Talk:Space Transport and Engineering Methods/Space Elevator

Skyhook
What's the vertical component of skyhook tip velocity over a time interval you consider reasonable for a launch vehicle to "dock" or "hook on"?

Suppose it has a 500km radius, with 1200sec full revolution period. Suppose you could work things so perfectly that the docking interval is just 10 seconds, or 1/120th of a revolution. 2*PI/120 angle. Half that descending, half rising, or PI/120 for each 5sec. The vertical distance travelled in 5 seconds is 500000(1 - cos(PI/120)) = 171m.

Even if you got the docking interval down to 2 seconds - one second descending, one rising - that's 1/600th of a revolution, or PI/300 angle. PI/600 each descending/rising. 500000(1-cos(PI/600)) = 6.85m vertical displacement in 1 second.

This is a big enough design consideration that it needs to be called out explicitly. Some have envisioned the Skyhook as being like a docking bay that a rocketplane lands in/on - not likely to work. It'll probably have to be more like a literal hook catching a loop on the end of the skyhook.

--TomCraver (discuss • contribs) 03:09, 2 June 2012 (UTC)


 * This has already been addressed under the heading Design Components > Structure > Landing Platform, but I added additional words about a capture net, navigation, and landing accuracy. Perhaps the conceptual difficulty is "docking" vs "landing"?  The former requires an exact position, the latter, like an airplane runway, has some tolerance in position.  I always assumed the landing is automated and you use things like radar/lidar and optical sensors to get your position accurate enough to hit the landing zone. Danielravennest (discuss • contribs) 20:55, 2 June 2012 (UTC)

Orbital Slingshot
Another tether based system of potential value is the orbital slingshot. This would take advantage of the tendency of a long object to auto-rotate from horizontal to vertical orientation with the center of mass at orbital velocity, due to "tidal" effects.

A relatively light weight vehicle would dock with a much more massive "orbital momentum bank" (likely consisting of discarded rocket stages left at the bank with each launch), and be hooked to a reel of tether. The vehicle would be pushed out to a somewhat higher orbit, where it would fall behind the momentum bank, with tether being paid out at a matching rate.

After sufficient tether has been paid out, it would be braked to a halt, putting it under tension. The momentum bank would slow and fall inward, while the vehicle would accelerate and fall outward, to be released at the desired orientation and velocity to transfer to a higher orbit. The tether need not be long enough to reach the ultimate orbit, as the vehicle will be "slung" outward. This transfer could be relatively fast - possibly useful for slinging crewed craft through the van Allen belts.

The momentum bank would lose velocity in this maneuver, but could use highly efficient thrusters (plasma, ion, magnetic) to recover that loss over an extended period.

If the momentum bank uses an elliptical orbit (cheaper for the launch vehicle to intercept), it should be possible to insert objects into near-circular orbits by slinging at apogee. Or the vehicle would reserve fuel to circularize orbit.

A couple of momentum banks could be used in series the achieve higher orbits or greater final velocities.

This needs some more math done to determine useful configurations.

--TomCraver (discuss • contribs) 03:09, 2 June 2012 (UTC)


 * Description of basic concepts should go in Part 2: Transport Methods. Part 4 is intended to be an extended example of a series of systems with worked out details.  So go ahead and insert your above concept in the appropriate place, even if you don't have all the numbers worked out. Even if it turns out not to be feasible, it is useful to record that someone thought it up, and then proved it's useless.  That will save future designers from chasing a bad idea, or prod them to think of a better version. Thanks for your comments, I always hoped other people would contribute to this book. Danielravennest (discuss • contribs) 21:08, 2 June 2012 (UTC)


 * The momentum transfer slingshot discussion has been moved to Part 2 of the book in the Structural Methods page (concept 2b). As mentioned in my previous comment, general transportation concepts belong in Part 2 of the book, while Part 4, of which this is a page, is a specific combined system approach. Each system in the combined set builds on the previous ones, and particular numbers are worked out as examples.  On the Structural Methods page I added some paragraphs about structural dynamics for space elevators.  They will be important for any elevator design, but especially so for one like this idea, because parts will be extending and swinging. Danielravennest (discuss • contribs) 14:00, 20 June 2012 (UTC)

Nomenclature Collision in Paul Birch's ORS Papers
I was just rereading Paul Birch's papers on Orbital Ring Systems, which are available here. The way he uses 'Skyhook' seems inconsistent with how you are using it here. His use of the term seems to be to refer to a hook that is attached to a maglev type coupling device that is attached to a short space elevator (Jacob's Ladder).

Relevant diagram: Fig 2 from the first paper.

So it seems like there are a total of at least three kinds of so-called Skyhooks:


 * 1) "Rotovator", which tumbles along through its orbit and dips to pick up a load at nearly zero relative velocity
 * 2) Tidally stabilized / vertical tether, which hangs down and can be latched onto by a moving craft such as a spaceplane
 * 3) A hook on a geostationary magnetic carriage which rides a (hyper)orbital mass stream, which is designed to attach to a short space elevator ("Jacob's Ladder")

Honestly, his nomenclature is kind of dated throughout. It could possibly benefit from republishing under more updated terms. "Orbital ring system" is astronomy terminology already (what else does Saturn have?). Skyhooks are supposed to grab payload near earth, not serve as joints to something in space. "Bootstrap" (Part II section 3) more intuitively to us today means manufacturing stuff in space from space resources, but in that context he manages to use it in contrast to that. "Jacob's Ladder" doesn't sound like a serious term to me (almost as bad as "Santa Clause Machine").

In addition, his suggestion of a solid ballistic wire stretching around the world doesn't make much sense (pellets would be easier to stabilize and likely much easier to scale up from a small starting point). Lsparrish (discuss • contribs) 01:38, 27 October 2016 (UTC)


 * There are number of other meanings for skyhooks noted in Wikipedia, and terminology for large space structures in general is confused. For example, NASA generally calls them "Tethers", others refer to all types as "Elevators", etc.  The way I think of them is a "tether" is a flexible cable connecting two points or objects in space.  An "elevator" includes some kind of structure, which may be flexible or rigid, and also has some method to change the potential and kinetic energy of a payload.  Large space structures in general may be classified by length, rotation rate, and where their center of mass is located.  The classic space elevator is then (60,000 km, 24 hours, 35,000 km altitude above Earth).  This is a special case where the bottom end has zero velocity relative to the surface.  In general, though, all three values are design variables, which may be chosen to suit the problem being solved.  Danielravennest (discuss • contribs) 22:33, 27 October 2016 (UTC)