
From julian_hiscox@micro.microbio.uab.edu Wed Jun  5 09:21:38 1996
Date: 5 Jun 1996 10:24:25 -0500
From: Julian Hiscox <julian_hiscox@micro.microbio.uab.edu>
To: "Dr. Julian Hiscox" <julian_hiscox@micro.microbio.uab.edu>
Subject: Marbugs- Vol.3. No.3.

Mail*Link SMTP               Marbugs: Vol.3. No.3.


MARSBUGS:  The Electronic Exobiology Newsletter
Volume 3, Number 3, 4th June, 1996.

Special Issue: Interstellar travel.

Co-editors:

David Thomas, Department of Biological Sciences, University of
Idaho, Moscow, ID, 83843, USA, thoma457@uidaho.edu.

Julian Hiscox, Microbiology Department, BBRB 17, Room 361,
University of Alabama at Birmingham, Birmingham, AL 35294-2170,
USA, Julian_hiscox@micro.microbio.uab.edu.

MARSBUGS is published on a weekly to quarterly basis as warranted by the
number of articles and announcements. Copyright exists with the co-editors,
except for specific articles, in which instance copyright exists with the
author/authors.  E-mail subscriptions are free, and may be obtained by
contacting either of the editors. Contributions are welcome, and should be
submitted to either of the two editors. Contributions should include a short
biographical statement about the author(s) along with the author(s)'
correspondence address.  Subscribers are advised to make appropriate
inquiries before joining societies, ordering goods etc.

----------------------------------------------------

INDEX

1) EDITORS INTRODUCTION

2) ON THE REALISM OF INTERSTELLAR TRAVEL

3) INTERSTELLAR PROPULSION RELATED MATERIAL AND SOCIETIES
-Eds.

----------------------------------------------------


1) EDITORS INTRODUCTION

We are pleased to present an issue devoted to interstellar travel.  In the
past year or so a number of extra-solar planets have been discovered and
verified.  Although planets orbiting within the habitable zones of such stars
have not been inferred, within the next few years the technology may become
developed enough to allow this.

Therefore, interstellar travel is of extreme importance when one considers
that the only way to actually sample extra-solar planets is to go there and
visit them with either robotic or crewed space craft.  We a very pleased to
present our featured article by Gerald Nordley, an astronautical engineer and
author with degrees in physics and systems management.  We have also included
a section that contains material on interstellar propulsion that might be of
interest.

----------------------------------------------------


2) ON THE REALISM OF INTERSTELLAR TRAVEL
by Gerald David Nordley

    With the pioneers and voyagers on their way out of the solar system, no
one seriously disputes the possibility of slow interstellar travel, at least
for automatic spacecraft.  But objections continue to be raised against
_fast_ interstellar travel, i.e. starships that travel close to the speed of
light.  The usual purpose of such arguments is to make interstellar
communications through radio or lasers seem like the only real possibility.
 (Well, obviously, if sentient beings can go, or send surrogates, nearly as
fast as light to some place where they can converse in real time; they might
prefer to do this rather than wait decades for an answer on the
radio--leaving not much radio traffic to hear.).  Therefore, some people with
vested interests in radio SETI often emphasize the futility of such
interstellar physical commerce.
    The late Dr. Barney Oliver was one such person, and he delighted in
making calculations of the incredible size and impossibly large energy
requirements for any reasonably feasible rocket designed to go between the
stars.  His mathematics were elegant and his formulae quite accurate, and
yes, indeed, an interstellar rocket designed to approach the speed of light
is a very daunting technological proposition.  While storing its propulsive
energy as antimatter might make rockets approaching half the speed of light
barely feasible for a Solar-system scale civilization, flights of such
rockets would seem to be necessarily awe inspiring and infrequent.
    But recent work in interstellar propulsion makes arguments concerning
rockets increasingly irrelevant, and the energy argument alone ignores the
implications of the cybernetic revolution already underway.    
    Let's take energy first.  The kinetic energy of a 1000 ton (1 E6 kg)
starship moving at  87% the speed of light (gamma = 2) is about 9 E22 joules.
 The total non-food energy consumed by human civilization today is something
like 1E 21 joules--about a hundredth of that.   If we are talking about
getting the spacecraft up to that speed and back down by rockets, many times
that energy is needed to move the reaction mass required, depending on
exhaust velocity, efficiency, and the weight of the engines.  (Even for
photon rockets--while the photons don't "weigh" anything, the energy needed
to generate them must have an inertial mass, in some form, of E/c^2, where E
is the total energy needed to generate all the photons required for the
mission.  The photon rocket must carry that mass.)  Here we have to note
that, lacking a breakthrough (like "The Kubota Effect"--see Analog, May '96)
in physics to make antimatter for rockets, several hundred times more solar
(or other) energy must be consumed to run the accelerators needed to make the
antimatter than one gets back in annihilating that antimatter.
    But while interstellar travel energy requirements are huge compared to
what we can generate on Earth today, they are not particularly impressive in
comparison to what might be generated with the fusion of deuterium taken from
a giant planet's atmosphere, or in comparison to the sun's output.  Practical
fusion remains to be seen, but the ability to collect the necessary solar
energy is easily demonstrated.
     Once we make self-replicating robots, they can also make solar power
collection stations.  With exponential growth, a few decades should suffice
to put the needed power infrastructure in place.  For instance, a the end of
two years, a system that each year produces a copy of itself and a
one-gigawatt solar power collection satellite (from moon or asteroidal
material) has made three powersats and three copies of itself.  At the end of
n years, there are 2^n production systems and 2^n - 1 power satellites.  In
fifteen years, the energy production would be on the order of magnitude of
Earth's current total.  In thirty years, the system would be producing 34,000
times as much and doubling that each year--until the solar system
environmental impact authorities start getting nervous about the number of
asteroids being consumed or the size of the (new, artificial) holes in
Mercury or the Moon.
    Obviously, a real system won't produce exactly one replica and exactly
one gigawatt powersat in exactly one year.  Also, I doubt such a system would
be fully autonomous--some human supervision, especially early on, will likely
be involved.  But this calculation should give a good idea of the power of
robotic systems and their exponential growth to get the energy needed for
starflight.
    It is not necessary to try to anticipate the future engineering details
nor the trades concerning which conversion systems are most appropriate, how
big the robots should be, and so on.  The work can be done.  Simple solar
power conversion systems have already been built--they will get better,
simpler, and more efficient with time.  Machines making parts of machines are
an increasingly relevant part of daily life in these times, as are robotic
assemblers.
    What robotic production does to conventional notions of cost is worth a
paper in itself--and a serious current issue regarding the displacement of
labor--I'm afraid I tend to snicker a little when people start talking about
interstellar travel in conventional economic terms.   But, clearly, the
energy requirements are such that robotic production of power producers is
needed, and, in kind of an anthropic principal argument, the civilizations
that achieve that will have developed the technology to deal with any
conceivable energy and material shortages along the way.  The distribution of
such largess remains, of course, a significant cultural issue--the robots are
coming and we'd best start dealing with it--humanely, I hope.  
    But we shall have to have solved that issue before we are ready to go to
the stars (or it will solve us!).  In projecting the future, as always, the
difference between science and engineering is very important.  Natural laws
do impose asymptotic limits on what engineering can do--but current practice
(such as the state of the art in robotics), is not a valid limitation on
future engineering capability.
    The huge energy numbers still have a lot of emotional impact in the
negative direction.  Dr. Oliver, for instance, dismissed the possibility of
self replicating robots as "handwaving arguments"  when we discussed this
following our papers in the 1986 IAF conference in Brighton.  I think he
understood full well that their potential advent was a monkey wrench in the
argument for a radio-only linked galactic civilization--that they could
destroy the energy objection to interstellar travel and make extraterrestrial
radio transmissions less likely to find.  
    At the time we were discussing getting energy to make antimatter for
rockets, but there are much better alternatives. Indeed, it is probably time
to forget about interstellar rockets.  It is increasingly clear that the way
to do interstellar travel is to leave the fuel tanks and heavy engines at
rest and push the spacecraft with beams of light or particles.  
    Photons of light are still somewhat wasteful starship-pushers at low
velocity--a reflected photon caries away a lot of energy until the spacecraft
is moving fast enough to downshift its frequency significantly.  
    But the velocity of incoming physical particles can be chosen to leave
the reflected particles dead in space--with no kinetic energy left.  If so,
except for some radiation and alignment losses, all the energy went into the
starship.  Thus the theoretical minimum energy required is simply the kinetic
energy of the vehicle at its cruising velocity--though a reasonable person
would apply a factor of ten to this, for system inefficiencies.   
    Yes, the beams have to hit the spacecraft--but there are all sorts of
ways of arranging that they do this.  And yes, the process can't be 100%
efficient--but it can come close in principal, especially with particles.
    Dr. Robert L. Forward has described in several papers and articles how to
accelerate and decelerate a photon propelled system.  The reflector materials
must perform near their physical limits.  For first time missions, big
(asteroid-sized or larger) Fresnel-type lenses floating in space are needed
to focus light from huge lasers across interstellar distances to staged
deceleration reflectors.  The engineering is advanced, but the physics works.
    In a particle beam propulsion system, much smaller lasers along the beam
route could push an occasional errant propulsion particle back to its path
toward the starship.  Or the particles could make use of oncoming
microtechnology to be smart enough to steer themselves, homing in on the
spacecraft reflector with tiny laser-diode photon rockets, or, as Forward
suggested to me, by using tiny mirrors to reflect a steering beam from the
ship, to one side or another.   Depending on the size of the particles
accelerated, the particle accelerators themselves could be mass produced
versions of today's linacs, or much longer versions for much heavier particles
(or pellets).        
    To slow a particle beam reflecting starship down at the target system, a
trail of the appropriate kind of mass needs to be laid out in front of the
oncoming starship.  For first time missions, this could be done by a colony
of small self-replicating robots sent ahead. The initial robots would
decelerate more slowly, with photon, magsail, or nuclear rocket decelerator
systems to the target system's asteroid belt or Oort cloud. Of course, if a
co-operating technical civilization is found, they could provide the
deceleration beam.
    Reflectors can be shiny thin films for photons, magnetic mirrors for
particles (which are first blasted into plasma as they approach the
starship), charged metal plates, or even ultra-thin sails designed to run
before an artificial particle wind.  And many other variants, of course.
    The upshot of these "new" techniques is that rocket calculations (and,
sadly, I started out in this field by doing them, too) are turning out to be
as relevant to the question of interstellar travel as calculating the supply
of helium for balloons is to the question of intercontinental air travel.
 Indeed, the gain in velocity and efficiency for beam supported propulsion is
so great that I am beginning to wonder whether rockets will be anything but
auxiliary propulsion by the end of the next century--even for solar system
travel.  It's trains versus horses.
        For comparison, the 9 E22 joules of energy mentioned above packaged
in a rocket with a final mass of 1000 tons and an exhaust velocity of 0.1 c
(optimistic even for nuclear fuels) would get the rocket up to just over 0.25
c--and this neglects practical considerations such as the mass of the engines
needed to give meaningful acceleration to a rocket with an initial mass of
173,000 tons.  Rocket engines, like car engines, scale with power.
 Accelerating a thousand tonne ship at one gravity or so takes a lot of
power, which means heavy engines, which means more power and more fuel, which
means more powerful engines, which. . . .   Well, even to approach this
performance requires the rocket to consume its engines for reaction mass
along the way, as its need for thrust decreases. 
    By comparison, beamed propulsion is technologically conservative.  The
large lasers, particle accelerators, beam cooling and steering (or
self-steering micropellets), solar power satellites, asteroid mining--taken
individually the necessary technologies are fairly reasonable extensions of
work already in progress.  Beamed propulsion doesn't need new science nor as
yet problematical engineering breakthroughs such as efficient antihydrogen
production, or D-He3 fusion reactors.  All the necessary elements, except the
software for the robots to make the energy collectors, have already been made
on small scale.  Progress in software is proceeding by leaps and bounds, and
it is the one area least affected by government funding cuts or private
investment restrictions.  If the parts are all there, the systems can, at
least in principal, be built.
    Unfortunately, when one puts them all together, the systems that can be
made of these pieces generate conceptual barriers many minds.  That, however,
is something for the sociologists and psychologists.  I think I must leave
this with the observation that intuition and judgement are honed by
experience, and in matters that are necessarily outside experience, negative
intuition is often (and sometimes hilariously) worthless.  I'll also note
that much of physics (particularly orbital dynamics) delights in being
counterintuitive.
    As with any "new" idea (the seminal work, by Forward on lightsails and
Singer on pellet beams, goes back at least 16 years), beamed propulsion is
taking a while to sink in.  It isn't an idea with a lot of emotional appeal.
 Beam supported propulsion systems (like railroads) require a substantial
infrastructure in addition to the vehicle and part of the resistance to the
concept (beyond vested interests) is, I suspect, that beamed propulsion
surrenders the romance of a self-sufficient spacecraft which (once built and
fuelled!) can go where its crew wants to go.  Beam riding spacecraft are much
more restricted in their destination--not very "Star Trek." 
    Whatever the reasons, there are as yet few mentions of beamed propulsion
in the interstellar propulsion literature compared to rockets.   But one
can't rule out interstellar travel just because the propulsion systems are
unfamiliar or the cornucopia of energy involved implies social changes that,
as we said back in the 60's, blow one's mind.  
    Yes, there is always the wild card of some new physics that allows one to
bypass the speed of light by throwing the power switch on the right piece of
equipment.  However it is one thing to propose engineering that will approach
the limits of nature after a reasonable amount of work and is quite another
thing to propose devices that require a significant recalculation of those
limits--if not a complete revision of physics as we know it.  Dyson spheres,
space stations, genetic engineering and robots--yes; but warp drive, Star
Trek's "Q," time travel, or switch-on gravity in spaceships--not very likely.
 
    But since beamed propulsion doesn't need new physics, I see nothing at
all unrealistic about spacecraft made by humans (or others) travelling at
speeds approaching (but not passing) the speed of light--the only question is
when.  My best guess right now is about 100 years--given all of humanity's
other priorities.  But if we really had to do it soon, I suspect we could get
at least probes up to that velocity in about 50 years, with starships shortly
thereafter.  Ad astra!

(Note:  The above is a slightly expanded and edited version of a response to
email concerning one of the late Dr. Oliver's papers on the difficulties of
interstellar travel.  For further reading, check interstellar
propulsion-related articles in the last three or four years of the Journal of
the British Interplanetary Society and the references in Bob Forward's latest
non-fiction book: Indistinguishable from Magic.  --G.D.N.) 

    Gerald (G. David) Nordley is an astronautical engineer and author with
degrees in physics and systems management.  After retiring from the Air
Force, he started writing as a second career, and has sold some 30 pieces of
short fiction and non fiction to various markets.   Novels are in work.  His
novella "Martian Valkyrie" appeared in the January 95 Analog and he has a
short story "The Kubota Effect" in the May 95 _Analog_ .  Upcoming are two
novellas: "Fugue on a Sunken Continent," based on the CONTACT world of Epona
and planned for the November issue of Analog,  and "Messengers of Chaos," a
lunar murder mystery to be published in a future issue of Asimov's.

----------------------------------------------------


3) INTERSTELLAR PROPULSION RELATED MATERIAL AND SOCIETIES
-Eds.

Material related to interstellar propulsion:


Books:

The Starflight Handbook. By Eugene Mallove and Gregory
Matloff. 1989. John Wiley & Sons, Inc. New York.
ISBN 0-471-61912-4. $27.95.

The Millennial Project: Colonizing the Galaxy in Eight Easy
Steps. By Marshall T. Savage. 1992. Empyrean Publishing Ltd.
ISBN 0-9633914-8-8. $24.94.
ISBN 0-9633914-9-6. $18.95.

Infinite in All Directions. By Freeman Dyson. 1988. Harper
and Row, New York (Perennial Library Edition).
ISBN 0-06-091569-2. $11.

Cosmos. By Carl Sagan. 1980. Random House, New York.
ISBN 0-517-12355-X. ~$30.


Journal of the British Interplanetary Society Issues
(recent):
Back issues may be obtained by contacting the society at:
BIS@CIX.COMPULINK.CO.UK

Electric Propulsion (Part 2). v49, no5. May, 1996.

Practical Robotics for Interstellar missions (Part 2). v49,
no4. April, 1996.

Practical Robotics for Interstellar missions (Part 1). v49,
no1. January, 1996.

Electric Propulsion (Part 1). v48, no12. December, 1995.

Exobiology (Part 4). v48, no11. November, 1995.

Space Missions and Astrodynamics (Part 2). v47, no11.
November, 1994.

Interstellar Studies. v41, no11. November, 1988.

Interstellar Studies. v39, no11. November, 1986.


Also, Ad Astra: v7, no4, four articles on interstellar
travel. (See National Space Society for details).



Societies:

The British Interplanetary Society, 27-29 South Lambeth
Road, London SW8 1SZ, UK.
BIS@CIX.COMPULINK.CO.UK
(Monthly Spaceflight or JBIS included in membership).


The Planetary Society, 65 North Catalina Avenue, Pasadena,
CA 91106-2301, USA.
tps@genie.geis.com
(One main bimonthly, also optional The Mars Underground News
and Bioastrononomy Newsletter).

National Space Society, call 1-800-543-1280.
(Includes one bimonthly magazine).

----------------------------------------------------
End. Marsbugs, Vol.3. No.3.



