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Subject: SPACE Digest V13 #247

SPACE Digest                                     Volume 13 : Issue 247

Today's Topics:
          Space Flight Acceleration Regimes

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Date: 7 Mar 91 06:42:06 GMT
From: agate!bionet!uwm.edu!linac!pacific.mps.ohio-state.edu!ohstpy!miavx1![e-mail]  (Frank Bynum)
Subject: Space Flight Acceleration Regimes


        Space Flight Acceleration Regimes
        Frank Bynum [*]

        <[e-mail]> (Dave O'Hagan), on Thu, 28 Feb 91 10:55
EST, in message to Leo J Irakliotis <[e-mail]>, who
forwarded it to <[e-mail]> (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
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