Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_0/V13_027.TXT

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Subject: SPACE Digest V13 #027

SPACE Digest                                      Volume 13 : Issue 27

Today's Topics:
    Re: Information sources for frequent space questions (2 of n)
               Re: Interstellar Travel
               Re: solar cells
               Re: Interstellar Travel
               Re: solar cells
               Re: Interstellar Travel
              Re: Future Headlines Today
        Re: Solar cell factor/Space computers

Administrivia:

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Date: 4 Jan 91 12:00:01 GMT
From: usc!zaphod.mps.ohio-state.edu!rpi!uupsi!sunic!fuug!news.funet.fi!tukki.jyu.fi!jyu.fi![e-mail]  (Otto J. Makela)
Organization: Turing Police, Criminal AI section
Subject: Re: Information sources for frequent space questions (2 of n)
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In article <[e-mail]> [e-mail] (Eugene N. Miya) writes:
   [Pioneer Venus 2] The main spacecraft bus
   burned up high in the atmosphere, while the four probes descended
   by parachute towards the surface.  Though none were expected to
   survive to the surface, the Day probe did make it and transmitted
   for 67 minutes on the ground before succumbing to the intense surface
   heat.  I only know what NASA tells me. :^)

The truth of course is, a venusian Glorkz monster ate the probe.
--
   /* * * Otto J. Makela <[e-mail]> * * * * * * * * * * * * * * * * * * */
  /* Phone: [phone], BBS: [phone] (CCITT, Bell 24/12/300) */
 /* Mail: Kauppakatu 1 B 18, SF-40100 Jyvaskyla, Finland, EUROPE         */
/* * * Computers Rule 01001111 01001011 * * * * * * * * * * * * * * * * */

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Date: Fri, 4 Jan 91 08:05:07 PST
From: [e-mail] (Tony Hamilton, WF1-81, x48142)
To: "[e-mail]"@HERMES.intel.com, [e-mail]
Subject: Re: Interstellar Travel

I am the fellow who started this thread a while back. Although I appreciate
all of the response, no one has really answered my fundamental question. It
is interesting to hear about fusion, antimatter, protons, etc., but I really
would like to know specifically how all this is being applied to the problem
of interstellar travel. Much of what has been said is simply theory. Is the
USAF, NASA, or any other agency actually designing an interstellar craft?

Anyway, I'll restate my original question, and add more:

1. Are there any viable designs for interstellar craft being worked on?

2. What speeds can be attained by various designs? I'm not a physicist, so
I'd need an explanation on why there are limitations. Would ships be able
to reach .1C, .5C, .9C, or what?

3. What are our closest interstellar neighbors? What do we know of them? Have
we ever found possible planets orbiting neighboring systems? If not, do we
have a good chance of finding such things?

I know, these are some real specific questions, and probably require long
explanations. Therefore, you might want to just E-mail me. Thanks

Tony

*******************************************************************************
* Tony Hamilton - Engineering Technician - Intel Corporation -  602-554-8142  *
*        -  or  - Sole Proprietor - Astral Gaming Enterprises - 602-834-5474  *
* iNET === [e-mail]  "I think, therefore I am .... thoughtful" *
* :::Astral Void BBS - 602-834-6065, mono-line, discussion/debate-300/1200::: *
*******************************************************************************

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Date: 4 Jan 91 15:17:05 GMT
From: swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!watserv1!watdragon!watyew![e-mail]  (Brian or James)
Organization: University of Waterloo
Subject: Re: solar cells
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
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In article <[e-mail]> [e-mail] (Charles K Hughes) writes:

    (tons of RTG and nuclear power stuff deleted)

>>    And another possible difficulty with solar cells -- how much
>>energy does it take to make them? They would not be too good if the
>>amount of energy needed to make them was only equal to their output
>>for several years of running. Has that question ever been addressed?
>
>  If the energy is free, who cares how much it took to make them?

    *Sigh* Let's say that a solar cell takes 10 arbitrary energy
units to make. Let's say it produces 9 AEU during its life. That means
every time you install one, the net cost to the power production system
is one AEU. Things that use up more of a resource than they produce do
not, on the whole, make good sources for that resource.

    It's reasoning like Mr. Hughes' that gives the anti-nuclear
folks a bad name.

                            James Nicoll

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Date: 4 Jan 91 17:00:12 GMT
From: swrinde!zaphod.mps.ohio-state.edu!wuarchive!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: Re: Interstellar Travel
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In article <[e-mail]> [e-mail] (Tony Hamilton, WF1-81, x48142) writes:
>... Much of what has been said is simply theory. Is the
>USAF, NASA, or any other agency actually designing an interstellar craft?

None of them is even designing an interplanetary craft, never mind an
interstellar one.  Unless spaceflight can be pulled out of its current
stagnation, it will be a long time before there is any need to think
seriously about starflight.

>1. Are there any viable designs for interstellar craft being worked on?

Depends on what you mean by "worked on".  Nobody is doing serious design
studies; see above.  Small-scale design speculation is being done here
and there.  The big problem is that any such design has to assume non-trivial
advances in propulsion, and has to guess at what those advances will look
like.

>2. What speeds can be attained by various designs? I'm not a physicist, so
>I'd need an explanation on why there are limitations. Would ships be able
>to reach .1C, .5C, .9C, or what?

There is no fundamental limitation except the speed of light, by current
physics, and most propulsion schemes don't have specific limits either.
However, 0.1c looks a whole lot more feasible in the near term than 0.9c,
given that the energy requirements go as the square of velocity.  (Energy
is the dominant problem of starflight.)  Multi-stage fusion rockets or
straightforward antimatter rockets ought to be able to manage 0.1c-0.2c
without too much trouble.  0.9c would need advanced antimatter engines
and very large quantities of antimatter.

>3. What are our closest interstellar neighbors? What do we know of them? Have
>we ever found possible planets orbiting neighboring systems? If not, do we
>have a good chance of finding such things?

The closest star is the three-star Alpha Centauri system.  Whether multiple
star systems are a good bet for planets is unclear.  Next out is Barnard's
Star, which is small and faint; evidence for planets around it is now
generally considered weak at best.  One has to go somewhat further out,
10-15 light-years, to find really good-looking single stars.

Nobody has positive evidence of planets around nearby stars, although the
dust disk around Gamma Pictoris [? my references aren't handy] has been
imaged.  There has long been indirect evidence that most modest single
stars have planets, and now there is increasingly strong spectroscopic
evidence directly supporting this for nearby stars.
--
"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: 4 Jan 91 21:07:16 GMT
From: sdd.hp.com!spool2.mu.edu!sol.ctr.columbia.edu!emory!wa4mei!ke4zv![e-mail]  (Gary Coffman)
Organization: Gannett Technologies Group
Subject: Re: solar cells
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In article <[e-mail]> [e-mail] (Charles K Hughes) writes:
>
>  I don't think the "allergy" is irrational given 3-mile island,
>Chernobyl, lists of missing nuclear fuel, 55 gallon drums of nuclear waste

Actually Three Mile Island showed that primary confinement works even in
an induced loss of cooling accident. Chernobyl showed that even the worst
scenario put up by the anti-nukes, core meltdown, *no* confinement,
and a core fire for God's sake, didn't result in the fearmongers predicted
mega-deaths.

>>    As to chemical poisons being decomposable, that depends on
>>what kind of chemical poison. Heavy metals cannot be chemically
>>decomposed. And some chemical poisons are difficult to decompose, such
>
>  Heavy metals don't need to be decomposed - they can be refined and reused.

So can nuclear fuels, but we're soooo scared we don't.

>>    I keep on being amazed by the anti-RTG movement. They complain
>
>  What is RTG?

Radioisotope Thermoelectric Generator. A completely sealed, no moving
parts, no active control system, lump of radioactive material that
gives off enough heat through natural radioactive decay to heat a
thermopile enough to generate useful amounts of electrical power.

>>    So either solar cells or RTG's are the way to go for
>>spacecraft. I presume that this is the standard argument.
>
>  Hmmm...why not ground or space power generation for those satellites
>that orbit the earth & moon?  Deep space satellites are of little concern
>here because once they leave, they're gone for good.

Beamed power has been very strongly opposed by the enviornmentalists because
of the supposed danger of the microwave power beam used to transmit the
energy. Or were you planning to use a *really* long extension cord.

>
>  RTGs (assuming they are small nuclear plants) are dangerous in any orbit
>that decays before the nuclear fuel becomes non-radioactive.

RTGs are designed to survive rentry without breaching their sealed shielding.
The designs used have been exhaustively tested by actually sending
dummy units up and causing them to renter. They work.

>>    And on the issue of safety, one should ask what kinds of
>>critical tests are possible. It is much easier to perform really tough
>>tests on an RTG than on a nuclear reactor, so one may feel more
>>confidence in their safety.
>
>  I still don't like the idea of a blob of nuclear goop falling from the
>sky into my living room. :)

Hook a couple of leads to it and run your computer off of it for a few
years. Now that's a UPS!

>>    And another possible difficulty with solar cells -- how much
>>energy does it take to make them? They would not be too good if the
>>amount of energy needed to make them was only equal to their output
>>for several years of running. Has that question ever been addressed?
>
>  If the energy is free, who cares how much it took to make them?

If it takes more fossil fuel to manufacture them than they will produce
over their operating lifetime you care. And it does take more energy
to manufacture them than they produce over their lifetime. They are
net energy losers. Also the manufacture of solar cells requires some
very nasty chemicals that must be disposed of after manufacture.

>  The real question (as I see it) is the *TRUE* cost.  Burning fossil fuels
>is cheaper than solar, nuclear is cheaper then solar, almost everything
>is cheaper than solar if only the current fuel costs are looked at.  If the
>total cost of burning fossil fuels, using nuclear energy, etc is
>totalled, solar will come out the clear winner.
>
>[e-mail]

For solar cells the answer is a clear no on an energy basis and an
enviornmental basis. For solar boilers driving freon turbines the
energy cost is a net win. But the enviornmental costs are bad considering
what the inevitable freon leaks will do to the ozone layer. Maintence
costs in general are high since efficiency is very low and you need a
lot of them to produce useful power. Perhaps the worst effect of using
large scale solar energy to replace fossil fuels or nuclear plants is the
effect on the climate. By placing large arrays of solar cells or solar
turbines on the surface of the earth, you dramatically change the reflectivity
of the earth in that area. A good solar collector absorbs almost all of the
solar energy striking it and reradiates very little thus creating a
hotspot in the local enviornment. The effects on the weather of the several
hundred square miles of solar collectors needed to replace one nuclear
plant should be spectacular.

Gary

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Date: 4 Jan 91 17:56:02 GMT
From: sdd.hp.com!usc!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: Re: Interstellar Travel
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I wrote:
>dust disk around Gamma Pictoris [? my references aren't handy] has been
>imaged...

Wrong Greek letter; it's Beta Pictoris.
--
"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: 1 Jan 91 13:10:02 GMT
From: hpl-opus!hpcc05!col!hpldola!hp-lsd!oldcolo![e-mail]  (Keith Hamburger)
Subject: Re: Future Headlines Today
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Hear, Hear... All but passing a law, There are far too many laws already.

Another option to consider would be to have NASA start to look at and
analyze the competition from private sector proposals fairly, and based
on such factors as accomplishment of mission designed for and RETURN ON
INVESTMENT.  (Well, I guess asking them to compare a positive cash flow
to their own system fairly would be asking to much.)

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Date: 1 Jan 91 20:26:02 GMT
From: sdd.hp.com!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo!censor!geac!torsqnt!lethe!telly!moore!eastern!egsgate![e-mail]  (Maury Markowitz)
Organization: EGS/Philo BBS Gateway, Toronto [phone]
Subject: Re: Solar cell factor/Space computers
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>Depends; what do you mean by "spaceable"?  Almost anything that
>doesn't need convection for cooling can fly in the shuttle cabin --
>for example, Radio Shack Model 100s have flown unmodified.  If

  Replaced by a Macintosh Portable as of late...

>you're talking about use in an unpressurized satellite, you need to
>worry a little about outgassing in vacuum and a lot about
>temperature control.  For long missions or critical applications,
>you also need to worry about radiation effects, both gradual
>degradation due to accumulated dose and transient hiccups due to
>single particle hits. --

  Any simply statements about the latter?  I just read the former post
about an amature satellite using Transputers (which are QUITE VLSI), but
I was under the impression that the radiation effects were much greater
for smaller devices.
  BTW, do normal CCD's outgas tremedously in space?

                                                       Maury



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...!{uunet, moore, lsuc}!eastern!egsgate

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End of SPACE Digest V13 #027
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