Talk:Launch loop

Close-Loop Cable?

The article makes the statement "In Bolonkin 2008[8] a simple rotated close-loop cable which can launch the space apparatus which, it is claimed, is suitable for current technology." Either I don't understand the statement (meaning it needs more explanation) or it is just plain wrong.

There is a quanitity known as specific velocity (not unlike the characteristic velocity of a rotovator) that is equal to the square root of the quantity strength divided by density (σ/ρ)^0.5. It is in essence 0.707 times the characteristic velocity which contains the factor 2 in the numerator (2σ/ρ)^0.5. The characteristic velocity is defined as the maximum tip speed a rotovator with a uniform, untapered cable can attain. The specific velocity is used for non-spinning tethers, and works out to be the maximum tangential velocity that a closed loop cable can withstand. Beyond that velocity, the inertial loads exceed the strength and the loop breaks.

I know of no current technology at has a specific velocity greater than about 2 km/sec, let alone the ~7+ km/sec needed to launch a payload. If I am wrong, what am I missing? If the statement is wrong, it should be removed.

KitemanSA (talk) 03:37, 19 July 2008 (UTC)

I haven't read the paper, but so far as I can make out Bolonkins idea is still to magnetically contain the moving parts of the loop, but some of the technical details are different. He does away with the high acceleration portions, stuff like that.- (User) WolfKeeper (Talk) 14:27, 19 July 2008 (UTC)

Vacuum Sheath?

The Description section is somewhat unclear, as it in the second paragraph starts talking about the vacuum sheath without actually telling how this is incorporated in the whole structure. Could someone who has better knowledge about the subject try to clarify this? OttoMäkelä (talk) 20:39, 30 December 2007 (UTC)

unclear article

'ts not clear how this works. Is just a spinning rope, or is it working as a magnetic realgun ? —Preceding unsigned comment added by 82.217.143.153 (talk) 23:09, 28 March 2008 (UTC)

It's not really exactly either. The moving metal rotor when dragged past a magnet generates huge eddy currents that pulls the magnet along after the rotor.- (User) WolfKeeper (Talk) 01:45, 29 March 2008 (UTC)

A good way to envision this is to think of a firehose with no one holding onto it. It will flail about in the air. The launch loop works on the same principle, except instead of moving water through the hose, you are moving an iron cable which is suspended magnetically with minimal friction. The "hose" is forced upward by the kinetic motion of the cable and held in check by the guy wires. —Preceding unsigned comment added by 63.211.201.174 (talk) 11:12, 26 August 2008 (UTC)

A few questions

Is the design limited inherently to 5 metric ton payloads, or is it possible to increase that size? The article says that the launch loop is, in and of itself, able to reach LEO, escape orbits, GEO, and others.

I understand how this would be possible with a "kick-start" booster on the payloads, but how is the launch loop capable of this "in and of itself"? It seems to me that at the given 3g acceleration, at the end of a 2000km long track an object would be traveling at about 10.5 km/s. If memory serves me that's not quite escape velocity on its own. I'm rusty on my physics, so that could be a wrong number. I might add at this point that by training I am not a physicist or engineer, although I feel that I can understand the concepts if pointed to the appropriate articles and given time.

I made it 10.8 km/s. The other thing is that the rotation speed of the earth is ~500m/s, which gets you there near enough. But making the track a bit longer or pushing the acceleration up by a few percent is not a big deal. Neither is a small kick rocket to make up the difference.- (User) WolfKeeper (Talk) 18:15, 19 May 2008 (UTC)

How exactly does it radiate excess heat? Through the casing when it enters the ocean at the ends?

Just radiation through to the casing which then it turn radiates as well.- (User) WolfKeeper (Talk) 18:15, 19 May 2008 (UTC)

What sort of materials / engineering is required to lift something 80km to hop on the track?

Kevlar maybe. Some sort of composite cable.- (User) WolfKeeper (Talk) 18:15, 19 May 2008 (UTC)

How does something detach from it at the end? Rockets, some sort of lifting body design, the fact that the loop drops off, magnetic forces, or some combination?

It just detaches and the cable curves away as it follows the horizon.- (User) WolfKeeper (Talk) 18:15, 19 May 2008 (UTC)

Finally, I know this question might be harder to answer, but how do the $/kg numbers change if the launch loop isn't used to capacity? I suppose this would be easy to calculate if the power to run it didn't vary much if it was being used to launch all the time as opposed to running without a load, but I doubt this is the case.

Roughly inversely proportional. Most of the cost is in loans for construction and so forth, although there are some fixed running cost in electricity.18:15, 19 May 2008 (UTC)

Sorry if these questions are uninformed or anything, and if anyone can answer them I'd be appreciative. 67.142.130.19 (talk) 17:29, 19 May 2008 (UTC)

PS: How exactly is the rotor envisioned to be constructed? Is it a monolithic, bendable, iron "pipe" or segmented with some sort of joint every few meters? 72.171.0.139 (talk) 01:06, 20 May 2008 (UTC)

It's probably not a solid pipe, the stake in the ground seems to be a joint every few meters. The exact details vary between the different published papers (which isn't surprising since they're 20 years apart!)- there's different ways to implement the concept described in the article.- (User) WolfKeeper (Talk) 15:02, 29 May 2008 (UTC)

Thanks, that made it a lot clearer for me (along with some reading I did on other articles). I wonder why a traditional space elevator is the focus of all the buzz and research when this concept is more plausible, buildable, and is economically cheaper? 72.171.0.139 (talk) 01:02, 20 May 2008 (UTC)

Thanks for answering these questions. It cleared things up for me also. My question: What are the latitude limits for the launch loop? --173.71.223.237 (talk) 16:22, 17 January 2009 (UTC)

I don't think there are any major ones, unlike space elevators that are quite constrained in that regard, but you'd have to check the paper on that. All launch systems benefit from being near the equator due to the rotation of the Earth, so I would guess you'd have to make the loop a bit longer as you move away, but not massively so. Hmm, it might be worth adding that to the comparison section as an advantage over space elevators.- (User) Wolfkeeper (Talk) 17:18, 17 January 2009 (UTC)

KeithLofstrom here, with a few comments

I think Wolfkeeper did a great job of summarizing the idea - more details at [1], which also has a wiki where folks can add their own ideas. More questions about this article can be asked and answered at [ http://wiki.launchloop.com//index.cgi?WikiPedia ], so we can respect the talk page guidelines here. —Preceding unsigned comment added by 96.253.164.73 (talk) 03:37, 11 July 2008 (UTC)

Well... I'm only doing so because if they ask questions or otherwise comment here then it helps us know whether the article is confusing and whether there's anything missing. I'm absolutely not guaranteeing to answer them though, although so far I have done so, and the level we're getting them at does not seem to be a problem; anything complicated I'll certainly forward to you ;-)- (User) Wolfkeeper (Talk) 17:07, 17 January 2009 (UTC)

Removed from the article

(these were completely unreferenced and unformatted)

10. Centrifugal Keeper for Space Stations and Satellites, by A. Bolonkin, JBIS, Vol.56, No. 9/10, 2003, p. 314-327. Author offered and researched the rotating cable which launches and keeps the moveless space station and satellites. Four projects are computed. 11. Kinetic Space Towers and Launchers, by A. Bolonkin, JBIS, Vol. 57, No.1/2, 2004, p.33-39. Author offered and researched new method for access to outer space. A cable stands up vertically and pulls up its payload to space. Five projects are computed. 12. “Non-Rocket Space Rope Launcher for People”, by A.Bolonkin. IAC-02-V.P.06, 53rd International Astronautical Congress, The World Space Congress – 2002, 10–19 Oct 2002, Houston, Texas, USA. 13. “Non-Rocket Missile Rope Launcher”, IAC-02-IAA.S.P.14, 53rd International Astronautical Congress, The World Space Congress – 2002, 10–19 Oct 2002, Houston, Texas, USA. 14. “Inexpensive Cable Space Launcher of High Capability”, IAC-02-V.P.07, 53rd International Astronautical Congress, The World Space Congress – 2002, 10–19 Oct 2002, Houston, Texas, USA.

Patents: 1. Method and Installation for Space Trip. Patent application US PTO 09/789,959 of 2/23/01. 2. Method and Installation for Space Launch, by A.Bolonkin. Patent application US PTO 09/873,985 of 6/04/01. 3. "Method for Launch and Payload Transportation at Long Distance and Installations for It", Patent Application USPTO # 09/978,507 of 10/18/01. 4. Cable Launcher. Patent application US PTO 09/974,670 of 10/11/01.

Why so Certain?

If you are going to state statistics such as launch velocity and the suchlike, you can not go without touting a few physics equations. Where is the proof this will even work? Much of the article is stated as fact, but if it is simply theory then say that at the beginnning.--MixMaestro (talk) 01:08, 5 September 2008 (UTC)

This is simple. If you start off at rest, have a constant acceleration a, and a target velocity v, it is simple to find the necessary distance s to achieve v--the formula is:

$s={\frac {v^{2}}{2a}}$

We want a constant acceleration that is about 3g's, and let us go with 30 m/s2 to keep it simple. Our target velocity is about 11 km/s.

We have: $a=30{\tfrac {m}{s^{2}}}=0.03{\tfrac {km}{s^{2}}},v=11{\tfrac {km}{s}}$

$s={\frac {(11{\tfrac {km}{s}})^{2}}{2(0.03{\tfrac {km}{s^{2}}})}}={\frac {121{\tfrac {km^{2}}{s^{2}}}}{0.06{\tfrac {km}{s^{2}}}}}=2016.{\overline {6}}km$

That is pretty close to the 2000 km number put out by designers of the launch loop. Cornince (talk) 01:56, 17 December 2008 (UTC)

Altitude maintance

This articles covers a lot things, but (from my reading), fails to mention how the cable way would either reach 80km up in the air, or be maintained there. —Sladen (talk) 13:40, 13 October 2008 (UTC)

It's carried there by the momentum of the rotor. It's a bit like a when you're watering the garden through a hose, if you put it on a straight flow setting and point it up, the water forms an arch. It's going too slowly to carry any major load, but perhaps you could imagine hanging a paper or foil wrapper on the arch or something. The launch loop works the same way, except the rotor is going ohmygod fast and it can carry a lot more weight.- (User) Wolfkeeper (Talk) 18:39, 13 October 2008 (UTC)

It would be good for the article to mention this. One other thing I'm uncertain about, these 2 towers that use the magnetic forces to keep up the launch loop, will they be 80 km high? Cornince (talk) 22:20, 16 December 2008 (UTC)

There's no towers, there's just 'elevator' cables hanging down from the docks. The docks are held up by the main launch loop cable, not the other way around.- (User) Wolfkeeper (Talk) 00:08, 17 December 2008 (UTC)

Also, it seems that this loop has varying altitudes, in that it is at certain points 80 km high, while at other points it is near ground level. The descriptions I've read don't seem to be clear on this point. Cornince (talk) 22:22, 16 December 2008 (UTC)

I'm not sure why you say that. The loop is at ground level at each end and 80 km in the middle, as the diagram shows.- (User) Wolfkeeper (Talk) 19:54, 18 December 2008 (UTC)

Elevator?

"To launch, vehicles are raised up on elevators to a loading dock at 80 km, and placed on the track"

...I personnally have never seen an 80 km high elevator. Anyone care to elaborate?--Perwfl (talk) 03:21, 21 November 2008 (UTC)

I will when you elaborate on the 80 km high structure that you have seen that would need it.- (User) Wolfkeeper (Talk) 03:37, 21 November 2008 (UTC)

That's not an answer to the person's implied question. Don't be snide. --12.21.161.34 (talk) 19:41, 11 December 2008 (UTC)

It's a valid question. The statement is that to get a vehicle on a launch loop, it needs to ride an elevator to 80 km above the surface, no easy feat. The article explains how, through the garden hose analogy, the launch loop itself would be 80 km above the surface, but it doesn't explain how we can get a loading dock, which I assume would be stationary, up 80 km high. Cornince (talk) 21:48, 16 December 2008 (UTC)

It's just a tapered cable hanging down from the dock that can be used to climb up to it. The self support length of Kevlar is 256 km for example.- (User) Wolfkeeper (Talk) 23:54, 16 December 2008 (UTC)

Could you not just ride up the part of the main cable that comes from the ground? No need for an extra 80 km cable, I think. 76.112.8.174 (talk) 02:33, 17 March 2009 (UTC)

Yes, that is theoretically possible, but there are difficulties due to the thickness of the sheath at the relatively high atmospheric pressures, as well as potential issues such as icing that can cause problems.- (User) Wolfkeeper (Talk) 02:43, 17 March 2009 (UTC)

Proof of Principle

Do we know that we can, using magnetic forces, rotate this iron 80 km above the ground and control its movements? Has this ever been demonstrated, even in miniature? If not, how would one go about demonstrating this principle with, say, a miniature launch loop, that would lift perhaps just a few feet high and have minor acceleration? One way to get investors in this project is to demonstrate physically that you can levitate and control this thing with magnets in a way that would facilitate launches. Cornince (talk) 21:52, 16 December 2008 (UTC)

That's not a concern for the wikipedia. The wikipedia describes notable concepts. Whether or not it even works, it's still a notable topic.- (User) Wolfkeeper (Talk) 22:14, 16 December 2008 (UTC)

Have any sources been found that mention such demonstrations of a working concept of a launch loop? If such sources exist, that would be notable. Cornince (talk) 22:16, 16 December 2008 (UTC)

It's a conceptual design which has never been built, so we cannot be totally sure whether it can be, but my understanding is that it's believed to be physically realisable, and there's no unobtainium or show-stopping problems that are known to exist and it has been examined fairly deeply over a number of years.- (User) Wolfkeeper (Talk) 23:58, 16 December 2008 (UTC)

I would say it's fractionally above technology readiness level 2.- (User) Wolfkeeper (Talk) 23:58, 16 December 2008 (UTC)

Great. When does the first testing of using magnets to run an iron pipe through a vacuum sheath while looping it around using magnets, with the streaming causing the pipe to levitate, but the levitation is supported by cables, occur? Who'll do it? If it's reasonably small scale, and the pipe doesn't need to move very fast for demonstration purposes, then the concept shouldn't cost too much to build. Cornince (talk) 02:27, 17 December 2008 (UTC)

The program to build stuff is unfunded right now. Lofstrom himself doesn't have the cash. NASA has tried some linear maglev launch assist a few years ago, but they didn't seem to like it much; I'm not aware of any ESA program.- (User) Wolfkeeper (Talk) 03:12, 17 December 2008 (UTC)

John Knapmann and others are doing theoretical investigations into essentially the same concept but for suborbital use (Space Cable) and publishing and presenting papers. Lofstrom still gives presentations as well.- (User) Wolfkeeper (Talk) 03:12, 17 December 2008 (UTC)

I thought the proof of concept model had to be full scale in order to escape the gravity restrictions that a scaled down version would not overcome? --173.71.223.237 (talk) 16:35, 17 January 2009 (UTC)

No, not at all, and the spaceCable described in the article is suborbital. Don't forget- it works just the same way as the water arch coming from a hose pipe, nothing needs to be orbital speed.- (User) Wolfkeeper (Talk) 17:36, 17 January 2009 (UTC)

Would there be atmospheric drag or other issues with friction that would require the proof of concept model to be full scale? Or would you just overcome that with a fully sheathed cable. Would there then be additional issues with a fully sheathed model? —Preceding unsigned comment added by Qwerspam (talk • contribs) 13:19, 9 March 2009 (UTC)

Well, Keith Lofstrom and Paul Birch built a small desktop model that basically worked.- (User) Wolfkeeper (Talk) 15:31, 9 March 2009 (UTC)

Source?- Cornince (talk) 08:11, 17 March 2009 (UTC)

I agree, is there a link to source material? --Qwerspam (talk) 19:20, 17 March 2009 (UTC)

Not as far as I know, I saw a video of it once on TV, I think it was on Tomorrow's World or something. Apparently it was reasonably unstable, the full-up system would have various stabilisation systems, and their model was too crude for that; but it did basically work and lift, but it wobbled.- (User) Wolfkeeper (Talk) 22:02, 17 March 2009 (UTC)

If anyone can find a source for that, that would be great. Basically, if Longstrom wants to make his dream a reality, he needs to make lots and lots of desktop models and keep trying to stabilize the system and work out basic principles of stabilizing the magnets so they can be applied to the larger models (it costs less for a desktop model to fail) and then he needs to work on using the desktop models to launch little desktop model ships and come up with basic principles for how to do that; only then, he should move on to the larger models and to start to factor in things like winds and weather and other environmental conditions--and at that point, he should be getting more support for funding such a project. Cornince (talk) 16:12, 24 May 2009 (UTC)

Safety?

The article claims "the magnetic suspension system would be highly redundant, with failures of small sections having essentially no effect at all." I don't see how this is possible. If the sheath breaks somewhere in the middle (say an airplane hits it), wouldn't the belt fly out of the broken sheath and the whole loop come falling down in a matter of minutes? And wouldn't there be a quick loss of vacuum accompanied by intense heating due to increased friction if there was a hole in any part of the sheath?