Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_0/V10_034.TXT

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Date: Wed, 13 Sep 89 23:37:09 -0400 (EDT)
From: "Todd L. Masco" <[e-mail]>
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Subject: SPACE Digest V10 #34
X-Press Pony: Must go through.


SPACE Digest                                      Volume 10 : Issue 34

Today's Topics:
             Re: Exotic Thrusters
    Geostationary Meteorological Satellite-4  [Forwarded]
               British Science
         U.S. commemorative stamp of VOYAGER?
     Intelsat selected for use of TDRS C-band (Forwarded)
         Re: Party excuse (Pluto perihelion)
               Re: Pluto fly-by
     Re: Galileo Jovian atmospheric probe -- is it sterilized???
----------------------------------------------------------------------

Date: 1 Sep 89 19:23:43 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: Exotic Thrusters

>In some article, [e-mail] (Paul Dietz) mentioned
>MPDs, Magnetoplasmadynamic thrusters. (That's a mouthful...) I too
>would like more information on these. I've heard that some have
>been tested, and had quite high thrust &c., but a very short
>lifespan: the components corroded or something. Sorry I don't have
>any references on this. Might someone else (specifically, Paul
>Dietz of `cs.rochester.edu'?)

I hope you saw the note I posted with the references (Progress in
Astro. and Aero. Vol 79).

I don't think corrosion is what would occur, since an MPD thruster
would use argon as a propellant, and argon is inert.  You would get
erosion on the electrodes, since they would carry a large current
(kiloamps).  According to the ~8 year old reference I have, they were
gearing up at Princeton qto do experiments to measure the "extremely
low ablation rates".

I should note that ion engines also have erosion problems, which are
severe because a thin metal mesh (the accelerating grid) is placed in
the ion flow.  Mercury ions sputter metal atoms off this grid.
According to my reference, this limits engine lifetime to ~15,000
hours, or about 1.7 years.  The electrodes in an MPD thruster would be
thick rods and cylinders made of solid tungsten or copper, which seem
much more robust to me.

    Paul F. Dietz
    [e-mail]

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

Date: 1 Sep 89 16:04:26 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Geostationary Meteorological Satellite-4  [Forwarded]

[Posted for Yoshiro Yamada.  Yoshiro may be reached at [e-mail].
-PEY]

* GMS-4 *

Geostationary Meteorological Satellite-4

Outline of Geostationary Meteorological Satellite-4

GMS-4 is a spin-stabilized satellite. It consists of a despun section and
a 100-rpm rotating spin section. The spin section contains the Visible
and Infrared Spin Scan Radiometer (VISSR), electronic devices, etc.,
while the despun section holds the earth-oriented antennas.

Purpose and History

GMS series have been developed to contribute to the improvement of Japan's
meteorological services and the development of weather satellite technology.
The satellites have been used for the World Meteorological Organization's
World Weather Watch Program which is sustained by five geostationary satellites,
etc. The first satellite in this series was launched by a U.S. Delta rocket in
July 1977. However, the GMS-2 and the GMS-3 are launched by Japanese N-II
rockets in August 1981 and August 1984, respectively. The GMS-4 is now being
developed by NASDA (National Space Development Agency of Japan).

Major Characteristics

Shape: Cylindrical, Diameter: 214.6cm, Height: (before AKM separation) 444.1cm
       (after) 345.1cm

Weight: About 725kg (at launch)
        About 325kg (beginning of life)

Attitude Control: Spin-stabilized

Life: five years or longer

Launch Vehicle: H-I

Launch Site: Tanegashima Space Center

Launch Window: August 1 - August 27  04:30-07:00 JST (UT+9h)
               August 28- September 14 04:00-06:00 JST

            Orbit: Geostationary orbit 140d(E) longitude


Visible and Infrared Spin Scan Radiometer

  The Visible and Infrared Spin Scan Radiometer (VISSR) is used to obtain
 visible and infrared spectrum mappings of the earth and its cloud cover
 with a specially designed optical telescope and detector system.
  A full imagery of earth disk can be obtained every 30 minutes utilizing
 the spacecraft's 100 rpm spin motion for west-east scans and 2500 steps
 (140 microradians each) of motor actuated rotation of VISSR mirror for
 north-south scans.

Feature and Function

 The main mission of the GMS-4 is to utilize the Visible and Infrared
Spin Scan Radiometer (VISSR) to obtain the imagery of the earth from a
geostationary orbit for observations of the cloud distribution and the
other meteorological phenomena. The earth pictures (cloud distribution)
can be taken every 30 minutes simulataneously in both visible and
infrared band. Resolution of the images (at the subsatellite point) is
1.25 kilometers in the visible and 5 kilometers in the infrared.

Communication Subsystem

 The GMS-4 communication subsystem consists of antenna, rotary joint,
primary and redundant S band, UHF, and USB receivers and transmitters.
Either the primary or redundant units can be activated by ground
command, except for the USB receivers which are always kept "on". The
communication subsystem is divided into three groups: S band
transponder, UHF transponder, and USB tranponder.



Space Environment Monitor (SEM)

 The Space Environment Monitor (SEM) measures the flux of three kinds of
solar particles (protons, alpha particles, and electrons) by the amount
of energy absorbed in five silicon detectors. Energetic particles
entering detectors deposit their energy, creating charge pulses
proportional to the energy absorbed. The categorized energy pulses are
then counted and sent to the telemetry subsystem.

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

Date: 1 Sep 89 19:01:49 GMT
From: agate!shelby!portia![e-mail]  (Mark Patterson)
Subject: British Science


CALLING ALL BRITISH SCIENTISTS WORKING OUTSIDE THE UK!

We are a group of British scientists in California organising a petition to
send to Mrs. Thatcher, regarding the state of British science.

The text on the petition reads as follows:

"Dear Mrs. Thatcher,

    As British scientists working abroad we are very concerned that
British scientific research is being starved of necessary funding, with the
consequent emigration of many scientists like ourselves.  The dearth of
funding for state-of-the-art equipment and supplies, coupled with the lack
of jobs and career prospects for young academics, are major obstacles in our
considering returning to the UK.  We urge the Government to reform its science
policy along the lines suggested by Save British Science, particularly as
follows:
(1)  Government support for science, as a fraction of national wealth
invested in civil research and development, should be increased to be in
line with other major European nations.
(2)  Tax incentives for industrial support of fundamental research in
institutions with open, academic type research and publication practices,
should be improved.
(3)  The Government should recognise its responsibility to safeguard a
broad academic base of independent scientific research on which future
technological progress can be based."

We've already collected about 200 signatures, mainly from life scientists,
but we need lots more!

If you'd like to sign the petition and help to distribute it further afield
please mail me your address and I'll send you a copy asap.

Thanks

Mark Patterson

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

Date: 1 Sep 89 23:41:48 GMT
From: wrksys.dec.com![e-mail]  (CUP/ASG, MLO5-2/G1 6A, 223-3283 01-Sep-1989 1438)
Subject: U.S. commemorative stamp of VOYAGER?


        Is there a plan for the United States Postal Service to issue
    a stamp commemorating the VOYAGER planetary probes?  The spacecraft
    and those who worked with them certainly deserve that as one of many
    acknowledgments for their efforts and results.

        For the record, the U.S. did commemorate on stamps the MARINER 10
    mission to Mercury in 1974-1975, the PIONEER 10 and 11 probes, which
    first explored Jupiter and Saturn from 1973 to 1979, and the VIKING
    1 and 2 probes to Mars, which landed on the planet in 1976.  The
    Postal Service has also commemorated a number of other important
    space missions on stamps, including the ECHO communication satellites,
    Project MERCURY, GEMINI, APOLLO 11, APOLLO-SOYUZ, SKYLAB, and the
    Space Shuttle.

        Larry Klaes  [e-mail]
             or - ...!decwrl!wrksys.dec.com!klaes
                 or - [e-mail]

        EJASA Editor, Astronomical Society of the Atlantic

             N = R*fgfpneflfifaL

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

Date: 1 Sep 89 20:24:17 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Intelsat selected for use of TDRS C-band (Forwarded)

Dwayne C. Brown
Headquarters, Washington, D.C.


RELEASE: 89-137


INTELSAT SELECTED FOR USE OF TDRS C-BAND


     NASA today concluded an agreement with INTELSAT, Washington,
D.C., for the use of the C-band capacity on two Tracking and Data
Relay Satellites (TDRS) for international telecommunication
purposes.  INTELSAT may initiate testing and C-band services upon
the completion of NASA's final operational preparations later
this year.

     NASA received bids for the C-band services on July 7, 1989.
The bids resulted from a June 12, 1989, solicitation package from
NASA's Office of Space Operations, Washington, D.C., in which 11
organizations expressed interest.

     In return for its bid of $51 million, INTELSAT will have the
use of 24 C-band transponders on the TDRS satellites at 41
degrees and 171 degrees West longitude, utilizing the C-band
service for a period of 6 years.  Each satellite has twelve 36-
MHZ C-Band transponders available.

     NASA will provide station-keeping control to 0.1 degree and
perform operational tracking, telemetry and command for the
spacecraft.

     The two TDRS spacecraft are part of NASA's new space-based
network for tracking and communication with the Space Shuttle and
other spacecraft in low-Earth orbit.

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

Date: 1 Sep 89 22:40:51 GMT
From: frooz![e-mail]  (Doug Mink, OIR)
Subject: Re: Party excuse (Pluto perihelion)

From article <[e-mail]>, by [e-mail] (Peter Scott):
> If you want a *really* good excuse for a party, Pluto reaches perihelion
> on September 5.  Since this only happens every 248 years, the party should
> be spectacular.
>
> Peter Scott ([e-mail])

Actually, the barycenter (center of mass) of the Pluto-Charon system is at
perihelion on September 5 at 2:31 UT.  Charon is closest to the Sun on
September 4 at 19:15 UT, and Pluto is closest to the Sun on September 7 at
23:31 UT.  I computed thses times using the solar system ephemeris developed
by E. Myles Standish at JPL for the Voyager Neptune encounter (and last year's
Pluto occultation) and the Charon ephemeris developed by Dave Tholen at the
University of Hawaii to predict Pluto-Charon mutual eclipses.  The times
have been published in *Ninth Planet News*, the Pluto observers' newsletter.

Myles Standish and I have discovered that the pericenter of Pluto's orbit,
it's closest approach to the solar system barycenter, doesn't occur until
October 11.  Dave Tholen notes that Pluto's closest approach to Earth happens
next year on May 7.  Charon and the Pluto-Charon barycenter reach perigee
on the same day.

The next major event in Pluto's orbit comes when it once again becomes the
most distant planet from the Sun, passing Neptune on February 10, 1999.

Doug Mink
Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts

Internet:  [e-mail]
BITNET:    mink@cfa
SPAN:      cfa::mink
Phone:     [phone]
FTS:       830-7408

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

Date: 1 Sep 89 16:41:32 GMT
From: meccts!viper![e-mail]  (David Messer)
Subject: Re: Pluto fly-by

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
 >In article <[e-mail]> [e-mail] (d. scott hess) writes:
 >>From: [e-mail]
 >>}I assume a fly-by of Jupiter would shorten the [Pluto] trip (with
 >>}respect to a direct flight), but by how much?
 >
 >Infinite -- we cannot reach Pluto with current technology without a Jupiter
 >flyby.

Actually we can, but the Jupiter assist increases the payload, and decreases
the flight time by a large factor.

 >I'd guess a Jupiter-Pluto mission at perhaps 7-8 years, but I don't
 >have real numbers handy.

It should be longer than the Voyager mission since Voyager got an assist
from Saturn and Uranus.  That would make it 12+ years.  (However, it
could be that Voyager didn't get the most out of Jupiter, so you might
be right.)

 >Remember, also, that Jupiter will be in the right
 >place only about once every 8 years (its orbital period).

Twelve years.

 >>}Would going
 >>}via a third planet, perhaps prior to Jupiter, make the trip
 >>}any shorter?
 >
 >An intermediate stop before Jupiter will probably make it longer, although
 >it may reduce fuel requirements a bit.  Galileo will pay a considerable price
 >in transit time for its inner-planets gravity assists, since it means doing
 >several more orbits around the Sun to pass said planets.  Multi-planet
 >gravity assists shorten trips only when the planets are in *exactly* the
 >right places, and particularly in the outer solar system that isn't common;
 >the Voyager 2 Jupiter-Saturn-Uranus-Neptune window won't be open again for
 >a couple of centuries.

Going past Mars would shorten the trip a little, but it probably isn't
worth it.  A Jupiter-Saturn-Pluto mission should be possible every
thirty years or so.
 --
Remember Tiananmen Square.           | David Messer       [e-mail] -or-
                                     | Lynx Data Systems  ...!bungia!viper!dave

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

Date: 1 Sep 89 16:03:51 GMT
From: calvin![e-mail]  (John Sahr)
Subject: Re: Galileo Jovian atmospheric probe -- is it sterilized???

In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>In article <[e-mail]> [e-mail] (Andy Stadler) writes:
>>In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>>> [..regarding sterilization of Galileo to protect Jovian life..]
>>>The technophobes might worry, but I'm not going to.
[]
>>Why must concern for life and environment == technophobe?
[]
>It's a question of perceived risk.  It is believed that the risk is very
>small.  If one asks that the risk be zero, then one is a technophobe --
>and, IMHO, a fool.
>    Paul F. Dietz

Apparently A. Stadler perceives more risk than P. Dietz, who "it" seems
perceives very little.  I perceive a small enough risk to let me support
its launch.

"We're going to send 50 pounds of plutonium through the atmosphere on a
big rocket, and drop an unsterilized probe into Jupiter's atmosphere.
It is believe that the risks are very small."

"Better chemicals for better living."

More power to anyone who takes the time to question that.

"Question Authority" - HD Thoreau.
"Always Question All Authority" - EA Abbey's corollary to HD Thoreau.

[my opinions, of course]--
John Sahr,     Dept. of Electrical Eng., Cornell University, Ithaca, NY 14853
johns@{alfven,calvin}.ee.cornell.edu,  {rochester,cmcl2}!cornell!calvin!johns
--When the dust settles, each B2 bomber will fund NSF for more than a year--

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

End of SPACE Digest V10 #34
*******************

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