More on Interstellar Travel
In contrast to Dr. Cassenti, the main emphasis of Dr.
Gregory Matloff's presentation was on "world ships" or
Dr. Matloff received his doctorate in physics from New York
University, where he specialized in atmospheric physics. He has
worked as a NASA consultant at the Goddard Spaceflight Center.
He has also held a position on the staff of Pratt Institute. He
now divides his time between a professorship at Baruch College
and the Environmental Services Corporation. Dr. Matloff is a
member of the British Interplanetary Society, the Space Studies
Institute and several other groups. Dr. Matloff has published
several important papers in physics. He is the author of an
article on world ships which appeared in the Journal of the
British Interplanetary Society.
Dr. Matloff began by noting that the ability to develop the
necessary technology wouldn't necessarily make relativistic space
vehicles practical. A related problem is economic. To get to
the stars and possibly return in one lifetime would require
enormous amounts of money. An antimatter rocket capable of
attaining one-tenth the speed of light would cost about 100,000
times the annual U.S. gross national product . Added to this
problem is that there would be no tangible financial return from
such a project. In short, Dr. Matloff believes antimatter
rockets to be economically impractical. [SEE COMMENT 12]
The costs of laser-pushed light sail vehicles might, in Dr.
Matloff's judgment be less by a sufficient magnitude to make such
vehicles financially practical. However, it would still be
enormous. Nevertheless, this concept is subject to another
problem: It requires directing a very large laser at the
starship for between several decades and several centuries. A
necessary precondition, therefore, is the essentially total
political and economic stability of the society launching the
starship. "What happens," Dr. Matloff asked rhetorically, "if
there is a revolution? What happens if there is an energy
Similarly, a laser capable of powering a two-way
interstellar mission would have a power output 47,000 times as
great as the total power output now being used by the entire
human race. Such a laser would be, potentially, an enormously
powerful weapon. "What happens" asked Dr. Matloff if the group
who is operating the laser would like to take the world over?"
It would, he stated be very difficult to prevent them from so
As a result, Dr. Matloff stated, "two-way fast missions,
although *** scientifically and technically practical, are
farther away than slow, one-way trips." According to Dr.
Matloff, perhaps "forty to fifty percent" of what he called "the
interstellar community" share this view.
On the other hand, Dr. Matloff contended that what he
described as "an interstellar ark or world-ship" can be
engineered today. Not only that, but, in his view, the
engineering would be relatively easy.
In particular, a variety of propulsion options would be
available for such a vehicle. These include very thin solar
sails deployed when the ship is close to the Sun. However, this
would necessitate launching the "world-ship" on a trajectory that
would take it within 1 to 3 million miles of the Solar center.
Dr. Matloff admitted that this "would be an unpleasant trajectory
**** most people would like to sleep through that." Hence, Dr.
Matloff suggested this be dubbed "the valium trajectory." Other
possibilities are variants of nuclear-electric or fusion-ion
rockets. Even the Orion nuclear-bomb propulsion concept would,
Dr. Matloff stated, be practical for such a vehicle. Nominal
mission duration would be 1,000 years.
The problem with interstellar arks, Dr. Matloff admitted, is
that while the engineering problems, including deceleration at
the destination star, become relatively easy, "you run into a
whole lot of sociological problems." As a result "on the one
had, you have easy technology and difficult sociology, on the
other hand you have difficult technology and easy sociology."
Hence during the remainder of his presentation he concentrated on
what he called "the human aspects of interstellar flight."
Dr. Matloff began by showing the now familiar slide
illustrating an artist's rendition of a space colony as conceived
by Dr. Gerald O'Neill. This slide, Dr. Matloff commented, both
illustrates the life support requirements of an interstellar ark
and "points out a very interesting psychological aspect of these
As depicted in the slide, the interior of the space colony
(which would be very similar to the interior of an interstellar
ark) resembles a suburb of Princeton, New Jersey. (For the
benefit of anyone who may not already know it, Dr. O'Neill was,
until his retirement, a professor at Princeton University.)
Another artist's conception of space colony interior looked like
a suburb of Palo Alto, California, while a third was similar to
a hippie commune. The interior of yet another space colony, this
one proposed by the British Interplanetary Society is suggestive
of the English countryside. Dr. Matloff speculated that an
artist's conception of as Soviet space colony would be
reminiscent of a Siberian Gulag. The point being that the
initial population of an interstellar ark will want the interior
to look as much like home as possible.
Certain things, however, will have to common to any
interstellar ark design. One of these is that the spacecraft
will have to spin at a certain rate. This, in turn, is the
result of the need to provide artificial gravity. However, this
need not necessarily be a full 1G. Some concepts call for as
little as one-twentieth G. The object is to limit the amount of
artificial gravity to the lowest level consistent with the health
of the crew. The reason for this is that if the spacecraft spins
too fast about 20% to 30% of the population will experience
serious, and constant, cases of motion sickness. This, Dr.
Matloff commented, would make things unpleasant for those of the
space ark's crew assigned to provide janitorial services. [SEE
A world-ship will also need some radiation protection, both
against galactic cosmic rays and against our own Sun, especially
if the "valium trajectory" is used. This would be located on the
vehicle's outer walls. It would vary in thickness from tens of
centimeters up to about two meters.
Likewise, any world-ship would have to have an agricultural
area both to provide food for its population and recycle the
oxygen supply. Various options are available in this regard.
These include using the 0G area in the center of the spacecraft
for that purpose. According to Dr. Matloff, "there have been
some very interesting possibilities suggested" as regards the
latter, "some of which I think are very nice, others which I
think are rather impractical." The former include plants
floating in air. The latter include a 0G fishpond. (Disposal of
fish waste would present problems.)
The optimum population for a space ark has not been defined.
Most writers who have considered this question suggest that the
population should be on the order of 10,000 persons. Dr. Matloff
suggested, however, that this is based upon the figure derived by
Dr. Gerard O'Neill in his work paper on space colonies in the mid
1970s. In turn, in Dr. Matloff's words, that became an
"institutionalized number" as a result of a subsequent study of
space colonies at Stanford University. However, Dr. Matloff
pointed out that both the O'Neill and Stanford studies were
considering an independent industrial community. Even if a
population of 10,000 was be the smallest practical number for
that purpose, the same would not necessarily hold true for an
As a result various sociologists (who, according to Dr.
Matloff, are now beginning to consider this question) have
suggested much smaller populations. One suggestion is for a
minimum population of 1,000 that being the smallest number that
will permit all professions to be represented. Another is a
minimum population of 100 that being the size of the smallest
primitive human communities. The smallest number that can be
justified, according to Dr. Matloff, is about 25 people. In any
case, the limiting factor is not, as formerly thought, the size
of the gene pool. If genetic screening is used, the initial
population of a world-ship can be as small as 15 people.
The population density of a space ark is likewise as yet
undefined. Estimates range from 10 to 1,000 persons per acre.
The question, to which there can be no answer until at least the
first space colony is built, is whether an urban, suburban or
rural type environment is preferable.
Another open question is a world-ship's interior design.
Arguments can be made for simulating anything from mountainous or
desert terrain to "something like the starship Enterprise from
Star Trek." Likewise, the interior might or might not include
either greenhouses or natural vegetation. The problem, according
to Dr. Matloff, is that there have been very few experiments on
closed cycle environments. Moreover, whether the work that has
been done is applicable to space colonies or interstellar
expeditions is not known . Counterbalancing this, however, is
that the first interstellar ark is not likely to be built until
we have reached what Dr. Matloff characterized as the "mature
period" of space colonization. By then, many space colonies will
have been built with varying designs. This experience will
supply the answer to some world-ship design questions. [SEE
In any event, given the long duration of world-ship
missions, the appropriate historical model is not voyages of
exploration. Rather, it is colonization of various portions of
the planet Earth. The model most frequently resorted to is
European colonization of the Western Hemisphere. According to
Dr. Matloff, "a more interesting *** and perhaps *** a more
reasonable one is the exploration and colonization of the ***
Pacific Basin." This began about 40,000 years ago when people in
Southeast Asia began migrating to Australia. Then some of these
people began moving out from there into the Pacific. This
process took tens of thousands of years to complete, but
eventually almost every habitable island in the Pacific was
populated. Why this was done can only be guessed at. As to how
it was accomplished, Dr. Matloff commented "we know the
technology they finished with" but "we don't know all the
technology they started with."
This 40,000 year time span, Dr. Matloff stated is extremely
interesting, because it perhaps gives some indication as to how
long it may take one species to populate the galaxy. In
Matloff's view, the time period is dependent, not on the duration
of the interstellar voyage, but on the length of the stopover.
Using very optimistic assumptions, he stated, it might be
possible for humanity to occupy the entire galaxy in 10 million
years. Using very pessimistic assumptions, the process could
take 100 million years. Some authorities, mostly SETI (search
for extraterrestrial intelligence) advocates such as Carl Sagan,
have argued for even longer time spans. Historical models, they
contend deal with a wave of colonization. Interstellar
colonization, particularly if world-ships are the vehicles used,
might be more like a random walk. That is, only the most
promising stars will be selected as targets. Futhermore, once
the colonists arrive at the destination star perhaps ten thousand
years may elapse before their descendants move on to another.
[SEE COMMENT 15]
Dr. Matloff presented several concepts for interstellar
arks. One problem is that if the ark is a single vehicle its
mass will be one the order of billions of pounds. Assuming
selection of solar sailing as the means of propulsion, the sail
must be thousands of kilometers in diameter. The weight of the
cables needed to tether the ark to the sail then becomes
enormous. Hence it may be necessary to divide the world-ship
into a number of modules which would rendezvous and dock with
each other once the acceleration phase of the voyage was over.
(The vehicle or vehicles would only be accelerating for a few
days. After that, as Dr. Matloff put it, "they have a thousand
years to get together, build the colony and have their cocktail
parties.") [SEE COMMENT 16]
However, while rendezvous may be necessary, construction of
a colony on the voyage may not. Dr. Matloff again used primitive
nomadic peoples as an example. In some cases, he noted, these
peoples did not live together in large tribes. Rather they spent
most of their time in small family groups of about 25.
Periodically, however, the entire tribe came together for
ceremonial and other purposes. Interstellar voyagers, he
suggested could do the same. These meetings, he humorously
suggested, could include the sacrifice of a virgin (computer
chip) to keep the mission going.
Dr. Matloff displayed one interstellar ark concept, dating
from about 1976, which he himself designed for the British
Interplanetary Society. The propulsion system would be the same
as the Orion vehicle. Dr. Matloff described the vehicle as being
similar to "O'Neill Model One," meaning Gerard O'Neill's first
space colony. It would have windows, but in between stars these
would be closed for radiation protection. Another concept showed
a similar type colony, but using a solar sail for propulsion.
Mass would be about 10 billion pounds. In the illustration the
colony is showing moving out from the Sun a about one-one
thousandths of the speed of light. (Presumably, it is still
Another concept would use a perforated solar sail. This
idea originated with Freeman Dyson. Professor Dyson did his
calculations on the back of an envelope which he then showed to
Robert Forward. (Dr. Matloff proposed preserving that envelope
be the Smithsonian Institution. It should, he suggested, be
displayed in the same exhibit case as models of the Starship
Enterprise and the Orion vehicle. That one envelope had, he
noted kept several scientists busy for an entire year.)
Another slide shown by Dr. Matloff depicted the proposed
trajectory of a world-ship. One problem is that the solar sail
deployment cannot occur until the vehicle is at the point of its
closest approach to the Sun. The vehicle would therefore begin
its journey from the asteroid belt, perhaps using nuclear-
electric propulsion on the inward journey. An asteroid or comet
with perhaps 10 times the mass of the starship would be used for
shielding during passage close to the Sun. After the sail was
deployed, the asteroid and the starship would separate.
In conclusion, Dr. Matloff noted there are many ways of
getting to the stars. Some of them, he believes will be tried.
Futhermore, people traveling in interstellar space will have a
very wide range of options as to such things as gravity and
radiation levels. Some groups, for example, may prefer a high
mutation rate. Others may feed less than Earth-normal gravity to
be desirable. At some point in the remote future, he suggested,
perhaps 50 to 100 thousand years from now, the different streams
of interstellar humanity, those traveling by world-ships and
those using faster means, will meet. By then, however they may,
because of these factors, have evolved so far down different
paths that they will not recognize each other as human. In the
manner of countless spy novels, it might, therefore, be necessary
to "program" starfarers with a sociological recognition code to
use when meeting other intelligent beings in space.
There is another problem if we elect to go to the stars (as
Dr. Matloff put it) "the slow way." People will not willingly
isolate themselves and their descendants from the rest of the
human community. Hence, humanity may well decide to explore the
stars with robots for now, knowing manned vehicles can follow if
it becomes desirable or necessary. On the other hand, if the
Hubble Space Telescope or its successors indicate that habitable
planets exist around other stars the urge for humans to go there
may become overwhelming. [SEE COMMENT 17]
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