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From: Henry Spencer <>
Date: Tue, 23 Jul 1996 22:05:14 GMT

In article <4sqrmu$> (Kirt Undercoffer) writes:
>Dyson disparages Orion as a dirty system that would basically
>pollute the solar system by leaving a radioactive trail.  Is
>there really anything to this claim? ...

Yes and no.  If used in interplanetary space, the fireballs will expand
until they merge with the solar wind, and will be carried out of the solar
system by it (blending in with all the other junk it carries).  Some care
to avoid creating particulate debris is in order, but that shouldn't be
much of a problem. 

However, using an Orion on or near a planet is another story.  In
particular, in the place where it would be of greatest value -- for
*really* heavylift launch from Earth's surface -- its exhaust is
utterly unacceptable.
 ...the truly fundamental discoveries seldom       |       Henry Spencer
occur where we have decided to look.  --B. Forman  |

From: Henry Spencer <>
Subject: Re: Revive Orion?
Date: Sun, 17 Aug 1997 00:00:38 GMT

In article <>,
John Bicketts <> wrote:
>The Orion project of the 50's and 60's designed a workable spacecraft
>powered by small atom bomb explosions. The ships could be big...
> Anyway, does anyone think they could be revived today?

There are a number of problems, and overall it is not a good idea.

For one thing, it is illegal.  The treaty is still in effect.  Admittedly,
it would be easier to negotiate changes to it now, with the Cold War gone.

For another, Orion always had a problem that was never satisfactorily
solved:  its fuel was horribly expensive.  Fission bombs are costly.  Most
of the enthusiasm for Orion (and most of the optimistic commentary about
how little environmental impact ground-launched Orions would have) was
based on the assumption that "fission-free" nuclear bombs -- pure-fusion
bombs triggered by some non-fission means -- would soon be available.
Optimism on that score seems to have been widespread in the weapons
community circa 1960, but it was misplaced:  we still do not have such
bombs, and there is no prospect of them any time soon.  (While this is
unfortunate for Orion, it may be just as well for nuclear arms control.)

A nasty practical problem that was not adequately appreciated in Orion's
heyday was that nuclear explosions can badly damage satellites even at
very long range.  If (dim) memory serves, the X-ray pulse -- which carries
much of the energy of a bomb exploded in vacuum -- essentially kicks up
ionization in the outer surface of the satellite, and the resulting
electrical phenomena are quite destructive.  Note that this problem does
*not* go away if you somehow get the Orion outside the magnetosphere
before firing it up.  A large nuclear explosion -- or a bunch of small
ones -- anywhere within, say, the Earth-Moon system could wreak havoc
with all satellites within line of sight.

>I dont imagine
>launching them from the ground- too much of  a radiation hazard- but
>how about assembling them in orbit and using them only in space?

The idea was seriously proposed, late in Orion's history.  (There were
drawings of an Orion third stage for the Saturn V, for example.)
Unfortunately, it removes one of Orion's great advantages -- its
near-total insensitivity to adding a bit of extra mass -- by requiring
that you lift everything into orbit the hard way.  It's particularly
bad because Orion does not scale down well; it works best at very large
sizes.  (The Orion S-IVB, for example, was too small to perform well.)

>...would really be great for interplantary exploration....

If we can just sort out a cheap way of getting stuff into orbit -- which
would be needed for a space-assembled Orion anyway -- we can deal with
the rest of the problems in other ways.  Not as good as Orion, perhaps,
but cheaper and without its nasty side effects.
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |

From: (Andrew Higgins)
Subject: Re: New fusion based Orion concept
Date: Wed, 03 Jun 1998 23:51:02 +0200

In article <>, (Henry Spencer)

> >On yet another track, would the parachute-type Orion scheme work better
> >in conjunction with the Mag-sail concept?
> Interesting thought.  I don't know that anyone's explored this combination.

Bob Zubrin and Dana Andrews (the authors of the original Mag Sail concept)
had a paper on an Orion-driven Mag Sail at the AIAA Joint Propulsion
Conference last summer:

     Andrews, D., and Zubrin, R., "Nuclear Device-Pushed Magnetic Sails
     (MagOrion)," AIAA-97-3072, 33rd AIAA/ASME/SAE/ASEE Joint Propulsion
     Conference & Exhibit, July 6-9, 1997, Seattle, WA.

Andrews and Zubrin's numbers show that a MagOrion has a specific impulse
about one order of magnitude greater than the "classic" Orion.  It also
has the advantage that a "raw" nuke (as opposed to a nuke with additional
propellant to slow down products and shield the pusher plate) can be used.

Their baseline mission was a 25,000 ton vehicle (100,000 ton initial
mass), with an average Isp of 72,000 sec, providing nearly 1 g constant
acceleration for a total delta-V of nearly 1000 km/s.  They're talking
about round-trip to Jupiter in a couple of months!

Dana Andrews mentioned in his talk that the biggest uncertainty in
estimating the performance of a MagOrion is knowing the energy
distribution in the nuclear detonation products (i.e., how much energy
goes into debris, and what are the constituents of the debris?).  This
kind of information is not readily available; Andrews was using numbers
from a "Scientific American" article written by Theodore Taylor about 10
years ago.
     Andrew J. Higgins            Department of Mechanical Eng.
     Shock Wave Physics Group     McGill University    Montreal, Quebec

From: (Henry Spencer)
Subject: Re: The Orion Myth (Re: nuclear shaped charges)
Date: Wed, 27 Jan 1999 03:38:28 GMT

In article <>,
James A Davis  <> wrote:
>There is no prohibition forbidding nuclear reactors or materials in
>space, only nuclear *explosions*. If you think this prohibition is too
>restrictive please make the case that there are worthwhile goals in
>space that only be achieved by exploding bombs behind a massive pusher
>plate that uses only a few percent of the energy content of the fissile

The situation can be improved substantially using the Medusa concept,
in which the pusher plate is replaced by a (very large) high-temperature
parachute, which can intercept half or more of the fireball, and also
helps provide the shock absorption that was a major technical question
mark for Orion.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: Orion Shall Rise
Date: Mon, 16 Aug 1999 13:35:12 GMT

In article <7oq8l3$cfd$>,
Michael Miller <> wrote:
> it within
>reason that a ground-launched, single-stage Orion could
>deliver 10,000 tons of payload to the lunar surface? Or
>are there upper mass constraints on even an Orion drive?

My impression is that any upper mass constraints are way, way up there.
But for big vehicles you do need big bombs.

>On a side note, what are the EMP effects of high altitude
>"propulsion units" in the 0.1-50 kiloton range?

My impression is that the information needed for a detailed assessment of
EMP effects tends to be classified.

However, that's not necessarily the biggest worry.  Particle injection
into the magnetosphere may be more serious, ditto soft-X-ray effects on
satellites in the line of sight.  Exploding big nuclear bombs in space
anywhere near Earth is an extremely antisocial act.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: orion vehicles...
Date: Mon, 16 Aug 1999 13:38:08 GMT

In article <7ok624$ohp$>,  <> wrote:
>Wasn't Orion some sort of pusher craft. Where as some fissionable or
>like material was dropped out the back, and it went boom and cause of
>the giant plate on the rear of the craft it went forward?

Basically correct.

>On a serious note, what if you had some form of laser on the main craft
>that caused fussion/fission of the Uranium/Plutonium 235/238 pellet?

This is basically just another way of triggering the bombs.  It is of some
interest, because it makes it possible to use smaller bombs.  (Orthodox
fission bombs are hard to make at small sizes, except by taking a larger
bomb and spoiling its efficiency, which is dirty and costly.)
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: Orion Shocks
Date: Sat, 28 Oct 2000 19:29:39 GMT

In article <>,
Paul F. Dietz <> wrote:
>> So, is there a clever way to avoid turning a significant
>> part of the energy of the moving pusher plate into heat?
>You could have the vibrations from one bomb cancel
>those from the previous one, I guess.

If you've got a shock system with a nice long period of oscillation, you
don't need to worry about damping vibrations.  The first bomb shoves the
plate up.  Springs gradually impart its momentum to the rest of the ship,
decelerating it and then accelerating it downward again.  As it passes
the neutral position, where the springs are exerting no force, fire the
next bomb.  That reverses its motion, and the cycle repeats.  The only
time when you have to think about damping is at "engine cutoff" time.

For bonus points, do something clever with mechanical design or active
systems so that the spring force is roughly constant, rather than rising
as the springs compress.  In that case, the pusher plate is bouncing up
and down but the force exerted on the vehicle is roughly constant, so it
feels a steady acceleration rather than a series of hammer blows.
Microsoft shouldn't be broken up.       |  Henry Spencer
It should be shut down.  -- Phil Agre   |      (aka

From: "Paul F. Dietz" <>
Subject: Re: An Out There question.
Date: Sun, 29 Oct 2000 16:22:50 -0600 wrote:

> Further, I think Ian was emphasizing "fusion Orion" for a
> reason: all-fusion thrust units. No fallout to speak of.
> Again, calm down. I don't think repeated launch of Orions
> from a few launch sites is going to destroy the ecosphere.

Fusion will produce lots of neutrons, which will
produce carbon-14 in the atmosphere.

Atmospheric nuclear testing *doubled* the atmospheric
concentration of 14C.

I really don't want extra 14C in my DNA, thank you.


From: (Henry Spencer)
Subject: Re: Medusa (was: Re: atomic umbrella?)
Date: Wed, 1 Nov 2000 23:51:19 GMT

In article <>,
Alvaro Agustin Fernandez  <> wrote:
>> This concept is known as "Medusa".
>I'm not sure I understand. Are you "running into" the explosion?
>(The umbrella's in front of you, right?)

Yes, the explosion is between the parachute and the ship.  There is
nothing wrong with this; the ship is considerably farther away from the
blast than an Orion's payload area would be.

>And how  is this is
>better/cleaner than just deploying the conventional Orion in space?

Mostly, it performs much better.  For one thing, an Orion's pusher plate
intercepts only a modest fraction of the blast (even with semi-directional
bombs), while Medusa's parachute can fill half the sky from the detonation
point.  For another, Orion performance turns out to be a function of the
length of shock-absorber travel, and Medusa (which does shock absorption
by reeling out its parachute shroud lines) has much longer absorption
Microsoft shouldn't be broken up.       |  Henry Spencer
It should be shut down.  -- Phil Agre   |      (aka

From: (Henry Spencer)
Subject: Re: Medusa (was: Re: atomic umbrella?)
Date: Sat, 4 Nov 2000 20:18:17 GMT

In article <>, Aaron Smith  <> wrote:
>> ...For another, Orion performance turns out to be a function of the
>> length of shock-absorber travel, and Medusa (which does shock absorption
>> by reeling out its parachute shroud lines) has much longer absorption
>> distances.
>I'm not really going for a t-shirt, but isn't Orion performance dictated
>primarily by the size of the pusher plate?

Only if it's unmanned.  For manned systems, the crew are often the
limiting factor.  The achievable delta-V is roughly n*sqrt(d*a), where n
is number of bombs, d is shock-absorber stroke distance, and a is maximum
tolerable acceleration.  A system with a small d ends up being quite
inefficient, because it can absorb only a small amount of momentum per
bomb, while bombs get better and cheaper and cleaner as they get bigger.
Microsoft shouldn't be broken up.       |  Henry Spencer
It should be shut down.  -- Phil Agre   |      (aka

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