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Phoenix Aerospace

Launch Loops: A viable alternative to space elevators?

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300px-LaunchLoop.svg.png

This is a discussion thread, in which we will discuss the viability of the Launch Loop, or in more technical terms, the Lofstrom Loop; an obscure design for a permanent space launch platform which could dramatically reduce costs for spaceflight. For those not "in the loop" (pun unintended), the Launch Loop is a large structure consisting mainly of a long, flexible tube. This tube, approximately 10cm in diameter is in fact composed of two nested tubes, one inside the other. The outer tube, or the stator, drives the inner tube, or the rotor, by the means of linear induction motors, which may or may not be superconducting in nature. This tube is joined together at the ends, in order to form a loop, one half is affixed to the ground, and the other is secured by the means of a long tether. When the rotor is accelerated, it generates a strong centripetal force. This has the curious effect of lifting the tethered half of the loop off the ground. Once it reaches the limit of the tether, at 80 kilometers above the ground, the loop takes on the shape of a rough parallelogram, with the top measuring roughly 2000 kilometers. Payloads are lifted to the top of this loop by elevator, and grapple onto the madly spinning rotor using electromagnets. At a comfortable rate of 2gs, this accelerates the payload to orbital speeds, where it is released. At apogee, the payload would then fire its own thrusters to circularize its orbit.

Pros and cons of a Launch Loop

Pros

  • Can launch large volumes of material. A large loop could launch up to 6 million tons per year.
  • Costs are lower than conventional rockets, or even space elevators. Space elevators would cost anywhere from 3,000$ to 1,600$ per kilo, wheras a launch loop could bring costs down to 300$ to 3$ per kilo. By comparison, launch on an existing Proton rocket costs approximately 4,300$ per kilogram.
  • Higher launch rate than conventional rockets (up to several per hour).
  • Can be built with current or near-future materials. Requires no new high tensile strength materials.
  • Depending on energy source and erection area, can be more environmentally friendly than conventional rockets.
  • Payloads spend less time in radiation-heavy Van Allen Belts.
  • Main structure is situated at an altitude free of space debris.

Cons

  • If the linear induction system fails, particularly in the unstable turnaround sections, the rotor may collide with the stator. Due to the accumulated kinetic energy, this would release roughly 1.5 petajoules of energy; roughly equvalent to the detonation of a nuclear weapon.
  • Requires precise electronic control over linear induction elements in order to compensate for weather effects.
  • The necessity for expansion joints in the rotor presents severe engineering challenges.
  • Requires the vehicles to have their own engines for circularization.

So, despite the difficulties, would you still consider this a viable method for space access? Why?

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I read the wiki page, your post and googled the youtubes - and I still don't understand how this concept works. I'm dumb that way.

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It sounds like a viable alternative minus the bad day if there is a catastrophic failure. Not to mention, the engineering nightmare it would take to set it up and keep running smoothly.

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I googled it once, but the forces at the ends where the rotor turns are grotesque. Not sure how they want to do it. Maybe by making the loop turning points be several dozen kilometers in diameter. And the entire thing needs several nuclear powerplants running 24/7 because no power = explosive disintegration.

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It is a cool idea nonetheless because it does not need any exotic materials.

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Interesting concept, never heard of it before. Looks like it could be worth a shot if we need to get an extreme amount of payload into orbit like in the far future when humanity wants to settle Mars or something. But for now, even though they say that it needs no exotic materials, any engineering project that spans over 2,000k is going to have a lot of engineering obstacles to overcome. My first thought for why it won't work is that if you need to service it you have to drop the cables... into the ocean(no need to go into details of difficulties there). And there's no way you could put this over any stretch of land.

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We had a huge discussion on the subject already, but I guess it was eaten by the forum kraken.

A launch loop is a 4000km long 5cm wide bicycle cable that runs inside a sheath at 14000km/s, which is equivalent to the fastest man-made object ever made (Voyager 1 is travelling at 17km/s). Due to the mass of the cable, thousands of tons, the energy involved is tremendous.

The sheath has to maintain a perfect vacuum, because if any air leaked into the system, the friction would melt the cable and the system would explode. If any of the magnets fails, the cable touches the sheath and cause the whole thing to burn up and explode. If any temperature variations along the 2000km loop cause either the sheath or the cable to dilate or retract, even slightly, there will be slack or breakage, and it will explode.

But the biggest issue is that there is no known way to raise or lower the cable or to stop it for maintenance, and the engineering problems involved in building hundreds of platforms on the oceanic seabed and assembling the cable is huge.

Basically, it's even less viable than a space elevator.

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We had a huge discussion on the subject already, but I guess it was eaten by the forum kraken.

A launch loop is a 4000km long 5cm wide bicycle cable that runs inside a sheath at 14000km/s, which is equivalent to the fastest man-made object ever made (Voyager 1 is travelling at 17km/s). Due to the mass of the cable, thousands of tons, the energy involved is tremendous.

The sheath has to maintain a perfect vacuum, because if any air leaked into the system, the friction would melt the cable and the system would explode. If any of the magnets fails, the cable touches the sheath and cause the whole thing to burn up and explode. If any temperature variations along the 2000km loop cause either the sheath or the cable to dilate or retract, even slightly, there will be slack or breakage, and it will explode.

But the biggest issue is that there is no known way to raise or lower the cable or to stop it for maintenance, and the engineering problems involved in building hundreds of platforms on the oceanic seabed and assembling the cable is huge.

Basically, it's even less viable than a space elevator.

-snip-

Sure there are issues to iron out with a launch loop. However, its main advantage over a space elevator is that is can be made using modern materials, and is a lot cheaper.

I would be willing to bet this method would be constructed before a space elevator on Earth. That is to say if we don't find a more economical traditional rocket to get us into space, by the time humanity is ready to actually become a space faring species, we'll build a launch loop.

Edited by KasperVld

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Interesting in concept, pointless in practice. The engineering difficulties of this and similar designs (including space elevator-type designs) render it impractical. It is large, expensive, and not robust against failure; the potential savings are far out-weighed by the costs of actually building the thing. Further, the potential savings will vanish in the near future; rockets may be expensive today, but they will not remain so indefinitely.

While ideas like these are fun to contemplate, it's very difficult to beat the advantages potentially offered by reusable rockets: cost effectiveness, distributed modular launch capability, and the system as a whole is robust against failures of single components. SSTOs, should they become a thing (and they probably will) will render launch loops and elevators obsolete. Why take a train when you can fly?

-snip-

Edited by KasperVld

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If the linear induction system fails, particularly in the unstable turnaround sections, the rotor may collide with the stator. Due to the accumulated kinetic energy, this would release roughly 1.5 petajoules of energy; roughly equvalent to the detonation of a nuclear weapon.

A failure mode which leads to that much energy release near a shipping hub would seem to render it non viable...

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-snip- concepts like this (like giant railguns, space elevators, balloons to orbit, and so on...) have been floating around for decades, yet nobody is building them, because I'm not the only one who thinks they are ont viable or practical.

On the other hand, a lot of people on this forum wear pink-tinted glasses. Many of us are young, somewhat inexperienced, and have been raised on science fiction. Now, Star Trek is fun, with warp drives, time travel, and teleportation, but real-life constraints and physics say that it's not reasonable to expect these to happen any time soon.

Powerpoint presentations are easy. Real engineering is hard. Some concepts look appealing in theory but are hard to actually build because all sorts of petty real-life concerns crop up when you want to convert theory into a robust operational system. You know, stuff like money, politics, weather, patents, regulations, maintenance, human resources...

I'd love to see someone come up with a cheap and feasible way to put people and stuff into orbit. However, handwaving the problems that I raised away by calling them naysaying doesn't make them go away and certainly doesn't provide an decent answer to those issues.

Edited by KasperVld

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A launch loop is a 4000km long 5cm wide bicycle cable that runs inside a sheath at 14000km/s, which is equivalent to the fastest man-made object ever made (Voyager 1 is travelling at 17km/s).

Now that I'm actually thinking about this, I wonder if it's not possible to change the design to render it more robust against the specific failures that you mentioned.

What's actually keeping the outer shell up is the magnetic coupling between it and the interior cable - but there's no actual need for the interior to be a solid capable. It's the angular momentum that's keeping the whole structure supported, and that could be just as easily achieved by a particle beam (or a bunch of tennis balls, or whatever) with the same mass as long as you could keep it aimed down the center of the tube. That would resolve the worst of the problems caused by flexing or thermal expansion/contraction and in the event of failure possibly allow you to distribute the energy around the entirety of the ring rather than concentrating most of it as the point of failure. Of course, now you're left with the problem of building a 4000km long flexible particle accelerator, and if you can do that I've got a whole lot of more important things to use it for than launching stuff into orbit.

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So let me get this straight. You move something back and forth... on Earth... until it reaches orbital velocities... then release it?

"Look, mommy! That train is on fire!"

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You move something back and forth... on Earth... until it reaches orbital velocities... then release it?

No. That's not how it works. Reread the design specs.

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I might be wrong 99% of the time, but concepts like this (like giant railguns, space elevators, balloons to orbit, and so on...) have been floating around for decades, yet nobody is building them, because I'm not the only one who thinks they are ont viable or practical.

On the other hand, a lot of people on this forum wear pink-tinted glasses.

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People have heard that many times from you. Nah, it can't be done, nah, too difficult, nah, physics ( always in general, never saying in detail why not ) , nah this, nah, that. Always dismissing things right out of the bat.

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As I said in another thread. Who wants, seeks ways, who does not want, seeks reasons.

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And, seems to me, you are all about seeking reasons why not.

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Something this big that even has a slight possibility of a total catastrophic failure will never be built. If you lose a rocket it's a bad day. If you have a massive international construction project that would take years to produce suddenly flies apart it's not like "oops chain snapped.... okay guys, lets set it back up again for another go"

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*re-reads OP*

How would you attach the payload? He said you turn it on first, and I assume that this thing would be electrified and moving fast enough to tear off limbs.

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*re-reads OP*

How would you attach the payload? He said you turn it on first, and I assume that this thing would be electrified and moving fast enough to tear off limbs.

Maglev. I think the concept is just how to build a massive rail system. The actual launch vehicle just rides it as if were a static track (it being metal).

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*re-reads OP*

How would you attach the payload? He said you turn it on first, and I assume that this thing would be electrified and moving fast enough to tear off limbs.

Electromagnetic induction - the payload hangs off the sheath, and electro magnets set up an induction effect in the moving core that provides traction. Varying the electromagnet power will adjust the force provided, allowing for a controlled pick-up of traction *IF* somebody can work out the details of doing so in such a way as to not cause destructive oscillations in the moving core!

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*re-reads OP*

How would you attach the payload? He said you turn it on first, and I assume that this thing would be electrified and moving fast enough to tear off limbs.

I'm pretty sure it's a mag-lev setup. It would be moving a little faster than tear-off-limbs speed. 31,000mph, if I remember the wiki's number correctly. A 2km long, solid metal cable moving at orbital velocity suspended inside a vacuum sheath...yeah, that's a lot of energy and totally impractical.

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Just because it is less impossible than a space elevator does not make it plausible or realistic.

Actually, I disagree that the launch loop is less impossible than a space elevator. The engineering challenges for a launch loop are significantly greater. All an elevator really needs is a large quantity of material with a sufficiently high tensile strength and a way to put that quantity of material into orbit. We even have candidate materials existing (carbon nanotubes may work), but lack the infrastructure to manufacture, launch and assemble the thing (space elevators are a chicken-and-egg problem; by the time you have the capability of putting one into orbit, you've solved the problem of getting to orbit cheaply).

Launch loops, on the other hand, require a whole slew of technical capabilities we do not possess: high temperature light weight super conductors; materials of sufficient strength - requirements in this regard may be greater than even those for an elevator; efficient transmission of power along the whole 4000km length; and a whole slew of others. The problem of failsafing the device boggles the mind - I cannot even imagine how one would go about it.

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we can't create a sheath that long that is air-tight

the only difference between several km of sealed tube and a few thousand kilometers of sealed tube is cost nothing more. And I would add, that our particle colliders need ultra high vacuum. for this, normal vacuum would be enough.

we can't create electromagnets light enough and powerful enough

Yeah, right, that's why the LHC was never built :rolleyes:

we can't build any of this in such a way as to be maintenance-free (which they would need to be),

yeah right, that is why the LHC that has never been built because of your point 1 and 2 needs thousands of workers inspecting and repairing the magnets each day :)

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The LHC doesn't fall 80KM into the ocean when you turn it off.

The LHC did actually blow apart a segment of it because of superconductor failure. And in worst case scenario can damage itself beyond repair in case of sudden catastrophic failure.

And fall into ocean per se is not a big deal. parachutes and stuff.

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Yeah, right, that's why the LHC was never built

If you have a viable plan for turning the LHC into a system capable of launching payloads into orbit, please let me know. After all, now that the Higgs has been discovered, we need to find a use for it.

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