HR AMSAT NEWS SERVICE BULLETIN 001.02 FROM AMSAT HQ
SILVER SPRING, MD January 1, 1994
TO ALL RADIO AMATEURS BT
BID: $ANS-001.02

RV3DR, QSL manager for MIR contacts, advises that on December 24,
1993, December 31, 1993 and January 6, 1994 the MIR space station
will be transmitting special digitized voice messages on its
normal frequency of 145.55 MHz.  The message repeats every tow
minutes.  Sergey says that the developer of this equipment is
DL2MDE.

ANS thanks RV3DR for the information that went into this bulletin
and James Mollica N2NRD for relaying it to us.

/EX


HR AMSAT NEWS SERVICE BULLETIN 001.01 FROM AMSAT HQ
SILVER SPRING, MD January 1, 1994
TO ALL RADIO AMATEURS BT
BID: $ANS-001.01

A number of messages have recently been posted to the AMSAT BBS
concerning the schedules for the various satellites and how they
are arrived at.  In the case of OSCAR-13, the schedule is
determined by the AO-13 Command Team consisting of James Miller
G3RUH, Peter Guelzow DB2OS and Graham Ratcliff VK5AGR.  As to how
these volunteers determine the schedule, a very fine set of
comments was posted by Paul Beckmann WA0RSE Internet address
wa0rse@amsat.org.  The AMSAT News Service thanks Paul for his well-
put comments and has taken the liberty of extracting them for this
bulletin.

Paul begins by asking himself: What determines the mode schedule
for a satellite? He says thae he found an answer in the very
clearly written piece in the 1993 Space Symposium Proceedings by,
you guessed it, James, G3RUH.

In his attempt to put the article by James in terms that may not be
obvious to new to satellites as well as many not so new
"bird-watchers", Paul offers a list of some of the important
considerations:

1. All modern satellites are battery-powered with solar cell
recharging systems. In order to work, the batteries must stay
charged.

2. Most satellites do not have solar cells covering their entire
surface.  This means the attitude of the satellite with relation to
the sun must be managed to keep the batteries charged.

3. The antennas are fixed to the satellite, not steerable, and
necessarily "go along for the ride" when accomplishing Item 2.)

4. Each mode involves a receiver, a transmitter, and a pair of
antennas.  The receivers vary in sensitivity, the transmitters in
power, and the antennas in gain and beamwidth.

5. Because of Item 3, the characteristics of item 4 allow
transponder operation only in particular modes, when the distances
and spacecraft attitudes are within certain limits.  For example,
a narrowbeam antenna pointing away from the Earth will not support
communications.  If a particular mode requires the use of that
antenna, it would not do any good to place the satellite in that
mode, no matter how badly it was desired.  To change the attitude
of the spacecraft to point the antenna at the Earth could very well
compromise solar cell illumination, hence battery charge, hence
spacecraft operation - and possibly even its life expectancy.

6. Because some modes draw more power than others, the battery
power must be budgeted. This also constrains how long the satellite
can operate in any particular mode.

Paul admits to possibly missing some other major points, but he
believes that these demonstrate to him, at least, that the mode
schedule on AO-13, or any other bird, is not a self-serving
decision made by some "elite superclass" who treat the bird as a
"toy", but are considered decisions, constrained by the physics of
the orbit, solar cells, batteries, equipment aboard, antennas,
etc., designed to offer the best long-term schedule of transponder
operation and to further the state-of-the-art for the next birds'
designs.

WA0RSE strongly suggests reading the article by James in the
Proceedings.  He says that he was amazed at the number of
specialized programs that had been written, complete with graphical
output, to aid in the decision-making process to keep the AO-13
satellite operational.  He expressed his opinion that
James, and others like him, should be thanked for bringing clear
explanations like these to the rest of us and for fostering
experimentation in modes that have proven to provide better two-way
satellite communications for our fellow hams across the globe.

Paul sums up his message by saying that we need everyone interested
in AMSAT, with their opinions, tempers, passions, talents, and good
humor.  He also wishes all a Happy New Year. Peace on Earth. Good
will toward all.

Information on ordering a copy of the Space Symposium Proceedings,
which contains James Miller's article can be found on page 12 of
the Nov/Dec AMSAT Journal.

/EX