                      Why Not Observe Earth Satellites?

                           (C) Ted Molczan, 1990


A Little History
----------------

Many of us are old enough to remember going out on the porch to look for
Sputnik 1 when it passed overhead in the fall of 1957.  (In fact Sputnik was
too small to be seen with the naked eye.  Most people saw its large final
stage rocket which had also gone into orbit).  Satellite launches were big
news in those days.  It wasn't easy to launch one, and many ended up in
spectacular fireballs on or near the launch pad.  Newspapers gave advance
notice of expected overhead passages of bright satellites.  Today a satellite
is launched about every three days and most are not considered newsworthy
except on the now rare occasion that one does blow up.

More [Y]es,N)o,C)ontinuous,A)bort? c
                                    

In the early days of satellites, amateur and professional astronomers were
enlisted to help keep track of the few objects in orbit.  Thousands of
amateurs contributed observations to the Smithsonian Astrophysical
Observatory's Project Moonwatch.  Their observations were valuable to
geophysicists who studied small changes in satellite orbits to learn about the
density of the upper atmosphere and the shape of the Earth.  Moonwatch ended
about fifteen years ago, and today only NORAD tracks the nearly 7,000 objects
in orbit using a global network of radar and optical sensors.

As with most of mankind's inventions, satellites have quickly gone the route
from "eighth wonder of the world" to commonplace.  They are a familiar sight
to amateur astronomers, who generally ignore them.  Scientists now make little
use of amateur satellite observations, relying instead on laser and radar
tracking systems.  So why observe?


Why Observe?
------------

Satellite observation has much to offer amateur astronomers and space
enthusiasts.  As an amateur astronomer, I find in satellites many of the
appealing features found in traditional areas of astronomy.  For example, the
observational challenges involved in spotting a specific faint satellite are
comparable with spotting a distant galaxy.  Also, satellites move at speeds up
to several degrees per second!  As a space enthusiast, satellite observation
has led me to improve my knowledge of orbital motion, propulsion, scientific
and military applications of satellites and government space policy.

Some satellite related phenomena are related to other phenomena observed by
amateur astronomers.  For example, the northern lights are the visible
manifestation of the effect of solar storms on the Earth's upper atmosphere.
Those same storms also cause the density of the upper atmosphere to increase
many fold.  This was discovered by observing the great increase in the rate of
orbital decay of satellites which follows most solar storms.  Skilled amateur
observers are able to detect and measure these orbital changes and determine
how closely they correlate with solar activity.

Many space enthusiasts who observe satellites focus their attention on secret
military Soviet and U.S. space programs.  England's Kettering Group is highly
respected for its many discoveries about the Soviet space program.









One of the attractions of astronomy is that it encourages the development of
interests and skills in related areas such as photography and dark-room
methods, optics, mathematics, physics, navigation, computer programming and
electronics.  Satellites also offer challenges in each of these fields.


How To See Satellites
---------------------

Whether or not you decide to take up satellite observation in a serious way,
you may find it enjoyable to do casually.  In fact you can "satellite gaze"
at the same time that you "star gaze".  The following are some tips on how to
spot satellites with the naked eye.

There are about 300 satellites that are large enough and low enough to be seen
with the naked eye.  They look like stars, a little less bright than those of
the Big Dipper, and appear to move at about the same speed as high airplanes.

The average naked eye satellite is about 3 or 4 metres across and less than
1,000 km above the Earth.  They are visible because they reflect sunlight just
like the moon and planets.  The best time to see them is during the first hour
or two after the sky becomes dark after sunset or during the same period
before dawn.  At those times the sky is dark enough to see satellites, and the
Earth's shadow is low enough so that the satellites are in sunlight.

If you are observing in the evening then you should look for satellites in the
eastern half of the sky.  It is difficult to see all but the largest
satellites in the west because they are between you and the recently set sun,
so you are looking at their dark side.  It is exactly the same phenomenon as
the phases of the moon.  In the morning, the situation is reversed, so look
for satellites in the west.

Most satellites move roughly north to south or south to north.  A few move
west to east.  If you think that you have spotted a satellite moving from east
to west it is probably an airplane.  Only a few satellites have been launched
in a westerly direction.  The easterly direction is prefered because rockets
receive a boost from the Earth's rotation, which reduces their need for fuel.

Most satellites shine with a fairly steady light except for the gradual change
which occurs as their phase changes as they move across the sky.  A few tumble
end over end and their brightness may vary regularly over a period of less
than one second.  Observers refer to these as "flashers".  In the evening you
will often see a satellite rapidly fade out and disappear in the east, all in
the space of about ten seconds.  This is the satellite's entry into the
Earth's shadow, which is sunset from its vantage point!

On a typical night it is easy to spot ten satellites per hour from a city back
yard, and many more under a dark country sky.  Why not give it a try?

If you find observing random satellite passages enjoyable, then you might wish
to consider going into the hobby in greater depth.  The next logical step is
to observe specific satellites.  To do so, you will need a computer, orbit
prediction software and a source of orbital elements (the numbers which define
the size, shape and orientation of a satellite's orbit).  One way to obtain
the software and elements is through the Canadian Space Society's computer
bulletin board in Toronto, which is operated as a free public service.  The
phone number is 416-458-5907, and the speed is up to 2400 baud, 8N1.

The Dallas Remote Imaging Group is dedicated to satellite tracking and
capture of weather satellite imagery in a real-time mode.

The DRIG group operates a BBS service at 214-394-7438 that contains
hundreds of images from weather satellites (U.S., Soviet, Chinese)
that may be viewed on personal computers for some spectacular imagery.

Members interested in satellite tracking, intellgence satellite reports,
satellite imagery, sate  GALILEO
                       MISSION STATUS REPORT
                         September 6, 1990
 
     As of noon (PDT) Thursday, September 6, 1990, the Galileo spacecraft is
55,791,470 miles from the Earth and traveling at a heliocentric speed of
49,755 miles per hour; distance to the Sun is 118,463,405 miles (1.26 AU).
The spacecraft continues it 3.15 rpm spin in dual spin mode and the
downlink telemetry is at 40 bps.  Round trip light time is 10 minutes, 4
seconds.
 
     A SITURN was successfully performed on September 4. This turn was about
17 degrees.  Spacecraft performance throughout this activity was as expected;
there were no problems.  The turn resulted in the spacecraft leading the sun
by about 8.5 degrees.
 
     A NO-OP command was sent on September 4 to reset the Command Loss Timer
to 264 hours, the planned value for this mission phase.
 
     Cruise Science Memory Readouts (MROs) were successfully performed for
the Extreme Ultraviolet (EUV), Dust Detector (DDS) and Magnetometer (MAG)
instruments on September 4 and 6.
 
     The data collection for the periodically planned Attitude and
Articulation Control Subsystem (AACS) spin detector sensor calibration was
completed on September 6.
 
     A Ultra Stable Oscillator (USO) test was conducted on August 31. This
test provides continuing trend information characterizing the performance of
the ultra-stable RF downlink frequency source.
 
     A North/South delta DOR using the 70 meter antennas in Goldstone and
Australia was conducted on September 6.  Delta DOR is an additional
navigation data source in addition to doppler and ranging data.  When the
Delta DOR signal is modulating the downlink carrier spacecraft telemetry data
from the Telemetry Modulation Unit (TMU) is interrupted; no spacecraft
telemetry data is transmitted during this interruption.  This Delta DOR was
successful; it is the third of 10 Delta DOR data gathering activities prior to
the Earth closest approach.
 
     The AC/DC bus imbalance measurements remained relatively stable with
only slight variations observed.  The AC measurement is stable near 47.6 volts
while the DC measurement is stable near 18.6 volts.  All other power-related
and subsystem telemetry measurements are normal.
 
     Ultraviolet Spectrometer (UVS) Lyman Alpha data gathering continued on
September 4. This data is stored on the spacecraft tape recorder for replay
along with the Venus Encounter data planned for November 19-21.  This is the
fifth of eight UVS Lyman Alpha data gathering sequences in the Venus-Earth-5
(VE-5) sequence.
      ___    _____     ___
     /_ /|  /____/ \  /_ /|
     | | | |  __ \ /| | | |      Ron Baalke         | baalke@mars.jpl.nasa.gov
  ___| | | | |__) |/  | | |___   Jet Propulsion Lab | baalke@jems.jpl.nasa.gov
 /___| | | |  ___/    | |/__ /|  M/S 301-355        |
 |_____|/  |_|/       |_____|/   Pasadena, CA 91109 |
Path: mcduck!smunews!texsun!newstop!sun-barr!cs.utexas.edu!usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov!baalke
From: baalke@mars.jpl.nasa.gov (Ron Baalke)
Newsgroups: sci.space,sci.astro
Subject: Galileo Update - 08/31/90
Keywords: Galileo, JPL
Message-ID: <4724@jato.Jpl.Nasa.Gov>
Date: 1 Sep 90 18:28:10 GMT
Sender: news@jato.Jpl.Nasa.Gov
Reply-To: baalke@mars.jpl.nasa.gov (Ron Baalke)
Organization: Jet Propulsion Laboratory, Pasadena, CA.
Lines: 24
Xref: mcduck sci.space:2563 sci.astro:2073
