Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v11_3/v11_386.txt

Internet Message Format | 1991-07-08 | 17KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/oaGZ3SG00VcJIIU05X>;
          Fri, 11 May 90 01:42:55 -0400 (EDT)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Fri, 11 May 90 01:42:26 -0400 (EDT)
Subject: SPACE Digest V11 #386

SPACE Digest                                     Volume 11 : Issue 386

Today's Topics:
Re: Dirigible launchers (was Re: Pegasus launchers, space-going DUCT TAPE)
              Re: launch windows
           Re: Looking for a good telescope
               Re: why there are no ETs
     Hubble Space Telescope Update - 05/10/90 (Forwarded)
             Radioactive Shuttle?
    Re: Terraforming Venus (was: Manned mission to Venus)
             Re: Re: Dyson spheres (long)
          Re: Manned mission to Venus (long)
----------------------------------------------------------------------

Date: 10 May 90 11:47:23 GMT
From: mcsun!ukc!edcastle!hwcs![e-mail]  (Adrian Hurt)
Subject: Re: Dirigible launchers (was Re: Pegasus launchers, space-going DUCT TAPE)

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Cliff White) writes:
>>why reject the B-1?
>>It's fast, new, designed for dropping things...
>>and has no useful current mission that i've heard about...
>
>The B-1 is not particularly fast, actually.  With occasional exceptions,
>military aircraft have been getting slower over the past 20-30 years, as
>people came to realize that high supersonic speeds are of very little use
>for most military missions.

That's the B-1B you're thinking of.  Are there any of the prototype B-1A's
still around?

Even the B-1B can go faster and higher than a B-52, although in its military
role it probably wouldn't do so.  The B-52 can't go beyond Mach 1; the B-1B
can; and the B-1A could go at Mach 2.  The B-52 can't get over 50,000 feet;
both B-1 types can get over 60,000 feet.

 "Keyboard?  How quaint!" - M. Scott

 Adrian Hurt                 |    JANET:  [e-mail]
 UUCP: ..!ukc!cs.hw.ac.uk!adrian     |  ARPA:   [e-mail]

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

Date: 11 May 90 02:39:53 GMT
From: [e-mail]  (Patty Winter)
Subject: Re: launch windows

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Gregory N. Bond) writes:
>>And why is there any launch window at all for satelites, shuttles and
>>stuff?  An orbit is an orbit, and the only reference point is the
>>earth, no?
>
>The Sun matters too, and that's the reason for a lot of launch windows
>in one way or another.

What I've been trying to figure out (and some of my friends say the
same) is why there was a "launch" (release) window for HST. I would've
thought NASA would want it released while they were in visual
communication with the shuttle. What gives?


Patty


--
*****************************************************************************
Patty Winter N6BIS                        INTERNET: [e-mail]
AMPR.ORG: [44.4.0.44]                     UUCP: {decwrl,nsc,sun}!apple!winter
*****************************************************************************

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

Date: 10 May 90 17:12:18 GMT
From: hplabsb![e-mail]  (David Smith)
Subject: Re: Looking for a good telescope

In article <[e-mail]> [e-mail] (Sid Shapiro) writes:
>Hi folks, I hope this is the right place to ask this...
>I'm looking for a good telescope for under $1000.  What are the
>possibilities?  Are there any?  Must I go to $2000 or more?  Are there
>any places that I might look for used scopes?

Watch the want ads.  A fellow I met placed a "telescope wanted" classified
ad, and got two good bites.  The second came after he had already bought the
first.  He passed the lead on to me, and I bought the scope.

Seeing that you're from the SF Bay area, I'll depress you by saying that
you missed a great opportunity last Saturday.  The San Jose Astronomical
Association held its annual (or apparently now semiannual) swap meet and
auction.  My, were those prices depressed! (And now you're really depressed.)
A brand new 8" Dobsonian built by Earl Watts (excellent reputation) got no
takers at $300 minimum bid.  Earl waived the minimum bid, and it sold at
$175.  Other scopes went cheaply, as well.  The bidders pretty much already
had good telescopes, and weren't motivated to bid the prices up.  Finders
and eyepieces went for a higher fraction of value.

I am told that Earl Watts runs a telescope making workshop every Friday
night in Berkeley.  Send me a note if you want his number.
--
    David R. Smith, HP Labs
    [e-mail]
    [phone]

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

Date: 10 May 90 04:41:46 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: why there are no ETs

In article <[e-mail]> acad!megalon![e-mail] (Paul Baclaski) writes:
>It just occured to me that one of the possible reasons we have not
>discovered extraterrestrial intelligence in the universe is that they
>have created full fledged virtual reality systems and feel no need to go
>exploring space because they have enough fun exploring the inner space
>of their collective minds.

I'm not sure how serious this was intended to be, but it has the same
flaw as all the other "they're not seen because they don't want to be"
arguments: it assumes that ALL civilizations come to the identical
conclusion.  All it would take is one exception, or one ACTIVE exception
at any time in the history of the cosmos, to flood the galaxy with
lifesigns even if 95% of the beings in the galaxy were "SETI dark
matter" sitting plugged into nine dimensional Nintendo games.

I still like my explanation.  When you achieve interstellar travel
or communication, someone comes along and kills you.  Fits the nature
of the universe, i.e., a real bitch.

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

Date: 10 May 90 16:32:52 GMT
From: snorkelwacker!usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov![e-mail]  (Ron Baalke)
Subject: Hubble Space Telescope Update - 05/10/90 (Forwarded)

THE NEW YORK TIMES -- MAY 10

"Old Error Stalls Focusing of Space Telescope"

By John Noble Wilford

"An error made years ago in planning has set back efforts to
focus the Hubble Space Telescope and delayed by at least another
week an attempt to take the first picture of the heavens with the
$1.5 billion instrument."

Revised commands radioed to the telescope tonight could result in
the first picture being snapped Wednesday according to the
Times.  If a second test becomes necessary, the picture may be
delayed another two days.

Wilford says engineers found that a pointing error of half a
degree caused by use of an outdated star chart had been
programmed into the telescope computer.

The Times report states that the first picture should magnify
objects about as well as fairly large Earth-based telescopes
while later pictures will be able to see objects out close to the
edge of the universe seven times clearer than the largest ground
telescopes.

The first test photo subject is a 3-billion year-old star field,
Theta Carina, the "Ship's Keel", some 1,260 light years away.

                      * * * * * * * *

WASHINGTON TIMES -- MAY 10

"Math Mistake Points Hubble Wrong Way"

"A simple math mistake -- somebody added when he should have
subtracted, or vice versa -- caused the Hubble Space Telescope to
miss its target stars and point to the wrong spot in the heavens,
embarrassed scientists said yesterday."

The Times quotes Hubble deputy manager Jean Olivier saying, "when
we were trying to point the telescope to the center of a pretty
rich star field with a high probability of acquisition, we were
really off to one side of that."

The story says because of this error, the first picture from the
telescope won't be taken until sometime next week.

                      * * * * * * * *

WASHINGTON POST -- MAY 10

"First Space Pictures From Jittery
Hubble Telescope Still Several Days Away"

By Kathy Sawyer

"After two weeks in orbit, the Hubble Space Telescope has not
shaken its opening-night jitters and is not expected to return
its 'first light' images to Earth until at least next Wednesday,
its handlers said yesterday."

The Post story cites Hubble oscillation and jitter problems and
describes the math error committed by Space Telescope Science
Institute staff in correcting a 1954 sky chart for use by the
telescope fine guidance system.

Sawyer then quotes from the STS-31 post-flight crew press
conference and mission specialist Bruce McCandless, "this is not
your garden variety satellite.  What you're seeing now are the
first efforts in working our way through the things which are
zero-gravity and orbit related" and couldn't be tested before
launch.  Sawyer cites the astronauts' plea that the public and
media maintain patience while the telescope team tackles start-up
problems.

 Ron Baalke                       |    [e-mail]
 Jet Propulsion Lab  M/S 301-355  |    [e-mail]
 4800 Oak Grove Dr.               |
 Pasadena, CA 91109               |    Go Lakers!

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

Date:     Thu, 10 May 1990 08:31 EDT
From: SIMMONS DONALD F  <[e-mail]>
Subject:  Radioactive Shuttle?
To: <[e-mail]>

     I have recently heard that while in space, the belly of the shuttle
picks up radiation from the sun, so much so that after the shuttle has
landed they check it with a geiger counter before the astronauts can
disembark. Anyone know anything about this?

Donald Simmons   27000@aeclcr

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

Date: 10 May 90 14:11:07 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!watserv1!maytag!watdragon!watyew![e-mail]  (Brian or James)
Subject: Re: Terraforming Venus (was: Manned mission to Venus)


 I think using Saturn's rings as H2O fodder for terraforming
Venus is a Bad Idea. There are other sources of ice in the
Solar System, and destroying a beautiful ring sytem unecessarily
seems wrong. Kind of similar logic to national parks or
historic buildings. The Rings have a value where they are.
                        JDN

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

Date: 10 May 90 16:43:22 GMT
From: helios.ee.lbl.gov!hellgate.utah.edu!mailrus!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Re: Dyson spheres (long)

I was asked where the numbers came from. I'll summarize here, and send
the calculations to John through e-mail.

Unless otherwise indicated, all values are for a sphere at 1 AU. The Sun
is taken to shine at 1.4 kW/m^2 at a distance of 1 AU.

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>>From: usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
>>Subject: Re: Re: Dyson spheres?
>
>>The Sun subtends 6.8E-5 steradians of solid angle from the inner
>>surface of the sphere (at 1AU). Assuming that the radiation from any
>>element of the sphere is isotropic (I don't know how good an assumption
>>this is), the Sun catches 1.1E-5 of the reradiation, which raises the
>>surface temperature of the Sun by much less than 1 degree.
>
   Angle subtended is projected area divided by distance squared. The
radius of the Sun is 700000km, the distance is 150000000km. So, any
individual element on the inside surface of the sphere, assuming it
radiates equally in all directions over the 2pi steradians available to
it, casts 1.1E-5 of its radiation onto the disk of the Sun. The rest of
the radiation misses the Sun and hits another part of the sphere.
   So, the Sun's temperature has to increase, so that the power output
is 1.000011 times its former value. This corresponds to a temperature
increase of about 0.05 degrees.

>There's a much simpler approach, which I would have a greater tendency to
>trust:
>
   I did it this way first, but thought my other argument was more
intuitive.

>If
>we assume that the power output of the sun is constant, that everything acts
>like a black body, that the current temperature of the sun is 5000K, that the
>temperature of space is about 3K, and that the inside surface of the Dyson
>sphere is 500K, then putting a Dyson sphere around the sun will raise its
>surface temperature by about 1/8 of a degree K.
>
   Close enough to my value not to make a difference (I'm a physicist,
so if they agree to within a factor of ten, I'm happy).

>If I got the calculations right, a blackbody Dyson sphere at 1AU would be
>heated to about 400K rather than 500K.
>
   Yes, that's right. And at 1.4 AU, it would be 335K, at 2 AU it would
be 280K, which is close to freezing.

>Upon further consideration, I don't think the re-radiated heat will help
>to inflate a sphere of black body material which radiates equally to the
>inside and to the outside. Consider the situation you described (I think it
>was the nonreflecting surface): as you pointed out, the sphere in steady-state
>must radiate to the outside the same amount as the solar energy directly
>incident upon its inner surface - about 1400 W/m^2 at 1AU. It also radiates
>the same amount to the inside. According to my earlier spherical integration,
>the perpendicular force vector from this radiation is reduced by a factor of
>2 because the surface radiates in all directions.
>
   Yes, all right. I got the same result.

>The inside of the sphere
>absorbs 2800 W/m^2 (half from the sun, half uniformly distributed over a
>solid angle of 2*pi sr from the rest of the inner surface of the sphere).
>
   Ah hah! And half more from the radiation TO the inner volume of the
sphere. That's 1 (from the Sun), 1/2 (from radiation from other parts of
the sphere hitting it), and 1/2 more (from the radiation it is sending
to other parts of the sphere).

>The
>surface of the sphere thus experiences an outward force of 1.5 times that
>of the solar flux alone, and an inward force of .5 times the solar radiation
>pressure. The net result is that the sphere experiences no more outward force
>than if the surface radiation were ignored. (Again, if the inner surface is
>reflective, the situation is different - but the black body formula has to be
>modified.)
>
   Well, outward force of 2 times that of the solar flux, and an inward
force of 1/2 the solar momentum flux.
   Putting this back into the equations, the acceleration of gravity at
1 AU due to the Sun is 5.95E-3 m/s^2. The force per unit area of the
solar radiation pressure at 1AU in the Dyson sphere is 6.9E-6 N/m^2.
This means that the surface of the sphere could be held up by radiation
pressure if it had a mass density of 1 kg per 960 m^2 of area.

>I didn't quite follow how you got some of your numbers - more detail might
>be helpful.
>
   Hope this helps.

>              John Roberts
>              [e-mail]


--
 Christopher Neufeld....Just a graduate student  |  "Spock, comment?"
 [e-mail]              |  "Very bad poetry
 [e-mail]          Ad astra! | captain."
 "Don't edit reality for the sake of simplicity" |

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

Date: 10 May 90 04:30:28 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Manned mission to Venus (long)

Several points.

 * Why wouldn't powersats work for supplying a Venus base?  Radar
gets through.

 * You can always dig.  I know, I was the one with the snide remark a
few months back -- "if you want to live in a basement, how much does it
matter which planet the basement is on," but even so -- if you HAD to go
to Venus for some reason, you could dig.

 * The way things are going, top priority may be terraforming the Earth
before we get to the other planets. :-)

 * Regardless -- Mars before Venus.  Mars could be settled with a
century's work.  Venus may take a millenium, and I'm not sure why anyone
would care.

 * The one reason NOT to colonize the planets is lebensraum.  We added
three billion to Earth this century.  We can trash any biosphere you
give us.  There is no substitute for learning to manage our planet
sensibly.

--
"UNIX should be used          ::   Tom Neff <[e-mail]> or
 as an adjective." -- AT&T   ::    ...uunet!bfmny0!tneff (UUCP only)

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

End of SPACE Digest V11 #386
*******************