Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_0/V15NO059.TXT

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Date: Sat,  1 Aug 92 05:10:20
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #059
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Space Digest                Sat,  1 Aug 92       Volume 15 : Issue 059

Today's Topics:
        Antiproton-Boosted Microfission (was: Antimatter ...)
                             NASA Select
                            Origin of Life
                            Shuttle launch

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Date: 31 Jul 92 19:54:58 GMT
From: Roger Arnold <[e-mail]>
Subject: Antiproton-Boosted Microfission (was: Antimatter ...)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (R. Cage) writes:
> I'm skeptical about this microfission concept; [..]
> How is one neutron per 5.5e10 nuclei
> in a micropellet going to cause a significant rate of
> fission, even if it is compressed?  There is no unusual
> chaining or other amplification effect; once the p-bars
> are used up, the usual chain-reaction has to suffice.  A
> few billion neutrons could jump-start the process, but I
> don't see how a chain reaction can be sustained in only
> 70 mg of fissile material.
>
> While this concept has some extremely neat consequences
> if it is feasible (micropellet pulsed fission drives with
> magnetic nozzles, anyone?), I'm skeptical about the claims.
> Does anyone know more about the principles, such as the
> effect of pellet compression on the critical mass?

It's out of my field, but I believe the critical mass goes as the
inverse square of the density--or as the sixth power of the average
interatomic distance.

The antiproton generated neutrons must be just what you suggest: a
trigger to "jump-start" a natural chain reaction.  You need a *very*
fast trigger, in this case, because the compressed pellet is not
going to remain sufficiently compressed to support a chain reaction
for more than an instant.  What sort of pressure does it take to
increase the density of a plutonium pellet by a factor of 100?

Gary Hudson did propose a spacecraft based on micropellet pulsed
fission drives with magnetic nozzles.  That was at least five years
ago.  Maybe longer.  In the paper I saw, there was no suggestion of
antiproton triggering.  Because of the triggering problem, I was
inclined to dismiss the concept as another Gary Hudson pipe dream:
intriguing, with some substance behind it, but not really practical.
I had never heard of the idea of antiproton induced fission until I
read it here.  Possibly, Gary did know about it, but was keeping it
proprietary.

Are you out there, Gary?

--
Roger Arnold
[e-mail]

------------------------------

Date: 31 Jul 92 20:18:45 GMT
From: Gary Coffman <ke4zv!gary>
Subject: NASA Select
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>That made me wonder - is there a "NASA Select operations" phone number that
>a viewer could use to reach operations and tell them "there's no sound"
>or "you're playing the tape backwards"? Occasionally I'm up late enough that
>such a number would be useful, and assuming replays are from NASA Headquarters,
>it wouldn't cost me much to give them a call (definitely worthwhile for an
>important press conference).

As a broadcaster I can say with considerable assurance that the uplink
operators are well aware of any anomalies long before you could reach
them by phone. Generally they are running around in tight little circles
trying to solve the problem and the last thing they need to do is answer
a ringing phone from an irate viewer.

Gary

------------------------------

Date: 31 Jul 92 23:22:24 GMT
From: russell wallace <[e-mail]>
Subject: Origin of Life
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Tom) writes:

>>Has an RNA cluster unsupported by enzymes been demonstrated to
>>synthesize amino acids or peptide chains (actually, stringing amino
>>acids together into proteins is more important, because there would be
>>plenty of amino acid molecules already floating around)?

>>Russell Wallace, Trinity College, Dublin

>Say, Russell, this question of yours lends support to the idea that you do
>want the entire story handed to you on a silver platter.  You were correct
>about that criticism adding little to the discussion, but only since it
>left out a crucial question...What do YOU think is the origin of life?
>(Since a system of simple replicators, whether 'trivial' or not, which
>evolved into something more seems unacceptable to you)

>P.S- Please include a defintion of 'non-trivial self-replication.'

Certainly. First, a definition of non-trivial self-replication is a
system which contains some machinery, and a blueprint of the machinery.
The machinery builds a second set of machinery from the blueprint, and
then copies the blueprint, to form a new copy of the system. See William
Poundstone's "The Recursive Universe" for a more complete explanation of
this. (BTW: I did post this definition before; perhaps the message
didn't show up at your site.) The important thing about non-trivial as
opposed to trivial self-replication (the latter including things like
crystal growth) is the blueprint; mutations in this will create a
different system, and with an appropriate chemical or other basis for
the blueprint and machinery, the number of functionally different
possible systems can be extremely large. This allows Darwinian evolution
to take over and develop more complex systems. Trivial self-replication
does not allow this, because there is no blueprint for mutations to
occur in. If a strand of RNA can replicate itself in a medium, but the
sequence of bases in the RNA has no effect on the success of the RNA at
replication (other than simple effects such as using nucleotides which
happen to be in more abundant supply), then this is still trivial
self-replication.

Actually I believe that the explanations of how life got started that
are being put forward by my opponents in this debate are correct;
probably a cluster of RNA and proteins came together that had the
ability to replicate itself, using the information in the RNA as a
blueprint, and thus was the first life form (I think non-trivial
self-replication can reasonably serve as a definition of when life first
appeared). The suggestion I'm most impressed by is the one that perhaps
a strand of RNA can double as both blueprint AND machinery, by being
able to serve as an enzyme, with the four nucleic acids serving in place
of the 20 amino acids in proteins (and of course, unlike proteins, being
able to replicate by forming a twin strand); this would mean that RNA
alone, or fairly nearly alone, could start the process, without having
to have a complex set of proteins as well. The reason I'm asking
questions about how much of this has been demonstrated is not because I
expect the whole story to be handed to me on a platter, but because I'm
curious about the mechanisms involved.

But the point on which I disagree with most of the other people involved
in this discussion is that I still think the probability of this process
happening successfully on a planet is less than the reciprocal of the
number of planets in the visible universe, because before you have life,
Darwinian evolution cannot operate (even though a sort of chemical
"evolution" in a slightly different sense may - it's a different sense
in that there is no genetic material), and therefore the process is
governed by little more than unassisted random chance. I therefore make
the prediction that Earth is the only planet in the visible universe
which has life on it. (If life is ever found on other planets, unless it
somehow has a common ancestry with life on Earth, I will cheerfully
admit I was wrong.) The reason I think we are here is either that the
universe is infinite, or that the parallel worlds interpretation of
quantum theory is correct, thereby giving a sufficient number of
opportunities for any process, however improbable, to occur.

*Whew*. I do seem to have stirred up quite a debate with what I thought
originally was quite an innocent remark :-).

--
"To summarize the summary of the summary: people are a problem"
Russell Wallace, Trinity College, Dublin
[e-mail]

------------------------------

Date: 31 Jul 92 22:53:00 GMT
From: [e-mail]
Subject: Shuttle launch
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (John Roberts) writes...
>
>I usually find that if a Shuttle or other spacecraft is to launch late in
>the morning on a weekday, and I have to go to work, then it's almost
>impossible to find out the status until late afternoon or early evening -
>the major networks usually ignore it until the evening news, and radio
>news stations are erratic. Therefore, for the benefit of those who haven't
>heard yet and who receive this message quickly:
>
>Apparently the Shuttle was successfully launched this morning. (I phoned
>someone who was watching at his home.) No further details at present.
>
>John Roberts
>[e-mail]
>

I am happy to say that I lost my shuttle cherry at 9:56 EDT this morning when
my experiment (Acceleration Measurement System) that I designed lifted off
as a secondary payload (CONCAP III-01) on STS-46.  The purpose of this
experiment is to measure the acceleration forces on the shuttle by the
tether and its assocated end mass.  We expect the magnitude of these forces

to be about 40 microgee.

Our University also has another secondary payload (CONCAP II-01) which will
expose many samples of superconducting materials to the Atomic Oxygen flow
in order to ascertain if the unique oxidation states of the Atomic Oxygen
are suitable for raising the temperature of the transition state to
superconductivity for the ceramic typ superconducters that were first
invented here at UAH a few years ago.

Dennis Wingo, University of Alabama in Huntsville

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End of Space Digest Volume 15 : Issue 059
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