throopw@dg_rtp.UUCP (Wayne Throop) (01/02/86)
> At the intersection point the masses are moving > with a relative velocity of ~6000 mph (~2.7 kps). A deceleration > of 5g for 1 minute will bring them to relative rest - which doesn't > seem too hairy. I was assuming that the join must happen in a few dozens of meters distance, or at most a few hundred meters. To happen over many tens of kilometers as proposed above is much more reasonable. But about the only reasonable thing I can think of that would provide that kind of interaction between two masses over that kind of distance is a skyhook variant of some sort. Can a currently-designable skyhook provide ~2.7 KPS of delta-v? I suspect so. I'm not sure how to position and maintain the skyhook (or any other "joiner" device) in the two masses scenario, but this is much more reasonable than what I read into the proposal at first. (I was led to imagine an inelastic colision of two relativly small, dense, balls of silly-putty. Splat! :-) But what is wrong with the more "traditional" scenario of an asynchronous skyhook in medium-high orbit? Once constructed, it could provide the couple-of-KPS-delta-v needed to modify a long eliptical orbit (or suborbital arc) into a more nearly circular orbit, and could be kept on station by performing the reverse delta-v on ballast masses. (Note that these ballast masses could be provided from a ground catapult, or from high orbit. Providing the ballast from the ground is quite similar to the two-masses scenario, but the "join" strictly speaking never happens, and the interaction between the cargo mass and the ballast mass (which in this scheme might also be a cargo mass!) can be time-delayed.) Question: Is a (ground-catapult / orbital injection skyhook) system more economical than a (ground-catapult / traditional injection via a reaction motor) system? Even with the orbital skyhook, the injection would probably have to be modified by a "trim" reaction burn to get really good and precise orbits, and the station-keeping activities for the skyhook are probably not trivial. Answer: I don't know. I expect there is some volume of traffic at which a skyhook would be more economical, but not at the low volumes we now have. Question: since synchronous orbital skyhooks are considered feasible for Mars and the Moon, why isn't more attention given to asynchronous orbital skyhooks for providing various delta-vs in orbital injection scenarios near Earth? Is the idea intrinsically non-feasible, or what? Answer: I don't know, but I suspect they are most useful if the ground catapult problem is solved, and ground catapults aren't too terribly feasible yet. Question: Why wouldn't an asynchronous skyhook allow a high-flying air-breather (or detachable part thereof) to be injected into LEO? Answer: I don't know that either, but it may have something to do with "drag". Also, feeding such a skyhook ballast wouldn't be cheap. Sigh. -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!dg_rtp!throopw
davidson@sdcsvax.UUCP (J. Greg Davidson) (01/05/86)
Wayne Throop's recent article on skyhooks asked a series of very good questions in regard to applying skyhooks in conjunction with catapults and guessed at some answers. I will repeat his questions with another set of (equally speculative) answers. From: throopw@dg_rtp.UUCP (Wayne Throop) Newsgroups: net.space Subject: Asynchronous orbital skyhooks (those two masses...) Date: 2 Jan 86 20:30:52 GMT Question: Is a (ground-catapult / orbital injection skyhook) system more economical than a (ground-catapult / traditional injection via a reaction motor) system? Even with the orbital skyhook, the injection would probably have to be modified by a "trim" reaction burn to get really good and precise orbits, and the station-keeping activities for the skyhook are probably not trivial. Answer: One would expect the operating costs of a skyhook to be much lower than that of a reaction motor. However, the development costs and system costs (targeting, orbit correction, etc.) need to be considered. Note that if orbital correction is needed, there is no hurry about it since the orbit will not decay quickly. As an example, a solar pwered ion rocket tug would be sufficient. Also note that this analysis will need to take into consideration the increased traffic that lower costs should generate. There are several technologies available for station keeping: (1) balancing the mass transfers, (2) electrical interaction with the Earth's magnetic field, (3) continuous boost from an efficient, electrically powered, low thrust reaction motor. Method (1) could include catching mass sent up by the ground catapult into different trajectories. Methods (2) and (3) might be powered by an on-site solar electric plant. Possibilities for (3) include ion rockets and mass driver thrusters. Question: since synchronous orbital skyhooks are considered feasible for Mars and the Moon, why isn't more attention given to asynchronous orbital skyhooks for providing various delta-vs in orbital injection scenarios near Earth? Is the idea intrinsically non-feasible, or what? Answer: NASA seems politically unable to devote visible resources to any unproven propulsion technologies, including tethers, light sails, ion rockets, etc., regardless of their technical merit. The major contractors mostly follow NASA's lead. However, other organizations, e.g., CALSPACE, the World Space Foundation, SSI, and many independent researchers are concentrating their research on these unproven, but much more promising technologies. Question: Why wouldn't an asynchronous skyhook allow a high-flying air-breather (or detachable part thereof) to be injected into LEO? Answer: A familiar scenario from previous articles on asynchronous skyhooks is a rendezvous between a 747 carrying a cargo module piggyback, and a tether. In addition to the slight savings in work for the tether, this keeps the tether comfortably away from the ground and reduces its penetration into the bulk of the atmosphere. I doubt that significant savings would result from getting any higher in the atmosphere. I suspect that its more cheaper to have the tether do all of the velocity change, than to develop a hypersonic aircraft for the rendezvous. _Greg J. Greg Davidson Virtual Infinity Systems (619) 452-8059 6231 Branting St; San Diego, CA 92122 greg@vis.uucp ucbvax--| telesoft--| davidson@sdcsvax.uucp decvax--+--sdcsvax--+--vis davidson@ucsd.arpa ihnp4--| noscvax--| ~
hogg@utcsri.UUCP (John Hogg) (01/06/86)
In article <70@dg_rtp.UUCP> throopw@dg_rtp.UUCP (Wayne Throop) writes: >Question: since synchronous orbital skyhooks are considered feasible >for Mars and the Moon, why isn't more attention given to asynchronous >orbital skyhooks for providing various delta-vs in orbital injection >scenarios near Earth? Is the idea intrinsically non-feasible, or what? I like it, you like it, and most readers of this group will too, but... if things go wrong, skyhooks fall DOWN. Remember the Skylab hysteria? If a skyhook breaks at almost any point in its rotation, one part goes up, and the other hits the atmosphere FAST. Kevlar cable will burn up in short order. Anything larger, such as payload, stands a good chance of reaching the ground. Again, WE all know how dangerous this is in the context of our daily existence, but there could be real political problems in putting something "large" up there with the tight safety margins required to make this feasible. Californian lawyers could have a field day out of it even if nothing happened. By the way, Kevlar makes fast sails, but 1) How do you protect it from sunrot without an excessive weight penalty? 2) What about LEO free oxygen? 3) How well does it behave at the temperature extremes to be expected in space? These aren't reasons why it "can't be done"; I'm just wondering whether anybody has made the appropriate calculations. -- John Hogg Computer Systems Research Institute, UofT ...utzoo!utcsri!hogg Standard disclaimer: the above may or may not contain sarcasm, satire, irony or facetiousness. It does not contain smiley-faces.
henry@utzoo.UUCP (Henry Spencer) (01/07/86)
> if things go wrong, skyhooks fall DOWN. Remember the Skylab hysteria? If > a skyhook breaks at almost any point in its rotation, one part goes up, and > the other hits the atmosphere FAST. Kevlar cable will burn up in short > order... As somebody (Clarke?) pointed out, a falling skyhook cable hitting atmosphere would be incredibly spectacular: a *sheet* of flame across the sky! Might be worth doing just so you could sell tickets... :-) -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
eugene@ames.UUCP (Eugene Miya) (01/07/86)
> > Answer: NASA seems politically unable to devote visible resources to > any unproven propulsion technologies, including tethers, light sails, > ion rockets, etc., regardless of their technical merit. The major > contractors mostly follow NASA's lead. However, other organizations, > e.g., CALSPACE, the World Space Foundation, SSI, and many independent > researchers are concentrating their research on these unproven, but > much more promising technologies. "promising" is a value judgment. Some of these areas have had "visible resources" depending at what budget level you looked. An ion engine was the only way to seriously consider a Halley mission, but then the President cut this, Ed Meese even came to talk to Goldberger at Caltech about this and other directions for JPL. We need more of these technologies. Question: how do you balance these new technologies with the "research" which flies on the craft? You have to argue with the geologist and the planetary scientist who want results: tried and true. It's not just NASA, we're just caught in the middle. > Question: Why wouldn't an asynchronous skyhook allow a > high-flying air-breather (or detachable part thereof) to be > injected into LEO? > > Answer: A familiar scenario from previous articles on asynchronous skyhooks > is a rendezvous between a 747 carrying a cargo module piggyback, and > a tether. . . . > than to develop a hypersonic aircraft for the rendezvous. > > _Greg Can't wait till the test Tethered Satellite goes up eh? Yes we are looking at Mach 27 vehicles, and yes we are looking at cables. We can use the bucks, however. From the Rock of Ages Home for Retired Hackers: --eugene miya NASA Ames Research Center {hplabs,ihnp4,dual,hao,decwrl,allegra}!ames!aurora!eugene emiya@ames-vmsb.ARPA General disclaimer: the above are the opinions of the author and not the Center or Agency. Any mention of commerical products does not constitute an endorsement and is only mentioned as a point of reference.
throopw@dg_rtp.UUCP (Wayne Throop) (01/07/86)
> Question: Why wouldn't an asynchronous skyhook allow a > high-flying air-breather (or detachable part thereof) to be > injected into LEO? > Answer: A familiar scenario from previous articles on asynchronous skyhooks > is a rendezvous between a 747 carrying a cargo module piggyback, and > a tether. I think the tether/skyhook in the subsonic scenario would have to be beyond current engineering practice. My intent here was to ask if it was feasible with an asynchronous currently-designable skyhook (say, of Kevlar) to boost a cargo into LEO without using a ground catapult or any non-reusable reaction thrusters. This seems to imply a hypersonic transport of some sort, since the best delta-v from the skyhook won't boost from the near-standstill of a 747 to orbit. Note also that the investment in the hypersonic transport development would be swamped by the skyhook development costs (or so I suppose). I agree that it would be less costly to use the skyhook for the entire delta-v, but this (as far as I know) just can't be done yet. I was proposing a hybrid system to "get our feet wet" with skyhook technology. So let me rephrase. Is it possible with 198x technology to get to LEO using a totally reusable booster and an asynchronous skyhook, and would this be cheaper than using disposable or partly disposable reaction boosters. In essence this question rests on three issues: Can enough delta-v be supplied by a skyhook to make a nearly-off-the-shelf (and completely reusable) transport workable? Can some plausible and nearly-off-the-shelf station-keeping mechanism for this skyhook deal with atmospheric drag, at reasonable traffic densities? Will the money needed to get the skyhook in orbit and the transport designed and built be plausibly fundable, either governmentally or privately? These questions are left as an excersize for the interested reader :-). -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!dg_rtp!throopw