Date: Sun, 4 Feb 1990 17:11-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #43 Contents: Marc Ringuette Update on space-tech Marc Ringuette SSX (material from sci.space) John Roberts Re: SSX Henry Spencer Re: SSX Peter Scott Tether papers Marc Ringuette Launch Loop Tom Neff Hula Hoop Marc Ringuette Re: Hula Hoop Paul Dietz Re: Launch Loop Marc Ringuette Re: Launch Loop ------------------------------------------------------------ Just in case any of you are interested, here is an update on what's up with the mailing list. years of operation: 1.5 number of messages: 360 number of digests: 43 space-tech raw list: 170 people space-tech digest: 50 people I've archived all the digests, and prepared excerpts on these topics: EM Launchers Tether Propulsion CMU Mars Rover High Velocity Guns Mars Mission Ship Design If you want any excerpts or back issues, just send mail to space-tech-request. If you'd rather talk to a machine, Todd Masco has archives of SPACE Digest and space-tech available for anonymous ftp from fed.expres.cs.cmu.edu, in directories space/SPACE-Digest and space/space-tech. /////////////////////////////////////////////////////////////////////// /// Marc Ringuette /// Carnegie Mellon University, Comp. Sci. Dept. /// /// mnr@cs.cmu.edu /// Pittsburgh, PA 15213. Phone 412-268-3728(w) /// /////////////////////////////////////////////////////////////////////// ------------------------------ [ This was posted on sci.space. At the end is some discussion about who was involved in the proposal. Does anybody know whether a lightweight vehicle with a huge fuel tank is a realistic option for SSTO, as they claim? --Marc ] From: bpistr@cgch.UUCP Subject: SSX: Space Ship Experimental (summary) Date: 16 Jan 90 09:36:57 GMT Sender: usenet@ucbvax.BERKELEY.EDU >Organization: Ciba Geigy ZIT (Central Engineering) Basel, Switzerland The following was extracted from the Byte Information Exchange in the 'space' topic. The author is one of the reigning space technology gurus in that conference. I thought it might be of interest to readers of this list, so I'm passing it along... Apparently this vehicle (SSX) has been approved for concept validation studies by SDIO (the "Star Wars" people), as a cheaper possiblity for access to space. (God knows we need one!). US Vice President Dan Quayle, who seems to be the administration's point man for space, has made some supportive comments about the need for lower cost access to space, etc., so far without referring to this project by name, anyway. ========== space/long.messages #750, from hvanderbilt, 13708 chars, Fri Jan 12 02:24:37 1990 ---------- Space Ship Experimental The Case For SSX Rockets have been our only way into space for over thirty years. They've done the job, but recent events have made it all too clear that rockets as we know them have problems. Current rockets are hideously expensive, costing thousands of dollars per pound of payload. They're unreliable, with the loss of one mission in twenty par for the course. They're inconvenient as hell, with launches having to be booked years in advance. These problems are not inherent to rockets. Most of our current space vehicles were originally designed over thirty years ago as ballistic missiles. Their designs reflect both the limits of fifties technology and their original military missions. Fifties missile design habits persist to this day, despite changing missions and huge advances in the available technology. Many of our current problems with rockets are a direct result of approaching space vehicle design and operations as if nothing has changed in the last thirty years. Thirty years of progress in rocket engines and lightweight structures, combined with a fresh approach to the problem, can give us space vehicles far cheaper, safer, and more flexible than we're used to. One of our best shots at doing this soon is a project called Space Ship Experimental - SSX. We don't need ten or fifteen years of research before we can build SSX. All the technology and much of the actual hardware is available off-the-shelf. For about a billion dollars over four years we can build and fly SSX prototypes. If SSX works even half as well as predicted, SSX-type vehicles will be a revolutionary improvement in our access to space. Those are pretty strong statements to take on faith. What makes SSX so much better than our current rockets? The SSX Concept The most important difference between SSX and our current rockets isn't SSX's unconventional design, but rather the goals of the design: SSX is a fully reuseable, "savable", Single-Stage-To-Orbit (SSTO) vehicle, designed from the ground up to be operated more like an advanced aircraft than like a traditional rocket, with quick turnarounds between missions by a ground support crew of a few dozen. SSX's advantages in cost, reliability, and flexibility stem from these characteristics. SSX achieves these characteristics with a remarkably simple, uncluttered design. SSX Described SSX is a wingless SSTO rocket that takes off and lands vertically. The shape is a blunt-nosed cone about fifty feet high, with a wide, slightly rounded base just under thirty feet across. The base is covered with heat- shield material; a ring of twenty or so rocket vents pierces the heat shield about one-third of the way in from the edge. These rocket vents combine with the vehicle's base to form an "aerospike" engine, a distinctly non-traditional type of rocket motor. Unlike a traditional rocket motor with its bell-shaped expansion nozzle, an "aerospike" engine lets its exhaust gases expand against the aft surface of the vehicle. Aerospike has several advantages for SSX: An aerospike motor compensates for altitude automatically, maintaining high efficiency from sea level on up to vacuum, unlike a conventional rocket motor. Another advantage is that since the aft surface of SSX has to stand the hot rocket exhaust gases anyway, it can double as a reentry heat shield. Finally, aerospikes can match a conventional engine's efficiency at much lower operating pressure, allowing lighter, cheaper, more reliable fuel pumps and combustion chambers. Aerospike engines have been built and tested on the ground, but have never flown in a full-size vehicle. A key factor in how well SSX works is how close actual aerospike efficiency comes to the theoretical predictions. SSX stands on four retractable legs, rather like the Apollo Lunar Module. The bottom three-quarters of the vehicle is fuel tank and engines, with cargo and crew carried in the nose. The whole thing looks more like a fifty foot tall egg with legs than it does any traditional rocket. SSX takes off vertically from a fairly simple launch pad. The pad will support its launch weight of about 250 tons (about nine-tenths of this is fuel) over a flame trench that channels away the rocket exhaust safely. No complex gantry or multiple umbilical connections are needed, as SSX's avionics are self-contained with multiple redundancy and built-in self-test features, modeled more on airliner electronics than on current throwaway rocket controls. SSX is like an airliner another way: It is "savable". This means that SSX is designed so that, like an airliner, if it loses an engine, it can abort the mission and land safely, even at the most vulnerable moment in a flight, taking off with full fuel tanks. Current rockets that lose an engine on takeoff tend to become smoking holes in the ground. SSX lands vertically under rocket power after doing a largely unpowered aerodynamic reentry. With most of its fuel gone, SSX is light enough that it can use the same steering technique as the Apollo reentry capsules, "gliding" on its broad flat base and controlling direction by tilting the whole vehicle slightly on its axis. Apollo was able to achieve pinpoint accurate splashdowns this way. By the time SSX has descended to airliner altitudes, it will have slowed to a few hundred miles per hour on air drag alone. Lighting the engines for the last few miles of controlled descent will require very little fuel and only a small part of the engines' takeoff power rating. Vertical landings on rocket power were extensively tested and proven in the Apollo Lunar landers; SSX will be able to land on any hard flat surface a hundred yards across. Single Stage To Orbit (SSTO) Multi-stage rockets have two advantages over an equivalent SSTO. First, for a given payload and destination, a multi-stage rocket can be made significantly smaller than a single-stager. Breaking the rocket up into stages and dropping each stage as it runs out of fuel will reduce weight and increase performance considerably for the later part of the flight. The size advantage of multiple stages is greatest for missions where rocket motor performance is stretched to the limit. This was the case in the fifties; the single-stage equivalent of an early three-stage rocket would have been five or six times larger at takeoff. The size advantage decreases as motor efficiency improves and as structure weights drop, however. Our best rocket motors are about 50% more efficient than the best of thirty years ago, and we've made huge advances in lightweight high-strength structures. SSX takeoff mass will be less than twice that of an equivalent multi-stage expendable booster. One of the most pernicious holdovers of the fifties "missile mentality" is the assumption that the best rocket for a given job is the smallest one possible. Military missiles may need to be as compact and portable as possible, but space launchers don't, and trading away simplicity and reliability for minimum takeoff weight in a launcher makes no sense at all. Most of the extra takeoff mass of an SSTO is fuel, and fuel is cheap. An SSTO is simpler to operate, and much simpler to make reuseable. Multiple stages pretty much have to be expendable. Making dropped stages recoverable negates much of the size advantage, due to the extra weight of the recovery provisions. Nobody has yet come out ahead of the game trying to recover and reuse a dropped rocket stage. Even in an expendable, the weight and complexity of the extra engines and stage interconnection/release hardware hurts cost and reliability. Dropping stages on the way up also severely limits where you can launch from and in what direction. You end up confined to sites with a lot of wide open space downrange, like Kennedy and Vandenberg. An SSTO can fly from anywhere the locals don't mind the noise too much, and it can launch in any direction without worrying about flying over populated areas, since it isn't dropping junk all over the landscape. Multi-stagers' second advantage is that traditional rocket motor nozzles have to be sized for optimum performance at some particular altitude, and lose considerable efficiency elsewhere. Multiple stages allow matching each stage's motor to its operating altitude. An SSTO rocket needs either a motor with high enough efficiency that the losses can be tolerated, different motors for different altitudes, or a motor that compensates for altitude. SSX takes the last approach; a major advantage of the "aerospike" engine is that it automatically compensates for altitude, operating efficiently all the way from sea level to vacuum. Reusability and Savability The obvious advantage of reuseability is cost. No more throwing away expensive aerospace hardware after every mission. Imagine the cost of airline travel if 747's were scrapped after one flight! Reuseability alone is not enough, though. Airfares would still be outlandish if a 747 took months of work by thousands of mechanics between flights. Savability requires simple rugged systems with multiple redundancy; practical reuseability requires design margins large enough that equipment won't need to be overhauled after every flight. Combine these qualities with extensive built-in self-test capability, in a basically simple system like SSX, and you reduce maintenance requirements a lot. SSX is designed to be readied for flight by a few dozen technicians in a week or so, cutting personnel costs to a fraction of what we pay for the standing armies that operate our current launchers. A less obvious advantage of reuseability plus savability is reliability. Expendables get minimal flight testing during development because each flight means using up a vehicle. Some bugs won't be found until later, and the ones that do show up during test are tough to diagnose because as often as not, all that's left is a tape full of telemetry data and a smoking hole in the ground. A savable reuseable like SSX can have all the flight testing it needs, gradually working up from short hops with minimum fuel through suborbital flights and finally orbital missions. This conservative incremental flight test schedule, combined with savable design, means that bugs generally won't prevent a safe landing followed by hands-on bug fixing. SSX will enter operations far more thoroughly tested than current rockets. Even after an expendable's design bugs are swatted, every one launched is fresh from the factory, with no test flights to catch any flaws that got past QC. Operational SSX-type vehicles will be more reliable because the individual vehicles can be thoroughly flight tested out of the factory as well as after repairs. This will also save on personnel costs; a large part of the standing armies that fly current rockets spend their days triple-checking and documenting every last step of the process, trying to make up for the inherent unreliability of their vehicles, or failing that to at least have some record of what went wrong. Ballistic Versus Winged SSX is a ballistic vehicle; it has no wings and relies almost entirely on rocket thrust to fly. SSX's reentry "crossrange" - the distance it can depart from its previous orbital path before landing - will be less than that of a winged vehicle like Shuttle, but still several hundred miles. Combined with SSX's small landing field requirements, this crossrange should be adequate to allow safe emergency landings. There are a lot of parking lots out there... Ballistic flight allows SSX to use a very simple shape, easy to design and build light and strong, with very simple predictable aerodynamics. SSX should be much cheaper and quicker to develop than an equivalent winged vehicle. The lessened atmospheric maneuverability is a small price to pay. A ballistic lands and takes off vertically, giving SSX a unique capability: Park one SSX in low Earth orbit, refuel it with 20 or so SSX fuel tanker flights, and the refueled SSX can make a round trip from Earth orbit to the Lunar surface and back, carrying cargo in both directions. A refueled SSX can also function as an orbital transfer vehicle, carrying payloads to and from geosyncronous orbit. Rocket Versus Airbreathing Rockets have some of the same advantages over airbreathing launchers as ballistics do over winged vehicles. Rockets take less time and money to develop, and rockets can operate beyond low orbit. Again, the lower atmospheric performance is a small price to pay. SSX and NASP SSX is a useful hedge against delay or poor performance of NASP, and if both succeed, SSX's deep space capability will be a useful complement to NASP. SSX can be ready a lot sooner at lower cost than NASP, since SSX is much less complex and requires less advanced technology. SSX won't necessarily be at a fatal economic disadvantage even after NASP is a roaring success, since SSX's greater fuel consumption may well be offset by the higher initial cost of an NASP-type vehicle. We should develop both; each has a role to fill. ======= ======= Date: Tue, 16 Jan 1990 12:48-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: bpistr%cgch@uunet.uu.net Subject: Re: SSX: Space Ship Experimental (summary) Do you know where the SSX proposal came from, and who did the work on sketching the design? ======= ======= Subject: Re: SSX: Space Ship Experimental (summary) To: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU Date: Wed, 17 Jan 90 9:36:43 MEZ From: "Joseph C. Pistritto" Mailer: Elm [revision: 64.9] As far as I know, the idea was mainly being pushed by a fairly offbeat group, mainly 'High Frontier' a pro-SDI organization led by Retired General Graham. Dr. Jerry Pournelle had a hand in getting it pushed into the formal study phase. (Yes, that's the science fiction author I'm talking about). The Air Force did some studies of the rocket (aerospike) design like 10 or 15 years ago, including building a number of scale models, etc. I will post more of the information as it appears. The active discussion of SSX is in the 'SPACE' forum on BIX, the Byte Information Exchange. Unfortunately this is not internet available, it's a commercial service, but they've recently gone to a flat-rate price structure which makes it somewhat easier. I'm on that and Compuserve as well. -jcp- ====================================================================== Joseph C. Pistritto 'Think of it as Evolution in Action' Ciba Geigy AG, R1241.1.01, Postfach CH4002 Basel, Switzerland Internet: bpistr@cgch.uucp Phone: (+41) 61 697 6155 Bitnet: bpistr%cgch.uucp@cernvax.bitnet Fax: (+41) 61 697 2435 From US: cgch!bpistr@mcsun.eu.net ======= ======= From: mvp@v7fs1.UUCP (Mike Van Pelt) Subject: Re: SSX: Space Ship Experimental (summary) Date: 16 Jan 90 22:47:07 GMT Reply-To: mvp@v7fs1.UUCP (Mike Van Pelt) In article <9001121009.AA01853@zit.cigy.> bpistr@cgch.UUCP writes: > Space Ship Experimental > The Case For SSX Fascinating. This sounds a whole lot like the "Phoenix" proposal that Gary Hudson was involved with a number of years ago. Is it the same? Last I heard, Max Hunter was connected with it in some way. -- Mike Van Pelt I would like to electrocute everyone who uses the Headland Technology word 'fair' in connection with income tax policies. (was: Video Seven) -- William F. Buckley ...ames!vsi1!v7fs1!mvp ======= ======= From: henry@utzoo.uucp (Henry Spencer) Subject: Re: SSX: Space Ship Experimental (stolen propaganda?) Date: 17 Jan 90 19:30:36 GMT In article <13093.25b335f9@maven.u.washington.edu> games@maven.u.washington.edu writes: >The government wants 1 billion to do this? Gary Hudson says that he needs >only 25 million to get a prototype in flight... I think you may be confusing Phoenix with Liberty. (The former is Hudson's reusable SSTO spacecraft, the latter is his cheap expendable.) The projected bill for Phoenix development was always rather higher than that, unless my memory fails me badly. He was talking about costs comparable to an airliner, that is, a good fraction of a billion overall. >What I would like to find out is : Who is the brilliant guy that stole his >literature, and is passing it off as a new SSX? I strongly suspect it was done with his cooperation and support, given that Max Hunter (who is definitely involved) is a long-time associate of his. -- 1972: Saturn V #15 flight-ready| Henry Spencer at U of Toronto Zoology 1990: birds nesting in engines | uunet!attcan!utzoo!henry henry@zoo.toronto.edu ======= ======= [ That's the end of the material from sci.space. Does anybody know whether a lightweight vehicle with a huge fuel tank is a realistic option for SSTO, as they claim? --Marc ] ------------------------------ Date: Thu, 18 Jan 90 17:37:10 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@CS.CMU.EDU Subject: SSX It could work. As pointed out, fuel cost is a relatively small part of total launch cost. I'm more concerned about what they'll use for engines, and what kind of material they'll cover the bottom of the craft with that works as a heat shield, can withstand the thrust against it during takeoff, and doesn't need to be inspected/repaired between launches. I have a paper they put out, if I can find it. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ From: henry@utzoo.uucp To: CS.CMU.EDU!space-tech@cs.toronto.edu Subject: Re: SSX Date: Fri, 19 Jan 90 12:41:49 EST > ... does anybody know whether a lightweight > vehicle with a huge fuel tank is a realistic option for SSTO, as they claim? Doing SSTO by just cutting structural weight to the bone and having really big tanks has looked marginally feasible for a long time. It was looked at early in the shuttle program. The problem has always been that you end up with a large rocket carrying a small payload, meaning that any significant weight growth during development will have drastic effects on the payload capacity. It's always been judged overly risky. Doing it as an X-plane equivalent, which is basically what the SSX folks are proposing as I understand it, makes a lot of sense. There's no need to carry much payload, and an X-spaceship that can *almost* make it into orbit is still valuable for experimental work and proof of principle. The big problem with things like SSX has always been that nobody's ever flown one and the unknowns look daunting. Even an almost-successful experiment would have a large impact. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Wed, 24 Jan 90 12:08:49 PST From: Peter Scott Subject: Tether papers To: space-tech%daisy.learning.cs.cmu.edu@jato.Jpl.Nasa.Gov X-Vms-Mail-To: EXOS%"space-tech%daisy.learning.cs.cmu.edu@jato" Just went to an interesting presentation here by Dr. Paul A. Penzo, who has been funded for tether study for several years and has published a number of papers. Got to examine a piece of tether slated for a May '91 shuttle experiment: strands of copper around a Nomex core, sheathed in transparent insulation covered by braided Nomex and an outer layer of woven Kevlar. Anyway, here's the list. Sorry it's not in any standard biblio form, I'm not familiar with them. Penzo, P.A., "Overview of NASA Tether Activities", Int. Conf. 1989 Penzo, P.A., Ammann, P.W., _Tethers in Space Handbook - Second Edition_, NASA Hq, Code MD, May 1989 Penzo, P.A., "Design Options and Analysis of Variable Gravity Systems in Space", Paper 89-0100, AIAA 27th Aerospace Sciences Meeting, Reno, Nevada, Jan 1989. Ionasescu, R., and Penzo, P.A., "Space Tethers", British Interplanetary Society, _Spaceflight_, Vol 30, No. 5, May 1988. Ionasescu, R., Penzo, P., "Innovative Uses of Tethers in Space", Int. Conf. 1987. Penzo, P.A., "A Low Earth Orbit Skyhook Tether Transportation System", Paper AAS-87-436, AAS/AIAA Astrodynamics Specialist Conference, Kalispell, Montana, Aug. 1987. Penzo, P.A., "A Survey of Tether Applications to Planetary Exploration", AAS 86-206, Int. Conf. 1986. Penzo, P.A., and Mayer, H.L., "Tethers and Asteroids for Artificial Gravity Assist in the Solar System", _Journal of Spacecraft and Rockets_, Vol. 23, No. 1, Jan-Feb. 1986. Penzo, P.A., "Prospective Lunar, Planetary, and Deep Space Applications of Tethers", Paper 86-367, AAS 33rd Annual Meeting, Boulder, Colorado, Oct. 1986. Bekey, I., and Penzo, P.A., "Tether Propulsion", _Aerospace America_, Vol. 24, No. 7, p. 40-43, July 1986. Penzo, P.A., "Space Station Adaptability to Tether Applications", _22nd Space Congress Proceedings_, Apr. 1985. Penzo, P.A., "Tethers for Mars Space Operations", _The Case for Mars II_, Ed. C.P. McKay, AAS Vol. 62, Science and Technology Series, p. 445-465, July 1984. The handbook in the second reference is fairly thick and looks like a good buy. I can't help anyone who has trouble finding any of the above, sorry. Peter Scott (pjs@grouch.jpl.nasa.gov) ------------------------------ Date: Sun, 4 Feb 1990 02:28-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Launch Loop I'm sure many of you have heard of Keith Lofstrom's concept of the Launch Loop. I think it's incredibly cool, and I'll take a crack at describing what the principle of it is. 1. Kinetic Structures ===================== The physical basis of the concept is something which I call a kinetic structure. I'll explain it by example. Shoot a stream of water from a garden hose up in the air. It forms an arc. There is no need for material strength in the water: there's no tension or compression going on, but rather just the water's free-fall motion along the path prescribed by gravity. Imagine shooting a stream of water into a very high arc: it could go higher than you could build the tallest skyscraper, since it's not limited by the strengths of construction materials. Now imagine balancing a pie plate on top of the arc of water, so that it is supported by deflecting the water downwards slightly. The plate is suspended there, higher than you might have thought possible, by the force from the continuing deflection of the stream of water. 2. The Launch Loop ================== If you replace the stream of water with a segmented ribbon of iron, achieve the deflection of the stream by using magnets, and have two 'stations' suspended by the ribbon rather than a single pie plate, you have Lofstrom's launch loop. It is a structure about 2000km long and 80km high. The loop of iron runs along the earth's surface in one direction, is deflected upwards by magnets at an earth station, back parallel to the earth's surface by a station 80km high, downwards by another station, and back along the earth's surface. A --------->------------->------------->--------------- B / \ / \ / \ C ---------<----------<------------<--------------<---------- D ===============================Earth==================================== The Launch Loop. A and B are stations, 80 km high. C and D are deflector stations, 2000 km apart, on the ground. The segmented iron ribbon moves at 14 km/s. The horizontal sections, and the earth, are actually convex, not straight as shown. The whole loop of iron segments whizzes along at 14 km/s inside a vacuum sheath. The stations at A and B are held up by the force generated by magnetically deflecting the ribbon downwards; they are anchored to the ground by cables, which are needed for stability and to counteract the horizontal forces. 3. Say What? ============ I should head off your initial skepticism. This is no joke. The guy has worked out details of how you deflect the ribbon, what materials are required, how to anchor the stations, and all the other details. The idea has been reviewed by a lot of people, so if you think you see a glaring flaw, it's probably because I haven't conveyed the idea properly. The paper I have, AIAA-85-1368, has lots of numbers for everything. I'll mail it to you if you ask me for it. Some details that I should mention: - the iron ribbon consists of 200cm x 5cm x 1cm segments, which are slotted to fit into each other. - the ribbon undergoes no stress whatsoever; it is just a passive holder of kinetic energy. - starting up the launch loop is a difficult task, involving spinning up the ribbon while it is floating on the surface of the ocean. 4. Using the Launch Loop ======================== Once you have spun up this thing, what do you do with it? The stations themselves are useful things: they're outside the atmosphere, yet they are anchored to the surface by cables. You could put an observatory on one of them, and commute to it up and down the 80km cable. But the main use of the loop is to launch vehicles, weighing about 5 tons, including passenger vehicles. The idea is that the vehicle sits on the top section of track, and uses magnetic coupling with the moving ribbon to accelerate along the 2000km top portion until the desired velocity is reached (which could be orbital velocity or escape velocity). So to get into orbit, you winch yourself up a cable to station A, hop in a car, get accelerated up to orbital velocity on the cable, and let go. Because the loop is so massive, accelerating a vehicle doesn't decrease its velocity much; the velocity is added back in by the ground-based magnets. The result is that ground-based electrical power has been used to send a payload into orbit. 5. Practical Objections ======================= Lofstrom talks of the project as if it might be real, and even gives some guesses as to construction costs ($2 billion total). My evaluation of this whole thing is: incredibly cool physical concept, incredibly impractical engineering problem. Particularly, the ocean-based leg of the system is a 2000-km-long vacuum sheath which must be flawless. Spinning up the thing involves getting the entire 4000-km-long loop going perfectly on the first try, dealing with weather and all sorts of unpleasantness, and gradually lifting the stations up to their correct positions. 6. My preferred version: the hula hoop ====================================== I think the ground-based section of this thing is the worst part. So I propose having the loop go all the way around the earth, in low orbit. The ribbon will be moving faster than orbital velocity, so that it can be deflected by the stations to hold them up. I'd say there should be about 60 stations spaced around the equator, each of them fastened by cables to the ground. The ribbon moves in a shape somewhere between a 60-sided polygon and a circle. In between stations, it flies in free fall. It's still a really complex device, but at least it isn't in the weather. To spin up this structure, you could start with the stations in low orbit, and gradually decelerate them to a standstill as the ribbon is spun up and starts to support them. I notice that Lofstrom references some articles in the L-5 news and JBIS which discuss this idea. 6. Any Questions? ================= This is such a tough thing to describe, I really don't know if this has turned out. Please send me your questions and comments via Email, and I'll see if I need to do any major additional explaining. ================ ================ ================ ================ ================ ================ What do you think? I'm fascinated at such a different way to look at the problem of launching things off the Earth. It's another one to add to our repertoire of how to get off the planet: - chemically propelled rockets/spaceplanes - laser propelled rockets - nuclear-bomb propelled rockets - EM launchers - chemically propelled gun launchers - fixed skyhooks - rotating skyhooks - launch loops Fun! \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\ Marc Ringuette \\\ Carnegie Mellon University, Comp. Sci. Dept. \\\ \\\ mnr@cs.cmu.edu \\\ Pittsburgh, PA 15213. Phone 412-268-3728(w) \\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ ------------------------------ From: Tom Neff Date: Sun, 4 Feb 90 09:39:17 EST To: space-tech@CS.CMU.EDU Subject: Hula Hoop > I think the ground-based section of this thing is the worst part. So I > propose having the loop go all the way around the earth, in low orbit. I thought the point of the Launch Loop was that it could be powered from, and launch payloads from, the ground. The Hula Hoop might be easier to construct, but how do you power it and how does it get anything launched? ------------------------------ Date: Sun, 4 Feb 1990 16:18-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Re: Hula Hoop > From: tneff@bfmny0 (Tom Neff) > > I thought the point of the Launch Loop was that it could be powered from, > and launch payloads from, the ground. The Hula Loop might be easier to > construct, but how do you power it and how does it get anything launched? This isn't a problem: the ~60 stations are all _stationary_ with respect to the ground, approximately 100km up, and are anchored by cables. You can run power lines and elevators up the cables. I should amend that: power isn't a problem once you've got it started up. It's probably really expensive to get it started. ------------------------------ To: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU Cc: space-tech@CS.CMU.EDU, dietz@cs.rochester.edu Subject: Re: Launch Loop Date: Sun, 04 Feb 90 10:02:08 -0500 From: dietz@cs.rochester.edu One of my complaints with the launch loop is what happens when it fails. Should the loop break anywhere, or should the airtight jacket spring a leak, all the levitated sections fall back to earth, spread over thousands of kilometers. IMHO, the launch loop idea is more feasible on the moon. The levitation magnets can be anchored to the lunar surface, and can be externally powered. The loop provides a nice way to store energy over the lunar night. And, the required loop velocity is lower, if all you want to do is get to lunar orbit. Some work at Argonne National Labs has been inspired by the launch loop. A fellow there named Hull and some coworkers have looked into magnetically levitated rings for energy storage here on earth. The concept is nice, since (for fixed centripetal acceleration) the energy stored scales as R^2, and the energy stored per ring + magnet mass scales as R. Hull found a nifty *passively* stable attractive magnetic levitation scheme (Lofstrom used active stabilization). The idea works like this. Let o and + denote cables carrying currents into and out of the page, and let - represent the iron loop. Then, there are two positions where the magnetic field of the currents support the loop against gravity: + o + o - - In the first position, the loop is stable against vertical perturbations but unstable against lateral perturbations. In the second, the opposite is the case. Hull noticed that if you alternate sections of the two types, then the net effect, if the loop is moving in the right range of speeds, is to make it stable in *both* directions. This is the principle of Strong Focusing, which is vital to the operation of modern particle accelerators (where alternating gradient quadrupole magnets focus particle beams). Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sun, 4 Feb 1990 16:18-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Re: Launch Loop I guess I'd be more interested in launch loops on the moon if I actually cared about being able to launch things from the moon. But it seems like a tidy little mass driver would be a better bet there in any case. ======== Paul correctly points out a really big drawback of the design, namely the fact that the thing has to work flawlessly, all the time, or the whole thing falls down. Any system which must be in continuous operation is far, far less practical than a system which just goes BANG and is done. /////////////////////////////////////////////////////////////////////// /// Marc Ringuette /// Carnegie Mellon University, Comp. Sci. Dept. /// /// mnr@cs.cmu.edu /// Pittsburgh, PA 15213. Phone 412-268-3728(w) /// /////////////////////////////////////////////////////////////////////// ------------------------------ End of Space-tech Digest #43 *******************