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SCIENCE
9
~uly
1965, Volume 149, Number
3680
Death of
a
Project
Research is stopped on a system of space propulsion
which broke all the rules of the political game.
In January 1965, unnoticed and un-
mourned by the general public, Project
Orion died. The men who began the
project in 1958 and worked on it
through
7
strenuous years believe that
if offers the best hope, in the long run,
of a reasonable program for exploring
space. By "a reasonable program" they
mean a program comparable in cost
with our existing space program and
enormously superior in promise. They
aimed to create a propulsion system
commensurate with the real size of
the task of exploring the solar system,
at
a
cost which would be politically
acceptable, and they believe they have
demonstrated the way to do it. Now
the decision has been taken to follow
their road no further. The purpose of
this article is neither to bury Orion
nor to praise it. It is only to tell the
public for the first time the facts of
Orion's life and death, and to explain
as fairly as possible the political and
philosophical issues which are involved
in its fate.
Vehicle Design and Capabilities
First, a brief technical summary.
Orion is a project to design a vehicle
which would be propelled through space
by repeated nuclear explosions occur-
ring at a distance behind it. The vehicle
may be either manned or unmanned;
it carries
a
large supply of bombs,
and nlachinery for throwing them out
9
JULY
1965
Freeman
J.
Dyson
at the right place and time for efficient
propulsion; it carries shock absorbers
to protect the machinery and the crew
from destructive jolts, and sufficient
shielding to protect against heat and
radiation. The vehicle has, of course,
never been built. The project in its
7
years of existence was confined to
physics experiments, engineering tests
of components, design studies, and
theory. The total cost of the project
was $10 million, spread over
7
years,
and the end result was a rather firm
technical basis for believing that vehicles
of this type could be developed, tested,
and
flown. The technical findings of the
project have not been seriously chal-
lenged by anybody. Its major troubles
have been, from the beginning, political.
The level of scientific and engineering
talent devoted to it was, for a classified
project, unusually high.
The fundamental issue raised by such
a project is: Why should one not be
content with alternative
means of pro-
pulsion which are free from the obvious
biological and political disadvantages
of nuclear explosions? The answer to
this question is that, on the purely
technical level, an Orion vehicle has
capabilities which no other system can
approach. All alternative propulsion sys-
tems which we know how to build are
either temperature-limited or power-
limited. Conventional rocket systems,
whether
chemical or nuclear, are tem-
perature-limited in that they eject gas
at a velocity
V
limited by the temper-
ature of chemical reactions or of solid
structures. The upper limit for
V
ap-
pears to be about
4
kilometers per
second for chemical rockets, 8 kilo-
meters per second for nuclear rockets.
For missions involving velocity changes
many times
V,
multiple-staged rockets
are required, and the initial vehicle
size needed in order to carry a modest
payload soon becomes preposterous.
The initial weight is
multiplied
by about
a factor of
3
whenever an amount
V
is
added
to the velocity change of a
mission. It is for this reason that
programs based on conventional pro-
pulsion run into a law of heavily dimin-
ishing returns as soon as missions be-
yond the moon are contemplated.
The other class of propulsion systems
at present under
developn~ent is the
so-called nuclear-electric class. These
systems use a nuclear reactor to gen-
erate electricity, which then accelerates
a
jet of ions or plasma by means of
electric or magnetic forces. The velocity
of the jet is no longer limited by
considerations of temperature, but the
available thrust is
limited to very low
values by the power of the electric
generator. Vehicles using nuclear-elec-
tric propulsion necessarily accelerate
very slowly and require long times to
achieve useful velocities. They have un-
doubtedly an important role to play
in long-range
n~issions, but they offer
no hope of transporting men or ma-
chines rapidly around the solar system.
The Orion propulsion system
is
neither temperature-limited nor power-
limited. It escapes temperature limita-
tions because the contact between the
vehicle and the hot debris from the
explosions is so brief that the debris
does no more than superficial damage.
It escapes power limitations because the
nuclear engine (bomb) is outside the
vehicle and does not depend on coolants
and radiators for its functioning. An
Orion vehicle is unique in being able
to take full advantage of the enormous
energy content of nuclear fuel in order
The author is professor of physics at the
Institute for Advanced Study, Princeton, New
Jersey.