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Subject: SPACE Digest V11 #285

SPACE Digest                                     Volume 11 : Issue 285

Today's Topics:
           Risks (was Interstellar travel)
      Re: Listening to the Star (was RE: Drake Equation)
                 Comet Austin
          Re: Pegasus launch from Valkyrie  (or ...
              Re: Fermi Paradox
              Re: Arecibo (sp?) message
               Re: Interstellar travel
           Re: Questions about the Voyagers
----------------------------------------------------------------------

Date: Tue, 17 Apr 90 14:00:03 EDT
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Risks (was Interstellar travel)


>From: [e-mail]
>Date:     Mon, 16 Apr 90  08:05:50 EDT
>> Subject: Re: Interstellar travel

>> >2. I don't see mankind inventing practical anti-matter propulsion or
>> >whatever the current idea is in the next century or two.
>Considering the depletion of the ozone layer, pollution by nonbiodegradables,
>the greenhouse global warming effect due to the combination of increasing
>use of fossil fuels and deforestation of the major tropical rain forests,
>the wanton proliferation of nuclear weaponry among nations of religious fan-
>atics as well as here in a nation of madmen, the ever-increasing background
>radiation level due to BOTH nuclear power stations, and nuclear weapon-grade
>fissionable material production facilities, and the ABSOLUTELY uncontrol-
>lable waste products they produce, I DO NOT SEE MANKIND IN THE NEXT CENTURY.

Ozone depletion, global warming - possible hazards, with the jury still out
to some extent (see previous postings on this list). Loss of tropical
rainforests - a major concern over the long run. Nuclear weapons proliferation -
a valid concern, though it does not seem to be particularly rapid these days.
Pollution by nonbiodegradables - that's silly - the earth is 99.99999+ percent
nonbiodegradable, and the rest of it gets along fine. If you're concerned
about the amount of carbon being removed from the ecosystem, you shouldn't be
complaining about burning fossil fuels and greenhouse warming. There are many
far more serious chemical pollution problems than nonbiodegradables. Increasing
background radiation due to nuclear power plants and weapons production - I
think you're mistaken about this. It is my understanding that a typical
coal-burning power plant releases more radiation into the environment per
megawatt than the production, use, and waste storage cycle of a properly run
nuclear power plant. Waste storage has been a problem in this country largely
because of opposition to the construction of a long-term storage facility,
not because it's inherently impractical. Ironically, opposition to nuclear
power has had a significant harmful net effect on the environment, due largely
to a variety of pollutants that are put into the atmosphere by other power
plants. Also remember that the earth is naturally very radioactive - just try
living in an underground house in the eastern US mountain ranges with an
all-granite interior.

In your list of hazards, you also left out overpopulation - the single
greatest danger facing civilization today.

To step back slightly from this specific topic to the general topic of risk
analysis: there are few things more vital than the effort to obtain the best
possible estimates of hazards, especially those associated with specific
actions or inactions. However, it has been discovered that it's much easier
to rave and foam at the mouth and pontificate and call on public support by
celebrities than it is to actually conduct scientific research and determine
the facts of the case. The news media play along with this approach - when
a news item covers safety concerns at a shoe polish plant, most of the air
time will be spent interviewing a farm family living ten miles away who are
convinced that their cow gave birth to a three-headed calf because of pollution
from the plant - never mind the possibility that there may have been some
other cause. Often any scientific studies that may be relevant are discounted
because they don't agree with what "stands to reason". Then there is the
inevitable call to ban something or require something - and if that doesn't
have the expected result, then there's no possibility we were wrong - we must
have just not gone far enough.

This approach works reasonably well when the question is something simple
like "should we feed our schoolchildren a tablespoon of rat poison a day,
or not?" However, the question is seldom that simple. It is often necessary
to trade off the relative risks of two or more courses of action, such as
the slight risks from an inoculation versus the major risks from an epidemic,
if the actual chance of an epidemic is fairly low. (The medical profession
in particular is notoriously poor at fixing relative risks). Another common
tradeoff is risk versus expense. Most people would probably agree that it is
not cost-effective to spend a billion dollars to save one person - that money
could much more effectively be spent in different ways to save many people.
Most people would probably also agree that it is worth five dollars to save
a person. Where should the dividing line be? - it's a difficult social
question, and many people would rather fall back on pure emotion with no
logic or take the lofty moral position that human life is "priceless" than
attempt to honestly answer it.

A similar point of view as shown in the Galileo launch is that no amount of
risk, however small, is justified for any endeavor not tied in with some
short-term effort to help people. By that logic, ground-based telescopes
should not be built because the astronomers driving to work might run over
somebody.

>                                               Dardin Valpar
>                                          aka  Marc Arlen
>                                               AZM@NIHCU

Please do not interpret this as a personal attack on you - it's an attack
on the viewpoint you presented. I realize that many people share these
views, and that we are constantly bombarded with them in the news media, so
it's easy to fall into the trap of adopting them without critical analysis.
Clear reasoning and careful application of scientific principles are vital
for continued survival of our civilization in the coming decades.
                        John Roberts
                        [e-mail]

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

Date: 18 Apr 90 18:39:11 GMT
From: mailrus!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Listening to the Star (was RE: Drake Equation)

In article <[e-mail]> [e-mail] (Robert McGwier) writes:
>> The point that people are forgetting is the impracticality of advanced
>> civilisations using radio signals...
>
>I couldn't agree more.  While visiting JPL a couple of years ago...
>... Even at that time they were working on
>single photon laser detectors so that LIGHT could be used as the data
>link back to earth...

Before very long we will undoubtedly be using optical communications for
a number of things where we use radio now.  However, radio is *not* going
to become obsolete at any time in the foreseeable future:  it will merely
be restricted to applications where it has specific advantages.  Point-to-
point communication will probably be mostly optical, but optical broadcast,
especially to mobile targets, is not so easy.  It's hard to imagine that
even a very advanced race would completely abandon the radio spectrum.
--
With features like this,      |     Henry Spencer at U of Toronto Zoology
who needs bugs?               | uunet!attcan!utzoo!henry [e-mail]

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

Date: 18 Apr 90 12:11:09 GMT
From: mephisto!prism![e-mail]  (RUSSELL EARNEST)
Subject: Comet Austin

I remember reading here some time back that next week would be the best time to
view comet Austin with Wednesday being the height.

Could someone confirm this and, if true, tell us non astronomers where and when
to look for it?

Many Thanks.

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

Date: 18 Apr 90 16:39:09 GMT
From: usc!samsung!rex!rouge![e-mail]  (Fraering Philip)
Subject: Re: Pegasus launch from Valkyrie  (or ...

In article <[e-mail]> [e-mail] (Vincent Cate) writes:
o
o   Philip Fraering :
o   >A fully or partially reusable vehicle using RL-10 engines, similar to
o   >Third Millenium Inc.'s _original_ design for the Space Van, and with
o   >multiple stages, would probrably have a lower price.
o
o   Sounds interesting.  Can you tell us more about this?
o
o   >So, in summary: please stop bugging Mary Shafer about which of the
o   >experimental aircraft in her stable at Dryden will improve the
o   >performance of a launcher that uses 325 Isp fuel when (although with
o   >a little more difficulty) 450 Isp fuel (Hydrogen/Oxygen) could be used
o   >instead. Think about it.
o   >
o   >Remember: The cost of developing Pegasus from point zero: $40 million.
o   >Cost of refurbishing B-70 Valkyrie: probrably lots more.
o
o   Part of the reason the Pegasus cost only $40 million to develop was that
o   they used the simpler fuel.
o
o

Third Millenium Corp., also abbreviated as MMI, had been (and may still be)
seeking development money for a design for a mini-shuttle called the
"space van." The design was never frozen; one of the early ones involved a
vehicle that launched from a 747 which could either go into orbit itself on
the last gasp of fuel, with enough weight for one pilot and retrorocket fuel,
or could carry a space stage up to Mach 5 or so. The space stage could carry
3000 kg into orbit. The Space Van itself was recoverable; it had 6-8 RL-10
engines. The space stage had one, but it was not recoverable, except maybe
if the Space Van went up and recovered it. The details of recovering objects
with very small tugs, etc. have been covered extensively in the recent
postings on laser-launchings. Of course, the space stage could be refuelled,
or taken apart and the tankage used, ...

It should be noted that the RL-10 cryogenic engine is the oldest liquid
hydrogen engine ever used; it may have even been the first. (Anyone out
there have details?) I suspect that the first one may even have been shaped
using flint tools. (:-)"

Using it should be absurdly easy. It would even be cheaper than using
solid fuel due to the insurance savings: you can't abort a solid booster
very well. If something goes wrong, there goes the mission, or probrably
the vehicle.

The things with the winch or whip sound much more risky than changing to an
engine that has seen 20 years of reliable use. In fact, it sounds a lot like
what is called in the oilfield a "goat-roping exercise."

Winch launch has been used on low-speed gliders, but I doubt anything else.

Phil Fraering
dlbres10

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

Date: 18 Apr 90 01:33:21 GMT
From: zephyr.ens.tek.com!tektronix!sequent!mntgfx![e-mail]  (Mike Butts)
Subject: Re: Fermi Paradox

From article <[e-mail]>, by [e-mail] (Kendall Auel):
> Imagine how life on Earth would appear to Neptunians.  Very hot, fast-moving,
> short-lived creatures, stuck on a tiny rock whipping around the sun.  In
> contrast, the Neptunians would be large, nebulous, drifting globs of liquified
> gases.  Earth life reproduces at a blinding rate, and no single individual
> lives very long at all.  Even the oldest tree on Earth is just a few dozen
> Neptunian years old.  So, it makes sense that life on Earthlike planets
> will develop much more quickly than on the large gas giants or their moons.
>
On the subject of relative time, go read "Dragon's Egg" by Dr. Robert Forward.
Intelligent life evolves on the surface of a neutron star, based on nuclear
chemistry, not that lazy, slow, electron-shell stuff we use.  They live about
10^6 times faster than we do.  It's a great read, and backed up quantitatively
in the appendix.  In this context it's an instructive example on how alien
other life forms might be, and how different the universe might look to them.

> We may not be alone, but it is not too hard to imagine that we are among
> the first intelligent life forms in the galaxy.  Also, we may be blinded
> by our assumptions about what intelligent life looks like and how it
> behaves.  Humans are very Chauvinist when it comes to carbon and water.

Indeed we can be.  Isn't it the case that our solar system was formed about two
stellar lifetimes after the origin of the universe, according to best theory?
If so, how reasonable is it to assume that enough heavy elements existed for
intelligent life to have developed elsewhere, even before our own Sun was born?
Given a time scale like that, my personal opinion is that it's quite likely we
are many orders of magnitude below the universal average IQ.  Sufficiently
advanced life forms are probably not even perceptible in the sphere of mundane
matter.
--
Michael Butts, Research Engineer          KC7IT          503-626-1302(fax:1282)
Mentor Graphics Corporation, 8500 SW Creekside Place, Beaverton, Oregon   97005
!{ogicse,sequent,tessi,apollo}!mntgfx!mbutts              [e-mail]
Any opinions are my own, and aren't necessarily shared by Mentor Graphics Corp.

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

Date: 18 Apr 90 08:36:41 GMT
From: unmvax!nmtsun![e-mail]  (Daniel Briggs)
Subject: Re: Arecibo (sp?) message

In article <[e-mail]> [e-mail] (Arnold G. Gill) writes:
>     Also, remember that Arecibo is a transit telescope.  It doesn't move, and
>it's ability to move away from the zenith is limited.  Perhaps someone out
>there could give us an idea of just how much off axis Arecibo can see.

Not just a transit telescope, (one which cannot point in right ascention),
but also one that has a fixed (and fairly limited) range in declination.  The
latter limitation is more serious.  Being a transit telescope just means that
you have a limited time "on source".  In the fixed mount Arecibo case, if
the source is beyond your declination range, you simply can't see it.  Period.
[Actually, from your phrasing I think that you know that.  I just wanted to
point out that the observational restrictions on Arecibo are far more severe
than other transit telescopes.]

That aside, Arecibo can actually see a surprisingly large hunk of the sky,
given that the main reflector cannot be moved.  (It is pointed by moving
the secondary reflector.)  With its most extreme feed, it can see to a dec of
about 39 and a bit degrees.  Similarly, it can get down to about minus
two and a half degrees.  Of course, you have an "on source time" of about
10 seconds here!  In the optimum case, where the antenna is looking at a
source with a declination equal to its own lattitude (about 18.4 degress,
I think), you can track a source for a little over two hours.  (2h10m by
my quickie calcs.)

-----
This is a shared guest account, please send replies to
[e-mail] (Internet)
Dan Briggs / NRAO / P.O. Box O / Socorro, NM / 87801  (U.S. Snail)

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

Date: 18 Apr 90 18:15:00 GMT
From: mailrus!cs.utexas.edu!samsung!dali!uakari.primate.wisc.edu!zaphod.mps.ohio-state.edu!sdd.hp.com!apollo![e-mail]  (Steve Rehrauer)
Subject: Re: Interstellar travel

In article <[e-mail]> [e-mail] writes:
>  The Fermi paradox basically says,
>"Where is everybody???"  The Drake equation suggests that the galaxy should
>be teeming with life, given the number of stars we have.  *Our* presence
>as a technological society can readily be detected within a 50ly radius;
>yet we have found no signs, similar or other, that life exists elsewhere in
>the universe.  Speculation as to why this is the case runs rampant and I
>refer you to some excellent pop science discussions of same in _Analog_.

I don't see that "technological society" is necessarily an inevitable
end-product (or even mid-product) of "life".  How many worlds teeming
with algae, slime-molds and invertebrates could we detect from Earth?

I highly recommend Stephen Jay Gould's "Wonderful Life" for a very
readable -- by Average Interested Joes like me -- discussion of the
implausibility of our existence.  Perhaps other tool-builders would've
evolved had we not, but intelligent, social mammals certainly weren't
an inevitable development (the world's religions may beg to differ).
--
   >>"Aaiiyeeee!  Death from above!"<<     | (Steve) [e-mail]
"Spontaneous human combustion - what luck!"| Apollo Computer (Hewlett-Packard)

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

Date: 18 Apr 90 18:50:31 GMT
From: pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!samsung!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Questions about the Voyagers

In article <[e-mail]> [e-mail] (David Solana) writes:
>    * What are their positions in this moment?

Generally, on the fringes of the solar system, heading outward in different
directions, well outside the plane of the ecliptic.

>    * Where are they heading for? At what speed?

I don't have numbers, but the fast answers are "nowhere in particular" and
"a few kilometers per second".  Their trajectories are pretty much a result
of observing considerations on their last planetary encounters.

>    * Why didn't they visit Pluto? ...

Because it was nowhere near their flight paths, which were fixed by the
use of gravity-assist maneuvers from planets further in.

>      this decade would be ideal for sending a probe to Pluto.
>          Are there any plans to build such a probe?

"Plans" in the sense of "proposals", yes; in the sense of "money", no.

>    * What kind of data do the Voyagers transmit?

Telemetry reports on their internal systems, plus science data from their
fields-and-particles instruments.

>    * What can it be expected from these data? Are all of them "routine
>      science cruise data" as [e-mail] (Ron Baalke)
>          describes them? Are all the data lost due to lack of Deep
>      Space Network (DSN) coverage?

Not a lot can be expected unless something unusual happens, notably having
one of the Voyagers pass out of the Sun's atmosphere and into the interstellar
wind.  (There is some hope that this might happen before the Voyagers die,
but the location of the transition is very poorly known.)  Even so, things
like plasma particle counts are exciting only to specialists.

Yes, it's all routine cruise data now.  There are no more planets to pass.

I don't know what the situation is right now, but in the long run, as
projects like Magellan and Galileo demand increasing chunks of DSN's time,
much of the (fairly boring and routine) data the Voyagers are sending will
be lost.  It won't all be lost, as there is still some value to it, but
the more active missions have first call on the antennas.

>    * For how long will the probes be transmitting?

Until their isotope power packs run down too far to keep them alive, which
happens circa 2010 or so as I recall.
--
With features like this,      |     Henry Spencer at U of Toronto Zoology
who needs bugs?               | uunet!attcan!utzoo!henry [e-mail]

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

End of SPACE Digest V11 #285
*******************