### Difference in upper limit of V between chemical rockets & nucle...
Earth's escape velocity is 11.19 km/s. This is the velocity you nee...
In an electric engine (also known as an "ion engine") an electric p...
Part of the inspiration for Project Orion came from noticing compon...
### Nuclear Pulse Propulsion
Briefly, the Orion propulsion system ...
Conventional rocket engines produce thrust by the expulsion of an e...
The idea of using a series of explosive pulses to propel a rocket c...
Ted Taylor was an American theoretical physicist who worked at Los ...
One of the main reasons for the added secrecy of the Orion project ...
### Nuclear-powered aircraft
Physicist Enrico Fermi had introduced...
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.
to achieve, siniultaneousiy, high ex-
haust velocity and high thrust.
Let me give an example of the spe-
cific performance that would be
achieved by first-generation Orion ve-
hicles. Designs were worked out in de-
tail for vehicles that could carry eight
men and a payload of
100
tons on fast
trips to Mars and back. The vehicles
were sniall enough to be lifted into
space by
Sat~lrn chemical rockets, and
the cost of the Saturn boosters turned
out to be more than half the estimated
cost of the whole enterprise. These
designs do not, of course, prove that
a
manned expedition to Mars is a
worthwhile undertaking; they indicate
only that
if
you wish to go to Mars,
then Orion will take you there inore
rapidly and cheaply than other vehicles
that are now being developed.
So much for the technical back-
gro~lnd of Orion. Next comes the
political history. The idea of a bomb-
propelletl vehicle was first described
by Ulam and Everett in 120s Alamos
in 1955. It was transformed into a
serious ancl practical proposal by a
group of physicists and engineers at
General Atomic Division of General
Dynamics Corporation in 'San Diego,
~rnder the leadership of Theodore Tay-
lor. Work at General Atomic started in
the spring of 1958, as a direct response
to the first Sp~ltnilts. The initial gro~lp
at General Ato~liic, including Taylor,
were old weaponeers from 1.0s Alamos,
and they seized happily upon this op-
portunity to make their knowledge of
nuclear explosions serve a loftier pur-
pose than weaponry. Within
a
few
~iionths they hacl worked out the basic
theory of the Orion system, and found
that it worked evcn better than they
had supposed.
Government Sponsorship
The problem then arose of obtaining
government sponsorship and nioney for
the project. The National Aeronautics
and Space Administration (NASA) did
not yet exist. There was only one
gov-
ernment agency which could logically
take responsibility and fund the project
-namely, the Advanced Research Proj-
ects Agency (ARPA) of the Defense
Department.
It
was a thoroughly anoni-
alous situation to have a group of
weapons experts in a private company
working on a space project, and it
took many months of negotiation to
obtain the first contract from ARPA.
At that early date in its history ARPA
did not insist that anything which it
supported 11iust have a military justifica-
tion. The terms of the first contract
permitted designation of peacef~ll inter-
planetary exploration as the major
goal of the project. Nevertheless the
project was administered through De-
tense Department channels, and military
Force was told that if it wished to con-
tinue the project for nonmilitary rea-
sons
it
should enlist the cooperation
of NASA.
In
1963
NASA finally showed sonie
official interest in Orion. Jim Nance,
acting first as assistant director of the
project ~lnder Taylor and later as di-
influences were inevitably at work ~~pon rector in his own right, established
it.
Quite soon after Orion officially be-
gan, NASA was established, with legal
responsibility for all nonmilitary space
activities.
NASA quickly began to an-
nex parts of ARPA's nonmilitary func-
tions, and the Air Force responded by
annexing ARPA's military space proj-
ects, so that the situation of ARPA was
reminiscent of the partition of Poland
between Pr~lssia and Russia in the 18th
century. In the end, Orion was left as
the only space project in the hands
of ARPA, largely because neither
NASA nor the Air Force considered
it a valuable asset. Taylor's efforts to
interest NASA in Orion during this
period met with no success.
In 1960 ARPA decided to drop Ori-
on, and Taylor was compelled to go to
the Air Force for sponsorship. Ac-
cording to the law, the Air Force
may handle only military projects, and
must apply a rigid definition of the
word
r7iilitary.
A project is defined as
niilitary only if a direct military re-
quirement for it exists. There is no
niilitary requirement for interplanetary
exploration. Thus Taylor paid a high
price for his Air Force contract. Al-
though the technical substance of the
work was not changed, the project be-
came in name a niilitary enterprise di-
rected toward real or iliiagined military
requirements. This arrangement con-
tinued in force until the end of the
project in 1965.
The effect of the military sponsorship
of Orion was, in the
end, di5astrous.
The Air Force officials adni~nistering
the project were sympathetic to the
long-range and nonmilitary aspects of
the work, but they were
conipelled
by their own rules to disguise their
sympathies. Each year when they ap-
plied to the high authorities in the
Defense Department, Harold Brown
and McNamara, for more nioney to
expand the project, they had to argue
in terms of immediate military require-
ments. Men as wise and critical as
Harold Brown and McNaniara could
easily see that the military applications
of Orion are either spurious or positive-
ly undesirable. So the requests for ex-
pansion were turned down. The Air
friendly relations with the Marshall
Space Flight Center in Huntsville,
Alabama. Within NASA, Orion's pos-
sibilities appealed particularly to the
Office of Manned Space Flight, where
people are beginning to worry about
what they should do after the Apollo
mission is over. NASA awarded Orion
a sniall study contract, and froni this
resulted the design of ships for specific
interplanetary missions. Also in
1963
the test-ban treaty was signed, and
nuclear explosions became more than
ever politically questionable.
In 1964 the shadows began to close
in. The Air Force grew tired of sup-
porting a project which McNaniara
would not allow to grow, and an-
nounced that further support would be
forthcoming only if
NASA
would make
a serious contribution. At the eleventh
hour, in October 1964, Nance suc-
ceeded in getting the basic technical
facts concerning Orion
(I)
declas-
sified, so that it became possible for
the first time to discuss the issue
publicly. A certain interest in Orion
belatedly developed within the engineer-
ing coniniunity but did not extend to
the scientific community. In Deceliiber
1964 the questlon of the support
of
Orion came to a final decision with-
in NASA, with the result which was
announced in January 1965
Col~cerl~ingthe Verdict
As is proper in conducting an in-
quest, we have first assembled the his-
torical evidence, and now we come
to the question of a verdict. Who
ltilled Orion, and why? And was the
murder justifiable?
Four groups of people were directly
responsible for the death of Orion.
These are the Defense Department,
the heads of NASA, the promoters of
the test-ban treaty, and the scientific
cori~munityas a whole. Each group en-
countered Orion within the context of
a larger struggle in which Orion ap-
peared to then1 as a relatively minor
issue. In each group a negative attitude
toward Orion was dictated by general
principles which, in the wider context,
SCIENCE,
VOL.
149
were wise and enlightened. In each
group the men who killed Orion acted
from high and responsible motives. And
yet their
motives were strangely irrele-
vant to the real issues at stake in this
highly individual case. I will examine
the four groups in turn and describe
how the problem of Orion presented
itself to
them.
The Defense Department chiefs have
been waging for many years a suc-
cessful battle to stop the Air Force
from embarking upon a great variety
of technically interesting projects whose
military importance is questionable.
The nuclear-propelled airplane was one
such project, which was stopped only
after large sums of money had been
wasted on it. More recently, as in the
cases of the
B-70
bomber and the
Dynasoar orbital airplane, McNaniara
has been strong enough to call a halt
before the big money was spent. There
is little doubt that, when the Air Force
asked for more money for Orion, the
authorities in the Defense Department
mostly thought of it as one more in the
long series of Air Force extravaganzas
which it was their duty to suppress. The
way in which the money was requested
made it difficult for them to view it
otherwise. And within this context
their decision was unquestionably
right.
The heads of NASA were not in-
terested in Orion at the time NASA
began for the
simple reason that it was
a classified project supported by the
Defense Department and therefore out-
side their terms of reference. They were
explicitly enjoined by Congress not to
trespass upon military ground, and they
had no wish to become gratuitously
involved with a project encumbered by
all the bureaucratic nuisances of secre-
cy.
'The established policy of NASA is
to conduct as many as possible of its
operations openly and without requir-
ing all its employees to be cleared
for security. Few will question that
this policy is wise as a general rule,
and indeed essential to the maintenance
of a healthy scientific atmosphere with-
in NASA.
When the heads of NASA came to
their final decision concerning Orion,
in 1964, the jurisdictional issue was
no longer central. The Air Force had
officially appealed to NASA for a dec-
laration of support, and participation
in a future development of Orion would
not have compromised the nonmilitary
status of NASA. In 1964 the dominat-
ing concern at the top levels of NASA
was the search for political stability.
The heads of NASA have learned that
their first duty to the space program
is to keep it politically popular. With-
out consistent support from the public
and from Congress, there would be
no possibility of an effective program.
It is therefore wise to sacrifice technical
improvements if technical improve-
ments carry risks of failure which
may
be politically upsetting to the entire pro-
gram. Above all, spectacular and public
failures are to be avoided. When
a
re-
sponsible public official thinks of Orion
he inevitably envisions a shipload of
atomic bonlbs all detonating simulta-
neously and wiping out half of Florida.
Though it is technically easy to make
such an accident impossible, it is not
possible to exorcise the fear of it. The
heads of NASA know that fear is
the most potent force in politics, and
they have no wish to be feared.
The promoters of the test-ban treaty
are a heterogeneous group of people,
including the Arms Control and Dis-
armament Agency, the State Depart-
ment, a large segment of Congress,
the White House staff, and the Presi-
dent's Science Advisory Committee
(PSAC). About the only thing that
all the people working for the treaty
had in common was a total unconcern
for the welfare of Project Orion. Most
of them had never heard of Orion, and
most of those who had heard of it
(for example,
some influential mem-
bers of PSAC) had met it only in
a
context in which they were committed
to oppose it. They had met it within
the context of a continuing battle to
stop the military arm of the U.S.
Government from gratuitously expand-
ing the arms race into arenas where no
arms race yet existed. The PSAC had
been successful in opposing a race to
build bigger bombs than the U.S.S.R.
was building, and had also successfully
opposed the idea of placing offensive
nuclear weapons in orbit. The members
of PSAC have developed a deep com-
mitment to the policy of military re-
straint, of deploying new weapons sys-
tems only when a military need exists
and not just for the sake of technolog-
ical novelty. Their commitment to this
goal has served their country well, and
has borne fruit in many other wise de-
cisions besides the decision to negotiate
the test-ban treaty. Seeing Orion from
this viewpoint, as an Air Force project
ostensibly aimed at large-scale military
operations in space, they felt no
qualms in crushing it.
Lastly, the scientific community as
a whole is responsible, in a negative
sense, for the death of Orion. The
vast majority of scientists have con-
sistently refused to become interested
in the technical problems of propulsion,
believing that this was a job for en-
gineers. A clear illustration of their
point of
view is provided by the report
on national goals in space for the
years 1971-85, recently published by
the Space Science Board of the National
Academy of Sciences. This report de-
scribes in detail a recommended pro-
gram of space activities which is based
on the assumption that the propulsion
systems available until 1985 will be
those now under development. The
Space Science Board does not concern
itself with the question of whether a
scientific effort might bring radical im-
provements in the art of propulsion
before 1985. To sonlebody familiar with
the potentialities of Orion, the Space
Science Board program seems both
pitifully modest and absurdly expen-
sive.
Here again, the disinterest of scien-
tists in problems of propulsion arises
from attitudes which in a wider context
are wise and healthy. In their dealings
with NASA and with the public, scien-
tists have constantly preached that the
payload is more important than the
rocket, that what you do there is more
important than how you get there. They
have argued repeatedly, and usually
without success, that ten dollars spent
on unmanned vehicles are scientifically
more useful than a hundred spent on
manned vehicles, and that often one
dollar spent on ground-based observa-
tions is scientifically more useful still.
They have been alienated from the
field of propulsion by the spectacle of
NASA officials claiming a scientific
justification for space-propulsion de-
velopments which have little or nothing
to do with science. They have, after
long years of listening to the pseudo-
scientific propaganda of the manned
space program, learned to confine their
attention to that small part of the
NASA empire within which they have
some real influence-namely, the Office
of Space Science and Applications
(OSSA). Within OSSA they have cre-
ated an atmosphere of scientific sanity
which has allowed excellent and many-
sided programs of unmanned scientific
exploration to be carried out with the
eighth of the NASA budget which is
allotted to this purpose.
The Space Science Board of the Na-
tional Academy, in its consideration of
future activities, was mainly concerned
with preserving the quality and the
sci-
entific integrity of these existing un-
manned programs. The board rightly
sees as its primary task the definition
of the ends, rather than the means, of
the space science enterprise.
What then is the attitude of a scientist
who is actively engaged in scientific
space activities toward a project such
as Orion? He has perhaps just been
denied by NASA a half-niillion-dollar
ground-based telescope with which to
observe planets. Or he has designed
an experiment which was excluded,
because of space limitations,
from the
next orbiting solar observatory. And
then he hears that a wonderful new
propulsion systeni has been invented
which might allow him,
15
years later,
to ~iiake high-quality nearby observa-
tions of Jupiter and Saturn. The price
of the new systeni is quoted as only a
few billion dollars. He is understandably
not enthusiastic.
This brief summary of Orion's his-
tory has shown that every one of
the four murderers had good and laud-
able
motives for killing the project,
or, in the case of the scientific com-
munity, for not lifting a finger to save
it. Orion had a unique ability to an-
tagonize
sinlultaneously the four most
powerful sections of the Washington
establishment. The remarkable thing is
that, against such odds, with its future
never assured for more than a few
months at a time, the project survived
as long as it did. It held together for
7
long years a band of talented and de-
voted men, and produced in that time
a volume of scientific and engineering
work which in breadth and thorough-
ness has rarely been equaled.
The story of Orion is significant,
because this is the first time in
modern
history that a major expansion of
human technology has been suppressed
Conformity
as
a
Tactic
of
Ingratiation
Uses of agreement to enhance one's power in a
social relationship are explored experimentally.
There seems to be much promise
in looking at social interaction with an
cye to the unfolding of strategies de-
signed to gain or maintain personal
power. There is nothing novel in the
suggestion that there is a strategic side
to social behavior-that people try to
calculate ways to make the most of a
particular relationship-but the attempt
to study such strategies by laboratory
experimentation is
a
recent develop-
ment. Here
I
shall review several
studies which especially concern
in-
gratiation, or "strategic behaviors
.
.
.
designed to influence a particular other
person concerning the attractiveness
'The
author is professor of psychology,
Duke
University, Durham,
North
Carolina.
Edward
E.
Jones
of one's personal qualities"
(I).
I
hope,
in the process, not only to present re-
sults relevant to a developing theory of
strategic overtures, but also to illustrate
a form of experimental research which
seems to show promise of unraveling
the subtleties of social behavior.
All interpersonal relationships in-
volve
mutual dependence: this is the
equivalent of saying that each party
to
a
social interchange has potential
influence over certain rewards avail-
able to and costs incurred by the other.
If
the dependences of one on the other
are not only mutual but approxinlately
equal, then there is a balance of power
in which each can enforce a certain
minimal receipt of rewards through
for political reasons. Many will feel
that the precedent is a good one to
have established. It is perhaps wise
that radical advances in technology,
which may be used both for good and
for evil purposes, be delayed until the
human species is better organized to
cope with them. But those who have
worked on Project Orion cannot share
this view. They must continue to hope
that they may see their work bear
fruit in their own lifetimes. They can-
not lose sight of the dream which
fired their imaginations in
1958
and
sustained them through the years of
5truggle afterward-the dream that the
bombs which killed and maimed at
Hiroshima and Nagasaki may one day
open the skies to mankind.
Reference
1.
J.
C.
Nance, "Nuclear Pulse
Propulsion,"
Gen-
e~al
Aton7rc
Rept.
No.
GA-5572
(5
Oct.
1964),
unclasr~fied.
his capacity to enact or fail to enact
the responses sought by the other.
When the power in a two-person rela-
tionship is asymmetrical, however, the
more dependent person is somewhat
at the mercy of the more powerful
one. In any event, we can well under-
stand why the more dependent person
is concerned about his poor position
and, under most circun~stances, tries
in various ways to improve it.
When we look at the strategic
alternatives available to the more de-
pendent person, it appears that some
of these strategies guarantee him at
least a certain
minimum of rewards
but do so at the expense of confirming
or strengthening the power asymmetry
which defines his dependence. Other
strategies, however, may be effective
in modifying the
asymmetry itself so
that the dependent person's power is,
in the long run, increased. Compli-
ance is an example of one kind of
dependence-confirming tactic. The de-
pendent person may, through overt
obedience, avoid punishment and secure
the rewards available to him, but such
conlpliance tends to perpetuate the
power differential to which it is
a
re-
sponse. For example, the more reliable
the worker becomes in meeting the
supervisor's
demands, the more confi-
dent the supervisor will be that these
demands are reasonable, and that the
worker is happy with the "bargain"
symbolized by the difference in their
SCIENCE,
VOL.
149
Earth's escape velocity is 11.19 km/s. This is the velocity you need in order to escape Earth's gravitational pull. This means if a mission involves bringing payload to another planet, several stages must be used to obtain the necessary escape velocity.
Conventional rocket engines produce thrust by the expulsion of an exhaust fluid (usually high pressure gas) that has been accelerated to high speed through a propelling nozzle. Most rocket engines use the combustion of reactive chemicals to supply the necessary energy to accelerate the propellant . Nuclear thermal rockets use a nuclear reactor as the source of energy to accelerate the propellant.
*Conventional Rocket Engine Diagram*
One of the main reasons for the added secrecy of the Orion project is that cheap, easy to manufacture atomic bombs were key for the viability of the project. This is naturally highly classified work.
### Nuclear Pulse Propulsion
Briefly, the Orion propulsion system would operate as follows:
Low yield nuclear bombs are detonated consecutively (approx. one every four seconds) external to and behind the vehicle. A substantial fraction of the mass of each bomb - the propellant - is directed towards the base of the vehicle as a high-velocity high-density plasma which is intercepted by a large circular steel plate - the pusher. The momentum of the propellant is transferred to the pusher and the resulting high accelerations (the jerks) are smoothed out by shock absorbing devices to levels of a few g's in the upper vehicle (within human tolerance).
*Project Orion Diagram*
The idea of using a series of explosive pulses to propel a rocket can actually be traced back all the way to Hermann Ganswindt, a German inventor and spaceflight scientist who published his ideas in the 1890s. In the early 1900s, R.B. Gostkowski issued a scientific study of a concept using dynamite charges.
Ted Taylor was an American theoretical physicist who worked at Los Alamos during the development of the first nuclear weapons.
He invented the world's smallest nuclear weapon, nicknamed “the Davy Crockett,” and he also designed some of the largest Hydrogen bombs ever built. For years he was captivated by the “technical sweetness” of weapons physics; but when he realized the consequences of nuclear war, he changed. “It's all too easy for a madman, a terrorist, or a criminal to build his own atomic bomb,” he said in 1972. “I've been worried about it ever since I made my first one.” Ted Taylor believed that the world's number one problem is the proliferation of plutonium. He warned against the rash proliferation of nuclear power plants because they make plutonium available worldwide.
Ted Taylor was a prominent figure in Project Orion. He planned on taking part of Project Orion's first trip and even made plans to take his family along with him.
*Ted Taylor*
In an electric engine (also known as an "ion engine") an electric power generator supplies energy to ionize particles of a propellant and also provides the power for electric fields used to accelerate the resulting ions to high directed velocity. In essence, electric propulsion sacrifices high trust for high exhaust velocity, which isn't an issue if you are already in orbit and therefore don't need a thrust/weight ratio greater than 1.
As of 2019, over 500 spacecraft operated throughout the Solar System use electric propulsion.
*Electric Engine at the NASA JPL*
### Difference in upper limit of V between chemical rockets & nuclear rockets
The main reason for the difference in the upper limit for V between chemical and nuclear reactors is due to the choice of propellant gas.
The first thing to note is that V is proportional to $\sqrt{\frac{T}{M}}$ where M is the molecular weight of the propellant gas and T is the temperature of the gas after it is heated. Hydrogen has the lowest molecular weight of any gas (2 atomic mass units) and is, therefore, the ideal propellant gas when heated by either chemical or nuclear reactions.
With a chemical rocket, one is stuck with the propellant gases produced by a chemical reactions. For example, the space-shuttle boosters burn a mixture of hydrogen and oxygen to produce a propellant gas of hot water vapor. The gaseous product of this chemical reaction has one of the lowest molecular weights (18 atomic mass units) and the highest temperatures—and therefore one of the highest exhaust velocities—of any of the chemical reactions used to propel rockets. The molecular weight of water vapor is considerably higher—nine times higher—than the molecular weight of hydrogen.
However, in the case of a nuclear-thermal rocket the propellant gas can be freely chosen, as in this case, the stored propellant gas is heated with the energy from a nuclear reaction.
The temperature of the gas heated in a solid-core nuclear reactor is unlikely to exceed the temperature of the gas produced and heated by a chemical reaction. Burning a mixture of hydrogen and oxygen produces water vapor at a temperature of 5,555 K , twice the maximum temperature in a solid-core reactor (2,750 K).
Part of the inspiration for Project Orion came from noticing components that survived the Trinity test at close range, such as Jumbo (a containment vessel for an unsuccessful explosion, which was about ~730m away from the explosion) and rebar sticking up out of what was left of the concrete foundation of the tower holding the bomb.
*Jumbo container after the test*
### Nuclear-powered aircraft
Physicist Enrico Fermi had introduced the idea of nuclear flight as early as 1942. The advantages of nuclear-powered airplanes are similar to those of nuclear submarines. Nuclear submarines don't need to surface for fuel, and nuclear airplanes would not need to land.
There are obvious challenges to nuclear powered aviation: protecting crew from nuclear radiation and dealing with possible crashes being two obvious ones. At some point, engineers proposed to solve the problem of exposing the crew to radiation by hiring elderly Air Force crews to pilot the hypothetical nuclear planes, because they would die before radiation exposure gave them fatal cancers.
In the end, neither the US nor the Soviet Union created any operational nuclear powered aircraft.