Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_1/V15NO108.TXT

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Date: Fri, 14 Aug 92 05:02:51
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #108
To: Space Digest Readers
Precedence: bulk


Space Digest                Fri, 14 Aug 92       Volume 15 : Issue 108

Today's Topics:
                         beanstalk in Nevada
         Beanstalks, Tethers - something I forgot to mention
              Beanstalks in Nevada Sky (was Re: Tethers)
                   Capsule location list (at last!)
                      He3 Power Source (2 msgs)
                      Magellan Update - 08/13/92
                  Mini Energiya(?) & MIR replacement
                          Parsecs? (4 msgs)
                            Persied Shower
                           SPS feasibility
                        SPS fouling astronomy
                          Tethered Satellite
                           Topaz II Reactor

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

Date: 13 Aug 92 17:11:17 GMT
From: Mark Evans <[e-mail]>
Subject: beanstalk in Nevada
Newsgroups: sci.space

[e-mail] writes:
: Wouldn't it be possible to have a beanstalk terminus in Nevada just as long as
: you had a complimentary terminus an equal distance south of the equator, to
: form a dual stalk beanstalk?  As I envision this thing, there would be a single
: upper terminus, located directly above the equator, and the lines descending
: from it would have a catenary shape.  Of course, it would be difficult enough
: doing a beanstalk to a terminus on the equator, but as long as we are dreaming
:  ...

Why Nevada?

Nirobi would be far easier from the orbit point of view...

--
-------------------------------------------------------------------------
Mark Evans                                   |[e-mail]
+(44) 21 565 1979 (Home)                     |[e-mail]
+(44) 21 359 6531 x4039 (Office)             |

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

Date: 13 Aug 92 20:18:29 GMT
From: "Thomas J. Nugent" <[e-mail]>
Subject: Beanstalks, Tethers - something I forgot to mention
Newsgroups: sci.space

[e-mail] (Thomas J. Nugent) writes:

>Another possibility I forgot to mention along with space fountains was
>a variant of a launch loop.  You have, oh say six platforms above the
>Earth, moving such that they stay above the same point - but lower than
>GEO.  This normally can't happen, but if you have a huge "loop" around
>the Earth, of pellets, each of which sort of strikes each platform and
>bounces(??) in such a way as to maintain its altitude, and continue on to
>the next platform.  It's been awhile, so I don't remembert this in detail
>At some point, the pellets are boosted, to keep up their speed.  If anyone
>wants a better description, I could look up the info.  (I really should
>know this, though.)

That was a really lousy description.  After a conversation last night, things
have been cleared up.

The item I'm talking about is sometimes referred to as a "Jacob's  ladder".
Imagine a rope spinning fast enough that it maintains a circular shape.
Now imagine it big enough and fast enough so that it is "sitting" around
the Earth.  Now "hand" a platform on it in various places - the outward
force on the 'rope' due to its spinning will support a mass on it.  You
would of course want to balance masses on opposite sides of the planet and
have some station keeping devices in  use.  To keep the platforms above a
point on Earth, put the 'rope' in a polar orbit, then precess it (actually,
you might be able to have it in an inclined orbit and precess it) so that
it stays above the same places on Earth.  The rope is actually either a
huge metallic ribbon, or a series of pellets.  These are deflected
electromagnetically to produce the supporting force on the platforms.

"The future is a race between education and catastrophe."
        - H.G. Wells
--
"To be average scares the hell out of me." -- Anonymous
Tom Nugent        e-mail: [e-mail]

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

Date: Thu, 13 Aug 92 21:04:49 GMT
From: Dave Jones <[e-mail]>
Subject: Beanstalks in Nevada Sky (was Re: Tethers)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Michael K. Heney) writes:
>In article <[e-mail]> [e-mail] (Dave Jones) writes:
>>
>> [...]
>>
>>Clarke also had his tower made of that famous variety of unobtainium,
>>monomolecular filament.  Assuming he'd done some basic estimates, you
>>have to figure that's the kind of tensile strength you need for a cable
>>23,000 miles long.  He also had a captured asteroid stuck out on the
>>far end as a counter-weight, possibly at a height beyond GEO.
>>
>
>Don't forget the _2061: Odyssey Three_ approach - diamond.  I know diamond
>is used in presses to generate pressures in the millions of atmospheres
>(in very *small* volumes), but is it actually strong enough to handle the
>tensile forces a GEO-centered tether would need to handle?
>
I don't remember diamond featuring as tether material.  However, since
it is (theoretically) a single-molecule solid, the answer is
(theoretically) yes.  What weakens diamond (and metals, other crystals
etc.) is the existence of defects in the structure, where the regular
patterns of interatomic bonds are disrupted.  These defects act as
focus points for stress, and propagate themselves under that stress,
so most crystalline materials are much much (I forget how many orders
of magnitude) weaker than you'd expect if you did a theoretical
calculation based on the strengths of the bonds.


--
||)) Dump the Whatzit!  Ren and Stimpy for Olympic mascots in '96 !  )))))))|
||)) "What is it, man?!?" ))))))))))))))))))))))))))))))))))))))))))))))))))|
||))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))|
||Dave Jones ([e-mail]) | Eastman Kodak Co. Rochester, NY   |

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

Date: 13 Aug 92 21:33:08 GMT
From: Curtis Roelle <roelle@uars_mag.jhuapl.edu>
Subject: Capsule location list (at last!)
Newsgroups: sci.space

[e-mail] (Jerry Matulka) writes:

>In article <[e-mail]> [e-mail] (Chris Mastrangelo) writes:
>>In 1988-89 I visited the campus of the University of Nebraska in
>>Lincoln and was surprised to find a genuine Apollo capsule sitting
>>on display outside the Nebraska State Museum of Natural History
>>not far from the Cornhusker's football stadium. I think it had
>>been there at least since 1985 because it was outside exposed to the
>>elements which had taken their toll on the white paint which was
>>flaking off in places where the clear plastic was not protecting
>>the exterior. (The plastic was mostly around the heat shield area
>>through which you could see the effects of reentry.)
>>
>>Unfortunately I don't recall which Apollo number it was, but it
>>could have been Apollo 14, which evidently didn't make it to
>>Rockwell, or was donated to UNL after 1985.
>>
>>Can anyone else confirm or deny this??
>>
>>- Chris Mastrangelo
>>

>It is definitely not Apollo 14's Kittyhawk.  The command module that was
>at the University of Nebraska was from an unmanned flight of some sort.  It
>has been (I assume it's still there) at UNL for a considerable amount of time
>before 1985.  I think it's been there since about 1975 actually.  I think the
>reason that it wound up sitting outside was that it wouldn't fit through the
>doors of the museum, and they didn't want to or didn't have the funds to make
>a larger doorway.  Sad but true.  I'm sorry that I don't remember the exact
>lineage of this craft, but I don't think the newspapers back in 1975 even had
>it straight.  This command module not only was involved in a flight, but they
>conducted some sort of drop test on it afterwards, putting a fair dent in the
>heat shield.

I lived in Lincoln from about 1960-1980, and attended UN-L from 1975-80.
Don't remember when said capsule appeared, but it was in the mid-70's,
and a thrill for local space buffs.  As to its designation, I recall the
plaque gave a mission designation as "004".  My memory of 12+ years ago
isn't too precise, but this may have been the first Saturn V flight test.

C. Roelle
[e-mail]

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

Date: Thu, 13 Aug 92 19:35:31 GMT
From: Doug Mohney <[e-mail]>
Subject: He3 Power Source
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (thomas.vandoren) writes:
>.  It showed proposed lunar surface strip mining machines
>that would filter out the He3 and replace the regolith behind it thus having
>minimal environmental impact.  Other items such as oxygen and water could be
>extracted at that time as well.

Minimal environmental impact?

Hm, doesn't the moon have to have an ENVIRONMENT first?


                 Support U.N. military force against Serbia

  -- >                  [e-mail]                        < --

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

Date: 13 Aug 92 22:05:32 GMT
From: Don Roberts <[e-mail]>
Subject: He3 Power Source
Newsgroups: sci.space,sci.energy

[e-mail] (thomas.vandoren) writes:

>About 2 weeks ago I saw a series of 5 minute modern videos of great interest.
>One of them was about a proposal to use Helium3 mined from the moon as a power
>source on Earth. [...]
>
>Does anyone have more info, opinions on that proposal? [...]
>
>How hypothetical is this and is it practical?
>
>Lee

At present it's *very* hypothetical, and *highly* impractical. The way to
use He3 for power generation is via nuclear fusion [1]:

D + He3 -> He4(3.6MeV) + p(14.7MeV)

However, the reaction rate parameter (related to the fusion reaction cross
section and the relative speed of the reactants) is by far the highest for
the deuterium-tritium reaction:

D + T -> He4(3.5MeV) + n(14.1MeV)

Using D-T fusion, the major magnetic fusion experiments, in England and
the U.S., could presently only produce between 0.3 and 0.7 of the input
power needed to sustain the experiment [In fact these machines study D-D
fusion, which generates far less fusion power but only produces about half
as many neutrons, at lower energy.  D-T experiments are planned at each
facility within the next few years].

D-He3 fusion, while more environmentally benign (*much* lower neutron
production, leading to less activation, structural fatigue, etc.) requires
temperatures about ten times as great to attain similar reaction rates.
Even then, it would probably require higher plasma densities, further
complicating matters. In other words, we haven't licked the "simple"
problem yet (D-T) fusion, so don't hold your breath waiting for the tough
one (D-He3).

I think the lunar "environment" is safe from marauding bands of
strip-miners. For the time being...

Reference:

[1] NRL Plasma Formulary, 1990 ed. Naval Research Laboratory, Washington DC

--
 Dr. Donald W. Roberts
   University of California                                      Physicist
   Lawrence Livermore National Laboratory         Recreational Bodybuilder
   [e-mail]                                       (better poo? :)

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

Date: 14 Aug 92 04:31:57 GMT
From: Ron Baalke <[e-mail]>
Subject: Magellan Update - 08/13/92
Newsgroups: sci.space,sci.astro

Forwarded from the Magellan Project

                     MAGELLAN STATUS REPORT
                        August 13, 1992

1.  Magellan continues to operate normally, performing only
    starcals (star calibrations) and desats (desaturations of
    the reaction wheels).

2.  A week from now, Transmitter B will be  turned back on and
    the temperature gradually raised into the range of 50 to
    60 degrees C.  It is hoped that this operating mode which
    will allow the return of radar data at 115 kbps in order
    to fill the only significant gap in Magellan's global
    coverage of Venus.

3.  The critical period, a 10-day mapping segment at the end
    of the cycle, begins on September 3 and is included in the
    M2247 command sequence.

4.  The International Colloquium on Venus was concluded
    yesterday at Caltech. The meeting included over 120
    technical papers on Venus research, many based on Magellan
    data.  The colloquium ended with six "summarizers" who
    emphasized the areas for further Venus research and a
    panel discussion of prospects for future missions.  It was
    generally agreed that the highest priority was for a
    continuation of the Magellan mission and continued funding
    for research using the Magellan data.

5.  Magellan has explored Venus for 734 days.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | You can't hide broccoli in
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | a glass of milk -
|_____|/  |_|/       |_____|/                     | anonymous 7-year old.

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

Date: 13 Aug 92 19:43:58 GMT
From: Gary Hughes - VMS Development <[e-mail]>
Subject: Mini Energiya(?) & MIR replacement
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Gerald Cecil) writes...
>Last week's AW&ST had a CAD sketch of the redesigned MIR 2 station on a
>launch vehicle I can't identify.  It *looks* like a cut-down Energiya core,
>judging by the relative diameters of the strap-ons/core.  Has anyone seen
>this configuration before?  I recall that the brief article mentioned that
>MIR 1 will be operable until 1995. Someone here mentioned last week that the
>core module will have to be replaced soon. Details on this & MIR 2 anyone?

The launch vehicle shown is the configuration that they (Energia NPO, reported
in AvLeak) have talked about in the past as Energia-M.

Two strapons and a shortened core using a single engine (instead of the usual
4). The drawing also showed an unidentified upper stage that looked somewhat
like their proposed (under development?) RCS upper stage. This is the smaller
of the two upper stages proposed for Energia use.

gary

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

Date: 13 Aug 92 17:14:37 GMT
From: Jim Carr <[e-mail]>
Subject: Parsecs?
Newsgroups: sci.space,sci.physics

In article <[e-mail]> [e-mail] (A Colin Morton) writes:
>
>As other posts have stated, one parsec is equal to ~3.2616 light years.
>As we, on Earth, are only ~8 light minutes from the Sun, I don't think
>the Earth-Sun distance defines a parsec.                         ^^^^^

If you do not *know* how a parsec is defined, then you should look it up
before persisting pushing a wrong argument.

A parsec is a parallax-second and is defined to be the distance at
which one second of arc (1/3600 of a degree) subtends 1 A.U.  Simple
calculation (d = r * theta, theta in radians) will verify that this
is exactly the way that otherwise silly value of ~3.26 light years
is obtained.

The reason for this was spelled out in my earlier post: it is defined
as a convenient conversion factor between the angular shift in the
apparent position of a star when your viewing position is translated
by some distance (typically something like the diameter of the earths
orbit = 2 AU) and the distance of that star from the viewer.

--
J. A. Carr                                    |  "The New Frontier of which I

[e-mail]                           |  speak is not a set of promises
Florida State University  B-186               |  -- it is a set of challenges."
Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)

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

Date: 13 Aug 92 19:16:22 GMT
From: A Colin Morton <[e-mail]>
Subject: Parsecs?
Newsgroups: sci.space,sci.physics

In article <[e-mail]> [e-mail] (John C. Baez) writes:
>In article <[e-mail]> [e-mail] (A Colin Morton) writes:
>>In article <[e-mail]> [e-mail] (Keith Allan Schneider) writes:
>>>>Coincidence.  Remember, one AU is the distance from the Earth to the Sun...
>>>
>>>No, THAT, my friend, is the DEFINITION of a parsec...
>>>
>>As other posts have stated, one parsec is equal to ~3.2616 light years.
>>As we, on Earth, are only ~8 light minutes from the Sun, I don't think
>>the Earth-Sun distance defines a parsec.
>
>You seem to be deliberately misreading what has been written.  Nobody is
>claiming the Earth-Sun distance IS a parsec.  Only that the Earth-Sun
>distance is involved in the definition of a parsec.  (Since others have
>given the definition of a parsec I won't!)
>
Okay, I realise now that I did misread the original post.  It was not,
however, deliberate; rather, it was a consequence of not having my brain
fully in gear at the time, a condition which has been plaguing me all
day.  I apologise for what did sound like a smart-alec answer; however,
some of the e-mail I have been receiving as a result of this (honest,
Mr. Baez) mistake has been far less flattering than anything I posted.

Colin.

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

Date: Thu, 13 Aug 1992 15:19:07 GMT
From: Jeff Wilkinson <[e-mail]>
Subject: Parsecs?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Robert S. Hill) writes:

>>>|> Please forgive my ignorance, but what the heck is a parsec?
>>>|> Richard.
>> A star with a parallax of 'p' arc seconds is at a distance
>> 'd' parsecs, given by  d=1/p (accurate up to distances of about 30pc).
>> One parsec equals  30.857x10**12 km, 206265 astronomical units, and
>> 3.2616 light-years.
>
>Fun facts:  206265 is also the number of arcsec in a radian

Actually, its not so astounding, I think. The definition of a parsec
that I learned, is that it is the length of the "opposite" side of a
right triangle whose base is 1 AU, and whose included angle is 89
degrees 59' 59" (that is, its other angle is 1 arcsecond). So the
number of AU above is a natural consequence (tan 89-59-59 =
1 parsec / 1 AU).


There is nothing wrong with making        | Jeff Wilkinson at Medtronic
.signatures, but... make *new* ones! :-)  | [e-mail]

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

Date: 13 Aug 92 21:54:13 GMT
From: Anthony Frost <[e-mail]>
Subject: Parsecs?
Newsgroups: sci.space


  >> Hmmm...  at the distance of one parsec, one astronomical
  >> unit subtends an angle of one arc second.

  > Coincidence.  Remember, one AU is the distance from the
  > Earth to the Sun...

  > look ma, i can nitpick too! :)

Just thinking... At a distance of one parsec, wouldn't two astronomical
units subtend an angle of one arcsecond? An AU being the average radius of
the earths orbit, and the parallax being measured across the diameter?

        Anthony

Must make a sig one of these days...

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

Date: Thu, 13 Aug 1992 17:53:25 GMT
From: [e-mail]
Subject: Persied Shower
Newsgroups: sci.space

I was looking at the sky last evening, and I noticed that a bright star (like
the North star) was moving!  It was "travelling" from north to south, approx.
75 degrees across the horizon, at 10:25 p.m. EST in Massachusettes, at a speed
faster than our intercontinental jumbo jets.  It dimmed, and faded from view,
before it reached the center of the sky and never reappeared.  I wonder if this
was the soviet spacestation?  I remember, as a teenager, viewing our
spacestation (which travelled at a slower rate as viewed from the ground.) and
ours may have been brighter.

Hmmmm.  Just thinking...
"insert disclaimers here"
Tom Mehrtens <[e-mail]> Motorola Codex
 ////\\
  _  _
 (o)(o)
   .)
 )-_-(

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

Date: Thu, 13 Aug 92 17:12:19 EDT
From: Tom <[e-mail]>
Subject: SPS feasibility

>|> I've never seen 'multiple-orders-of-magnitude' projected improvements
>|) in my (limited) studies.

>Many things have to be done many orders of magnitude more cheaply
>than can be done at present.  For terrestrial-launched systems,
>launch costs have to come down about by a factor of nearly 1000.

1000 times?  That seems rather large.  If we consider the cost for
Shuttle launches ($7000/lb, if I remember right), then your'e saying
SPS will only become feasible when launch costs ar $7/lb?  And the
shuttle is on the high end for launch costs, right?   I think that about
any scheme would be possible at $7/lb; point being that costs don't
have to drop that much.  How about $70?  $700?  Even at $700.oo, we'd see
remarkable increases in space activity, including, among other
things, attempts to answer those questions at the heart of the SPS
debate on this thread.

>The cost
>of processing lunar materials has to come down enormously, if you

I wasn't aware that we were processing anything on the moon ;-)

Obviously, you are using projected costs, but, allowing those, since much
of the cost of lunar processing will be launches for supplies, etc., then
any drop in launch costs will be refelected almost immediately in
lunar-processing savings, too.  It seems that these points are not
independent, as you imply above.

>go that route (what's the cost per man hour of a lunar base using
>existing technology?  More than the cost on Freedom).  In general,
>space activities have to be scaled up by multiple orders of magnitude.

Well, current cost for lunar processing is infinite.  If we ever do any
processing of lunar material, there's your many-orders-of-magnitude, as
promised (infinite/any-number-you-can-imagine = many orders of mag. :-)

Serously, wouldn't a drop in launch costs by only a factor of ten imply,
maybe even necessitate, a corresponding increase in space activity?
How about a factor of 2?

>One microwave SPS has more mass than everything ever put into orbit combined.

Despite my doubts about the truth of that statement, I'll agree, but so what?
At one time, Skylab was the biggest space station, Saturn was the
bigggest rocket, etc.  Just 'cause it's big doesn't mean it's impossible.
Especially if we see launch costs drop by even one order of magnitude.
And, natuarally, I'd be remiss if I didn't point out that many SPS schemes
do not launch all the mass, so the mass of a SPS does not necessarily
imply having paid to launch it.

>|> Didn't I once read that solar-power-cells (to pick a competitor off the
>|> top of my head) were never expected to be more than ~40% efficient?
>|> And didn't I see Dennis post a bit about current developments in solar
>|> cells, with the best efficiency listed as 37%, and lots down in the 20%+
>|> range?  This seems to suggest to me that at least one, if not many,
>|> competing technologies have, indeed, reached the upper part of their
>|> 'learning' curves.

>You are in error: "efficiency" is not the correct figure of merit
>for terrestrial PV cells, "cost per peak watt installed" is.  The
>cost per watt of PV cells has over time declined quite rapidly,
>and is not near any fundamental limit.

But, cost of the material, and cost for the land (sun-intercepting-space)
are different things.  That cost/peak watt does not include land prices.
Or does it?   If it does not, then efficiency is a concern.  If land prices
dominate PV cell prices, it is THE concern.  If PV cell prices continue
to drop, then it is only a matter of time (if it isn't true already) before
they will have reached their fundamental limit, as far as massive power-
generation projects are concerned, because of land prices.

>|> Consider oil, for example, where the reserves in many places are
>|> well into the second, and working on the third level of extraction.
>|> (For oil, level 1 is when it comes out the ground for you.  Level 2
>|> is when you must pump it.  Level 3 is when you have to force water or
>|> mud down, to get any oil up.)

>But, in fact, it is getting cheaper to produce oil, because
>of improved reservoir modeling, horizontal drilling, and so on.
>In any case, the cost of oil is dominated by how much OPEC thinks
>it can charge without stimulating alternatives.  The cost of
>production in the Saudi Arabia is less than $3/barrel.

So the price of oil depends not just on the ease of getting it, but also
the market, labor schemes, etc.  Imagine how cheap shuttle launches would
be if the workers were paid comparably to Arabian oil workers.  And $3.00
per barrel still doesn't include x-port, refining, pollution (or pollution
control), etc.  Sure, we'll continue designing and modelling, and finding
cheaper ways to do it.  But oil is fundamentally limited.  It will become
permanantly more expensive, possibly in our life-times.

I can see a pretty good argument against SPS, along the lines of "We are
not yet at the point where SPS would pay high, and, therefore, we'll never
be able to finance the start-up project".  But I get the feeling that
this approach is not what I've seen here.  It seems more along the lines
of "SPS will never be worth it."  Maybe I'm mis-interpreting, but that's
what I see.

Let's try a different tack, just for grins:

I've seem many references to 'space infrastructure' on this net, almost
always along the lines of "I'd like to see, and help build, a self-sustaining
space infrastructure, too, but you seem to think...[flame deleted]."

Setting aside the question of whehter it's good, or whether it can ever be
done, since I agree with both, I'd like to ask:

HOW will it be done without SPS?  Will we be using oil, coal, et.al., to
fabricate all the fuel we use, until the day we can start harvesting
hydrocarbons from space?  Maybe we'll get launch costs down low enough
to make large-scale tourism possible?   We'll harvest heavy metals from
asteroids?  Fusion fuel from the moon?  Or what?

The big question for SPS, regardless of how we get from here to there,
is; Can it pay for itself, fully running?"  If yes, then we work on how.
But if SPS can't pay for itself, fully operational, can anything?
SPS is no bigger a project than any grand space resource scheme, with
the exception that the resource in question is free and (practically) infinite.
If we can't make it with those advantages, how can we make it without?

-Tommy Mac                     .  "                  +
.------------------------  +                      *       +
|   Tom McWilliams; scrub       ,     .                        "        +
|  astronomy undergrad, at     *       +;.     .  '             There is
| Michigan State University   '                      .    "   no Gosh!
|   [e-mail]                        '      ,   *
|       [phone]       ;  +  '                                 *
'-----------------------

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

Date: 13 Aug 92 17:58:39 GMT
From: Steve Willner <[e-mail]>
Subject: SPS fouling astronomy
Newsgroups: sci.space

In article <[e-mail]>,
[e-mail] (Frederick A. Ringwald) writes:
> W(out)/W(in) = aA/r^2
> It's easy enough, from this ratio, to estimate the apparent
> magnitude of the satellite, given V(Sun) = -26.7.

> More realistically, take a = 0.07, that of Lunar basalt. A Solar power
> satellite is supposed to absorb energy, after all: it'd be silly to
> make one as reflective as a mirror. This brings it to V = -3.0.

The calculation looks right to me, but we better look again at the
assumptions.  Making the albedo as small as 0.07 is _hard_; even the
best black paints are around 5% or so.  Uncoated silicon has an
albedo of around 40%.  (The index of refraction is about 3.5.)
Practical solar cells have some kind of coating, but it has to be
cheap if you want square kilometers of it.

> Now, a Solar power satellite would probably be blackened on purpose, to
> absorb more energy, so as a lower limit on albedo, take a = 0.01.

This is about the albedo of a laboratory blackbody, i.e. an absorbing
cavity.  No way will a large structure even approach this!

> 13.4 GW. So, ignoring losses - large assumption here - you'd need about
> 1000 of them to run the world, assuming rather profligate energy use,

US electric consumption is about E12 W, so about 100 satellites are
needed to supply that.  World energy use per capita is about 1/5 that
of the US, which has about 1/20 of the world's population, so
replacing electrical generation worldwide would take about 400
satellites at present rates and up to 2000 if the rest of the world
were to consume at the present US per capita rate.  Multiply by 2 if
you want to replace a good fraction of oil usage, by 3 if you want to
replace oil, coal, and gas.  Adjust for population growth and
conservation according to your best guess.  (Figures are from 1985
and come from "A Physicist's Desk Reference.")

Bottom line: the estimate of 1000 is a good round number for
discussion purposes, but we ought to keep the assumptions in mind.

>  So, the total integrated brightness is about V = -9, about 3% that
> of a Full Moon, for a necklace about the celestial equator.

I get -9.5 for albedo = 7% and -11 for a more reasonable albedo of
30%.  The latter is 0.2 of a full Moon.  Not necessarily a problem if
you are a bright time observer, as I am.  :-)

Seriously, if we are building enough space infrastructure for SPS's,
it should be easy for professional astronomers to have access to
space instruments.

> Also, the objection that
> "there'd be nowhere on Earth you could get away from the handiwork of
> humans - no remaining true wilderness" isn't really true: try Alaska

I give up.  The lattitude is only 60 to 70 degrees or so, and there
are plenty of flat places where the horizon is visible.  And the
aurora is seldom bright enough to obliterate the bright planets.
Maybe you were there during a _really_ bright display. :-)
--
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]
  member, League for Programming Freedom; contact [e-mail]

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

Date: Thu, 13 Aug 1992 18:37:57 GMT
From: "Thomas L. King" <[e-mail]>
Subject: Tethered Satellite
Newsgroups: sci.space,sci.space.shuttle

Everything I've read about the tethered satellite's electric generation
capacity has been that it will be able to generate up to 4000 volts.  This
in itself doesn't tell me very much.  Has anyone heard how much POWER it
will generate (or how much current will be generated)?  In addition, does
anyone know the current carrying capacity of the tether?  I can't imagine
any significant amount of current flowing through a wire as thin as a
"bootlace".  And one last wonder of mine:  how will the heat generated
by the current be dissipated in space without an atmosphere?

Any answers (or attempted explinations) will be appreciated.


Lee King
[e-mail]

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

Date: Thu, 13 Aug 1992 20:52:06 GMT
From: Paul Shawcross <[e-mail]>
Subject: Topaz II Reactor
Newsgroups: sci.space

Hi folks. I'm looking for information on the Soviet Topaz II space
nuclear reactor.  I know its a thermionic reactor and has been used
to power the radar ocean reconnaissance (RORSAT) satellites.  I also
know about the SDI buying one, the hassles they've had doing so, etc.

What I need is basic information such as the reactor's size, mass, power,
lifetime, and shielding.  I've been digging around, but haven't been
able to find out any of this info.

Either answers or directions towards answers would be appreciated.
Thanks.

Paul Shawcross
[e-mail]

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

End of Space Digest Volume 15 : Issue 108
------------------------------