Nuclear Rockets - Going up

Sep 4 19:06 UTC 1998

Subject: Fw: 100 Tons To Mars In 125 Days
   Date: Wed, 2 Sep 1998 14:48:35 -0400
   From: "Franklin Ratliff" <fratliff@lasetech.com>
----------
From: Franklin Ratliff <fratliff@lasetech.com>
To: CKAnderson@sff.net
Subject: 100 Tons To Mars In 125 Days
Date: Monday, August 31, 1998 11:15 AM

Here's a basic question worth thinking about. Is it realistic or even 
sane to contemplate a manned trip to Mars that takes six months to a 
year to even get there?

Sincerely, Franklin Ratliff

________________________________________________

Project Orion: Its Life, Death, and Possible Rebirth

An essay submitted for the Robert H. Goddard Historical Essay Contest

November 24th, 1992


Copyright (c) 1993 Michael R. Flora (root@isaac.msfc.nasa.gov)


Project Orion: Its Life, Death, and Possible Rebirth

The race to the moon, in the forms of Project Apollo and the 
still-shadowy Soviet lunarprogram, dominated manned space flight during 
the decade of the 1960's. In the United States, the project sequence 
Mercury-Gemini-Apollo succeeded in putting roughly sixty people into 
space, twelve of them on the moon. Yet, during the late 1950's and 
early 1960's, the U.S. government sponsored a project that could 
possibly have placed 150 people, most of them professional scientists, 
on the moon, and could even have sent expeditions to Mars and Saturn. 
This feat could conceivably have been accomplished during the same 
period of time as Apollo, and possibly for about the same amount of 
money. The code name of the project was Orion, and the concepts 
developed during its seven-year life are so good that they deserve 
serious consideration today.

Project Orion was a space vehicle propulsion system that depended on 
exploding atomic bombs roughly two hundred feet behind the vehicle (1). 
The seeming absurdity of this idea is one of the reasons why Orion 
failed; yet, many prominent physicists worked on the concept and were 
convinced that it could be made practical. Since atomic bombs are 
discrete entities, the system had to operate in a pulsed rather than a 
continuous mode. It is similar in this respect to an automobile engine, 
in which the peak combustion temperatures far exceed the melting points 
of the cylinders and pistons. The engine remains intact because the 
period of peak temperature is brief compared to the combustion cycle 
period.

The idea of an "atomic drive" was a science-fiction cliche by the 
1930's, but it appears that Stanislaw Ulam and Frederick de Hoffman 
conducted the first serious investigation of atomic propulsion for 
space flight in 1944, while they were working on the Manhattan Project 
(2). During the quarter-century following World War II, the U.S. Atomic 
Energy Commission (replaced by the Department of Energy in 1974) worked 
with various federal agencies on a series of nuclear engine projects 
with names like Dumbo, Kiwi, and Pluto, culminating in NERVA (Nuclear 
Engine for Rocket Vehicle Application) (3). Close to producing a flight 
prototype, NERVA was cancelled in 1972 (4). The basic idea behind all 
these engines was to heat a working fluid by pumping it through a 
nuclear reactor, then allowing it to expand through a nozzle to develop 
thrust. Although this sounds simple the engineering problems were 
horrendous. How good were these designs? A useful figure for comparing 
rocket engines is specific impulse (Isp), defined as pounds of thrust 
produced per pound of propellant consumed per second. The units of Isp 
are thus seconds. The best chemical rocket in service, the cryogenic 
hydrogen-oxygen engine, has an Isp of about 450 seconds (5). NERVA had 
an Isp roughly twice as great (6), a surprisingly small figure 
considering that nuclear fission fuel contains more than a million 
times as much energy per unit mass as chemical fuel. A major problem is 
that the reactor operates at a constant temperature, and this 
temperature must be less than the melting point of its structural 
materials, about 3000 K (7).
================
A number of designs were proposed in the late 1940's and 1950's to get 
around the temperature limitation and to exploit the enormous power of 
the atomic bomb, estimated to be on the order of 10 billion horsepower 
for a moderate-sized device (8). The Martin Company designed a nuclear 
pulse rocket engine with a "combustion chamber" 130 feet in diameter. 
Small atomic bombs with yields under 0.1 kiloton (a kiloton is the 
energy equivalent of 1000 tons of the high explosive TNT) would have 
been dropped into this chamber at a rate of about one per second (9); 
water would have been injected to serve as propellant. This design 
produced the relatively small Isp of 1150 seconds, and could have 
yielded a maximum velocity change for the vehicle of 26,000 
feet/second. The vehicle would have been boosted to an altitude of 150 
miles by chemical rockets, and the extra 8000 ft/sec or so thus 
provided would have allowed it to escape the Earth's gravity (10). The 
Lawrence Livermore Laboratory produced a similar although much smaller 
design called Helios at about the same time (11).

In a classified 1955 paper (12), Stanislaw Ulam and Cornelius Everett 
eliminated the combustion chamber entirely. Instead, bombs would be 
ejected backwards from the vehicle, followed by solid-propellant disks. 
The explosions would vaporize the disks, and the resulting plasma would 
impinge upon a pusher plate. The advantage of this system is that no 
attempt is made to confine the explosions, implying that relatively 
high-yield (hence high-power) bombs may be used. Such a system is 
neither temperature- nor power-limited. Ulam may have been influenced 
by experiments conducted at the Eniwetok proving grounds, where 
graphite-covered steel spheres were suspended thirty feet from the 
center of an atomic explosion. The spheres were later found intact; a 
thin layer of graphite had been ablated from their surfaces (13).  

Project Orion was born in 1958 at General Atomics in San Diego. The 
company, now a subsidiary of defense giant General Dynamics, was 
founded by Frederick de Hoffman to develop commercial nuclear reactors. 
The driving force behind Orion was Theodore Taylor, a veteran of the 
Los Alamos weapons programs. De Hoffman persuaded Freeman Dyson, a 
theoretical physicist then at the Institute for Advanced Study in 
Princeton, New Jersey, to come to San Diego to work on Orion during the 
1958-1959 academic year. Dyson says that Taylor adopted a specific 
management model for the project: the Verein fur Raumschiffahrt (VfR), 
the German rocket society of the 1920's and 1930's which numbered among 
its members Werner von Braun. The VfR had little structure: no 
bureaucracy and essentially no division of labor between its members; 
it accomplished much before it was taken over by the German army. Orion 
at first was similar: scientists did practical engineering and 
engineers built working scale models, all on a shoestring budget (14).

Taylor's specialty at Los Alamos had been the effects of atomic 
weapons. He was an expert at making small bombs at a time when the 
drive was toward ever-bigger superweapons.  He was also aware of 
techniques for shaping explosions, for making bomb debris squirt in one 
particular direction.  Taylor adopted Ulam's pusher-plate idea but 
instead of the propellant disks he combined propellant and bomb into a 
single pulse unit. The propellant material of choice was plastic, 
probably polyethylene (15). Plastic is good at absorbing the neutrons 
emitted by an atomic explosion (i.e. it couples well with the prompt 
radiation energy) and in addition it breaks down into low-weight atoms 
such as hydrogen and carbon which move at high speeds when agitated.  
There are indications that a plastic similar to Styrofoam is used 
inside hydrogen bombs to "channel" the energy from the atomic trigger 
into the fusible material (16). The advantage of the pusher plate 
design, as Taylor and Dyson saw it, was that it could simultaneously 
produce high thrust with high exhaust velocity. No other known 
propulsion system combined these two highly desirable features. The 
effective Isp could theoretically be as high as 10,000 to one million 
seconds (17). The calculated force exerted on the pusher plate was 
immense; it would have created intolerable acceleration for a manned 
vehicle. Therefore, a shock absorber system was placed between the 
plate and the vehicle itself. The impulse energy delivered to the plate 
was stored in the shock absorbers and released gradually to the 
vehicle.
==========================
The Orion workers built a series of models, called Put-Puts or Hot 
Rods, to test whether or not pusher plates made of aluminum could 
survive the momentary intense temperatures and pressures created by 
chemical explosives.  Several models were destroyed, but a 100-meter 
flight in November 1959, propelled by six charges, was successful and 
demonstrated that impulsive flight could be stable (18).  These 
experiments also proved that the plate should be thick in the middle 
and taper toward its edges for maximum strength with minimum weight 
(19).

The durability of the plate was a major issue. The expanding plasma 
bubble of each explosion could have a temperature of several tens of 
thousands of Kelvins even when the explosion occurred hundreds of feet 
from the plate.  Following the lead of the Eniwetok tests, a scheme was 
devised to spray grease (probably graphite-based) onto the plate 
between blasts (20). It is not known if this scheme was retained in 
later versions of the Orion design.  Extensive work was done on plate 
erosion using an explosive-driven helium plasma generator. The 
experimenters found that the plate would be exposed to extreme 
temperatures for only about one millisecond during each explosion, and 
that the ablation would occur only within a thin surface layer of the 
plate (21). The duration of high temperatures was so short that very 
little heat flowed into the plate; active cooling was apparently 
considered unnecessary. The experimenters concluded that either 
aluminum or steel would be durable enough to act as plate material.

The Orion workers realized early that the U.S. government had to become 
involved if the project was to have any chance of progressing beyond 
the tinkering stage.  Accordingly, the Advanced Research Projects 
Agency (ARPA - later DARPA with "D" standing for "Defense") was 
approached in April1958. In July, it agreed to sponsor the project at 
an initial funding level of $1 million per year; it was at this time 
that the code name of Orion was assigned (22).  Work proceeded under 
ARPA order 6, task 3, entitled "Study of Nuclear-Pulse-Propelled Space 
Vehicles" (23).

Taylor and Dyson were convinced that the approach to space flight being 
pursued by NASA (which had just been created in January 1958) was the 
wrong one. Von Braun's chemical rockets in their opinion were very 
expensive, had very limited payloads, and were essentially useless for 
flights beyond the moon (24). The Orion workers wanted a spaceship that 
was simple, rugged, capacious, and above all affordable. Taylor 
originally called for a ground launch, probably from the U.S. nuclear 
test site at Jackass Flats, Nevada (25). The vehicle has been described 
as looking like a bishop's miter or the tip of a bullet, sixteen 
stories high and with a pusher plate 135 feet in diameter (26). 
Intuitively it seems that the bigger the pusher plate, the more 
efficiently the system would perform. For a derivation of a formula for 
the effective specific impulse of a nuclear-pulse rocket and for the 
relations between pusher plate diameter, pulse energy, and Isp, the 
reader should consult Reynolds (27). The launch pad would have been 
composed of eight towers, each 250 feet high. The mass of the vehicle 
on takeoff would have been on the order of 10,000 TONS (28); most of 
this mass would have gone into orbit. The bomb units ejected on takeoff 
would have yielded 0.1 kiloton; initially the ejection rate would have 
been one per second. As the vehicle accelerated the rate would slow 
down and the yield would increase until 20-kiloton bombs would have 
been going off every ten seconds (29). The idea seems to have been for 
the vehicle to fly straight up until it cleared the atmosphere so as to 
minimize radioactive contamination.

At a time when the U.S. was struggling to put a single man into orbit 
aboard a modified military rocket, Taylor and Dyson were developing 
plans for a manned voyage of exploration through much of the solar 
system. The original Orion design called for 2000 pulse units, far more 
than enough to attain Earth escape velocity. "Our motto was 'Mars by 
1965, Saturn by 1970'", recalls Dyson (30). Orion would have been more 
akin to the rocket ships of science fiction than to the cramped 
capsules of Gagarin and Glenn. One hundred and fifty people could have 
lived aboard in relative comfort; the useful payload would have been 
measured in thousands of tons (31). Orion would have been built like a 
battleship, with no need for the excruciating weight-saving measures 
adopted by chemically-propelled spacecraft. It is unclear how the 
vehicle would have landed; it is reasonable to assume that specialized 
chemically-powered craft would have been used for exploration. Taylor 
may have anticipated that a conventional Space Shuttle-type vehicle 
would have been available to transport people to and from orbit. Dyson 
gives the astounding figure of $100 million per year as the cost of the 
proposed twelve-year program (32); surely this does not include 
development costs for the thousands of items from spacesuits to 
scientific instruments that such a program would require. The Orion 
program would have most likely "piggybacked" on the military weapons 
programs and the existing civilian space projects. Still, even if Dyson 
underestimated the cost by a factor of 20, the revised total would have 
been only $24 billion, roughly the same as the accepted cost for the 
Apollo program.
====================================
The times were changing, however. The fledgling space administration 
began to acquire all civil-oriented space projects run by the federal 
government; the Air Force got all projects with military applications. 
ARPA was left with Orion as its only space project, for two reasons. 
The Air Force felt that Orion had no value as a weapon, and NASA had 
made a strategic decision in 1959 that the civilian space program would 
be non-nuclear for the near future (33). NASA was and is a very 
publicity-conscious organization, and it is hard to overcome the 
negative perception of atomic devices of any kind on the part of the 
public. In addition,  NASA was filled with engineers who had spent 
their careers building ever-larger chemical rockets and either did not 
understand or were openly opposed to nuclear flight. In this situation 
the Orion workers were truly outsiders.

A crisis came in late 1959, when ARPA decided it could no longer 
support Orion on national-security grounds. Taylor had no choice but to 
approach the Air Force for funds. It was a hard sell. A common reaction 
from both military and civilian officials is displayed by the quote: 
"...you set off one big bomb and the whole shebang blows up."(34) The 
Air Force finally decided to take on Orion, but only on the condition 
that a military use be found for it. Dyson says that his Air Force 
contacts, although sympathetic to the goal of space exploration, felt 
that their hands were tied (35). One immediate result of the change of 
management was that all model flight testing was stopped (36). The 
freewheeling era was over; Taylor's dream of a company of "men of 
goodwill" exploring the solar system had died.

One can imagine that Orion could be used as a weapon platform, in a 
polar orbit so that it would eventually pass over every point on the 
Earth's surface. It could also protect itself easily, at least against 
attacks by small numbers of missiles. However, this idea has the same 
disadvantages as the early bomb-carrying satellite proposals. Terminal 
guidance would have been a problem (assuming that hardened, high-value 
installations were the intended targets), since the technology for 
steering missile warheads accurately had not yet been developed. Both 
the U.S. and the Soviet Union were deploying missiles that were capable 
of reaching their targets in fifteen minutes with multi-megaton 
warheads, making orbiting bomb platforms irrelevant.

Robert McNamara, Defense Secretary under the Kennedy Administration, 
realized that Orion was not a military asset. His department 
consistently rejected any increase in funding for the project, 
effectively limiting it to a feasibility study (37). Taylor and Dyson 
knew that another money source had to be found if a flyable vehicle was 
to be built. NASA was the only remaining option. Accordingly,  Taylor 
and James Nance, a General Atomics employee and later director of the 
project, made at least two trips to Marshall Space Flight Center (MSFC) 
in Huntsville, Alabama (38). MSFC was von Braun's domain and it was 
where most of NASA's space propulsion research and development took 
place. Von Braun was hard at work on the Saturn project, which NASA had 
inherited from the old Army Ballistic Missile Agency. The Saturn V 
would eventually transport men to the moon. The Orion workers had 
produced a new, "first generation" design that abandoned ground launch 
and instead would have been boosted into orbit as a Saturn V upper 
stage. The core of the vehicle was a 200,000-pound "propulsion module" 
with a pusher-plate diameter of 33 feet, limited by the diameter of the 
Saturn. This design limitation also restricted Isp to from 1800 to 2500 
seconds (39). While disappointingly low by nuclear- pulse standards, 
this figure still far exceeded those of other nuclear rocket designs. 
The shock absorber system had two sections: a primary unit made up of 
toroidal pneumatic bags located directly behind the pusher plate, and a 
secondary unit of four telescoping shocks (like those on a car) 
connecting the pusher plate assembly to the rest of the spacecraft 
(40).

How many Saturn V's would have been required to put this vehicle into 
orbit? Dyson says one or two (41); a simple inspection of published 
drawings indicates at least two, possibly three if the crew module 
(with crew aboard) was intended to be flown separately (42). In this 
case, some assembly would have been done on-orbit. Several mission 
profiles were contemplated; the one developed in greatest detail 
appears to have been a Mars flight. Eight astronauts, with around 100 
tons of equipment and supplies, could have made a round trip to Mars in 
125 days (43); most modern plans call for one-way times of at least 
nine months.  Another impressive figure is that as much as 45% of the 
gross vehicle weight in Earth orbit could have been payload (44). 
Presumably the flight would have been made when Mars was nearest to the 
Earth; still, so much energy was available that almost the 
fastest-possible path between the planets could have been chosen. 
Inspection of the drawings indicates that a lander may also have been 
carried.

What about the cost? Pedersen's 1964 estimate of $1.5 billion for the 
project (45) suggests the superior economics of nuclear pulse 
spaceships. Dyson felt that Orion's appeal was greatly diluted by the 
chemical booster restriction: the Saturns would have represented over 
50% of the total cost (46).
==================================
Von Braun became an enthusiastic Orion supporter, but he was able to 
make little headway among higher-level administration officials. In 
addition to the general injunction against nuclear power, very 
practical objections were raised: what if a Saturn bearing a propulsion 
module with hundreds of bombs aboard should explode? Was it possible to 
guarantee that not a single bomb would explode or even rupture? NASA's 
understandable fear of a public-relations disaster contributed to its 
reluctance to provide money (47); however, its Office of Manned 
Spaceflight was sufficiently interested to fund another study (48).

A hammer blow was delivered in August 1963 with the signing of the 
nuclear test-ban treaty by the U.S., U.K., and U.S.S.R. Orion was now 
illegal under international law.  Yet the project did not die 
immediately. It was still possible that an exemption could be granted 
for programs that were demonstrably peaceful. Surely the treaty reduced 
Orion's political capital even further, though. Yet another problem was 
that, because Orion was a classified project, very few people in the 
engineering and scientific communities were aware of its existence. In 
an attempt to rectify this, Nance (now managing the project) lobbied 
the Air Force to declassify at least the broad outline of the work that 
had been done. Eventually it agreed, and Nance published a brief 
description of the "first generation" vehicle in October 1964 (49).   

The Air Force, meanwhile, had become impatient with NASA's temporizing. 
It was willing to be a partner but only if NASA would contribute 
significant funds. Hard-pressed by the demands of Apollo, NASA made its 
decision in December 1964 and announced it publicly the following 
month: no money would be forthcoming (50). The Air Force then anounced 
the termination of all funding, and Orion quietly died. Some $11 
million had been spent over nearly seven years (51).

Overshadowed by the moon race, Orion was forgotten by almost everybody 
except Freeman Dyson and Theodore Taylor.  Dyson in particular seems to 
have been deeply affected by his experience. The story of Orion is 
important, he says, "...because this is the first time in modern 
history that a major expansion of human technology has been suppressed 
for political reasons"(52). His 1968 paper (53) gives more physical 
details of nuclear pulse drives, and even suggests extremely large 
starships powered by fusion explosions.  Ultimately he became 
disillusioned with the concept, primarily because of the radiation 
hazard associated with the early ground-launch idea. Yet he says that 
the most extensive flight program envisaged by Taylor and himself would 
have added no more than 1% to the atmospheric contamination then (circa 
1960) being created by the weapons-testing of the major powers (54).

Does it make any sense to even think of reviving the nuclear-pulse 
concept? Economically the answer is yes.  Pedersen (55) says that 
10,000-ton spaceships with 10,000-ton payloads are feasible. Spaceships 
like this could be relatively cheap compared to Shuttle-like vehicles 
due to their heavyweight construction. One tends to think of shipyards 
with heavy plates being lowered into place by cranes. How much would 
the pulse units cost? Pedersen gives the amazingly low figure of 
$10,000 to $40,000 per unit for the early Martin design (56); there is 
reason to think that $1 million is an upper limit (57). Primarily from 
strength of materials considerations, Dyson (58) argues that 30 
meters/second (about 100 feet/second) is the maximum velocity increment 
that could be obtained from a single pulse. Given that low-altitude 
orbital velocity is about 26,000 feet/second, around 350 pulses would 
be required (59). Using $500,000 as a reasonable pulse-unit cost, this 
implies a "fuel cost" of $175 million, cheaper than a Shuttle launch. 
Whereas the Shuttle might carry thirty tons of payload, the pulse 
vehicle would carry thousands. If one uses the extreme example of 
spending $5 billion to build a vehicle to lift 10,000 tons (or 20 
million pounds) to orbit, the cost if spread over a single flight is 
$250 per pound, far cheaper than the accepted figure of $5,000 to 
$6,000 per pound for a Shuttle flight.
======================
Efficiency improvements could be made by improving the design of the 
pulse units. Considerable progress has been made in nuclear bomb design 
over the past thirty years.  Neutron bombs, for instance, demonstrate 
that it is possible to change the form of the energy emitted by the 
explosion.  Recent work on X-ray lasers bears on the important problem 
of shaping the explosion into a beam. Yet it is impossible to prevent 
the formation of radioactive fission fragments.  For a ground launch, 
choosing a very remote site such as a floating platform in the extreme 
southern Atlantic or Pacific would minimize the radiation hazard to 
humans. The chemical-rocket imperative to launch as close to the 
equator as possible disappears when such an abundance of energy is 
available. Even this might be judged environmentally unacceptable, 
though; perhaps ANY release of radiation into the atmosphere is wrong. 
In this case the option of a space launch remains open. Even this has 
been criticized on the grounds that it would leave a radioactive debris 
trail in space. However, interplanetary space is a very dangerous 
environment to begin with, being periodically saturated with fast 
charged particles from solar flares and with extremely energetic cosmic 
rays occasionally blasting through. The notion that the bomb debris 
would form a trail is challenged by the fact that the velocity of most 
of the debris would exceed solar escape velocity (60).

Although the Saturn V no longer exists, U.S. engineers are currently 
studying several heavy-lift systems. Given the recent reduction in 
world tensions, even the Russian Energia could be considered. Russian 
nuclear scientists, unemployed after the Cold War, might collaborate 
with Americans on nuclear-pulse space projects. Fast flights to the 
planets might be made in ten years or less, at reasonable expense, 
instead of thirty to fifty years.

Unfortunately, the Orion concept is inherently "dirty" because it uses 
fission fuel. It is also inefficient; this is acceptable only because 
of the vast amounts of energy available. A much better alternative is 
fusion, since a fusion rocket would not leave a wake of heavy 
radioactive ions. The British Interplanetary Society's Daedalus project 
(61) was a study of an unmanned interstellar probe. It would have been 
driven by fusion "microexplosions" caused by irradiating fuel pellets 
with electron beams at pulse rates up to 250 Hz, in a magnetic 
"combustion chamber".  Confinement and shaping of the plasma with a 
magnetic field would make Daedalus vastly more efficient than Orion.   
Daedalus would work just as well in the solar system as between the 
stars, and one can imagine that in 75 to 100 years fusion freighters 
will be sailing regularly between the planets. An important point is 
that no one has yet produced controlled fusion energy with electron 
beams or anything else, while the technology required to build an 
Orion-type spaceship has existed for over thirty years.  Nuclear 
propulsion will get into space eventually. Orion might be the device 
that makes possible human occupation and economic exploitation of the 
solar system.


Notes

1.    Erik S. Pedersen, Nuclear Propulsion in Space (Englewood Cliffs, 
NJ: Prentice-Hall     Inc.,1964), p. 275.

2.    William R. Corliss, Nuclear Propulsion for Space (U.S.Atomic 
Energy Commission: Division of Technical Information, 1967), p. 11.

3.    Corliss, pp. 1-16.

4.    James A. Dewar, "Project Rover: The United States Nuclear Rocket 
Program", in History of Rocketry and Astronautics (John L. Sloop ed. - 
San Diego: American Astronautical Society Publications Office, 1991), 
p. 123.

5.    "Specific impulse", article in McGraw-Hill Encyclopedia of 
Science and Technology, vol. 17, p. 204.

6.    "Specific Impulse", p. 204

7.    Corliss, pp. 13-14.

8.    Pedersen (p. 276) gives 4.2 x 1019 ergs per kiloton exploding one 
such bomb per second yields 4.2 x 1012 joules / sec (i.e. watts) or 
roughly 5  
billion average horsepower.

9.  Pedersen, p. 276.

10. Pedersen, p. 276.

11. Eugene Mallove and Gregory Matloff, The Starflight Handbook (New 
York: John Wiley and Sons, 1989),  p. 60.

12. Mallove and Matloff, p. 61.

13. John McPhee, The Curve of Binding Energy (New York: Farrar,Straus 
and Giroux, 1974), pp. 167-168

14. Freeman Dyson, Disturbing the Universe (New York: Harper and Row, 
1979), pp. 109-110.

15. Mallove and Matloff, p. 63.

16. The Ground Zero Fund, Inc., Nuclear War: What's In It for You? (New 
York: Simon and Schuster Inc., 1977), p. 27.

17. Mallove and Matloff, pp. 60-61.

18. Dyson, Disturbing, p. 113

19. McPhee, p. 175.

20. McPhee, p. 175

21. J.C. Nance, "Nuclear Pulse Propulsion", IEEE Transactions on 
Nuclear Science (Feb. 1965),p. 177.

22. McPhee, p. 170.

23. DARPA letter to the author dated October 7th, 1992.

24. Dyson, Disturbing, pp. 109-110.

25. McPhee, pp. 173-174.

26. McPhee, pp. 173-174.

27. T.W. Reynolds, "Effective Specific Impulse of External Nuclear 
Pulse Propulsion Systems", Journal of Spacecraft and Rockets 10 (Oct. 
1973), pp.629-630

28. The volume of a cone 200 feet high with a base diameter of 135  
feet (the approximate dimensions of the proposed Orion vehicle) is 
about 1.5
million cubic feet.  If the average density is 10 pounds per cubic foot 
(about 1/6 that of water) the weight is 15 million pounds or 7500 tons.

29. McPhee, pp. 173-174.

30. McPhee, pp. 180-181.

31. McPhee, p. 158.

32. Dyson, Disturbing, p. 111.

33. Dyson, Disturbing, p. 113.

34. Nance, p. 177.

response 2 of 8:

Sep 7 21:29 UTC 1998

"Warning: long"?   ;)

This approach has almost become a cliche' in SF in the last few years.  I'd
guess that because of the nuclear part, political resistance would probably
prevent it from ever becoming reality.  (Before you complain about how
politics screw up space research, bear in mind that it was the Cold War that
first pumped all that money into the program.  Too bad the Russians lost.)

Question:  If the average acceleration isn't too bad, how is the vibration
from those periodic bursts of thrust?  

response 4 of 8:

Oct 3 23:27 UTC 1998

Re #2:  If you think of it as a "vehicle" on a "road", it becomes
obvious that the vibration becomes a function of the suspension
between the pusher plate and the crew cabin.  If you have some
long-travel springs with a low K, physics appears to say that you
could get as smooth a ride as you like.  Like a game of paddle-ball,
the pusher plate would be allowed to fly away from the cabin and
blown back by the next blast.  But be careful about mis-fires!
If there isn't anything to toss the plate back it is going to hit
the stops and toss everything onto the ceiling!
 
Re #3:  Building one in space appears feasible.  I can even think of
a mission which might garner political support:  intercepting and
diverting comets and asteroids which threaten to strike Earth.  This
relates to item #11.

response 6 of 8:

Oct 7 02:45 UTC 1998

Re #5:  I don't mean to sound like a pedant, but you ought to do some
order-of-magnitude calculations before mentioning figures like "miles".
Some reasonable assumptions are 0.1 - 1 pulse per second, and acceleration
from 1 to 3 G's.  The major variable is the mass-fraction constituted by
the pusher plate and anything attached directly to it.  Hint:  At 1 pps
and 1 G, you are talking small numbers of feet, not miles.
 
If you don't feel like doing it yourself and want to bring it up as a
physics question, the Science conference is open for business.  

response 8 of 8:

Jul 16 03:10 UTC 2002

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 trying it. I figured: "what have I got to lose except 6 stamps and
 $6.00,
 right??" Then I invested the measly $6.00. Well GUESS WHAT!!!^E Within 7
 days, I started getting cash in the mail!! I was shocked!! I figured it
 would
 end soon, but the cash just kept coming in. In my first week, I made
 about
 $25.00. By the end of the second week I had made a total of over
 $1,000.00!!
 In the third week I had over $10,000.00 and it's still growing. This is
 now my
 fourth week and I have made a total of just over $42,000.00 and it's
 still
 coming in rapidly. It's certainly worth $6.00, and stamps, I have spent
 more
 than that on the lottery!! Let me tell you how this works and most
 importantly, why it works^E Also, make sure you print a copy of this
 article
 NOW, so you can get the information off of it as you need it. I promise
 you that if you follow the directions exactly, that you will star making
 more cash
 than you thought possible by doing something so easy!!! Suggestion: Read
 this entire message carefully! (Print it out or download it) Follow the
 simple
 directions and watch the cash come in!! It's easy. It's legal. And, your
 investment is only $6.00 (plus postage) IMPORTANT: This is not a rip-
 off; it
 is not indecent; it is not illegal; and it is virtually no risk - it
 really works!!!! If
 all of the following instructions are adhered to, you will receive
 extraordinary
 dividends. PLEASE NOTE: Please follow these directions EXACTLY, and
 $50,000 or more can be yours in 20 to 60 days. This program remains
 successful because of the honesty and integrity of the participants.
 Please
 continue its success by carefully adhering to the instructions. You
 will now
 become part of the Mail Order business. In this business your product
 is not
 solid and tangible, it's a service. You are in the business of
 developing  developing
 Mailing Lists. Many large corporations are happy to pay big bucks for
 quality lists. However, the cash made from the mailing lists is
 secondary to
 the income which is made from people like you and me asking to be
 included
 in that list. Here are the 4 easy steps to success:
 STEP 1:  
 Get 6 separate
 pieces of paper and write the following on each piece of paper "PLEASE
 PUT ME ON YOUR MAILING LIST". Now get 6 us $1.00 bills and place ONE
 inside EACH of the 6 pieces of paper so the bill will not be seen
 through the
 envelope (to prevent thievery). Next, place one paper in each of the 6
 envelopes and seal them. You should now have 6 sealed envelopes, each
 with a piece of paper stating the above phrase, your name and address,
 and
 a $1.00 bill. What you are doing is creating a service. THIS IS
 ABSOLUTELY
 LEGAL! You are requesting a legitimate service and you are paying for
 it!
 Like most of us I was a little skeptical and a little worried about the
 legal
 aspects of it all. So I checked it out with the U.S. Post Office (1-800-
legal
 aspects of it all. So I checked it out with the U.S. Post Office (1-800-
 725-2161)
 and they confirmed that it is indeed legal! Mail the 6 envelopes to the
 following addresses:
 
 #1) Soaul Lopaza
 4096 N. Atlas Way
 Fresno, CA 93705

 #2)Micheal Kink 1800 Foster St.
 Lake Charles, LA 70601

 #3)Sharon P. Umbao
 2 Garden Dr. 10
 La Grange Park
 il 60526

 #4)Alice Keenan
 230 W 121st Ave.
 Anchorage Ak. 99515  
 
 #5)David Alva
 7055 Orchard Lane
 Hanover Park IL 60103
 
 #6)Peter Gizmo 
 5217 s.Laramie ave.
 Chicago il. 60638

 STEP 2: Now take the #1 name off the list that you see above, move the
 other
 names up (6 becomes 5, 5 becomes 4, etc^E) and add YOUR name as number
 6 on the list. STEP 3: Change anything you need to, but try to keep this
 article as close to original as possible. Now, post your amended
 article to at
 least 200 newsgroups. (I think there are close to 24,000 groups) All
 you need
 is 200, but remember, the more you post, the more cash you make! This is
 perfectly legal. If you have any doubts, refer to Title 18 Sec. 1302 &
 1341 of
 the Postal lottery laws. Keep a copy of these steps for yourself and,
 whenever you need cash, you can use it again and again. PLEASE
 REMEMBER that this program remains successful because of the honesty
 and integrity of the participants and by their carefully adhering to the
 directions. Look at it this way. If you are of integrity, the program
 will  continue and the cash that so many others have received will come your
 way. NOTE: You may want to retain every name and address sent to you,
 either on a computer or a hard copy and keep the notes people send you.
 This VERIFIES that you are truly providing a service. (Also it might be
 a
 good idea to wrap the $1 bill in dark paper to reduce the risk of mail
 theft) So,
 as each post is downloaded and the directions carefully followed, six
 members will be reimbursed for their participation as a List Developer
 with
 one dollar each. Your name will move up the list geometrically so that
 when
 your name reaches the #1 position you will be receiving thousands of
 cash
 in CASH!!! What an opportunity for only $6.00 ($1.00 for each of the
 first six
 people listed above) Send it now, add your own name to the list and
 you're
 in business!------DIRECTIONS----- FOR HOW TO POST TO
 NEWSGROUPS----------- STEP 1) You do not need to re-type this entire
 letter
 to do your own posting. Simply put your cursor at the beginning of this  
 letter and drag your cursor to the bottom of this document, and select
 "copy" from the edit menu. This will copy the entire letter into the
 computer's memory. STEP 2) Open a blank "notepad" file and place your
 cursor at the top of the blank page. From the edit menu select "paste".
 This
 will paste a copy of the letter into notepad so that you can add your
 name to
 the list. STEP 3)Save your new notepad file as a .txt file. If you want
 to do
 your postings in different settings, you'll always have this file to go
 back to.
 STEP 4)Use Netscape or Internet explorer and try searching for various
 newsgroups (on-line forums, message boards, chat sites, discussions.)
 STEP
 5) Visit these message boards and post this article as a new message by
 highlighting the text of this letter and selecting paste from the edit
 menu. Fill
 in the Subject, this will be the header that everyone sees as they
 scroll
 through the list of postings in a particular group, click the post
 message
 button. You're done with your first one! Congratulations^E THAT'S IT! All

 you have to do is jump to different newsgroups and post away, after you
 get
 the hang of it, it will take about 30 seconds for each newsgroup!
 **REMEMBER, THE MORE NEWSGROUPS YOU POST IN, THE MORE
 Cash YOU WILL MAKE!! BUT YOU HAVE TO POST A MINIMUM OF
 200** That's it! You will begin receiving cash from around the world
 within
 days! You may eventually want to rent a P.O. Box due to the large
 amount of
 mail you will receive. If you wish to stay anonymous, you can invent a
 name
 to use, as long as the postman will deliver it. ** JUST MAKE SURE ALL
 THE ADDRESSES ARE CORRECT** Now the WHY part: Out of 200
 postings, say I receive only 5 replies (a very low example). So then I
 made
 $5.00 with my name at #6 on the letter. Now, each of the 5 persons who
 just
 send me $1.00 make the MINIMUM 200 postings, each with my name at #5
 and only 5 persons respond to each of the original 5, that is another
 $25.00
 for me, now those 25 each make 200 MINIMUM posts with my name at #4
 and only 5 replies each, I will bring in an additional $125.00! Now  
 those 125
 persons turn around and post the MINIMUM 200 with my name at #3 and
 only receive 5 replies each, I will make an additional $626.00! OK, now
 here is
 the fun part, each of those 625 persons post a MINIMUM 200 letters with
 my name at #2 and they each only receive 5 replies, that just made me
 $3,125.00!!! Those 3,125 persons will all deliver this message to 200
 newsgroups with my name at #1 and if still 5 persons per 200 newsgroups
 react I will receive $15,625.00! With an original investment of only
 $6.00!
 AMAZING! When your name is no longer on the list, you just take the
 latest
 posting in the newsgroups, and send out another $6.00 to the names on
 the
 list, putting your name at number 6 again. And start posting again. The
 thing
 to remember is: do you realize that thousands of people all over the
 world are
 joining the internet and reading these articles everyday?, JUST LIKE YOU
 are now!! So, can you afford $6.00 and see if it really works?? I think
 so^E
 People have said, "what if the plan is played out and no one sends you 
 So what! What are the chances of that happening when there are
 tons
 of new honest users and new honest people who are joining the internet
 and
 newsgroups everyday and are willing to give it a try ? Estimates are at
 20,000
 to 50,000 new users, everyday, with thousands of those joining the
 actual
 internet. Remember, play FAIRLY and HONESTLY and this will really work.