Date: Fri, 23 Feb 1990 06:23-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #48 Contents: Jordin Kare hydrogen fuel; space fountain Lou Adornato Re: space fountain George Herbert Re: space fountain Mike Williams Re: space fountain Lou Adornato Re: Kevlar slingshot Edward Wright Re: Kevlar slingshot Henry Spencer Re: Kevlar slingshot Paul Dietz Re: Kevlar slingshot Bill Davidsen SSX/Space Documents Todd Masco Re: SSX/Space Documents ------------------------------------------------------------ Date: Tue, 20 Feb 90 11:55:22 PST From: Jordan Kare To: space-tech@CS.CMU.EDU Subject: hydrogen fuel; space fountain Two short comments on the running discussions: At a recent conference (NIST conf. on Space Infrastructure) Max Faget (another of the grand old men of rocketry) made an interesting comment in response to a presentation on the ALS (which is hydrogen-fuelled). He noted (and this is very rough; I don't have notes handy) that there are severe problems associated with ground startup of hydrogen fuelled engines. Basically, you have to pre-cool all the pumps, etc., which means you have to flow hydrogen through them for some time before startup, which means you leak a significant amount of hydrogen into the nozzle volume, where it has a distressing tendency to mix with air and detonate when you go to ignite the engine. You can get around this (obviously; the Shuttle flies) but it requires extensive pad support and safety precautions. Hence he has a strong preference for hydrocarbon fuels for "low cost" launch vehicles -- at least for the first stage. Out in space, of course, venting hydrogen is harmless... Remember, you need a vehicle/system that is cheap to run, and "minor" costs for the Space Shuttle can easily dominate the cost of such a system. The "space fountain" -- a tower supported by accelerating and decelerating a stream of particles -- was studied in detail by Rod Hyde here at LLNL (where it is known as the Starbridge). It is one of a class of "dynamically supported structures"; the Launch Loop is another. Starbridge does have a large advantage over the Launch Loop in that it can be built incrementally from the ground. It has the large disadvantage that, as noted, it does not supply orbital velocity until it approaches geosynchronous altitude. Rod's designs _did_ go to GEO altitude, and included such features as redundant distributed solar power for the acceleration/deceleration system that keeps the thing up. He also did some calculations on non- equatorial (at least at the base) towers; they are possible, and they have wonderfully complex curved shapes to maintain the balance between spherically-symmetric gravitational forces, cylindrically-symmetric centrifugal forces, and the assorted forces associated with accelerating the particle stream.. Jordin Kare jtk@mordor.s1.gov jtk@mordor.uucp Standard disclaimers apply... ------------------------------ Date: Tue, 20 Feb 90 13:28:07 CST From: Lou Adornato To: space-tech@CS.CMU.EDU Subject: Re: Space Fountain Jim Van Zandt (jrv@sdimax2.mitre.org) writes: >I'd like to add one scheme to the list: the space fountain. The first >description I saw was in "Starquake" by Robert L. Forward (a sequel to >"Dragon's Egg"), and it was one of several devices described in "The >Barsoom Project" by Pournelle and Barnes (a sequel to "Dream Park"). Does anyone know of any serious papers on this? >If you get the idea I enjoy science fiction, you're right. I do, too, but I wonder if we shouldn't try to cite some more rigorous publications in space-tech. Science fiction writers have something of a reputation for playing fast and loose with the "details", like the stability of the Ringworld or the oxygen content of the Martian atmosphere. (Speaking of references, I noticed that an article from _Analog_ was cited as a reference to Lofstrom's paper. You'll notice that the full name of the publication (i.e. _Analog Science Fiction/Science Fact_) was NOT used. Looks like I'm not the only one who's a little gun shy on this topic.) Lou Adornato | Statements herein do not represent the opinions or attitudes Cray Research | of Cray Research, Inc. or its subsidiaries. lfa@cray.com | (...yet) ------------------------------ Date: Tue, 20 Feb 90 14:49:56 PST From: gwh@ocf.berkeley.edu To: lfa@vielle.cray.com, space-tech@CS.CMU.EDU Subject: Re: Space Fountain >I do, too, but I wonder if we shouldn't try to cite some more rigorous >publications in space-tech. Science fiction writers have something of a >reputation for playing fast and loose with the "details", like the stability >of the Ringworld or the oxygen content of the Martian atmosphere. Forward is a Physicist, and he's usually pretty careful about keeping his fiction accurate. And Ringworld was actively stabilized...the last book was had details on it [a fusion rocket system]. But i do agree. Keep the science fiction out unless is's rigorous. ******************************************************************************* George William Herbert JOAT For Hire: Anything, Anywhere: My Price UCB Naval Architecture undergrad: Engineering with a Bouyant Attitude :-) ------------------------------------------------------------------------------- gwh@ocf.berkeley.edu ||||||||||| "What do I have to do to convince you?"-Q gwh@soda.berkeley.edu ||||||||||||||||||||||||||||||||||||||||| "Die."-Worf maniac@garnet.berkeley.edu||"Very good, Worf. Eaten any good books recently?"-Q ------------------------------ Date: Tue, 20 Feb 90 22:43 EST From: MRW104@PSUVM.PSU.EDU Subject: Re: Space Fountain To: jrv@sdimax2.mitre.org Cc: space-tech@CS.CMU.EDU From: jrv@sdimax2.mitre.org Hmm... this fountain thingy sounds kind of interesting, but it leaves you with the problem of getting your payload into the right orbit. As Mr. Van Zandt said, You couldn't get into orbit directly from an earth-stationary tower unless it was 36000 km tall, which would put you into a geostationary orbit. You could reduce the apogee kick by making the tower lean (eastward, of course), although that would make it look _really_ silly. The advantage over a regular EML is that the payload can accelerate in a vacuum. With a length of 356 km and an acceleration of 9 g's (which when added to gravity would feel like 10 g's) you could reach a speed of 8 km/sec. Maybe the fountain wouldn't need to be taller than 20 or 30 km for inanimate payloads - but if they can withstand high accelerations at launch then they could survive an upward passage through the atmosphere as well. The only problem with this scheme is that if you do that, the payload would have a perigee of 20 to 30 km and a corresponding speed at periapsis of ___________________________ / G * Earth's Mass V = / -------------------------- P \/ Earth's Radius + 20 or 30 I lost my calculator today, so I can't tell you what that number is, but it's big-- atmospheric drag would slag any payload we could put up in less than 1 orbit. *********************************************************************** Mike Williams mrw104@psuvm.edu ------------------------------ Date: Tue, 20 Feb 90 14:43:29 CST From: Lou Adornato To: space-tech@CS.CMU.EDU Subject: Kevlar slingshot Would someone like to answer some questions on the Kevlar slingshot concept? I've always assumed that the idea is to spin up a sling carrying the payload, and release it when the angular acceleration is equal to orbital (escape?) velocity. My main questions are: 1) Will the whole sling be released or just the payload (i.e, is this going to work like David's slingshot, or like the hammer throw? Kevlar doesn't grow well on the moon, so the former is unlikely. 2) What is going to be swinging the sling? I can imagine some monster stresses on whatever the Kevlar is anchored in, especially at the moment of release. 3) What mechanism would be used to release the sling? Explosive bolts would need to be shipped from Earth, any other mechanism would need to be strong enough to hold, without damageing the sling 4) What kind of orbital collection system would be needed. Something fired balistically from a point on the Lunar surface is going to have a perilune of ~0 agl, so a first orbit retreival is going to be necessary. Thanks in advance. Lou Adornato | Statements herein do not represent the opinions or attitudes Cray Research | of Cray Research, Inc. or its subsidiaries. lfa@cray.com | (...yet) ------------------------------ Date: Tue, 20 Feb 90 16:10:01 CST From: "Edward V. Wright" To: lfa@vielle.cray.com, space-tech@CS.CMU.EDU Subject: Re: Kevlar slingshot I can't answer the first three questions, but as far as the collection system goes, I would assume the slingshot would use the sort of mass catcher that the mass driver uses. If you locate it at a Lagrange point there is no problem with first-orbit retrieval (i.e., if you miss, it isn't going to come around again and hit you in the back of the head). From: henry@zoo.toronto.edu Date: Wed, 21 Feb 90 14:27:31 EST To: space-tech@CS.CMU.EDU Subject: Re: Kevlar slingshot > 1) Will the whole sling be released or just the payload (i.e, is this > going to work like David's slingshot, or like the hammer throw? I believe the intent was to release just the payload. > 2) What is going to be swinging the sling? I can imagine some monster > stresses on whatever the Kevlar is anchored in, especially at > the moment of release. At the center you have a big electric motor with some nice heavy-duty bearings. :-) > 3) What mechanism would be used to release the sling? Explosive bolts > would need to be shipped from Earth, any other mechanism would > need to be strong enough to hold, without damageing the sling Last I heard (this isn't something I've kept up on, mind you), this was a tricky area. It ought to be possible to do it mechanically, without expensive and dangerous pyrotechnics. The hold-down clamps for the Saturn V were mechanical, not pyrotechnic, so there is precedent. > 4) What kind of orbital collection system would be needed. Something > fired balistically from a point on the Lunar surface is going to > have a perilune of ~0 agl... Unless it reaches escape velocity, in which case that's not an issue. In any case, the sorts of collectors envisioned for mass-drivers and such should suffice. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Wed, 21 Feb 90 16:49:09 -0500 From: dietz@cs.rochester.edu To: henry@zoo.toronto.edu Cc: space-tech@CS.CMU.EDU, dietz@cs.rochester.edu Subject: Re: Kevlar slingshot The problem I see with the Kevlar sling shot idea is the very high accuracy required. A payload shot to a mass catcher at the L2 point will be in transit for tens of hours. Small velocity errors will build up over time. The initial velocity will have to be precise to a few meters per hour; i.e., about 1 part per million. The mass driver scheme proposed to do this by carefully tweaking the trajectory of the payload after it left the launcher. But it seems to me the lateral errors in the slingshot will be much worse. If the slingshot is 10 meters in radius, spinning at 2.4 km/s, an error of .1 ms will cause a lateral velocity error of 24 m/s. Achieving an accuracy of .1 msec with a mechanical release seems difficult; if a mechanism must move 1 cm in that time to release the payload, it must accelerate at over 200,000 gees. Paul ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Thu, 22 Feb 90 08:25:06 EST X-Mailer: Mail User's Shell (6.5 4/17/89) From: davidsen@crdos1.crd.ge.com To: space-tech@CS.CMU.EDU Subject: There may be a better way >From: hack@lock.span.nasa.gov >Subject: SSX Documents? >All the recent discussion about the SSX proposals has me wanting to see >the real thing. I think that someone mentioned in Space Digest a while >back that he had a copy of a paper on it by one of the originators. If >the paper is uncopyrighted (unlikely) or if an address is available to >ask for permission to copy, I'd be willing to send out copies at cost >to netland readers of space-tech. Cost would be based on how much a >copy shop (Kinko's) would charge to repro it, envelopes and postage. >Then, I'd send out a copy to anyone who sent me the requisite amount. You may be able to get the documents scanned and converted to nice Emailable postscript. Vincent {someone} does this for cold fusion papers, and might be willing to do it for this group, too. It could then be available for ftp (best), or mail. Of course you can still send paper if people need it. This assumes that the paper is <10 pages, not tytpical size of the actual RFP ;-) -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) "Stupidity, like virtue, is its own reward" -me ------------------------------ [ That's Vince Cate here at CMU. I personally just prefer paper and US mail. --Marc ] ------------------------------ Date: Thu, 22 Feb 90 19:35:17 -0500 (EST) From: "Todd L. Masco" To: space-tech@CS.CMU.EDU Subject: SSX/Space Documents If somebody can get the SSX Document, or any other space-related documents that may be of interest, I'd be willing to put them on fed.expres.cs.cmu.edu in the space archives, for anonymous ftp. -- Todd L. Masco | Quanum Mechanics: The dreams stuff is made of. r022tm2b@cmccvb | tm2b+@andrew.cmu.edu ------------------------------ End of Space-tech Digest #48 *******************