Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_3/V11_326.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/4aCHZ1G00VcJ02w05X>;
          Sat, 28 Apr 90 02:33:38 -0400 (EDT)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Sat, 28 Apr 90 02:32:50 -0400 (EDT)
Subject: SPACE Digest V11 #326

SPACE Digest                                     Volume 11 : Issue 326

Today's Topics:
                Re: Our galaxy
          Re: Shuttle C or Z alternate uses
             Re: Dyson spheres, heat flow
   ASTRO-1 mission and science briefings set for May 2 (Forwarded)
           Re: Space Station Distribution Frequency
               Re: French art in orbit?
              Re: Dyson spheres?
             Re: Dyson spheres, heat flow
Re: Not-so-Silent Running (Was Re: a bunch of other irrelvant things)
----------------------------------------------------------------------

Date: 27 Apr 90 14:30:35 GMT
From: frooz!cfa250![e-mail]  (Jonathan McDowell)
Subject: Re: Our galaxy

From article <[e-mail]>, by [e-mail] (Arnold G. Gill):
> In article <[e-mail]>,
> [e-mail] (Will Martin) says:
>>In a related topic, is there any "better" name for our galaxy than "the
>>Milky Way"?
>      The proper astronomical term is simply "the Galaxy", with a capital 'G'.

Well, if you're a galactic astronomer it is.  I find the usage pretty
confusing since I am often using "the galaxy", small 'g', to refer to
some other galaxy currently in question, and my impression is that most
extragalactic astronomers quite happily use "Milky Way" as the noun when
including our home in a list of galaxies, although we do use 'Galactic'
as the adjective, and would occasionally refer to "our Galaxy" in text.

I looked in the latest Astrophysical Journal (Apr 20, Vol 353 no 2) for examples:
Extragalactic papers:
Kenney et al 465        "Milky Way"
Irwin and Seaquist, 474        "the Galaxy" and "Milky Way"
Galactic papers:
Heithausen and Thaddeus, L50    "Milky Way"
Leonard and Tremaine, 486    "the Galaxy"
Frogel et al , 494        "the Galaxy" and "the Milky Way"
Dupree et al., 623        "the Galaxy"

Small number statistics, but I conclude:
1) Both usages are current
2) From context, "Milky Way" was definitely preferred in examples like
   "in the Milky Way and the Large Magellanic Cloud"
3) My hypothesis that preference correlates with whether the author is
   a galactic or extragalactic astronomer is tenable but not proven.
   (Of course, many astronomers do a bit of both, so it's not really
   well posed).



 .----------------------------------------------------------------.
 |  Jonathan McDowell       |  phone : [phone]              |
 |  Center for Astrophysics | uucp: husc6!harvard!cfa200!mcdowell |
 |  60 Garden Street        | bitnet : [e-mail]        |
 |  Cambridge  MA 02138     |  inter : [e-mail]   |
 |  USA                     |   span : cfa::mcdowell     (6699::) |
 |                          |  telex : 92148 SATELLITE CAM      |
 |                          |    FAX : [phone]              |
 '----------------------------------------------------------------'

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

Date: 27 Apr 90 16:51:53 GMT
From: swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Shuttle C or Z alternate uses

In article <[e-mail]> [e-mail] writes:
>     Is the current plan for a shuttle-c to be launched, deliver its payload
>and then be scrapped?  Is there a plan to at least re-use all of the engines by
>putting them in the cargo bay of a real shuttle?   There must be...

Old shuttle-derived-launcher proposals did envisage either recovering the
engines with a shuttle mission or bringing them and the electronics down
in a reentry module.  However, the current Shuttle-C scheme uses engines
that are already at the end of their useful lifetimes (which are much
shorter than originally intended!) and thus are not worth recovering.

>... could also be used in any future large orbital tugs or planetary
>missions, right?

They are not ideal for the job, given the need for extensive refurbishing
between uses, the unnecessarily high thrust (orbital maneuvering can get
by with much lower thrusts than are needed for the difficult climb up
to orbit), and their lack of restart capability.  The old RL-10 is a much
better choice:  its performance isn't quite as good, and it's much smaller,
but it is reliable, reasonably sized, and restartable.

>Has any company/agency spent dime 1 on assembling a tug
>out of used parts, or do they all want to get in on developing a vehicle from
>scratch (move over, its my turn at the pork barrel, oink oink)?

Nobody is going to spend a bunch of money on such a tug when there are no
customers in sight.  The closest analogy so far is a discouraging one:
Orbital Sciences spent a bundle on private development of the Transfer
Orbit Stage -- a medium-sized shuttle upper stage -- and is most unlikely
to ever recover that investment now that the shuttle is out of the commercial
cargo business.  If NASA were to state a firm requirement for such a thing
and promise to buy N uses of it, there would be plenty of interest in doing
it cheaply.  If/when such a need materializes, though, NASA is much more
likely to pay for development rather than just guaranteeing a market.  In
that case, it's almost guaranteed to be an expensive from-scratch effort.
If you pay for effort rather than results, any rational company trying to
make money for its shareholders will plan the project to maximize effort.

>     Also, do all of the above projects HAVE to wait until the space station
>is operational? ...

Not necessarily; indeed, Shuttle-C would be a useful thing to have for
launching the station.  However, Congress historically has not been
sympathetic to NASA's interest in doing more than one big project at
a time.
--
If OSI is the answer, what is |     Henry Spencer at U of Toronto Zoology
the question?? -Rolf Nordhagen| uunet!attcan!utzoo!henry [e-mail]

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

Date: 27 Apr 90 13:04:48 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!watserv1!maytag!watdragon!watyew![e-mail]  (Brian or James)
Subject: Re: Dyson spheres, heat flow


 I don't think the Hawking radiation from a ~3 solar mass black hole
would be noticable. Back when Hawking first published, a few fast
back-of-the-envelope calcultions seemed to indicate the apparent temperature
of 3 sm black holes was 'colder' than the 3 K background radiation of the
universe. It's only the smaller black holes [asteriod massed] that pour out
lots of radiation, and as far as I know, small black holes' existance
is very much in doubt. Mind you, I still don't see how a remote observer
could see a black hole, rather than a soon-to-be ex-star very very close
to becoming a black hole [I'm saying this badly, but if you drop an object
into an existing black hole, you won't see it cross the event horizon,
but just get closer and closer as its velocity approaches C].
                                JDN

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

Date: 27 Apr 90 21:14:09 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: ASTRO-1 mission and science briefings set for May 2 (Forwarded)

Paula Cleggett-Haleim
Headquarters, Washington, D.C.                     April 26, 1990
(Phone:  [phone])

Dave Drachlis
Marshall Space Flight Center, Huntsville, Ala.
(Phone:  [phone])

Jeff Carr
Johnson Space Center, Houston
(Phone:  [phone])


EDITORS NOTE:  N90-27

ASTRO-1 MISSION AND SCIENCE BRIEFINGS SET FOR MAY 2


     The Space Shuttle STS-35/Astro-1 mission and science
briefings will be held Wed., May 2, beginning at 10 a.m. EDT.
The mission briefing will originate from the Johnson Space Center
(JSC), Houston, and the science briefings from the Marshall Space
Flight Center (MSFC), Huntsville, Ala.

     All briefings will be carried live on NASA Select
television, Satcom F-2R, transponder 13, C-band, 72 degrees W.
longitude, at 3960.0 MHz.  Two-way question and answer capability
will be available at NASA Headquarters and centers.

     The line-up for Wed. is as follows.  All times are Eastern
Daylight Time:

     10:00 a.m.   STS-35 Mission Overview
                  Gary Coen, Lead Flight Director

     10:30 a.m.   Astro-1 and NASA's Astrophysics Program

     11:00 a.m.   Astro-1 Science Overview and Capabilities
                  (including separate briefings by Astro-1
                  science instrument principal investigators)

     12:00 Noon   Space Classroom

     12:30 p.m.   Astro-1 Mission Overview, Mission Management,
                  Payload Operations Control Center
                  activities and Science Operations on orbit

     1:00 p.m.    Media Coverage of the Astro-1 Mission


     The flight director briefing will be held in JSC Bldg. 2
briefing room.  Briefings from MSFC will originate from the TV
studio, Bldg. 4207.

     Following the science briefings, there will be an
opportunity for individual interviews with briefing participants
and tours of operational areas, including the Spacelab Mission
Operations Control facility from where science operations will be
directed.

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

Date: 27 Apr 90 03:49:46 GMT
From: usc!jarthur!nntp-server.caltech.edu!gap![e-mail]  (David Palmer)
Subject: Re: Space Station Distribution Frequency

[e-mail] (Steve Nuchia) writes:
>There is also a great deal of experience with DC, but I wonder
>how the voltage was chosen?  Looks suspiciously like sqrt(2)*120,
>which is the nominal value for rectified line current.  That's
>what you work with before the inverter in a transformerless switching
>mode power supply, like the ones in PCs.  160 VDC is higher than
>you'd like from a shock hazard standpoint, but I suppose that
>48V would increase the mass of copper and/or the copper losses too much.

...
>An argument in favor of DC is that there will be no conversion
>loss when running from batteries.  If they had used any AC
>there would have been losses just getting it onto the bus, which
>would have been wasted if the load was resistive.  Of couse they
>may decide to *regulate* the DC bus, in which case you get those
>losses anyway.


The Power bus is regulated.   The DC voltage is well below the output voltage
from the solar panels.  Loss in the regulation system is estimated at 20%.
According to the power subcommittee, giving power-hungry instruments
and devices unregulated power (to save the 20%) is 'not an option'.

This from a friend who has had many long arguments with the power committee.

--
        David Palmer
        [e-mail]
        ...rutgers!cit-vax!tybalt.caltech.edu!palmer
    I have the power to cloud men's minds -- or at least my own.

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

Date: 26 Apr 90 22:42:00 GMT
From: pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!uxa.cso.uiuc.edu![e-mail]
Subject: Re: French art in orbit?


/* Written 10:20 pm  Apr 24, 1990 by [e-mail] in uxa.cso.uiuc.edu:sci.space */
I recently heard that someone from France was planning/is planning to launch
a sattelite that consists of mylar balloons strung in a circle.  Something
large enough to be seen from the ground.
/* End of text from uxa.cso.uiuc.edu:sci.space */

I remember seeing something like this several years ago, so its definitely
not new news.  If my memory serves me right (flame if I'm wrong) one of the
earliest US satelites was a mylar balloon which was designed to be
just shiny enough to be seen from the ground.  Is this the same circumstance?

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

Date: Fri, 27 Apr 90 15:01:10 EDT
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
To: [e-mail], [e-mail]
Subject: Re: Dyson spheres?


>Date: 25 Apr 90 19:14:04 GMT
>From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
>Subject: Re: Dyson spheres?

>>...suspend habitats from solar sails, and have them just balance their
>>star's gravity with reflected light. Problem with that is that the 'sun'
>>light has to be reflected back at the star providing it, and that'll make
>>the star burn hotter for a shorter time. I'm sure this is a minor problem...

>I'll class it as a minor problem after you've tried it on a few other stars!
>Reflecting most of the output of a star back into it is probably *not* a good
>idea, to put it mildly.

>Better would be to use absorbing sails (make them out of doped silicon and
>you've solved your power problems too!), which only give half as much thrust
>but don't have this particular problem.  Well, don't have it so badly, at
>any rate, given suitable coatings etc to reduce infrared re-emission inward.

With nonreflecting sails, you *have* to allow radiation in both directions, or
else the photon pressure of the radiation (dependent only on energy, not
wavelength) will offset the photon pressure of the incident light, and there
will be no net force. Assuming the simplest case, half of the energy will be
directed back inward, so that if you have an entire sphere, the net force on
the surface of the sphere should be doubled by this phenomemon (until it
affects the behavior of the sun).

Ignoring the infrared feedback, one can calculate the maximum mass of a
nonreflecting, nonrotating sphere that can be supported by light pressure
from the sun. At Earth's orbit, using a value of 1400W/m^2 solar flux, the
pressure on a nonreflecting object is 4.66E-6 Newtons/m^2. Since the
gravitational pull of the sun at this distance is about .0059m/s^2, the
photon pressure will support a nonreflecting object of no more than .00079kg
per m^2 facing the sun. Noting that both solar flux and gravitational pull
are inversely proportional to the square of the distance from the sun, this
value should be approximately correct at any distance, except close in, where
the sun can not be treated as a point source. The total mass of the sphere
is therefore directly proportional to the square of the distance from the sun.

Suppose we want the inner surface of the sphere to receive the same average
amount of sunlight as the surface of the Earth at the equator. Then the radius
of the sphere should be sqrt(2) times the current radius of Earth's orbit.
Given the allowed mass per square meter for the sphere, the total permissible
mass of the sphere would be about 4.4E20kg, or about .008% of the mass of the
Earth. Incidentally, to the inhabitants of the sphere, the sun would be "down",
with the local force of gravity about 1/3000 of that on earth. If you fell off
of the sphere, you would most likely hit the sun, though it would take a while
to get there.

Photon pressure allows only spheres of very low mass per square meter. What
about the use of electromagnetic forces between the components of the sphere?
It would seem that considerably higher density could be supported.
                    John Roberts
                    [e-mail]

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

Date: 27 Apr 90 05:04:45 GMT
From: uokmax![e-mail]  (Steven P Coltrin)
Subject: Re: Dyson spheres, heat flow

In article <[e-mail]> [e-mail] (Daniel Ake CAROSONE) writes:
>In article <[e-mail]>, [e-mail] (Steven P Coltrin) writes:
>> That would depend on how good your heat sink and pump (and insulation) were...
>> and how much risks you want to take.
>> A better system occurred to me awhile ago; presuming the _Lying Bastard_ was
>> fusion-powered (I don't remember if it was ever stated, even), then the power
>> plant is going to be producing helium exhaust.  Just pump your waste heat into
>> it and jettison.  Comments?
>
>From what I remember of the series (been a while)
>most of the ships ran on inertialess drives imported from th
>puppeteers. What use an inertialess drive would have of helium
>exhaust? (other than as a heat sink for its own sake!)

Absolutely right.  An inertialess thruster would probably have nothing to do
with helium exhaust.  But they would draw power, and that does NOT come from
the thrusters!

And, while the series never explicitly states where humans acquired inertialess
thrusters from, it is strongly implied that they bought it from the Outsiders
at some truly ungodly price.

   --SPC

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

Date: 26 Apr 90 18:16:25 GMT
From: att!cbnewsh![e-mail]  (lawrence.m.geary)
Subject: Re: Not-so-Silent Running (Was Re: a bunch of other irrelvant things)

If *I* remember correctly, they had 4 separate nuclear explosions.
It never made sense that the first bomb didn't explode or disable
the other three.
--

     --Larry: [e-mail]

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

End of SPACE Digest V11 #326
*******************