you know, there's an obvious solution to the atmospheric drag part that I didn't even realize. Just goes to show you that a human's normal experience sucks for trying to figure out orbital dynamics.

Incidentally, the full system design is here, and it's moderately more fleshed out than we're ever going to do in a Slashdot post. But anyway...

The solution to the atmospheric drag part is easy - only the perigee is at low altitude. The apogee is at high altitude. This, of course, solves the atmospheric drag part elegantly - the vast majority of the travel is well outside of the atmosphere. Thus you experience a small amount of drag once per orbit (which lowers your apogee), but you have a long time to recover that via solar power. Quite elegant - it basically utilizes the fact that the magnetosphere is immensely larger than the atmosphere.

The solution they're proposing is for assisting LEO to GTO, but the design is scalable and could eventually do suborbital to LEO. Oddly enough, they also used 2 gee acceleration, and listed mach 10-12 as the needed suborbital velocities (on a different page). Apparently I did my math somewhat right.

Not true. It is not trivially easy to build up that extra velocity, because you have to lug all of the extra propellant through the atmosphere.

Well, kindof true. If you want to have a single-vehicle-to-orbit solution, yah, you have to lug all of the extra propellant. But there are solutions in design which could definitely utilize a suborbital reusable spacecraft.

In fact, you can make docking and pickup very easy, if you make the rotation opposite the direction of orbit at the right rotation to match velocities. Someone would have to do the math on the acceleration to figure out how big it would be to allow for safe human transport on the craft, but it's definitely doable for small satellites.

Anyway, I know I'm glossing over a lot of details (like how do you guarantee the "human module" that an SS1-like craft would dump off has a safe abort procedure) but the point is that there can be very interesting uses for a suborbital craft. You're out of the atmosphere. That's a huge benefit right there.

The most promising propellantless launch technology is rotating tethers.

Check out this for plenty of information about what is possible. here is a paper about a tether for LEO to GTO boost that could be built today.

All the other things like electric catapults are much too large to be practical if you want reasonable g-forces.

--

The most promising propellantless launch technology is rotating tethers.

Check out this for plenty of information about what is possible. here is a paper about a tether for LEO to GTO boost that could be built today.

All the other things like electric catapults are much too large to be practical if you want reasonable g-forces.

--

Was joke, tovarich. But after all...

Consider whether, in the coming era, breakthrough technologies may owe less to the mechanical engineering paradigm, like towering steel cylinders with a million pounds of thrust, and more to haute couture. Gossamer tethers, smart flexible structures; the technology of nylon hose and artful two-strap suspension.

I would love to see consciously astro-chic designs carrying off future Tether X-Prizes. Actually, Rutan's elegant Space Ship One is getting there. But I wish we could have had more explicit encouragement in the President's statement for stuff like the Hoytether design.

Tethers, Inc. supposedly has a tether system design that could reach far enough down out of orbit to snatch an object moving at Mach 16 out of the upper atmosphere. I can't find the exact link, but here's the gist of the idea:

http://www.tethers.com/OrbitToOrbit.html

Was anybody else reminded of the black wire from Larry Niven's Ringworld. . The wire that holds the shadow squares together, that is. The application, especially the one at tethers.com about satellites in tight formation is very similar to this, right?

Check out this link, from the same guys: High-Voltage Orbiting Long Tether (HiVOLT): A System for Remediation of the Van Allen Radiation Belts

This sounds like an interesting idea, but what other concequences would there be to getting rid of the Van Allen Belts? There plans involve just remediating (dispersing particles from) the inner belt, but still... Since most of the particles in the van allen belts are created primarily by interactions in the upper atmosphere, would dispersing the particles in the belt closest to the atmosphere also mean that particles in the outer belts would not be replenished?

I don't know what the effects would be becasue IANAP, and there is no info on their site about it. Would anyone out there more informed about this subject than me care to share their thoughts?

That's the electrodynamic bit. The conducting tether cuts magnetic field lines. This induces a voltage and causes a current to flow along it. (You emit ions at both ends to complete the circuit). Normally, that causes electromagnetic damping (like a dynamo). But, if you use solar cells to drive the current the opposite way, you can get a propulsion force... See here for more.

Oh, man, I read your post and thought "Robert Forward is dead? I hope he's mistaken about that." Unfortunately, he died last year, and I for one will miss him for his unique style of hard science-fiction and his innovations in physics and space travel. He did a lot of work on tether propulsion systems. Unlike Arthur Clarke, he patented a lot of his inventions. I wonder if the company he set up will see any money from their use, or if he was just a little too far ahead of his time?

This morning I was typing in a long post on my /. journal (which I use as a blog) about the Hoytether article at space.com. It had lots of great stuff, with links to physicist and Hard Science Fiction writer Dr. Robert L. Forward (who introducted me to the tether concept) and to Tether's Unlimited (the company that Robert Hoyt and Robert Forward started to commercialize it).

Hell I even wrote about listening to Bob Forward (Dr. Forward to you, heh heh) tell me the story of how he found a kilt-making company in Scotland that still had old-fashioned weaving machines which could be modified to create the tethers. In fact I went so far as to link to a eulogy I wrote about Bob when he died. It was a great post! It had everything!

But then /. ate it when I clicked 'Preview' and the back-button gave me an empty form. It was time to go to work so I said screw it; I can write it again when I come home. Yeah right. Like I would still want to post it after somebody else gets a dumber version on the /. front page!

It's like I was never meant to blog it...

• Electrodynamic Reboost In order for the tether facility to boost multiple payloads, it must have the capability to restore its orbital energy and momentum after each payload transfer operation. If the tether facility has a power supply, and a portion of the tether contains conducting wire, then the power supply can drive current along the tether so as to generate thrust through electro-dynamic interactions with the Earth's magnetic field. By properly controlling the tether current during an orbit, the tether facility can reboost itself to its original orbit, as illustrated in Figure 1. The tether facility essentially serves as a large "orbital energy battery," allowing solar energy to be converted to orbital energy gradually over a long period of time and then rapidly transferred to the payload. [Learn more about ED Tethers]

And, in fact, Tethers Unlimited, the company proposing this beast, was founded by scientist, engineer and science fiction writer Dr Robert L Forward. Sadly, Dr Forward died last September.

I'd imagine you want to make it a Hoytether, or some equivilant, so that it's self repairing.

Tethers ( 1, 2, 3 ) attached to counterweights can be used to transfer spacecraft from one orbit to another. The first tether has an orbit that skims the atmosphere, where a craft catches and connects to the end of the tether. The craft is lifted into low earth orbit and subsequent tethers help it to reach escape velocity. Using the tethers takes energy out of the orbits of the counterweights, some of which can be put back by using the tethers for descent as well as launch.

J. Storrs-Hall (once moderator of sci.nanotech) envisioned a space dock, a linear motor suspended 100 km above the ground that accelerates spacecraft to an elliptical orbit. He computes an amortized cost of reaching low earth orbit of 42 cents per kilogram. From the elliptical orbit, it's a relatively small safe step to escape velocity.

A space elevator ( 1, 2 ) is an excellent long-term solution. A cable is hung from a weight in geosynchronous orbit, reaching down to the Earth's surface. The elevator climbs the cable, carrying a craft. When it reaches GEO, the craft detaches and spends only a little fuel getting to escape velocity.

Tethers and the space elevator require novel materials for strong cables, probably using carbon nanotubes. The frame to hold up the space dock is in compression, and something we could build with little or no advance in material science. Any of these alternatives would be vastly cheaper and vastly safer than putting human lives on the noses of fuel tanks subjected to unreasonable speeds and stresses.