Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from hogtown.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Sat, 9 Mar 91 02:15:48 -0500 (EST) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sat, 9 Mar 91 02:15:44 -0500 (EST) Subject: SPACE Digest V13 #247 SPACE Digest Volume 13 : Issue 247 Today's Topics: Space Flight Acceleration Regimes Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription requests, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 7 Mar 91 06:42:06 GMT From: agate!bionet!uwm.edu!linac!pacific.mps.ohio-state.edu!ohstpy!miavx1!bynum@ucbvax.Berkeley.EDU (Frank Bynum) Subject: Space Flight Acceleration Regimes Space Flight Acceleration Regimes Frank Bynum [*] (Dave O'Hagan), on Thu, 28 Feb 91 10:55 EST, in message to Leo J Irakliotis , who forwarded it to (Frank Bynum) Thu, 28 Feb 91 20:51:55 EST, writes: . . . >The problem that I wish to address is >the effect on living organisms under high acceleration. How can we >achieve substantial acceleration, for effective space travel, >without the destruction of the organism inside the speeding ship? > The only force that I can think of using to counteract this >extreme force of acceleration, is centrifugal force. My thinking is >that the centrifugal force will expand the organism and the force of >acceleration will keep it contained. > The propulsion would be an alternating blast from three separate >energy ports. Is any of this possible, or am I breaking an obvious >law? Thank you again for your time. > Sincerely [UNEF] > Dave O'Hagan It seems Dave O'Hagan was inquiring about strengths / weaknesses of idea for measures to reduce the effects of acceleration [on crew of humans?] which may be imposed by space flight methods. Would spinning systems to impose centrifugal 'forces' be helpful? Those who have seen many late show movies may perhaps recall seeing depiction of some notion of this type in a 1950's to '60's vintage film. It was based on the stories, _From Earth To Moon_; and _Around the Moon_ by J. Vern. (There were Hollywood updates stemming from the era when filmed. These included such as gizmos for nuclear propulsion, for use after launch, and a method for humans to not be crushed by the shock from launch via cannon blast. ) Note that linear acceleration in some direction, and centrifugal acceleration due to rotation, add as vectors. At a particular moment, radius, rotation angle combination, the 2 effects might perhaps add to zero. But at another instant and angle, the effects would combine together with the same sign. There are conditions in which imposing spin on a system to generate centrifugal 'forces' may serve useful functions. But the above does not happen to be one of them. However, lets review what are some of the various regimes of acceleration levels and durations encountered with space flight systems. Also note where centrifugal 'forces' may be helpful. Table: Accelerations in space flight accel/g0 magnitude duration description of situation 1 to 7; 5 - 20 min.; X-15, Mercury, Gemini, Apollo. up to 3-8; 1/12 - 1 min each; Planes in air combat dog fights. 1.5 to 3; 10 - 20 min. NASA Space Shuttle. [any_Per] 0.1 to 1; 2 to 20 min each time; current interplanetary vehic. Micro-grav., near 0; Few min. to months; Coasting sp. flt. About 1; Few min. to 2 weeks; Advanced solar sys. ships [LN] 1E-5 to 1E-4; weeks to years; electrical propulsion and solar pushed light sails few E-2; days to months; laser pushed light sails or deep space laser rocketry [f_a_c] up to 20; few min.; limit of human physiol. endur. 10 - 100; 5-15 min.; cargo; ground-space, laser launch 4-P [4-P] 1E3 to 3E4; 1.2 to 0.02 sec; cargo, ground-space, EM canon. 1E2 to 3E4; few E-3 sec. 1/2 hz rate; classic Orion pusher plate 1.5 to 3 avg., +- fluc.; 10 to 20 + min.; classic Orion crew cabin The preceding table summarizes the ranges of acceleration levels to be expected by space vehicles and/ or stations. The first five entries are the conditions historically and at present. The 7-th is almost ready to fly as main propulsion for orbit-raising (near Earth) or in cis-Lunar or interplanetary ranges. For a few of these, human crews could be present. The 6-th would be vary convenient. But we won't be likely to do it for quite a few decades. High school physics classes style, simple constant acceleration motion calculations, tell all you need to know about flight speeds and durations for such ships. (Accelerate for the first half, decelerate for the second half of flight, approximately in a straight line.) Entries 12 & 13 apply to 'classic Orion' type vehicles capable of launch from planetary surfaces, if legally permitted. It was an early idea for nuclear pulse propulsion. Explosions, with yield in the range of 1 to 50 kt, perhaps 1/2 to 2 sec. between pulses, occur to the rear of the space ship, thrusting it forward. (Vehicle size might be similar to an ocean going battleship.)[NP-II] A pusher plate, exposed directly to the blasts, would experience HIGH accelerations for brief instants. A spring system would transfer the impulse from the pusher plate mass to the main ship mass over a time period much longer than that of any individual impulse. Thus a crew could ride in the forward compartments, experiencing tolerable acceleration levels, not tremendously different from those experienced in Saturn and earlier launch vehicles. The 'shock absorber' system would result in the crew feeling an average maximum acceleration less than 3-7 g's. Fluctuations about the mean could be specified to fall within + or - 1/10 to 1 g, at the same frequency as the explosions. Freeman Dyson said a couple of memorable things of the Orian concept. First was in _Curve of Binding Energy_ --the Amazing Nuclear World of T.B. Taylor, by Mr. McPhee: "For a moment, the Door to the Solar System started to open for us. Then it closed again." In his own book, _Disturbing the Universe_, Dyson added, "The excited times in 1958, just after Sputnik-I, were unique in providing a chance for a program such as Orion to be seriously considered." Entries 10 & 11 indicate methods which expose cargo, not people, to particularly high acceleration levels. They provide substantial potential economic savings for moving space cargo around. In the "4-p" case, a repeatedly pulsed high energy and average power laser beam ablates away the bottom of a block of ice (with some payload on its top). The ablated material rushes away, causing a rocket type effect. The other case is once again the use of a cannon to put things into space. J. Vern wrote about this. And the late Dr. Gerald V. Bull had done some development work on relevant hardware. Bull's variant did not use EM (electro-magnetic) effects though, but rather chemical explosive propellants. Unless something of still unforseen nature is developed, personnel will not be moved under the conditions of 10 & 11. People can physiologically survive difficult conditions such as 1 and 9, but why bother? Surely the need is more for personnel transport types usable by most members of the public. This should not limited to a few unusually fit and highly trained people, nor be postponed until discoveries of unknown principles occur. What are ways in which the judgments from 1 paragraph earlier might be altered? 1. There has been lab research, demonstrated on test animals, on breathing of oxygenated liquids. Perhaps that might permit humans to tolerate high pressures, quite high accelerations. This concept, applied to humans, has been used in stories of fiction. Recall the film called _The Abyss_, and a G. Anderson T.V. series titled _U.F.O_. 2. Many stories have involved suspended animation of humans at cryogenic temperatures. If revival were solved, easy, inexpensive, reliable, legal, then their transport at very high accelerations while in this condition might be agreeable. 3. E. Drexler has written about the "Nano-Technology" concept in _Engines of Creation_ (non-fiction). Microscopic self replicating robot factories--assemblers-- were envisioned to rearrange large amounts of complex matter, at the sub-molecular scale. It might eventually be possible for a human, at a whim, for the length of a trip, to have self rebuilt into a form in which currently lethal conditions were not a barrier. (Without specifying whether the scale would be macroscopic or microscopic, self-replicating factories/ assemblers have been dealt with previously by F.J. Dyson, and perhaps originally, by von Niemann). Many of the people currently affiliated with cryonics activities, such as those at Alcore, believe that nano-technology may be required to make feasible revival from cryogenic suspended animation. 4. In fiction, there have been many cases which use the plot devices, "force field", "stasis field", "artificial gravity and acceleration-compensation field". In V. Vinge's novels _The Peace War_ and _Marooned in Real Time_, there were "bauble" fields. We do not yet know what basis in science to use in creating these effects. The same lack of knowledge applies to FTL (faster than light) travel, or teleportation. Any readers out there have any sound suggestions? Experimental and/or theoretical exploration of the relevant mathematical models would be much appreciated by a few of us at least. Lets turn now to spin-gravity for orbiting stations or space vehicles on interplanetary trajectories. If this technique were not used, all parts of such objects in space would be in 'micro-gravity'/ '0-g'/ 'free-fall'. If there were a crew present, whose tour of duty lasted for weeks to many months before landing again (on Earth, Mars, or Venus), unduly severe physiological changes might occur. Usage of 'spin-grav' avoids this type of problem. accl/g0 = r * omega^2 / g0; omega = 2 pi / period . If accel/g0 = 1, and rotation period = 30 sec, then r becomes 224 m (733 ft). For systems having internal volume for crew within the ranges spanning from Apollo CMS & LEM to that for Skylab, under 1/2 km of cables between similar sized modules would do. (The combination would rotate about the combined center of mass.) Space systems in most cases have a premium placed on being of low in mass for any given linear size. Tension members might be cables or thin sheets of metal, polymer, or fabric. Members to resist applied forces in bending or compression tend to be more massive per unit force. Their form tends to be more complex in shape--shells or truss work-- than the former. It is sometimes possible to design a structure in space which uses centrifugal "forces" due to rotation to substitute for compression and bending members. Such a thing is called a 'spin- tensioned structure'. Light sails, large optical element surfaces, or deplorable aero-breaking drag devices, are among the applications where such principles could be used to very good effect. Centrifugal accelerations may be of use in separating materials which differ by density. Devices which separate mixtures which contain liquids from vapor and gas phases are needed. Injection of the flow tangentially to a cylindrical surface will result in swirl. The higher density components will be drawn radially outward. There is a nuclear rocket design which uses this arrangement. The fissionable fuel is a dust. The swirling flow heats hydrogen, which is injected tangentially at the outer cylindrical wall. It flows inward, then expands rearward out of a nozzle at the axis. The dust bed is kept confined against the reaction mass flow by its centrifugal acceleration. These writings were formed as a response to a question which was relayed via electronic mail. It was in regard to centrifugal "forces" and the coping with accelerations which may occur with the use of space systems. An answer, based on my interpretation of the question is given. The ranges for acceleration levels are tabulated for different space applications. Speculations are entertained, for the far term, about subjection of humans to higher than present normal accelerations (above 3 g's). And finally, some of the circumstances, where centrifugal accelerations may be employed in space system designs, are described. ---------------- Notes Notation: g0 = 9.8 m/sec^2, grav. acceleration at earth surface omega, angular frequency number 'E' number: exponential notation 3E-2 is 0.03 avg. -average; fluc. -fluctuation; hz Hertz or cycles/sec r radius of rotating object [*] Sat. 3-2-91 by f.a.b. file is spacl.txt [UNEF] The quotations are formatted according to the pattern common on Use Net News. [any_Per] At such a level --3 g's and less-- your grand parents (any reasonably healthy person) can stand the ride. [LN] Larry Nivin uses such ships for the solar system spanning 'Belters' in many of his stories set 1 to 2 centuries in our future. They give you 3 hours, Earth to Moon, 14 days Earth to Pluto. They assume advanced on board fusion reactors, "High Thrust" engines, which have far surpassed our present 'power limited' and 'energy limited' cases. The term for that case is 'acceleration limited', according to C. Powel, formerly of UTSI (Univ. of Tenn. Sp. Inst.), now perhaps at Vogt Co. [f_a_c] These are foreseeable advanced concepts. We now see ways by which this level may be accomplished, more clearly than how L. Nivin's fictional ideal ships might be done. [4-P] Quoting A. Kantrowitz, cited by Jordan Kare, "take along payload, propellent, photons, period!" [NP-II] The successor to 'classic Orion' has been nuclear pulse propulsion at the smaller yield level. Thrust is obtained from inertial confinement fusion micro-explosions. Each pulse may have an energy release similar to several sticks of dynamite. The repetition frequency might be a few hundred hz. Vehicle designs result which would be easier, than the earlier larger scale, to build and test, once ICF became available. { Frank Bynum (Power Beam Spacer) h nu + A* --> A + 2 h nu \ | / bynum@miavx or fb3zphyg@miamiu D1 D2 = 1.44 R Lambda ---------+--- followed by .bitnet, or (on internet) by .acs.muohio.edu / | \ mail c/o Physics Dept. Ofc., Miami Univ. Oxford OH. 45056 USA or c/o C.A. Bynum, 1616 Rosewood Ave., Louisville KY 40204 USA } "No grimmer fate can be imagined than that of humans, possessed of god like powers, confined to one single fragile world."-- Kraft Ericke ------------------------------ End of SPACE Digest V13 #247 *******************