Problems with Problems With The Orion Spacecraft #9: Stress

Thomas Womack wrote:

In article ,
Derek Lyons wrote:

With a higher velocity gun, and better ability to calculate the
effects of pre-detonation, all manner of things become possible.

OTOH, there have been references to 'supergrade' plutonium, I.E.
having less -240 than is the norm. I don't know if the -240 is
separated out or if the Pu is produced using methods that create less
-240.

If you have vast amounts of lightly-enriched uranium (or, I suspect,
even fully-depleted uranium if you've already got a reactor producing
decent neutron flux), you can cycle it through the reactor fairly
quickly; you don't get _much_ 239-Pu in the result, so it's
inefficient in terms of uranium usage and, more importantly, reactor
and reprocessing capital cost, but you get proportionally
substantially less 240-Pu. I suspect that's easier than going for
actual enrichment.

One suspects that a close reading of the various accounts available on
the web of operations at Hanford might yield clues.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

wrote:

I am surprised that this would come up in connection with Orion. There
you want small devices, which are already hard to make efficient.
Without the compression of implosion, efficiency drops dramatically.
You need a lot of devices, which means you want light weight and low
cost. This certain doesn't qualify.

This [plutonium gun] is the first stage - it's never loaded on the
craft, but is fired beneath it as it sits on the launch towers. Thus
the size/weight of this unit is not restricted the way the onboard
units are.

Orion also puts design constraints on the arrangement of tamper in the
device, to try to directionalize the thrust. I would expect that the
design constraints of a gun would interfere with that.

No. The designs I've seen to date place a fusion device inside a
larger holhraum which focuses the output of the device onto/into the
ablative material that provides the thrust. No alterations to the
tampers at all.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Kelly McDonald wrote:

This "Super" grade Pu was just barely on the edge for an extremely
large scale gun weapon, in which two sub-critical masses would be
fired at one another. It was huge, heavy and was still very suceptable
to a fizzle. This was why the whole idea was discarded as it would not
have lead to a practical weapon, and would have been horribly
inefficient. Not the kind of device I could see being used on an Orion

This was intended to be the first 'stage', fired beneath the craft
while it rested on the launch towers. As it was never loaded aboard
the craft, the 'normal' limits on PPU's do not apply.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

John Schilling wrote:

In article , Pat Flannery says...



John Schilling wrote:

Or they were paying attention to the *Very Low Yield* part.

This is not something we heard here first. It has been publicly known
for about sixty years now, that what happens if you try to build a Pu
gun is that it predetonates, resulting in a very low yield. Normally,
this is undesirable behavior and we thus don't build a plutonium gun.
If a very low yield is what you actually *want*, go ahead and buuld
the gun - it's a simple and reliable, if somewhat heavy, way to get
a very low nuclear yield.

Wouldn't you end up with very inefficient fission and a lot of
unfissioned plutonium getting sprayed around?

Yes, precisely. Now, just what were you imagining a very low yield
nuclear explosion would be, if *not* "very inefficient fission an a
lot of unfissioned plutonium getting sprayed around"?

And a very effective way of killing off one's neighbours!

Just think what that'd do for property values!

Well, OK, the early Orion proponents imagined that they'd get fusion
explosions of whatever yield they needed from the Fission-Free Hydrogen
Bombs That Were Going To Be Invented Any Day Now, Really!, but that
seems to have not worked out real well. The techniques that actually
work to produce nuclear explosions start with a critical mass[1] of
highly enriched uranium and/or plutonium, and a full critical mass
efficiently fissioned results in a high-yield explosion.


[1] An imprecise term that incorporates lots of assumptions about things
like geometry, compression, and tamping, but is measured in kilograms,
not grams, for any currently plausible arrangement of these.



--
"Good, late in to more rewarding well."Â*Â*"Well,Â*youÂ*tonight.Â*Â*AndÂ*IÂ*was
lookintelligent woman of Ming home.Â*Â*IÂ*trustÂ*youÂ*withÂ*aÂ*tenderÂ*silence." Â*Â*I
get a word into my hands, a different and unbelike, probably - 'she
fortunate fat woman', wrong word.Â*Â*IÂ*thinkÂ*toÂ*me,Â*IÂ*justupid.
Let not emacs meta-X dissociate-press write your romantic dialogs...!!!

wrote:

With the initial microgram samples of cyclotron-generated plutonium,
which was almost pure Pu-239, the plutonium gun was considered
difficult but possible by Los Alamos. It would have required a gun
velocity of around 3000 m/s, which would have required a long and heavy
device.

With the first reactor-generated plutonium, the Pu-240 problem became
apparent. That was made in research reactors with lower burnups than
planned for the production reactors under construction at Hanford. The
Hanford plutonium was around 0.9% Pu-239. Modern 'supergrade'
plutonium is around 1.5% to 3.0% Pu-239, with ordinary weapons grade
plutonium at around 6.5%.

Increasing gun velocity only gives you a proportional improvement in
how much Pu-240 you can accept, while the gun weight is going up as
something like the fourth power. A double-gun arrangement can only get
you a factor of two in effective velocity. And at some point you run
into a speed-of-sound limitation that requires moving to a light gas
gun. That might get you a total factor of 5 over the marginal 3000 m/s
device. I estimate that would allow the use of plutonium with about
0.1% Pu-240 with a 10% predetonation probability. That isn't very
practical, but not completely ridiculous.

An implosion device can guarantee a decent minimum yield even with
predetonation. This can be large enough to ignite fusion boosting,
after which
predetonation isn't really a problem. If a gun device fizzles, odds
are that you get no significant yield.

I don't see why anyone would use isotope separation to eliminate
Pu-240. If you want to use a gun, why don't you use U-235? It is much
easier to separate, due to the larger mass difference. You don't need
to get it anywhere near as pure, since 80% enriched uranium is better
than 100% Pu-239 for predetonation. Yes, plutonium is a more efficient
fissile material, but you give up any mass advantage for that when you
try to use a gun.

I am surprised that this would come up in connection with Orion. There
you want small devices, which are already hard to make efficient.
Without the compression of implosion, efficiency drops dramatically.
You need a lot of devices, which means you want light weight and low
cost. This certain doesn't qualify.

Precisely. Launch from a gravity well requires almost constant thrust -
which is why I could not believe it when I first read about it in one of
Arthur C. Clarke's non-fiction books, "The Lost Worlds of 2001".

I imagined it would make a very powerful drive for launching from orbit.
Back then I hadn't learnt about the ElectroMagnetic Pulse. Launching from
orbit's no bloody good if you wipe out your telemetry!

Orion also wants highly reliable devices. A dud screws up the
resonance of the shock absorption on the pusher plate, putting
dangerous stress on the system. Devices vulnerable to predetonation
are not appropriate.

Orion also puts design constraints on the arrangement of tamper in the
device, to try to directionalize the thrust. I would expect that the

Yes, absolutely right! Thrust directionalizing is already a ticklish
subject with rockets. And that's just constant combustion.

If the explosions get out of sequence and slightly out of the thrust line,
you're screwed, you're ****ed, you're toast.

design constraints of a gun would interfere with that.

Wesley Parish
--
"Good, late in to more rewarding well."Â*Â*"Well,Â*youÂ*tonight.Â*Â*AndÂ*IÂ*was
lookintelligent woman of Ming home.Â*Â*IÂ*trustÂ*youÂ*withÂ*aÂ*tenderÂ*silence." Â*Â*I
get a word into my hands, a different and unbelike, probably - 'she
fortunate fat woman', wrong word.Â*Â*IÂ*thinkÂ*toÂ*me,Â*IÂ*justupid.
Let not emacs meta-X dissociate-press write your romantic dialogs...!!!

Derek Lyons wrote:

(Henry Spencer) wrote:

In article ,
Derek Lyons wrote:

one of the problems cited with schemes to do major revisions to the
Iowa-class battleships was that the USN apparently no longer has a
shipyard crane that can lift one of those turrets.)

That's a bit of a red herring - as the turrets were not lifted on in
one piece in the first place... (In the second place, at least one of
the cranes used for such jobs is still operational...

Note that I said it had been cited -- I didn't say I believed it. :-)
(I *thought* at the time that it had a smell of technical rationalization
for a decision made on political grounds...)

Fiscal grounds mostly - the varied conversions would have been
*extremely* expensive for very little return in the way of combat
power. (There's some doubt as to whether some of them would have even
been possible - the hull girder was 'prestressed' to account for the
weight of the turrets, as well as the balance and stability curves.
Removing them would have had all manner of interesting effects.)

The Navy was not unanimous in it's admiration of the battlewagons.

I imagine the accountants would've had a rahter different opinion of them.
Consider it from that point of view - a battlewagon is a huge investment.
Its weaponry are in modern terms, short range, so you have to get up
relatively close to the enmy to do any harm. The damage it is capable of
doing is thus, less than ships of a lesser cost. At the same time, it is a
hugely inviting target, so it is costing the navy an extra magnitude of
cost in defending it, a cost which it does not return since its offensive
capability is reduced by comparison.

So if an enemy can tie up a battlewagon, it can bleed said battlewagon's
navy and country while suffering comparatively minor damage itself.

Useful thing to remember when you write the Great SF Space War Opera!

D.

Wesley Parish
--
"Good, late in to more rewarding well."Â*Â*"Well,Â*youÂ*tonight.Â*Â*AndÂ*IÂ*was
lookintelligent woman of Ming home.Â*Â*IÂ*trustÂ*youÂ*withÂ*aÂ*tenderÂ*silence." Â*Â*I
get a word into my hands, a different and unbelike, probably - 'she
fortunate fat woman', wrong word.Â*Â*IÂ*thinkÂ*toÂ*me,Â*IÂ*justupid.
Let not emacs meta-X dissociate-press write your romantic dialogs...!!!

It would start out as a pseudo-underground explosion, with the bomb being
only metres away from the spacecraft's "bumper".

Here's the first fireball at .1 -.94 ms, actual distance to plate
should be about 5r.

http://spacebombardment.blogspot.com...to-launch.html

Here's the drawing at .5 sec...
http://spacebombardment.blogspot.com...launch_18.html


This is assuming a tower or cable supported initial position. The first
pulse could be chemical, but at the same 20kt energy level to loft this
571,000 ton ship.

In article , John Dallman says...

In article ,
(Derek Lyons) wrote:

You heard it here first- a gun assembly nuclear device employing
plutonium, not uranium, as its fissile material.

Well, from what the thread has been saying, it sounds as if this was a
static testing device, not a Orion driver bomb.

One might suspect the existence of devices like LENS for use in the
warhead hardening program. You need to simulate the effects of an ABM
warhead going off a mile or two away? A deliberate fizzle from something
parked next to the thing you're trying to test is going to be much easier
to arrange - underground in Navada - than setting up a thoroughly
realistic test,

And if you envision doing a whole lot of such tests, whether for EMP
effects or Orion development or any other such thing, it may be helpful
that you can park the gun itself far enough from the test chamber that
it is survivable and reusable. Just put another Pu target (low-grade
Pu; you *want* predetonation) in the test chamber, load another Pu slug
into the gun, and fire away.

Cleaning the test chamber after a series of such shots is going to be a
double-plus unfun job however you do it; just one more reason to consider
whether a plan that requires a great many nuclear explosions even of low
yield, might need rethinking. But if you're going to do it, a reusable
plutonium gun mounted outside a large and sturdy test chamber might be
the way to do it.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *

Sander Vesik wrote:

Hmmm.... I though concentrated solution of Plutonium Nitrate in a good
reflector would be critical near a kilogram ? No idea if it would be
usable in a weapon or if you would need a special geometry.



In the LENS system the blast gets projected out of the barrel at the
test target. In this concept one can see the germ of the Casaba Howitzer
concept as well as the Orion's nuclear propulsion bomblets that shoot a
cloud of vaporized tungsten and beryllium oxide upwards at the pusher plate.

Pat

wrote:


I don't see why anyone would use isotope separation to eliminate
Pu-240. If you want to use a gun, why don't you use U-235? It is much
easier to separate, due to the larger mass difference. You don't need
to get it anywhere near as pure, since 80% enriched uranium is better
than 100% Pu-239 for predetonation. Yes, plutonium is a more efficient
fissile material, but you give up any mass advantage for that when you
try to use a gun.


In the case of LENS this has me baffled also- but the report
specifically states that it uses plutonium, not uranium.

I am surprised that this would come up in connection with Orion. There
you want small devices, which are already hard to make efficient.
Without the compression of implosion, efficiency drops dramatically.
You need a lot of devices, which means you want light weight and low
cost. This certain doesn't qualify.



LENS is just for ground tests of the pusher plate; the actual propulsion
bomblets are shown cutaway in the .pdf, and they have a spherical
nuclear device in them, so I assume they use classic plutonium implosion
principles.

Orion also wants highly reliable devices. A dud screws up the
resonance of the shock absorption on the pusher plate, putting
dangerous stress on the system. Devices vulnerable to predetonation
are not appropriate.



They go into that in the report. The one I'd be concerned about is a
bomblet that goes off at lower that inspected yield, so that instead of
a cloud of vaporized tungsten being shot up at the propellant plate, you
end up with a thick disc of tungsten being shot up into it at very high
velocity.
And given the total number of propulsion bomblets they envision being
used on a mission, that doesn't sound like a completely groundless fear.

Pat