Talk:Skyhook (structure)

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could it be possible to create a skyhook? a 100 mile long cable attached to a space station.Along which tractor units powered by a giant flywheel,which will partsially send these units into orbit or at least half way {the rest of the way they drag themselves} i personally think its not too far fetched all it needs is Bill gates to fund it and we'll have one in orbit within 10 years.where are the Brunnels and the Stevensons when you need them.I betcha if the victorians had even a fraction of the technology that we do.they would have put one up.without worrying about micro meteors they would have delt with those when the time came instead of worrying about them on computer simulation.

Depends on the materials you use. Currently, no.

The space station would have to be somewhere beyond the geostationary orbit to keep the cable up. That gives us at least 35786km of cable. I do not know what kind of cable you are thinking of - let's take for example a high tech climbing rope, which is comparatively lightweight and sturdy. It weighs some 62g/m, and can hold a few tons of weight. At 35786000m of rope, it will have a mass of 2219t. Even though gravity diminishes the more you approach the orbit, you see that it is not even close to holding it own mass. -- 195.37.79.52 11:04, 21 June 2006 (UTC)

The factor of merit that applies to materials in this application is essentially (yield_strength/density), which, once divided by acceleration of gravity g, becomes a length l -- the length of a uniform cable that can support its own weight without breaking. For all current "normal" engineering materials, this is much much less than the radius of the Earth.

Oceanographers encountered this problem decades ago, as they lowered long instrument-carrying cables into the abyss from ships. I suspect the 1966 letter in Science (from Scripps Institute of Oceanography) was partly inspired by their experience. Their solution was to use a tapered cable: as you go up, the diameter of the cable increases so it can always support the weight below, and never breaks. It is easy to show that this leads to a cable design in which the area of the cable grows exponentially, as you go up against gravity. The exponential scale length is essentially just the factor of merit length mentioned above. Bottom line is that the total mass required grows exponentially with the height of the cable, and inverse exponentially with the scale length parameter.

Since gravity changes with height for the space application, you have to multiply length as you go up times the local effective gravity, which includes both the Earth's g, diminishing as 1/r², and also the centrifugal acceleration due to rotation, which acts upward and is proportional to r. This must be summed (integrated, that is) as you go up.

For a non-rotating spherical gravitating planet, the sum -- with no centrifugal contribution -- is just the radius of the planet, times the surface gravity. We may call this the "potential height" H to be overcome. For the Earth cable extending to geosynchronous orbit (GSO) and rotating at 1 revolution per day, the accumulated centrifugal effect reduces the total by about 20%, to something like 5500 km equivalent 1 g height. Upshot is that for normal engineering materials, the exponential growth kills you as the total mass for a cable with a macroscopic load carrying capacity comes out literally astronomical. But—the good news—is that for carbon nanotubes the Earth-to-GSO case looks challenging, but maybe possible.

Thus we are awaiting the development of real engineering materials that we can actually buy, with yield strengths we can trust, before we can estimate the total mass, and the cost. Wwheaton 01:34, 29 August 2007 (UTC)

It seems to me this whole subject should be under space exploration, as it is pretty remote from any kind of known or terrestrial architecture. I look forward to the day when "Space Architecture" becomes a recognized discipline!

Also, for the Earth-to-GSO case, there are big problems due to the hundreds of billions of dollars already invested in satellites (assets) below GSO (not to mention the tremendous amount of accumulated junk from dead satellites and collision debris), which will pose a constant threat to a surface-to-GSO cable. All that must be pretty much cleared out before the surface can be reached by a cable coming down from above (as it would have to be built in practice).

This main article needs to be expanded to cover the general subject properly, as it is a shadow of the Lunar_space_elevator article that really should build on it. Yet the lunar application has received much less attention, although from lunar surface over Earth-Moon L1 it is vastly easier, as although the length is great, the exponential growth issue mentioned above is not a problem due to the low g and correspondingly small H involved.

The statements and numbers from the previous remark addressing the June 2006 discussion are published in the literature somewhere, but essentially off the top of my memory and/or from my own calculations. I hope this sort of information, perhaps with a caveat, is acceptable for "talk" pages? Anyway, do beware, as I am still new to the Wiki game. Wwheaton 01:34, 29 August 2007 (UTC)

After yet a little more looking around, I see that the really substantial articles on this subject are under space elevator and tether propulsion. I prefer "skyhook" personally for the configurations attached quasi-statically to a planet or satellite surface, but in view of the existing pages, maybe this one should be suppressed, and simply redirect to the appropriate section of the space elevator page? Wwheaton 06:06, 29 August 2007 (UTC)

[edit] A Skyhook is not a space elevator

There is a large conceptual error in this article. The term "skyhook" should not be used interchangeably or as a subset of "space elevators". The term originated from early cable and hook systems the U.S. Air Force used to retrieve packages and people from the ground and midair into cargo aircraft. http://en.wikipedia.org/wiki/Fulton_surface-to-air_recovery_system Likewise in orbital skyhooks, a moving hook grapples with a cargo to be lifted into orbit from the ground or midair. Lazyquasar 02:18, 25 September 2007 (UTC)

I deleted the incorrect sentence. Lazyquasar 02:42, 25 September 2007 (UTC)

I retract the above statement that a "skyhook" is not a "space elevator". Apparently the terms have been used almost interchangeably for quite a while. http://www.frc.ri.cmu.edu/~hpm/project.archive/general.articles/1987/skyhook.ltx It would seem to me that to begin increasing understanding of this technology it would be useful to restrict the use of the term "skyhook" to techniques similar to the moving capture technology that used it originally and the term "space elevator" to stationary attached structures/tethers similar in technical approach to the traditional elevator. What do others think? Lazyquasar 14:17, 25 September 2007 (UTC)

This engineering paper [1] restricts itself to the terms "tether". When the tether is anchored to Earth then it is referred to as an "elevator" or "beanstalk". Lazyquasar 14:24, 25 September 2007 (UTC)

This engineering paper[2] has a short section at front on history and terms "beanstalk" and "skyhook" and "space elevator". Lazyquasar 14:29, 25 September 2007 (UTC)

This engineering paper uses terms rotating space tethers and when tether is anchored to lunar surface refers to the ensemble as a "Lunar Space Elevator". Lazyquasar 14:37, 25 September 2007 (UTC)

Bah! This paper[3] uses the term "Skyhook" as the generic category and then details engineering approaches to building a space elevator ... i.e. a structure or tether anchored to ground. Structure perhaps supported dynamically by internal momentum exchange mechanism. Lazyquasar 14:52, 25 September 2007 (UTC)

More terminology. "Orbital Slings", "Rotovator", Nice diagram showing basics of skyhook or orbital tether operation. Lazyquasar 15:02, 25 September 2007 (UTC)

Bibliography (with many online links) of tech papers on space tethers[4] by a company attempting to patent and control space tether technologies. These seem limited to orbital transfer tethers technically feasible today. Lazyquasar 15:07, 25 September 2007 (UTC)

No help here[5], nice diagrams though. This person at NASA appears to define "space elevator" as anything that changes potential energy in a gravity well. Lazyquasar 15:14, 25 September 2007 (UTC)

Speculative design of a skyhook structure with a dock replacing the traditional grappling hook.[6] Tourists then take an elevator up the skyhook to the orbital waystation on way to elsewhere. Lazyquasar 15:21, 25 September 2007 (UTC)

Authur C. Clark, when writing for popular audiences, uses the terms interchangeably. "The space elevator (alias Sky Hook, Heavenly Ladder, Orbital Tower, or Cosmic Funicular)" [7]] No mention of space tethers, only ground to orbit applications. Lots of good historical detail and basic science and engineering regarding elevators. Lazyquasar 15:28, 25 September 2007 (UTC)

2001 Conceptual design of a "Tether Launch System" between Earth and Mars. No use of term "Skyhook". Lazyquasar 15:43, 25 September 2007 (UTC)

Pearson[8] identifies the term "skyhook" entering the nomenclature ... "Unaware of the work of Artsutanov, a group of American oceanographers led by Isaacs [7] independently discovered the concept in 1966 and proposed a much smaller-scale version which they called a ”skyhook.” They proposed a pair of fine wires which could be alternately raised and lowered by ground-based machines to ”walk” payloads into orbit, and performed a static analysis of the wire strength requirements." The time frame seems appropriate for the term to have been borrowed from U.S. Air Force skyhook operations but it could have been original. Lazyquasar 15:59, 25 September 2007 (UTC)

Basically, you should just copy that lot into the article and tidy it up a bit. The use of the term is really quite inconsistent.WolfKeeper 22:15, 25 September 2007 (UTC)