Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v11_3/v11_346.txt

Internet Message Format | 1991-07-08 | 22KB

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/waDwG8S00VcJQ1xk4v>;
          Thu,  3 May 90 01:41:30 -0400 (EDT)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Thu,  3 May 90 01:40:59 -0400 (EDT)
Subject: SPACE Digest V11 #346

SPACE Digest                                     Volume 11 : Issue 346

Today's Topics:
       Re: NASA Headline News for 05/02/90 (Forwarded)
        Re: Black Holes (was Dyson spheres, heat flow)
            Re: Re: Fermi paradox
             Re: Hubble Telescope
         Off-the-shelf hardware for launchers
         NASA Headline News for 05/02/90 (Forwarded)
      Looking to the Limit (was Re: ... thoughts on STS-31 ...)
        Re: (How to get rid of) space garbage
----------------------------------------------------------------------

Date: Wed, 2 May 90 16:28:15 cdt
From: [e-mail] (Thanistha Phrasavath)

add me to the space digest list. thanks.

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

Date: 2 May 90 23:19:53 GMT
From: sdd.hp.com!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!netnews.upenn.edu!grad1.cis.upenn.edu![e-mail]  (Michael Gilbert)
Subject: Re: NASA Headline News for 05/02/90 (Forwarded)

In article <[e-mail]> [e-mail] (John H. Kim) writes:
>In article <[e-mail]> [e-mail] (Peter E. Yee) writes:
>>
>>The 747 carrier aircraft with Discovery firmly attached is
>                                         ^^^^^^
>
>Does this mean a shuttle was once "loosely" attached and
>almost fell off? :-)

How about the Enterprise? :)

>--
>John H. Kim                 | (This space to be filled when I
>[e-mail] | think of something very clever
>uunet!jarthur!jokim         | to use as a disclaimer)

===============================================================================
| CONSIDER IT DISCLAIMED               | #include <disclaim.h>                |
|-----------------------------------------------------------------------------|
|  _ _ _                               | Better the pride that resides,       |
| ' ) ) )   /                          | In a citizen of the world,           |
|  / / / o /_  _                       | Than the pride that divides,         |
| / ' (_<_/ <_</_                      | When a colourful rag is unfurled     |
| [e-mail]          |      --- Neil Peart                  |
| [e-mail]         |                                      |
|-----------------------------------------------------------------------------|
| CZECHOSLOVAKIA CHIEFS --- IGBA Champs 1984-1985 1986-Tourney 1987 1988-1989 |
===============================================================================

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

Date: 1 May 90 16:23:44 GMT
From: zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!peregrine!ccicpg!legs![e-mail]  (Tom Roden)
Subject: Re: Black Holes (was Dyson spheres, heat flow)

in article <[e-mail]>, [e-mail] (Brian or James) says:
[Stuff Deleted]
| [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].

    I thought that it would never see itself cross the event
horizon (due to time dilation), but that you could see it
from the outside just fine.  Is that correct?

--
Thomas A. Roden                     uucp:      ...!uunet!ccicpg!legs!rodentia
AST Research Inc. Dept 659
P.O. Box 19658                      Voice:     [phone]
Irvine, CA  92713-9658              Fax:       [phone]

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

Date: 2 May 90 04:09:04 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Re: Fermi paradox

In article <[e-mail]> [e-mail] (John Roberts) writes:
>My opinion is that given our current level of knowledge, calculating the
>probability of life elsewhere may provide useful insights, but that's about
>all.

Yes, but that's plenty.  Saying "we don't know enough" is ostrich talk.
Research into life processes continues apace.  The knowledge curve trends
in one direction only.  Hubble and Martian sample return will expand our
wisdom about precise conditions elsewhere, now and in the past.

The truth is that the only interesting empirical results we could possibly
hope to get in the next century or two are (a) life or proto-life remnants
elsewhere in the Solar System, say on Mars; or (b) SETI.  Even if we prove
that life is probable in other systems, we're not going to be able to do
anything about it unless we find someone to talk to.  Extrapolation will
the growth field in exobiology for some time to come :-)
--
"DO NOT, repeat, DO NOT blow the hatch!"  /)\   Tom Neff
"Roger....hatch blown!"                   \(/   [e-mail]

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

Date: 2 May 90 21:22:34 GMT
From: usc!jarthur![e-mail]  (Astronerd)
Subject: Re: Hubble Telescope

.>>I remember back in the 70's, that while enroute to
.>>Jupiter, Pioneer took a picture of both the earth and the moon in the same
.>>frame.  A picture like that get's people thinking!
.>    My copy attributes the picture to Voyager and says it's the only
.>one of its kind. I can't imagine why Pioneer or Mariner or Viking
.>couldn't have done it. Can anyone say definitely which it is? Definitely
.>a picture that makes you say "Wow!"
.>        Tony
.>
It was Voyager 1, outbound in 1977.
I agree, it was a spectacular shot.  Of course, the apparent distance between
the earth and moon isn't accurate, since thw camera was looking at our
system in perspective. Also, the pixels around and including the moon were
enhanced so you could see the sucker.  Things like that happen when your
albedo is 5%!  The earth is a little brighter, since it's much larger and has
an albedo of 39%.  Take a look again.  The moon really is black.

Great shot anyway. *I* can't wait for the "family portrait" to be released!

-David L. Williamson
"Smog sucks.  Especially when you look for a comet. on the horizon. in LA."

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

Date:     Wed, 2 May 90 11:47 EDT
From: <[e-mail]>
Subject:  Off-the-shelf hardware for launchers


   With all the discussion on the net about how the RL-10 is "in production",
I've been wondering how much other stuff is out there.  Is there enough so that
someone could design a launcher without building custom hardware?

                                                       Joe

Disclaimer:  Any opinions expressed above are entirely mine, and if anyone else
             takes credit for them they'll be in big trouble!

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

Date: 2 May 90 19:16:25 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: NASA Headline News for 05/02/90 (Forwarded)

-----------------------------------------------------------------
Wednesday, May 2, 1990                Audio Service: 202/755-1788
-----------------------------------------------------------------
This is NASA Headline News for Wednesday, May 2...

The Hubble Space Telescope continues to operate in good health
and in full communications with the Space Telescope Control
Center.  During a Pointing and Safemode Electronics Assembly
self-test mode last night at 7:00 P.M., engineers overlooked
activating an aperture door inhibit switch.  As a result, the
motion put the safecraft into safemode status.  Operating as it
should, the computer commanded the door shut.  This morning, the
HST was brought completely out of safemode, the door is open and
the spacecraft is operating normally.
                            ********
Analysts are also reviewing Hubble Space Telescope data received
last night from two high gain antenna tests in order to map out
safe operating regions where both antenna can function without
obstruction and then adapt the software to those specifics.
Deputy project manager at Marshall Space Flight Center, Jean
Olivier is optimistic this will not prevent any scientific work,
merely postpone an activity to "tomorrow rather than today."
                            ********
The shuttle Columbia's upcoming night launch--with the Spacelab
astronomy mission Astro-1 aboard--from Kennedy Space Center is
now targeted for May 16.  A one-day slip is possible, but for now
the seven-member crew is scheduled to take off at 12:45 a.m.,
EDT, on a flight to study high-energy sources in the cosmos.
                            ********
Launch pad 39A at Kennedy Space Center is clear of all but
essential personnel today as hypergolics are being loaded aboard
Columbia.  Auxiliary Power Unit number three underwent a
successful seven minute hot fire test, yesterday.  And, a
propellant line has been replaced after engineers found a small
leak during a helium signature leak test.  The payload bay doors
will remain closed throughout the weekend.
                            ********
Processing of the orbiter Discovery for its return to Kennedy
Space Center continues at Dryden Flight Research Facility.
The 747 carrier aircraft with Discovery firmly attached is
scheduled to leave California at dawn, Saturday, refuel at Kelly
Air Force Base, Texas and arrive at KSC late that afternoon,
weather permitting.
                            ********
The Apollo 204 spacecraft will be moved from the Langley Research
Center, May 20 and placed in permanent storage in an abandoned
missile silo at Cape Canaveral Air Force Station in Florida.  The
Apollo has been in storage at Langley Research Center since 1967.
                            ********








----------------------------------------------------------------
Here's the broadcast schedule for Public Affairs events on NASA
Select TV.  The following times listed are Eastern.

Thursday, May 3......

                   11:30 A.M.     NASA Update will be
                                  transmitted.



----------------------------------------------------------------
All events and times are subject to change without notice.
These reports are filed daily, Monday through Friday, at 12:00
Noon, EDT.  This is a service of the Internal Communications
Branch, NASA Headquarters.

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

Date: Wed, 2 May 90 21:03:51 +0200
From: [e-mail] (Daniel Fischer)
Subject: Looking to the Limit (was Re: ... thoughts on STS-31 ...)

In <26 Apr 90 14:28 UT> Jeff Bakke wrote on the most distant celestial objects:
> When [we] hear of 15+ billion lightyear objects being detected, more than
> likely it was found by radio telescopes...
  In <27 Apr 90 00.20 UT> Dan Briggs of the Nat'l Radio Asytron. Obs. replied:
> You've got the right idea that it is easier *in general* to see with radio
> than with optical... The problem is finding it [a quasar]. What radio does
> for you is put out a banner that there is something inter[e]sting at a
> particular point in the sky.
The way nearly all quasars at record distances were discovered didn't involve
radio waves at all! There's a 'race' going on between astronomers in Great
Britain & the U.S. to find more and more distant quasars, but all use optical
telescopes - so far they've discovered > 15 objects with redshifts z>4 in the
past three years - and the record is z=4.773 (ASTRONOMICAL JOURNAL Vol.98 (Dec.
1989) 1951-1958; an overview as of 1987 was given in NATURE of 3 Dec. 1987 426).
  But the original question was: will the HST be able to look distinctly
farther into the universe than we can from the ground?, and the answer is with
great certainty: no. As with the quasars there's no big deal in seeing them
even at the edge of the Universe as they're so bright, but recent work by A.
Tyson (see ASTRONOMICAL JOURNAL Vol.96 (July 1988) 1-23) seems to indicate that
our knowledge of all major galaxies in the universe might be complete as well.
  For his CCD camera (mounted to 4m scopes on the ground) the sky is covered
with faint galaxies with (as he believes from statistics) 1<z<3. But behind z=3
there seems to be a cutoff: galaxies could still be detected but just aren't
there. (An extrapolation in SCIENCE of 13 Apr. 1990 178-183 consequently
denies HST's chances to discover new classes of big, important galaxies!) Only
some isolated objects other than quasars are known behind z=3; the record
holder is the radio source 4C41.17 (aah - here radio was the winner) which is
also visible in the optical where a redshift of 3.8 was measured.
  And where was this discovery announced first? In the PRESS RELEASES #5/88 of
the Space Telescope Science Institute and #27/88 of the European Space Agency -
I have the vague idea that both have something to do with HST. But none of them
seems to object to the NASA nonsense of our present universal knowledge ending
at 2 billion light years (that's z~0.2 or so) with only HST being able to
increase that limit exactly 7fold, right to the end of the universe. Do they
really have to lie to the public to sell this marvellous satellite? Why can't
they just confess that it won't show a larger universe but will (hopefully)
give a distinctly sharper & brighter view of what we already know. And if
something really unexpected pops up (something both faint and very small it
would have to be), there would be all the more to celebrate. Having already
spent $ 2.1 billion, though, might hamper rational thinking somewhat...

+- [e-mail] --- Daniel Fischer --- [e-mail] -+
| Max-Planck-Institut f. Radioastronomie, Auf dem Huegel 69, D-5300 Bonn 1,FRG |
+----- Enjoy the Universe - it's the only one you're likely to experience -----+

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

Date: 3 May 90 00:40:13 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: (How to get rid of) space garbage

In article <[e-mail]> [e-mail] writes:
>In article <[e-mail]>, [e-mail] (Jonathan
>Leech) writes:
>>
>>     In light of the current 'life of HST' discussion, maybe we could
>> talk about ways to get rid of orbital debris.  First off the wall
>> suggestion: use high-powered lasers to accelerate decay from the
>> Poynting-Robinson effect.  If this thread takes off, I'll run some
>> numbers on this suggestion.
>
>Since I saw a similar suggestion in the space-tech group, I've been
>impressed with this idea.  The suggestion was to use a mirror to
>reflect sunlight onto trash to deorbit it gradually.
>
   Yes. I've put the sample calculations I made for this proposal at the
end of this article. My proposal was to have a 300km diameter mirror out
around 80000km from the Earth, balanced off the solar radiation pressure
and the Earth's gravitational pull. Essentially, it is a solar sail which
can't quite get away from the Earth's pull when it's 80000km out. The
existing solar sail technology seems to indicate it should work.
   Anyway, the radiation pressure selectively decelerates small objects.
Heavier things like comsats would be relatively unaffected. It also only
works in one orbital direction, so the obvious choice is west to east.
Because of the way it is positioned, it has a 100% duty cycle. It does not
orbit the Earth, but floats ahead of it in orbit around the Sun.
   This scheme would deorbit grit, paint flecks, and the like in a very
wide swath of orbits, essentially any particle which passes through the
300km diameter beam spot reflected from the sail.
   The mirror is not a replacement for the scheme Henry mentioned, which
uses a laser to deorbit larger pieces by vaporising their leading surfaces.
That scheme works well with large sized objects which can be tracked on
radar. Mine works well on general dust and debris, without knowing where it
is, but would have trouble dealing with even a medium-sized bolt because of
the high mass to surface ratio.

>Of course, one would hope that it wasn't in the wrong position when
>Hubble came around one orbit, or whoops...
>
   Well, I chose 80000km for my proposal. It's out of the way of pretty
well everything. This scheme wouldn't be workable in LEO because of the
very low density of the sail needed to hold up against 1g of acceleration
(remember, the object isn't orbiting, so there is no "centrifugal
pseudo-force").

>Maybe you could run some numbers for the mirror; what diameter Mylar
>film to deorbit 50% of LEO junk < .5cm within 6 months, say?
>
   Here are the calculations, make of them what you will.

>This is news.  This is your       |    Peter Scott, NASA/JPL/Caltech
>brain on news.  Any questions?    |    ([e-mail])


Sample calculation and parameters:

   Particle is a cylinder: 1 mm in diameter
                           0.1 mm thick
   Particle's specific gravity: exactly 7x10^3 kg/m^3
   Particle orbiting at exactly 300 km in a circular orbit
   Mass of the earth: exactly 6x10^24 kg
   Earth has no higher order gravitational moments.
   Gravitational constant: exactly 6.67x10^-11 N m^2/kg^2
   Gravitational acceleration at the earth's surface: exactly 9.81 m/s^2

The following figures were calculated from those numbers:
   Radius of the earth: 6.387x10^6 m
   Radius of the orbit: 6.687x10^6 m
   Orbital velocity: 7.736x10^3 m/s

For purposes of momentum transfer from the particle: I used the effective
area of the particle as 1/2 the area of an end cap, and assumed that all
radiation incident on the (tumbling) flake was absorbed. This is actually a
conservative estimate, since the actual figure goes from 1/2 for a perfectly
absorbing slab to 2/3 for a perfectly reflecting slab. This under-estimation
of the area will absorb any inefficiencies in the mirror, since I am still
using a power flux at the particle of 1.4 kW/m^2, the solar flux in space
at one astronomical unit.
   Force on the particle is Psolar/(speed of light) * area of particle.
This gives an acceleration of 3.333x10^-4 m/s^2 for as long as the particle
is in the beam.

   Now, it is necessary to find the delta-v on a particle orbiting at
300 km to drop the perigee to 100 km. This turns out to be about 60 m/s. See
the note at the end of this article for the math behind this calculation.
The acceleration will provide this impulse in only 50 hours. If we have 5%
coverage, this is 1000 hours real time, or roughly six weeks.
   Now, I have to justify my assumption that hitting the particle several
times will result in the lowering of the perigee, but will not change the
apogee, which will stay at 300 km. Assume that the orbit is initially
circular. I hit it with the beam as it traverses some 15 degrees of its
orbit. The particle slows down by some small amount, then continues in its
orbit as a free particle. From classical mechanics, a gravitational orbit
is closed (no precession). So, the particle must return to the point at
which it received the initial impulse. This argument then repeats for each
orbit. So, after giving it a delta-v of 60 m/s, the apogee is at 300 km
while the perigee is at 100 km. It is now hitting atmosphere, and will
quickly be removed from worry.

   For a Clarke orbit, the delta-v is 1500 m/s, which takes quite a bit
longer, but the algebra is essentially the same. In this case, though, the
mirror has to rotate to track the sun as it moves relative to the orbit
over a period of one year. The mirror must shine into the orbits always at
apogee to get the efficiency I've postulated, and apogee will precess with
respect to the earth and sun, since it will always point to the same fixed
stars.
   If that is too convoluted to make sense of, send me mail and I'll clarify
it.

--
   Calculation of the delta-v to drop the perigee of an initially circular
orbit: I could have used all sorts of classical mechanics equations, but I
was too lazy to solve the differential equation. Instead, I used
conservation of energy and conservation of angular momentum.

Initial parameters:
   Orbiting particle has mass m
   Circular orbit, radius r1 around primary of mass M
   Initial velocity v0 so that   m v0^2 / 2 =  G M m / (2 r1)   which is
just the virial theorom.
   Unknown change in velocity dv
   Aphelion at r1 (still)
   Perihelion now at r2

Immediately following the application of dv, what is the initial energy and
angular momentum of the system?
E1 = m (v0 - dv)^2 / 2  -  G M m / r1
L1 = m (v0 - dv) r1    (Note: velocity and radial vectors are orthogonal
                         at this point (apogee) in the orbit)
The particle now falls to perihelion at r2, and we have to solve for dv.
At r2:
E2 = m v2^2 / 2  -  G M m / r2
L2 = m v2 r2

Since the gravitational field is conservative and has SO(3) symmetry (from
the assumption that there were no higer order multipoles), energy and
angular momentum respectively are conserved.
So, E1 = E2 and L1 = L2.
>From L1 = L2, we get     v2 = (v0 - dv) * r1 / r2
Plugging this into E2, and setting it equal to E1, we get:
(eliminating factors of  m/2)
((v0 - dv) * r1 / r2)^2  -  2 G M / r2  =  (v0 - dv)^2  -  2 G M / r1
-->  (v0 - dv)^2 ((r1/r2)^2 - 1) = 2 G M (1/r2 - 1/r1)
-->  (v0 - dv)^2 = 2 G M (r1 - r2) r2^2 / (r1 r2 (r1^2 - r2^2))
-->  (v0 - dv)^2 = 2 G M r2 / (r1 (r1 + r2))
-->  dv = v0 - sqrt( 2 G M r2 / (r1 (r1 + r2)) )

Remember, r1 and r2 are radii from the earth's centre, not heights above the
surface.



--
 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" |

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

End of SPACE Digest V11 #346
*******************