Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_0/V13_012.TXT

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Subject: SPACE Digest V13 #012

SPACE Digest                                      Volume 13 : Issue 12

Today's Topics:
              Chiron and asteroid belts
               Re: Interstellar travel
            size limits on space colonies
               Re: Interstellar travel
          Solar cell factor/Space computers
               Re: Interstellar travel
            Re: Chiron and asteroid belts
            looking for T S Kelso
               Re: Interstellar travel
               Re: Interstellar travel

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Date: 29 Dec 90 06:58:50 GMT
From: swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Chiron and asteroid belts

In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>Also, the discovery of Chiron led to some talk about the possibility of
>a second asteroid belt between Jupiter and Saturn.  Does anyone know
>anything about this?

It was an appealing idea at the time, badly weakened by the fact that
nobody has found any more objects at those distances.

>Also, does the existence of Chrion suggest that
>there might be large bodies like it in the cometary halo (most people
>think the average size of comets will be about 3-4 km., with the biggest
>ones being about 30-40 km.--I'm talking about the nucleus here, not the
>coma or the tail)?  Any ideas?

Seems a good possibility.  Last I heard, the dominant theory was that
Chiron is a dormant supercomet.  Triton and Pluto may well be the same sort
of thing on an even larger scale.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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Date: 29 Dec 90 07:05:22 GMT
From: swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: Re: Interstellar travel
References: <[e-mail]>, <[e-mail]>
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In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>... [fusion drives] It may be that the technology is simply too far in
>the future, but people seem to drool over matter-antimatter, or
>solar sails, but never talk about the possibilities of fusion
>for interplanetary travel.  Any comments?

Antimatter is probably easier than fusion, unless some seriously oddball
approach to fusion gives us a practical way to use the high-order reactions
with minimum neutron emission, or we find some way to reflect fast neutrons
efficiently.  Even the D-He3 reaction produces enough neutrons to be
troublesome, and He3 is almost impossible to find or make in the quantities
needed for large-scale high-performance rocketry.  (Terrestrial power needs
negligible amounts by comparison.)
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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Date: 29 Dec 90 06:51:00 GMT
From: mips!swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: size limits on space colonies
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
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In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>O'neill claims that there is "no strict upper size limit" for his cylinder-
>ical space habitats, although the big ones need more support materials.
>Obviously, if you start building them as big as the moon their own mass
>with create enough gravity to collapse them, but does anyone know how big
>you could practically build them? ...

If you do not need spin for artificial gravity, the limit is tidal effects.
Freeman Dyson estimated a limit of something like 10,000km -- do not take
this number as gospel, it's a dim memory, but that's the right order of
magnitude -- based on theoretical strengths of materials, for a structure
orbiting the Sun at 1AU.  Of course, if you move further out, things get
better, since tidal effects go on an inverse-cube law while the collecting
area for a given amount of solar energy is only a square law.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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

Date: 29 Dec 90 07:11:59 GMT
From: cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Interstellar travel

In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>...the lack of discussion of fusion drives...I know there are a
>LOT of technical problems involved, but doesn't a mass production
>facility for anti-matter involve just as many problems?

Believe it or not, they actually look to be easier problems.

>... so little about fusion drives, for which there is
>the advantage of a huge fuel source in deuterium.)

Deuterium is almost useless as a fusion fuel for high-performance rockets
because of the fierce neutron emission, which is not just a radiation
hazard but also a very serious heating problem.

>... By the way, what would be involved in an anti-matter
>mass production facility, one large enough to provide a large
>civilization with fuel for all its spacecraft?

It depends on how many spacecraft, and how ambitious they are.  If you're
willing to start with a large, ambitious program of solar-system exploration
(manned) plus extensive operations in Earth orbit, something the size of
the Hanford nuclear works would do.  (That is, it's within the scale of
what has already been done in very-large-scale industrial activity.)
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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

Date: 29 Dec 90 10:57:00 CST
From: "86FTSCCQ" <[e-mail]>
Subject: Solar cell factor/Space computers
To: "space+" <[e-mail]>


I have two questions that I'm sure can be answered by the readership
here:

1) If I have a solar cell that puts out 0.5a at 6 volts on Earth,
   how much power will it produce of the various planets/sattels in
   our solar system? Is there a straight forward set of factors for
   each planet that I can multiply time any given solar cell rating
   on Earth to get the power output at that planet?

2) Is it possible to make "spaceable" a regular circuit board....
   such as a embedded computer hardware controller?

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Date: 29 Dec 90 17:00:10 GMT
From: elroy.jpl.nasa.gov!usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!watserv1!watdragon!watyew![e-mail]  (Brian or James)
Organization: University of Waterloo
Subject: Re: Interstellar travel
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    Are there any show-stoppers for the idea of a thermonuclear
version of the Orion-style propulsion system? If memory serves, those
can get up to 3,000 km/s delta Vee, which is really booting it.
That would put the nearest known star (in case any sneaky dim
stars turn up closer than 4.3 ly) less than half a millenium away,
and we *know* how to build H-bombs.

                            James Nicoll

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Date: 29 Dec 90 22:23:50 GMT
From: munnari.oz.au!uhccux![e-mail]  (David Tholen)
Organization: University of Hawaii
Subject: Re: Chiron and asteroid belts
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Henry Spencer writes:

> Mark Gellis writes:

> >Also, the discovery of Chiron led to some talk about the possibility of
> >a second asteroid belt between Jupiter and Saturn.  Does anyone know
> >anything about this?
>
> It was an appealing idea at the time, badly weakened by the fact that
> nobody has found any more objects at those distances.

It's true that there are no other small objects at Chiron's distance with
reasonably circular orbits, but closer in we do have P/Schwassmann-Wachmann 1,
which orbits exclusively between Jupiter and Saturn.  In addition, there
are many other objects with highly elongated orbits that reach those
distances.  944 Hidalgo is a Jupiter crosser with an aphelion distance of
9.7 AU; 3552 1983 SA has an aphelion distance of 7.3 AU; 1984 BC has an
aphelion distance of 5.4 AU.  Comet P/Crommelin has a semimajor axis of 9.1
AU; P/Brorsen-Metcalf has a semimajor axis of 17.1 AU; P/Bradfield 2 has a
semimajor axis of 18.8 AU; P/Hartley-IRAS has a semimajor axis of 7.7 AU.
And, of course, comet P/Halley crosses through that region as well.
Just recently, another new Jupiter-crossing asteroid was discovered,
designated 1990 UL3, that has an aphelion distance of 7 AU.  Even more
recently, however, deep imaging revealed the presence of a faint tail,
so the object has been redesignated a comet, 1990p, and named
P/Shoemaker-Levy 2.  And there are many other periodic comets that reach
those distances.

> >Also, does the existence of Chrion suggest that
> >there might be large bodies like it in the cometary halo (most people
> >think the average size of comets will be about 3-4 km., with the biggest
> >ones being about 30-40 km.--I'm talking about the nucleus here, not the
> >coma or the tail)?  Any ideas?
>
> Seems a good possibility.  Last I heard, the dominant theory was that
> Chiron is a dormant supercomet.  Triton and Pluto may well be the same sort
> of thing on an even larger scale.

Chiron is no longer dormant!  We caught it in outburst during a 1988 February
observing run and estimate that the outburst started sometime in late 1987.
Since then, it's tenuous coma has been imaged by several different observers.
Triton and Pluto, as well as all the other icy satellites of the outer planets
have the potential for outgassing if they could be brought in closer to the
Sun.  In fact, Pluto is probably losing some of its atmosphere due to Jeans
escape, so one could argue that it is behaving something like a comet.  The
terminology really gets muddled when one examines all the fine details.

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

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Date: 29 Dec 90 20:51:55 GMT
From: zaphod.mps.ohio-state.edu!magnus.ircc.ohio-state.edu![e-mail]  (Earl W Phillips)
Organization: The Ohio State University
Subject: looking for T S Kelso
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Sorry to do this, but.... I am looking for the internet
address for TS Kelso. Please email to the address below....

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Date: 30 Dec 90 00:28:28 GMT
From: cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: Re: Interstellar travel
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
Sender: [e-mail]
To: [e-mail]

In article <[e-mail]> [e-mail] (Brian or James) writes:
>    Are there any show-stoppers for the idea of a thermonuclear
>version of the Orion-style propulsion system? ...

The sheer size needed is a practical obstacle, as are the costs of the
bombs and the legal problems of exploding nuclear bombs in space.  But
it is pretty definitely workable, although rather marginal as an
interstellar propulsion system.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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

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Date: 29 Dec 90 10:46:19 GMT
From: prometheus![e-mail]  (Paul M. Koloc)
Organization: Prometheus II, Ltd.
Subject: Re: Interstellar travel
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In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>I seem to recall reading that there is some fundamental problem with the
>>Bussard Ramjet idea and that the thing can't work...

>Setting aside the mythical "ramjet speed limit", there are two or three
>big, nasty problems with the Bussard ramjet:

>2. The inverse-square law demands humongous magnetic field intensities
>    at the ship to get useful intensities at very long distances
>    (interstellar gas is thin and a ramscoop must be big).  Internal
>    repulsion within the field coils will try to tear them apart, and
>    the structural strength needed to hold them together is pushing
>    fundamental limits on the strengths of materials.

Inverse SQUARE law? ..  think the pressure a reasonable distance from a
magnetic dipole drops off by the inverse sixth power of the distance (R).
Of course, the coil diameter could be MUCH larger than the ship's diameter.
Also, the field coil could be wound as a torsatron, where the toroidal
field significantly bucks (counters) the major radius "hoop stress", thus
taking some of the load off from the tensile requirements of the materials.
It's still a trade off.  They will need a humongous field anyway just to
hold their antimatter fuel inventory ..  :-)

>3. Interstellar gas is not very ionized, and something might have to be
>    done to ionize it before you could get a useful grip on it with
>    a magnetic field, and doing that at reasonable energy cost is hard.

Perhaps at a reasonable fraction of light speed, the path local change
in the relativistically flattened forward flux enhanced intensity might
be helpful to promote ionization, and that coupled with other heroic
efforts, i.e. optical pumping schemes (narrow tuned forward beam), would
improve the situation.  This doesn't look likely.  Certainly, there may
be localities where the density of protium or even other light element-
isotopes could make the difference.   However, it looks like our
immediate several thousand generations of off-spring will have to do it
the hard way: gradual expansion through successive colonizations to get
to such fuel rich regions.    :-)

                         Gee, I hope running into
                  all that fuel doesn't slow us down..?
                          Lower the Mag Scoops,
                                Lassie!
+---------------------------------------------------------+**********+
|                                                         +Commercial*
| Paul M. Koloc, President          [phone]        ***FUSION***
| Prometheus II, Ltd.; College Park, MD 20740-0222        ***in the***
| mimsy!prometheus!pmk; [e-mail]               **Nineties**
+---------------------------------------------------------************

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End of SPACE Digest V13 #012
*******************