[ExI] "NASA's 1st Deep-Space Capsule in 40 Years Ready for Launch Debut"

[John Clark]

On Thu, Dec 4, 2014 at 10:47 AM, spike <spike66 at att.net> wrote:

> Ulam wrote about Orion in his book.  From the article: ...water would
> have been injected to serve as propellant. This design produced the
> relatively
> small Isp of 1150 seconds...
>

I think that was a very early design where a small nuclear bomb would be
injected into a combustion chamber 130 feet across. Later in a 1955 paper
Stanislaw Ulam and Cornelius Everett came up with a new design that didn't
need a combustion chamber at all. They noted that if the fissile material
(U235 or Plutonium)  was imploded into a disk rather than a sphere the
resulting explosion would not be spherically symmetrical but instead result
in 2 highly directional jets 180 degrees apart that contained nearly all
the bomb's energy, one of the jets would be directed directly at the pusher
plate which would be connected to the spacecraft by means of a huge shock
absorber. Water or cheap plastic would still make up much of the reaction
mass because both are good at stopping neutrons. According to Gregory L.
Matloff in his book  "Deep-Space Probes" with this design much more of the
energy in the bombs can be used and unlike the combustion chamber method no
attempt is made to contain the explosion, so much more powerful bombs can
be used and the more energy you have under your command the greater the isp
can theoretically become. Matloff thinks the Isp would be between 10,000 to
one million depending on the particulars. Incidentally about the same time
it was proposed that such highly directional bombs be used to instantly
make tunnels through mountains, it was a different time.

The durability of the pusher plate was obviously of concern, It was found
that if you explode a powerful bomb near a circular plate of constant
thickness it will shatter because of the uneven stresses that build up, but
it turns out that if you carefully taper the plate and make certain that
the explosion is dead
center, the plate will be extraordinary  resistant to damage. And Ulam
noted that graphite-covered steel spheres were suspended just 30 feet from
a nuclear detonation at Eniwetok and they were found intact with just a
thin layer of graphite ablated from their surfaces, so he propose a
graphite based oil be sprayed on the plate just before every detonation.
The plate would be subjected to very high temperatures but only for about a
millasecond, so he figured the plate would be good for 2000 blasts.

  John K Clark
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