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Problems with Problems With The Orion Spacecraft #9: Stress



 
 
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  #1  
Old October 21st 05, 03:30 PM
bombardmentforce
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Default Problems with Problems With The Orion Spacecraft #9: Stress

Myth:
The ship's structure itself ... has to be able to take the stress of
sitting next to a bunch of exploding nuclear bombs. Even with shock
absorbers, it would be under repeated stress of a type not experienced
by any vehicle we have ever built. The ability of a battleship to
survive the strain of firing its own guns was the subject of a
considerable amount of development efforts in the early 20th century,
and that strain would be dramatically less than the strain experienced
by an Orion. -POS

----
Fact:

"Both the pulse frequency and the acceleration profile are reasonably
well simulated by a child's backyard swing operating through an arc
65deg each way from vertical". GA-5009 Volume 1 page 14
Quoted in Project Orion Page 179
http://spacebombardment.blogspot.com...-orion_21.html
http://ntrs.nasa.gov/archive/nasa/ca...1965058729.pdf

  #2  
Old October 22nd 05, 01:00 PM
Tux Wonder-Dog
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Default Problems with Problems With The Orion Spacecraft #9: Stress

bombardmentforce wrote:

Myth:
The ship's structure itself ... has to be able to take the stress of
sitting next to a bunch of exploding nuclear bombs. Even with shock
absorbers, it would be under repeated stress of a type not experienced
by any vehicle we have ever built. The ability of a battleship to
survive the strain of firing its own guns was the subject of a
considerable amount of development efforts in the early 20th century,
and that strain would be dramatically less than the strain experienced
by an Orion. -POS

----
Fact:

"Both the pulse frequency and the acceleration profile are reasonably
well simulated by a child's backyard swing operating through an arc
65deg each way from vertical". GA-5009 Volume 1 page 14
Quoted in Project Orion Page 179

http://spacebombardment.blogspot.com...-orion_21.html

http://ntrs.nasa.gov/archive/nasa/ca...1965058729.pdf

Fact: Based on my recall of Footfall and my knowledge of thermonuclear tests
in the Pacific and elsewhe Taking off in Orion would be one hell of an
experience. Quite literally.

It would start out as a pseudo-underground explosion, with the bomb being
only metres away from the spacecraft's "bumper". Think vitrification.
Think sublimation of metal. Think superhot gaseous vitrified rock and
metal gases spewing out all sides.

And you need to fire another within the next few seconds to maintain your
momentum so you won't fall back down to the ground again.

Designing a hatchway that can be blocked against subliming metal and yet
pass a functioning thermonuclear device through, is beyond _my_
capabilities. I presume the Cavalry in those circumstances get Superman -
Jor-El - to throw them in, albeit from a safe distance? I missed seeing
Jor-El in Footfall - perhaps Niven and Pournelle couldn't pay him enough
for a cameo deus ex machina appearance?

Wesley Parish

(And note: that factoid about the child's swing, fails to make the link
between the child's swing and the thermonuclear explosion. The energy
released in a thermonuclear explosion is orders of magnitude vaster than
that expended in a child's swing.

And that's the crux of the matter. If that vast instantaneous pulse of
energy is to be absorbed to pass it on to the spacecraft, then it will be
like being inside a battleship while firing a broadside. Except that
battleship will have it helluva lot easier. And if it isn't passed on to
the spacecraft, then it has been wasted. No ifs, no buts.)
--
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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...!!!
  #3  
Old October 22nd 05, 09:10 PM
Henry Spencer
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Default Problems with Problems With The Orion Spacecraft #9: Stress

In article ,
Tux Wonder-Dog wrote:
It would start out as a pseudo-underground explosion, with the bomb being
only metres away from the spacecraft's "bumper". Think vitrification.
Think sublimation of metal. Think superhot gaseous vitrified rock and
metal gases spewing out all sides.


The ship would be up on towers, not flat on the ground, for launch. The
initial bomb would be a small one, with bomb size ramping up thereafter.

These would not be bare bombs, but packages with ablative propellant
incorporated, so what would strike the pusher plate would be a jet of
vaporized propellant, chosen by design to be within the limits of what the
plate could take. (For a technical overview, see the paper on Orion and
nuclear-pulse propulsion in the May/June 2002 issue of the AIAA's Journal
of Propulsion and Power.)

The plate surface would be sprayed with, roughly speaking, grease before
each explosion; the plate itself would not ablate. This was tested, and
it was effective enough to eliminate any need to make the plate itself out
of anything exotic.

And you need to fire another within the next few seconds to maintain your
momentum so you won't fall back down to the ground again.


Correct. It's a bad day for any vertical-takeoff vehicle if the engine
cuts out just after takeoff.

Designing a hatchway that can be blocked against subliming metal and yet
pass a functioning thermonuclear device through, is beyond _my_
capabilities.


See above -- no exotic materials required. And they would be fission
devices, not fusion, barring the hypothetical pure-fusion bombs that some
of the Orion designers were hoping for.

Fast-acting mechanical devices are not magic. The best of the supersonic
interceptors of the late 1950s could open weapons-bay doors, toss out a
long-range air-to-air missile, and close the doors again, in something
like 300 milliseconds, despite a supersonic slipstream.

...I missed seeing Jor-El in Footfall ...


Note that Footfall is fiction, and should not be used as a textbook on
Orion design. George Dyson's book "Project Orion" is a better source.

(And note: that factoid about the child's swing, fails to make the link
between the child's swing and the thermonuclear explosion. The energy
released in a thermonuclear explosion is orders of magnitude vaster than
that expended in a child's swing.


The principles, however, remain the same. The shock-absorber system is
resonant at a particular frequency, like the swing. You toss out bombs at
that frequency. A charge for a battleship gun has orders of magnitude
more energy than that of a .22 rifle, but the same physics applies to
both, although the engineering is a bit harder for the big one.

And that's the crux of the matter. If that vast instantaneous pulse of
energy is to be absorbed to pass it on to the spacecraft, then it will be
like being inside a battleship while firing a broadside. Except that
battleship will have it helluva lot easier.


No, the battleship has it a lot worse -- it has nowhere near the
shock-absorber stroke that an Orion would. The recoil stroke for a
battleship gun is severely limited by the requirement that the whole
motion fit within a cramped turret even when the guns are elevated at a
high angle. (You can't just make the turrets bigger because their walls
and roof are thick armor, and they're already enormously heavy -- 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.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #4  
Old October 23rd 05, 08:29 AM
Derek Lyons
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Default Problems with Problems With The Orion Spacecraft #9: Stress

(Henry Spencer) wrote:

In article ,
Tux Wonder-Dog wrote:

The plate surface would be sprayed with, roughly speaking, grease before
each explosion; the plate itself would not ablate. This was tested, and
it was effective enough to eliminate any need to make the plate itself out
of anything exotic.


Tested at small scale - it's one of the Big Unknowns for a full scale
Orion. (There are a couple of unanswered questions about design
principles and details IIRC. No showstoppers, but contrary to the
handwaving of bombardmentfarce, we can't build one from a standing
start - a non trivial amount of development must be done first.)

And that's the crux of the matter. If that vast instantaneous pulse of
energy is to be absorbed to pass it on to the spacecraft, then it will be
like being inside a battleship while firing a broadside. Except that
battleship will have it helluva lot easier.


No, the battleship has it a lot worse -- it has nowhere near the
shock-absorber stroke that an Orion would.


Yet big-gun recoil absorbers are fairly simple and compact devices.

The recoil stroke for a battleship gun is severely limited by the
requirement that the whole motion fit within a cramped turret even when
the guns are elevated at a high angle. (You can't just make the turrets
bigger because their walls and roof are thick armor, and they're already
enormously heavy --


Which is why 'modern' (I.E. early 1930's) big guns push the trunnions
as far forward as possible - right against the mantlet plate. When
you look at the back of one of the Iowa's guns, most of what you see
is a honkin' big counterweight. This combo allows you to increase the
length of the recoil stroke without materially increasing the size of
the turret.

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. They are designed to come apart for
regunning or to repair battle damage. It's a non trivial job, but
it's doable. (In the second place, at least one of the cranes used
for such jobs is still operational about 10 blocks from where I sit.)

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

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
  #5  
Old October 23rd 05, 10:12 PM
Henry Spencer
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Default Problems with Problems With The Orion Spacecraft #9: Stress

In article ,
Derek Lyons wrote:
... (There are a couple of unanswered questions about design
principles and details IIRC. No showstoppers, but contrary to the
handwaving of bombardmentfarce, we can't build one from a standing
start - a non trivial amount of development must be done first.)


No question about that. Outside reviewers consistently thought the Orion
enthusiasts were being seriously optimistic about schedule and budget,
with a lot of optimism about incompletely-solved problems.

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...)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #7  
Old October 24th 05, 05:57 AM
OM
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Default Problems with Problems With The Orion Spacecraft #9: Stress

On Sun, 23 Oct 2005 21:12:58 GMT, (Henry Spencer)
wrote:

Note that I said it had been cited -- I didn't say I believed it. :-)


....You forgot something, Henry:

[/weasel]

:-) :-) ;-)

OM

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  #8  
Old October 24th 05, 10:38 AM
Pat Flannery
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Default Problems with Problems With The Orion Spacecraft #9: Stress



Henry Spencer wrote:

In article ,
Derek Lyons wrote:


... (There are a couple of unanswered questions about design
principles and details IIRC. No showstoppers, but contrary to the
handwaving of bombardmentfarce, we can't build one from a standing
start - a non trivial amount of development must be done first.)



No question about that. Outside reviewers consistently thought the Orion
enthusiasts were being seriously optimistic about schedule and budget,
with a lot of optimism about incompletely-solved problems.


Here's something _very_ interesting from that Orion .pdf that Rusty found:
http://ntrs.nasa.gov/archive/nasa/ca...1977085619.pdf
If you go over to page 134 of the report (pdf page 146) you will run
into LENS (Low Energy Nuclear Source); a very low yield nuclear device
that will is to be detonated near the pusher plate to check out how it
behaves...nothing unusual in that...except that LENS is a....ready for
this? "the LENS system, which is a very-low-yield "gun-type" plutonium
assembly (see Fig. 7. 10)."
You heard it here first- a gun assembly nuclear device employing
plutonium, not uranium, as its fissile material.
That was supposed to be impossible due to a unstable isotope of
plutonium (Pu-240) that would cause it to pre-react if gun assembly was
used, and which was supposed to not be separable from the Pu-239.
Well, either the Orion team made a major slip in their report, or by
1964 we knew how to separate Pu-239 and Pu-240.

Pat
  #9  
Old October 24th 05, 12:34 PM
Jack Linthicum
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Posts: n/a
Default Problems with Problems With The Orion Spacecraft #9: Stress


Henry Spencer wrote:
In article ,
Tux Wonder-Dog wrote:
It would start out as a pseudo-underground explosion, with the bomb being
only metres away from the spacecraft's "bumper". Think vitrification.
Think sublimation of metal. Think superhot gaseous vitrified rock and
metal gases spewing out all sides.


The ship would be up on towers, not flat on the ground, for launch. The
initial bomb would be a small one, with bomb size ramping up thereafter.

These would not be bare bombs, but packages with ablative propellant
incorporated, so what would strike the pusher plate would be a jet of
vaporized propellant, chosen by design to be within the limits of what the
plate could take. (For a technical overview, see the paper on Orion and
nuclear-pulse propulsion in the May/June 2002 issue of the AIAA's Journal
of Propulsion and Power.)

The plate surface would be sprayed with, roughly speaking, grease before
each explosion; the plate itself would not ablate. This was tested, and
it was effective enough to eliminate any need to make the plate itself out
of anything exotic.

And you need to fire another within the next few seconds to maintain your
momentum so you won't fall back down to the ground again.


Correct. It's a bad day for any vertical-takeoff vehicle if the engine
cuts out just after takeoff.

Designing a hatchway that can be blocked against subliming metal and yet
pass a functioning thermonuclear device through, is beyond _my_
capabilities.


See above -- no exotic materials required. And they would be fission
devices, not fusion, barring the hypothetical pure-fusion bombs that some
of the Orion designers were hoping for.

Fast-acting mechanical devices are not magic. The best of the supersonic
interceptors of the late 1950s could open weapons-bay doors, toss out a
long-range air-to-air missile, and close the doors again, in something
like 300 milliseconds, despite a supersonic slipstream.

...I missed seeing Jor-El in Footfall ...


Note that Footfall is fiction, and should not be used as a textbook on
Orion design. George Dyson's book "Project Orion" is a better source.

(And note: that factoid about the child's swing, fails to make the link
between the child's swing and the thermonuclear explosion. The energy
released in a thermonuclear explosion is orders of magnitude vaster than
that expended in a child's swing.


The principles, however, remain the same. The shock-absorber system is
resonant at a particular frequency, like the swing. You toss out bombs at
that frequency. A charge for a battleship gun has orders of magnitude
more energy than that of a .22 rifle, but the same physics applies to
both, although the engineering is a bit harder for the big one.

And that's the crux of the matter. If that vast instantaneous pulse of
energy is to be absorbed to pass it on to the spacecraft, then it will be
like being inside a battleship while firing a broadside. Except that
battleship will have it helluva lot easier.


No, the battleship has it a lot worse -- it has nowhere near the
shock-absorber stroke that an Orion would. The recoil stroke for a
battleship gun is severely limited by the requirement that the whole
motion fit within a cramped turret even when the guns are elevated at a
high angle. (You can't just make the turrets bigger because their walls
and roof are thick armor, and they're already enormously heavy -- 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.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |



You are aware that the original launch point for Orion was either at
Torrey Pines or Point Loma in the San Diego area. They had to leave TP
when their test shots, with C4, distrubed the neighbors. Think what the
real deal, even in a 'shallow silo', would have done for property
values?

  #10  
Old October 24th 05, 12:41 PM
Paul F. Dietz
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Posts: n/a
Default Problems with Problems With The Orion Spacecraft #9: Stress

Pat Flannery wrote:

You heard it here first- a gun assembly nuclear device employing
plutonium, not uranium, as its fissile material.
That was supposed to be impossible due to a unstable isotope of
plutonium (Pu-240) that would cause it to pre-react if gun assembly was
used, and which was supposed to not be separable from the Pu-239.
Well, either the Orion team made a major slip in their report, or by
1964 we knew how to separate Pu-239 and Pu-240.


.... or maybe that pre-reacting is perfectly acceptable
in the low yield situation here?

Paul
 




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