Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V12_5/V12_525.TXT

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Subject: SPACE Digest V12 #525

SPACE Digest                                     Volume 12 : Issue 525

Today's Topics:
              Magellan Update - 11/02/90
            Re: Creationists and Moon Dust
                <None>
    NASA, TADCORPS sign information exchange agreement (Forwarded)
            Re: Creationists and Moon Dust

Administrivia:

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  [e-mail].  Other mail, esp. [un]subscription notices,
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Date: 2 Nov 90 22:52:53 GMT
From: usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov![e-mail]  (Ron Baalke)
Organization: Jet Propulsion Laboratory, Pasadena, CA.
Subject: Magellan Update - 11/02/90
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                      MAGELLAN STATUS REPORT
                         November 2, 1990

     The Magellan spacecraft passed the point of Superior Conjunction at
5:00 PM (PST) yesterday when the Sun-Earth-Magellan angle was 0.87 degree.
Engineering telemetry at both S and X-band has been maintained and all systems
are nominal.  No spacecraft command activity is planned for today.  The
earliest date that mapping will resume is November 7.

     Analysis of the spacecraft solar panel oscillations during mapping has
identified an error in the control loop tracking algorithm when the sun
incidence angle is greater than 64 degrees.  The immediate fix will be to set
the panels at an average value position.  The longer term solution will be to
control the panels using ephemeris values of the sun position.

     Twelve new standard image swaths were produced in the past 24 hours by
the SAR (Synthetic Aperture Radar) Data Processor.  The digital processing
was completed on 5 full resolution mosaics, called engineering F-MIDRs.
Photo products from the 13 mosaic set are now being prepared for analysis by
investigators in preparation for a science press conference on November 16.
      ___    _____     ___
     /_ /|  /____/ \  /_ /|
     | | | |  __ \ /| | | |      Ron Baalke         | [e-mail]
  ___| | | | |__) |/  | | |___   Jet Propulsion Lab | [e-mail]
 /___| | | |  ___/    | |/__ /|  M/S 301-355        |
 |_____|/  |_|/       |_____|/   Pasadena, CA 91109 |

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

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Date: 2 Nov 90 16:32:05 GMT
From: swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: Re: Creationists and Moon Dust
References: <s64421.657561762@zeus>
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In article <s64421.657561762@zeus> [e-mail] (house ron) writes:
>Creationists around here are claiming that before the moon shots,
>scientists were worried about the space craft sinking in metres of
>dust which they thought should have accumulated since the moon was
>formed.  As we know, very little dust was there, and they say this is
>proof that the moon is only six thousand years old.
>
>Does any one know whether their claim about prior expectations is
>correct?  If it is, does any one know why there is so little moon
>dust?

There was some concern about the possibility of lots of highly fluid dust.
The Surveyor missions laid that worry to rest ahead of time.  There actually
*is* a whole lot of dust there, but it sticks to itself fairly well and
things don't sink in it -- the astronauts compared the consistency to
wet sand.  Even the LM descent engine jet didn't make a shallow crater as
had been expected, although it did blow the uppermost few mm of dust around.
--
"I don't *want* to be normal!"         | Henry Spencer at U of Toronto Zoology
"Not to worry."                        |  [e-mail]   utzoo!henry

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

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Date: 3 Nov 90 01:01:16 GMT
From: sputnik![e-mail]  (dave warkentin)
Organization: Massachvsetts Institvte of Technology
Subject: <None>
References: <[e-mail]>, <[e-mail]>
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 GMT
Message-ID: <[e-mail]>
Reply-To: [e-mail] (dave warkentin)
Organization: M.I.T.
Subject: Re: Ulysses speeding up rel. to the sun
Keywords: tangent

In article <[e-mail]>, [e-mail] (Steve Masters) writes:
 > [e-mail] (Stuart Warmink) writes:
 >
 > >Assume that Ulysses was boosted out of Earth orbit in such a direction
 > >that it was originally at a tangent to the Earth's orbit - not an
 > >unusual direction for a boost to the outer planets. If started of in such
 > >a direction its velocity w.r.t. the Sun would be 0. As Ulysses gained
 >                                                  ^^^
 > ...not unless it were launched directly against the earth's orbital velocity
 > at the earth's orbital speed...Ulysses, upon leaving earth's orbit,
was almost
 > certainly moving close to the earth's orbital velocity (about 18.5
mi/sec,
 > I think) relative to the sun.
 >
 > This doesn't explain an increase in sun-relative speed...are we sure
there isn't
 > a typo?  Unless there is a gravity assist from Venus, there is no way
to get
 > to Jupiter by dropping closer to the sun (I don't think, anyway :) )
 >
 > Steve Masters    [e-mail]
 > ENSCO, Inc.
 > Melbourne, FL  32940  USA

I too was puzzled by Ulysses's increase in speed, so I performed a few
calculations to see if I couldn't come up with an answer (in the absence
of more authoritative pronouncements :-).  First of all, the most
obvious transfer orbit from Earth to Jupiter is the ever-popular Hohmann
transfer - the 1/2 ellipse which is tangent to Earth's orbit at
perihelion and to Jupiter's at aphelion.  Event schedules have been
posted for Ulysses which give the launch date as 10/6/90 and the Jupiter
encounter date as 2/8/92 for a time of flight of 490 days.  The TOF (in
years) in the Hohmann orbit, though, is .5*(a^1.5), where a is the
semi-major axis in AU.  Jupiter averages 5.2 AU and Earth about 1 AU, so
a for the transfer would be .5*(1+5.2)=3.1 and the TOF is 2.73 years, or
997 days! Clearly the Hohmann transfer is not being used.  Presumably
the mission planners wanted to a) shorten the flight time and b) have
more speed for the Jupiter gravity assist, so they launched from Earth
with a velocity greater than that needed for the Hohmann.

It still seems reasonable to assume (as Stuart did above) that Ulysses
leaves on a path tangent to Earth's orbit, in order to take fullest
advantage of Earth's orbital velocity.  So now we need to find an orbit
which leaves Earth on a certain date tangent to Earth's orbit and which
arrives at Jupiter on another specified date.  According to my home-made
ephemeris program, Earth was 1.000 AU from the Sun at launch and Jupiter
will be 5.401 AU from the Sun at encounter, and the angle between these
two points is 145.2 degrees (just using heliocentric longitude and
ignoring Jupiter's latitude at encounter, which I think is about 1
degree).

It turns out, though, that a Keplerian orbit satisfying all these
conditions does not exist!  The one which connects these two points and
is tangent to Earth's orbit takes 558 days.  Assuming no really major
mid-course corrections, we have to through out the assumption that the
departure is tangent to Earth's orbit.  After some trial and error, I
found that if you assume that Ulysses actually does move closer to the
Sun before heading out to Jupiter, you can make the transfer orbit
satisfy the conditions.  This means transfer orbit perihelion doesn't
occur at launch, but some 6.24 days (8.445 degrees true anomaly) _after_
launch, and so at first speeds up with respect to the Sun before moving
away and slowing down. Using this assumption, I find that Ulysses
reaches Jupiter with enough energy to perform a hyperbolic fly-by
gravity assist maneuver to redirect its velocity vector so than as it
leaves Jupiter's sphere of influence it can be in an orbit with aphelion
at 5.401 AU, perihelion at 1.374 AU, a period of 6.235 years, and an
inclination to the ecliptic plane of 83 degrees.  This looks fairly
good, since previous postings have mentioned a perihelion of 1.4 AU
(signif. digit?) on 2/5/95 (period of just under 6 years).

A couple of questions remain.  First of all, why didn't they launch
tangent to Earth's orbit?  My tentative answer - that was the nominal
trajectory, but it just so happened that they got it off in the first
half of the launch window, so they adjusted injection conditions so as
not to throw everything else off schedule.  Sky and Telescope (Nov. '90,
p.498) mentions a 19-day launch window starting on Oct. 5, so the
mid-point would have been Oct. 14-15.  Thus it could well be that they
launched a few days early, thus producing the 6.2 day time to
perihelion.

More importantly - why didn't they put it in a higher inclination?
Perihelion of the solar orbit is 1.4 (maybe 1.374) AU - why didn't they
trade some of that energy to reach a higher angle?

And perhaps most important of all - what does this imply for the
question of when Ulysses was closest to the Sun?  Unfortunately, not
much - I calculate the perihelion distance of the transfer orbit to be
.9949 AU, as opposed to the Earth's .9836, so it was still closer to the
Sun on Earth than it ever was/will be in orbit.

(N.B. It occurs to me that in the above arguments about the transfer not
being tangent to Earth's orbit I haven't taken Earth's non-zero flight
path angle into account, but I believe this effect is minor and doesn't
substantially affect the calculations.

A good reference for would-be space cadets:
  Fundamentals of Astrodynamics by Bate, Mueller, and White : ISBN
0-486-60061-0
It is (or was) the USAF Academy textbook on the subject.  It's a Dover
publication, and cost me $5.50 about 10-12 years ago, so it probably
costs a bit more now.)

For those who actually read this far, thanks for letting me put my $.02
in.  Maybe someone with more info can correct/supplement these wild
computations.


--
Dave Warkentin
[e-mail]

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

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Date: 3 Nov 90 02:42:51 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Organization: NASA Ames Research Center, Moffett Field, CA
Subject: NASA, TADCORPS sign information exchange agreement (Forwarded)
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Barbara Selby
Headquarters, Washington, D.C.                   November 2, 1990
(Phone:  [phone])


RELEASE:  90-148

NASA, TADCORPS SIGN INFORMATION EXCHANGE AGREEMENT


     The National Aeronautics and Space Administration and the
Technical and Administrative Services Corp. (TADCORPS),
Washington, D.C., have signed a memorandum of understanding which
will provide a forum for the exchange of research information
associated with closed environment systems related to food
production both on Earth and in space.

     NASA and TADCORPS have mutual interests in the development
of hydroponic technology for possible microgravity and partial
gravity life sciences support.  NASA is interested in exploring
controlled environment systems and hydroponics technology to
develop the food production systems necessary to sustain
crewmembers on long-duration space missions such as establishment
of lunar communities or an expedition to Mars.  The agency also
is interested in chemical processes associated with waste
recycling and management.

     TADCORPS is exploring development research concepts for test
facilities which could provide technology applications for
domestic farm crop enrichment in hostile environments in remote
regions of the world.

     The 2-year agreement, which involves no exchange of funds,
provides for NASA and TADCORPS to share information generated
from studies in three areas:

      * Potential development of hydroponic systems and
        agricultural experiments and uses aboard the Space
        Shuttle and Space Station Freedom;

      * Potential chemical processing technology in support of
        life support and hydroponic systems; and

      * Possible terrestrial applications of closed environment
        systems and hydroponic technology through fixed
        and deployable hydroponic test facilities.

     TADCORPS will provide a summary report to NASA prior to the
conclusion of the agreement.

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

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Date: 2 Nov 90 20:08:09 GMT
From: optilink![e-mail]  (Clayton Cramer)
Organization: Optilink Corporation, Petaluma, CA
Subject: Re: Creationists and Moon Dust
References: <s64421.657561762@zeus>
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To: [e-mail]

In article <s64421.657561762@zeus>, [e-mail] (house ron) writes:
> Creationists around here are claiming that before the moon shots,
> scientists were worried about the space craft sinking in metres of
> dust which they thought should have accumulated since the moon was
> formed.  As we know, very little dust was there, and they say this is
> proof that the moon is only six thousand years old.
>
> Does any one know whether their claim about prior expectations is
> correct?  If it is, does any one know why there is so little moon
> dust?
> --
> Ron House.   ([e-mail])

The concern was real.  The answer is that vacuums tend to cause
cementing of fine particles together.  (Similar to vacuum welding
of metals?)

I've given up trying to intelligently argue with "creation
scientists".  When I get the energy, I will be posting a review
of a wonderful book for dealing with creationists called _The_
Fingerprint_Of_God_, written by a guy with a Ph.D. from University
of Toronto in astrophysics which is simultaneously:

1. A splendid introduction to cosmology and astrophysics, that's
sufficiently up to date to include the recent discovery of
objects with red shifts where Z > 4;

2. A rather thorough debunking of the "creation science" arguments
for the 6000 year old Earth;

3. An excellent, though abbreviated demonstration that the 6000
year old Earth isn't a valid interpretation of the Old Testament,
EVEN FROM THE LITERALIST PERSPECTIVE;

4. Written by an evangelical Christian who attempts to use the
evidence to argue for a theistic cosmology, and so makes it even
harder for the "creation scientists" to reject what he has to
say about the age of the Earth.

--
Clayton E. Cramer {pyramid,pixar,tekbspa}!optilink!cramer
Alcohol prohibition didn't work; drug prohibition doesn't work; gun
prohibition won't work.
You must be kidding!  No company would hold opinions like mine!

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

End of SPACE Digest V12 #525
*******************