PREDICT(1)                KD2BD Software               PREDICT(1)



NAME
       predict  - Track and predict passes of satellites in Earth
       orbit

SYNOPSIS
       predict [-u tle_update_source] [-t tlefile]  [-q  qthfile]
       [-a  serial_port]  [-n  network_port]  [-f sat_name start-
       ing_date/time  ending_date/time]   [-p   sat_name   start-
       ing_date/time] [-o output_file] [-s]

DESCRIPTION
       PREDICT  is  a  multi-user  satellite tracking and orbital
       prediction program written under the Linux operating  sys-
       tem  by  John  A. Magliacane, KD2BD. PREDICT is free soft-
       ware. You can redistribute it and/or modify it  under  the
       terms  of  the  GNU General Public License as published by
       the Free Software Foundation,  either  version  2  of  the
       License or any later version.

       PREDICT is distributed in the hope that it will be useful,
       but WITHOUT ANY WARRANTY, without even  the  implied  war-
       ranty  of MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR-
       POSE. See the GNU General Public License for more details.

FIRST TIME USE
       PREDICT  tracks and predicts passes of satellites based on
       the geographical location of the ground station, the  cur-
       rent  date  and  time as provided by the computer system's
       clock, and Keplerian orbital data for  the  satellites  of
       interest  to  the ground station. First time users of PRE-
       DICT are provided  default  ground  station  location  and
       orbital data information files. These files are managed by
       the program, and are normally located  in  a  user's  home
       directory  under  a  hidden  subdirectory  named .predict.
       First time users will be prompted to supply  PREDICT  with
       their  geographical location (the same as selecting option
       [G] from the program's main menu) the first time the  pro-
       gram is run. Latitude is entered in decimal degrees north.
       Latitudes south of the equator  are  entered  as  negative
       numbers.  Longitude  is  entered  as decimal degrees west.
       Eastern longitudes may be  entered  as  negative  numbers.
       Station  altitude  is  entered as the number of meters the
       ground station is located above sea level. This  parameter
       is  not  very critical.  If unsure, make a realistic guess
       or simply enter 0.

       Users of PREDICT  need  Keplerian  orbital  data  for  the
       satellites  they wish to track that is preferably no older
       than one month. The default orbital data supplied with the
       program  is liable to be quite old, and so must be brought
       up to date if accurate results are to  be  expected.  This
       may be accomplished by selecting option [E] from PREDICT's
       main menu and manually entering Keplerian  data  for  each
       satellite  in  the  program's  database,  or  by selecting
       option [U] and specifying a file containing recent  2-line
       Keplerian  element data sets that correspond to the satel-
       lites in the program's database.  Keplerian  orbital  data
       is   available   from  a  variety  of  sources,  including
       http://www.celestrak.com/ and http://www.amsat.org/.

PROGRAM OPERATION
       The operation of PREDICT is uncomplicated by  design.  The
       start-up  screen  of  the program lists the program's main
       functions. Several tracking and orbital  prediction  modes
       are  available, as well as several utilities to manage the
       program's orbital database.

PREDICTING SATELLITE PASSES
       Orbital predictions are useful for determining in  advance
       when  a  satellite  is  expected to come within range of a
       ground station. They can also be used to look back to pre-
       vious  passes to help to confirm or identify past observa-
       tions.

       PREDICT includes two orbital prediction modes  to  predict
       any pass above a ground station (main menu option [P]), or
       list only those passes that might be visible to  a  ground
       station  through optical means (main menu option [V]).  In
       either mode, the user is asked to select  a  satellite  of
       interest from a menu, and then asked to enter the date and
       time (in UTC)  at  which  prediction  calculations  should
       start.

       The  current  date  and time may be selected by default by
       entering nothing and hitting simply  the  ENTER  key  when
       prompted to enter the starting date and time.

       Otherwise, the starting date and time should be entered in
       the form:

            DDMonYY HH:MM:SS

       Entering the time is optional.  If it is omitted, midnight
       (00:00:00)  is  assumed.   Once complete, orbital calcula-
       tions are started and prediction information is  displayed
       on the screen.

       The  date and time in UTC, along with the satellite's ele-
       vation above ground, azimuth heading, modulo  256  orbital
       phase,  sub-satellite  point latitude and longitude, slant
       range between the ground station and  the  satellite,  and
       the  satellite's orbit number are all displayed. An aster-
       isk (*) displayed to the right of the orbit  number  means
       the  satellite  is in sunlight at the date and time listed
       on the line. A plus symbol (+) means the satellite  is  in
       sunlight  while  the  ground station is under the cover of
       darkness at the time and date listed.  Under good  viewing
       conditions,  large  satellites  such  as the International
       Space Station (ISS), the US  Space  Shuttles,  and  Hubble
       Space  Telescope, and the Upper Atmosphere Research Satel-
       lite (UARS) are visible to the naked  eye.  If  no  symbol
       appears  to the right of the orbit number, then the satel-
       lite is in the Earth's shadow at the time and date listed,
       and is not receiving any illumination from the sun.

       Pressing  the  ENTER  key,  the  'Y' key, or the space bar
       advances the orbital predictions to a screen  listing  the
       next  available  passes.   Pressing the 'L' key allows the
       currently displayed screen plus any subsequent screens  to
       be  logged  to  a text file in your current working direc-
       tory. The name given to this  file  is  the  name  of  the
       satellite  plus a ".txt" extension.  Any slashes or spaces
       appearing in the satellite name are replaced by the under-
       score  (_)  symbol.  The logging feature may be toggled on
       and off at any time by pressing the 'L' key.  Exiting  the
       orbital  prediction  mode  by  pressing 'N' or hitting the
       ESCape key will also close the log file. The log file will
       be  appended  with  additional  information  if additional
       predictions are conducted for the same satellite with  the
       logging feature turned on.

       Selecting  [V]  from  PREDICT's  main  menu  will permit a
       ground station to only predict passes for satellites  that
       are  potentially  visible through optical means. Since all
       other passes are filtered out in this mode, and since some
       satellites  may  never  arrive  over a ground station when
       optical viewing conditions are possible, the program  pro-
       vides the option of breaking out of visual orbital predic-
       tion mode by pressing the [ESC]ape key as calculations are
       made. A prompt is displayed at the bottom of the screen to
       alert the user of this option.

       In either orbital prediction mode, predictions will not be
       attempted  for  satellites  that  can never rise above the
       ground station's horizon, or for satellites in geostation-
       ary  orbits.  If  a  satellite is in range at the starting
       date and time specified, PREDICT will adjust the  starting
       date  back in time until the point of AOS so that the pre-
       diction screen displays the first  pass  in  its  entirety
       from start to finish.

SINGLE SATELLITE TRACKING MODE
       In addition to predicting satellite passes, PREDICT allows
       satellites to be tracked singly in  real-time  using  PRE-
       DICT's  Single  Satellite  Tracking Mode (main menu option
       [T]), or simultaneously as a group of 24  using  the  pro-
       gram's  Multi-Satellite  Tracking  Mode  (main menu option
       [M]).  The positions of the Sun and  Moon  are  also  dis-
       played when tracking satellites in real-time.

       Selecting  option  [T] from PREDICT's main menu places the
       program in Single Satellite Tracking Mode. The  user  will
       be  prompted  to  select  the satellite of interest, after
       which a screen will appear and display tracking  positions
       for the satellite selected.

       In  Single  Satellite  Tracking Mode, the current date and
       time are displayed along with the  satellite's  sub-satel-
       lite  point,  its  orbital altitude in both kilometers and
       statute miles, the slant range distance between the ground
       station  and  the satellite in both kilometers and statute
       miles, the current azimuth and elevation  headings  toward
       the  satellite,  the  orbital velocity of the satellite in
       both kilometers per hour and statute miles per  hour,  the
       footprint  of the satellite in both kilometers and statute
       miles, the orbital phase of the satellite in  both  modulo
       256  and  360, as well as the current orbit number.  Addi-
       tionally, if the satellite is currently in  range  of  the
       ground station, the amount of Doppler shift experienced by
       the ground station receiving downlinks at 146 MHz and  435
       MHz  are  displayed,  as well as the one-way path loss for
       these frequencies. The predicted time of LOS  as  well  as
       sunlight  and visibility information are also displayed at
       the bottom of the screen.  If  the  satellite  is  not  in
       range,  then  the Doppler shift and path loss calculations
       are not performed, and the next  predicted  AOS  date  and
       time is shown at the bottom of the screen.

       If  a  soundcard is present on your machine and the Single
       Satellite Tracking Mode is invoked with an  uppercase  'T'
       rather  than  a  lowercase 't', PREDICT will make periodic
       voice announcements stating the satellite's tracking coor-
       dinates in real-time. Announcements such as:

       "This is PREDICT.  Satellite is at 5 6 degrees azimuth and
       4 5 degrees elevation, and approaching."

       are made at intervals that are a function of  how  quickly
       the  satellite is moving across the sky. Announcements can
       occur as frequently as every 50 seconds for satellites  in
       low  earth  orbits such as the International Space Station
       (370 km), or as infrequently as every 8 minutes for satel-
       lites  in very high orbits, such as the GE-2 geostationary
       satellite (35780 km). Voice announcements are performed as
       background  processes so as not to interfere with tracking
       calculations as the announcements are made.  Announcements
       can  be forced at any time by pressing the 'T' key in Sin-
       gle Satellite Tracking Mode.

MULTI-SATELLITE TRACKING MODE
       Selecting [M] from PREDICT's main menu places the  program
       in  a  real-time  multi-satellite  tracking  mode. In this
       mode, all 24 satellites  in  the  program's  database  are
       tracked simultaneously along with the positions of the Sun
       and Moon. Tracking data for the satellites is displayed in
       two columns of 12 satellites each. The name, azimuth head-
       ing, elevation, sub-satellite point latitude  (in  degrees
       North)  and longitude (in degrees West) positions are pro-
       vided, along with the slant  range  distance  between  the
       satellite and the ground station (in kilometers).

       A  letter  displayed to the right of the slant range indi-
       cates the satellite's sunlight and eclipse conditions.  If
       the  satellite  is experiencing an eclipse period, an N is
       displayed. If the satellite is in sunlight and the  ground
       station  is  under the cover of darkness, a V is displayed
       to indicate the possibility that the satellite is  visible
       under  the current conditions. If the satellite is in sun-
       light while conditions at the ground station do not  allow
       the satellite to be seen, a D is displayed.  Satellites in
       range of the ground station are displayed in BOLD  letter-
       ing. The AOS dates and times for the next three satellites
       predicted to come into range are displayed on  the  bottom
       of  the screen between the tracking coordinates of the Sun
       and Moon.  Predictions are not made for satellites in geo-
       stationary  orbits or for satellites so low in inclination
       and/or altitude that they can never rise above the horizon
       of the ground station.

SOLAR ILLUMINATION PREDICTIONS
       Selecting  [S]  from  PREDICT's main menu will allow solar
       illumination predictions to be  made.   These  predictions
       indicate  how  much  sunlight  a particular satellite will
       receive in a 24 hour period.  This  information  is  espe-
       cially  valuable  to  spacecraft  designers  and satellite
       groundstation  controllers  who  must  monitor  spacecraft
       power  budgets or thermal conditions on-board their space-
       craft due to sunlight and eclipse periods.  It can even be
       used  to  predict the optimum times for astronauts to per-
       form extra-vehicular activities in space. Solar  illumina-
       tion  predictions may be logged to a file in the same man-
       ner that orbital predictions may be  logged  (by  pressing
       L).

OPERATING UNDER THE X-WINDOW SYSTEM
       PREDICT  may  be run under the X-Window System by invoking
       it through the xpredict script contained with  this  soft-
       ware. xpredict can invoke rxvt, xterm, Eterm, gnome-termi-
       nal, or kvt, and display PREDICT  in  a  virtual  terminal
       window.   xpredict  should be edited for best results.  In
       many cases, holding down the SHIFT key while pressing  the
       plus  (+) and minus (-) keys allows PREDICT's window to be
       re-sized when started under xpredict.

COMMAND LINE ARGUMENTS
       By default, PREDICT  reads  ground  station  location  and
       orbital  data  information from a pair of files located in
       the user's home  directory  under  a  hidden  subdirectory
       named  .predict.  Ground  station  location information is
       held in a  file  named  predict.qth,  while  orbital  data
       information for 24 satellites is held in a file named pre-
       dict.tle.

       If we wish  to  run  PREDICT  using  data  from  alternate
       sources  instead of these default files, the names of such
       files may be passed to PREDICT on the  command  line  when
       the  program  is  started. For example, if we wish to read
       the TLE file  visual.tle  and  the  QTH  file  holiday.qth
       rather  than the default files, we could start PREDICT and
       pass the names of these alternate files to the program  in
       the following manner:

            predict -t visual.tle -q holiday.qth

       or

            predict -q holiday.qth -t visual.tle

       If  the  files  specified  are  not located in the current
       working directory, then their relative or  absolute  paths
       should  also  be specified along with their names (predict
       -t /home/kd2bd/orbs/visual.tle).

       It is also possible to specify  only  one  alternate  file
       while using the default for the other. For example,

            predict -t visual.tle

       reads  QTH  information  from  the default ~/.predict/pre-
       dict.qth location, and TLE  information  from  visual.tle,
       while

            predict -q bobs.qth

       reads  QTH  information  from bobs.qth and TLE information
       from the default ~/.predict/predict.tle location.

QUIET ORBITAL DATABASE UPDATES
       It is also possible to update PREDICT's satellite  orbital
       database  using  another  command line option that updates
       the database from a NASA two-line element data  set.  PRE-
       DICT then quietly exits without displaying anything to the
       screen, thereby eliminating the need for entering the pro-
       gram  and  selecting  the  appropriate  menu options. This
       option is invoked using the -u command line switch as fol-
       lows:

            predict -u orbs248.tle

       This  example  updates  PREDICT's default orbital database
       with the Keplerian elements found in the file orbs248.tle.
       PREDICT may be updated from a list of files as well:

            predict -u amateur.tle visual.tle weather.tle

       If an alternate datafile requires updating, it may also be
       specified on the command line using the -t switch as  fol-
       lows:

            predict -t oscar.tle -u amateur.tle

       This  example  updates the oscar.tle orbital database with
       the two-line element data contained in amateur.tle.

       These options permit the  automatic  update  of  PREDICT's
       orbital  data  files using Keplerian orbital data obtained
       through automatic means  such  as  FTP,  HTTP,  or  pacsat
       satellite download.

       For  example,  the  following script can be used to update
       PREDICT's orbital database via the Internet:

          #!/bin/sh
          wget  -qc  www.celestrak.com/NORAD/elements/amateur.txt
       -O amateur.txt
          wget -qc www.celestrak.com/NORAD/elements/visual.txt -O
       visual.txt
          wget  -qc  www.celestrak.com/NORAD/elements/weather.txt
       -O weather.txt
          /usr/local/bin/predict    -u   amateur.txt   visual.txt
       weather.txt

       To truly automate the process  of  updating  your  orbital
       database,  save  the above commands to a file in your home
       directory (such as kepupdate), and add the following  line
       to your crontab (type crontab -e to edit your crontab):

            0 2 * * * kepupdate

       and  PREDICT  will automatically update its database every
       day at 2:00 AM.

AUTOMATIC ANTENNA TRACKING
       Using the PIC/TRACK antenna rotator interface  created  by
       Vicenzo       Mezzalira,      IW3FOL      <http://digilan-
       der.iol.it/iw3fol/pictrack.html>,  PREDICT  can  automati-
       cally  control the position of AZ/EL antenna rotators, and
       keep antennas accurately pointed toward a satellite  being
       tracked  by  PREDICT.   The  PIC/TRACK  interface connects
       between the PC's serial port  and  the  antenna  rotators.
       Tracking  data from PREDICT is directed to the appropriate
       serial port using the -a command line option.   For  exam-
       ple:

            predict -a /dev/ttyS0

       will  send tracking data to the first serial port when the
       program is tracking a satellite in  the  Single  Satellite
       Tracking Mode.  The data sent to the serial port is of the
       form: "AZ241.0 EL26.0".

ADDITIONAL OPTIONS
       The -f command-line option, when followed by  a  satellite
       name  or object number and starting date/time, allows PRE-
       DICT to respond  with  satellite  positional  information.
       This  feature  allows  PREDICT  to be invoked within other
       applications that need to  determine  the  location  of  a
       satellite at a particular point in time, such as the loca-
       tion of where a CCD camera image was  taken  by  a  Pacsat
       satellite based on its timestamp.

       The  information  produced  includes the date/time in Unix
       format (the number of seconds since midnight UTC  on  Jan-
       uary 1, 1970), the date/time in ASCII (UTC), the elevation
       of the satellite in degrees, the azimuth  heading  of  the
       satellite,  the  orbital  phase (modulo 256), the latitude
       (N) and longitude (W)  of  the  satellite's  sub-satellite
       point at the time specified, the slant range to the satel-
       lite in kilometers with respect to  the  ground  station's
       location,  the orbit number, and the spacecraft's sunlight
       visibility information.

       The date/time must be specified in Unix format (number  of
       seconds  since  midnight  UTC  on January 1, 1970).  If no
       starting  or  ending  time  is  specified,   the   current
       date/time  is  assumed and a single line of output is pro-
       duced.  If a starting and ending  time  are  specified,  a
       list  of  coordinates  beginning at the starting time/date
       and ending with the ending time/date will be  returned  by
       the program with a one second resolution.  If the letter m
       is  appended  to  the  ending  time/date,  then  the  data
       returned by the program will have a one minute resolution.
       The -o option allows the program to write  the  calculated
       data  to  an  output  file rather than directing it to the
       standard output device if desired.

       The proper syntax for this option is as follows:

            predict -f ISS 977446390 977446400 -o datafile

       A list of coordinates starting at  the  current  date/time
       and ending 10 seconds later may be produced by the follow-
       ing command:

            predict -f ISS +10

       If a list of coordinates specifying the  position  of  the
       satellite every minute for the next 10 minutes is desired,
       the following command may be used:

            predict -f ISS +10m

       If a satellite name contains spaces, then the entire  name
       must be enclosed by "quotes".

       The -p option allows orbital predictions for a single pass
       to be generated by  PREDICT  via  the  command-line.   For
       example:

            predict -p OSCAR-11 1003536767

       starts  predictions  for  the OSCAR-11 satellite at a Unix
       time of 1003536767 (Sat 20Oct01  00:12:47  UTC).   If  the
       starting  date/time  is  omitted, the current date/time is
       used.  If a pass is already in progress  at  the  starting
       date/time specified, orbital predictions are moved back to
       the beginning of AOS of the current pass, and data for the
       entire pass from AOS to LOS is provided.

       When  either  the  -f or -p options are used, PREDICT pro-
       duces an output consisting of the date/time in  Unix  for-
       mat,  the  date  and time in ASCII (UTC), the elevation of
       the satellite in degrees, the azimuth of the satellite  in
       degrees,  the orbital phase (modulo 256), the latitude (N)
       and longitude (W) of the satellite's sub-satellite  point,
       the  slant  range  to  the  satellite (in kilometers), the
       orbit number, and  the  spacecraft's  sunlight  visibility
       information.  For example:

       1003611710  Sat  20Oct01 21:01:50   11    6  164   51   72
       1389  16669 *

       The output isn't annotated, but then again, it's meant  to
       be read by other software.


SERVER MODE
       PREDICT's  network  socket interface allows the program to
       operate as a server capable of providing tracking data and
       other  information  to  client  applications using the UDP
       protocol.  It is even possible to have the PREDICT  server
       and  client applications running on separate machines pro-
       vided the clients are connected to the  server  through  a
       functioning network connection.

       The -s switch is used to start PREDICT in server mode:

            predict -s

       By  default, PREDICT uses socket port 1210 for communicat-
       ing with client applications.   Therefore,  the  following
       line needs to be added to the end your /etc/services file:

            predict   1210/udp

       The port number (1210) can be changed to something else if
       desired.   There is no need to recompile the program if it
       is changed.  To run more than one instance of  PREDICT  in
       server  mode  on  a single host, an alternate port must be
       specified when invoking the additional instances  of  PRE-
       DICT.  This can be accomplished by using the -n switch:

            predict -n 1211 -t other_tle_file -s

       When  invoked  in  server mode, PREDICT immediately enters
       Multi-Satellite Tracking Mode,  and  makes  live  tracking
       data  available  to clients.  Clients may poll PREDICT for
       tracking data when the program is running  in  either  the
       Multi-Satellite  or  Single Satellite Tracking Mode.  When
       in Multi-Satellite Tracking mode, tracking data for any of
       the  24  satellites  in  the  program's  database  may  be
       accessed by client applications.  When in Single-Satellite
       Tracking  mode,  only  live  tracking  data for the single
       satellite being tracked may be accessed.  Either  tracking
       mode may be ended at any time.  When this is done, PREDICT
       will return the last calculated  satellite  tracking  data
       until  the  program is again put into a real-time tracking
       mode.  This allows the user to return to  the  main  menu,
       and  use  other  features  of  the program without sending
       potentially harmful data to client applications.

       The best way to write a client application is to  use  the
       demonstration  program (demo.c) included in this distribu-
       tion of PREDICT as a guide.  The sample program  has  com-
       ments  to explain how each component operates.  It is use-
       ful to pipe the output of this  program  through  less  to
       easily browse through the data returned (demo | less).

       In operation, a character array is filled with the command
       and arguments to be sent to PREDICT.  A socket  connection
       is  then  opened,  the  request  is  sent,  a  response is
       received, and the socket connection is closed.   The  com-
       mand and arguments are in ASCII text format.

       Several excellent network client applications are included
       in this release of PREDICT, and may  be  found  under  the
       predict/clients directory.


ADDING SATELLITES
       One  of  the most frequently asked questions is how satel-
       lites in PREDICT's orbital database may  be  added,  modi-
       fied,  or  replaced.   As  it turns out, there are several
       ways in which this can be done.  Probably the  easiest  is
       to  manually  edit  your  ~/.predict/predict.tle file, and
       replace an existing satellite's entry with  2-line  Keple-
       rian  data  for the new satellite.  If this method is cho-
       sen, however, just make sure to include ONLY the two  line
       data, and nothing else.

       Another  way is to is select the Keyboard Edit option from
       the program's Main Menu, select a satellite  you  wish  to
       replace.   Edit  the name and object number (replacing the
       old information  with  the  new  information).   Just  hit
       ENTER,  and accept all the other orbital parameters shown.
       Get back to PREDICT's Main Menu.  Select Auto Update,  and
       then enter the filename containing the 2-line element data
       for your favorite new satellite.  The new  satellite  data
       should  be  detected  by PREDICT, and the orbital data for
       the old satellite will be overwritten by the new data.

NEAT TRICKS
       In addition to tracking and predicting  passes  of  satel-
       lites,  PREDICT  may  also be used to generate a NASA two-
       line Keplerian element data set from data entered via key-
       board.  For  example,  let's say you're listening to Space
       Shuttle audio re-broadcasts via WA3NAN and Keplerian  ele-
       ments  for  the  Space  Shuttle's  orbit  are given by the
       announcer. The orbital data provided by WA3NAN  in  verbal
       form  may  be  manually  entered  into  PREDICT's  orbital
       database using option [E] of the program's main menu (Key-
       board  Edit of Orbital Database). The orbital data for the
       Space Shuttle in NASA two-line element form  can  then  be
       found  in  your orbital database file, and may imported to
       any other satellite tracking program that accepts two-line
       element files or distributed to others electronically.

       It is also possible to run PREDICT as a background process
       and direct its display to an  unused  virtual  console  by
       using the following command:

               predict < /dev/tty8 > /dev/tty8 &

       Switching  to  virtual  console  number  8 (ALT-F8 in text
       mode) will allow PREDICT to be  controlled  and  displayed
       even  after  you've  logged out.  This is especially handy
       when running PREDICT in server mode on a remote machine.

GLOSSARY OF TERMS
       The following terms are  frequently  used  in  association
       with satellite communications and space technology:

AOS:
       Acquisition of Signal - the time at which a ground station
       first acquires radio signals  from  a  satellite.  PREDICT
       defines  AOS  as the time when the satellite being tracked
       comes within  +/-  0.03  degrees  of  the  local  horizon,
       although  it may have to rise higher than this before sig-
       nals are first heard.

Apogee:
       Point in a satellite's orbit when the satellite is at  its
       farthest distance from the earth's surface.

Anomalistic Period:
       A  satellite orbital parameter specifying the time between
       successive perigees.

Ascending Node:
       Point in a satellite's orbit when its sub-satellite  point
       crosses the equator moving south to north.

Azimuth:
       The  compass direction measured clockwise from true north.
       North = 0 degrees, East = 90 degrees, South = 180 degrees,
       and West = 270 degrees.

Descending Node:
       Point  in a satellite's orbit when its sub-satellite point
       crosses the equator moving north to south.

Doppler Shift:
       The motion of a satellite in its orbit around  the  earth,
       and  in  many  cases  the  rotational  motion of the earth
       itself, causes radio signals generated by satellites to be
       received  on  Earth at frequencies slightly different than
       those upon which they were transmitted. PREDICT calculates
       what  effect  these  motions  have  upon  the reception of
       satellites transmitting on the 146 MHz and 435 MHz Amateur
       Radio bands.

Elevation:
       The  angle  between  the local horizon and the position of
       the satellite. A satellite that appears directly  above  a
       particular  location is said to be located at an elevation
       of 90 degrees. A satellite located on  the  horizon  of  a
       particular  location is said to be located at an elevation
       of 0 degrees.  A satellite with an elevation of less  than
       zero is positioned below the local horizon, and radio com-
       munication with a satellite in such a position is not pos-
       sible under normal circumstances.

Footprint:
       Diameter  of the Earth's surface visible from a satellite.
       The higher the satellite's orbital altitude,  the  greater
       the  footprint,  and  the wider the satellite's communica-
       tions coverage.

LOS:
       Loss of Signal - the time at which a ground station  loses
       radio contact with a satellite. PREDICT defines LOS as the
       time when the satellite being  tracked  comes  within  +/-
       0.03 degrees of the local horizon.

Orbital Phase:
       An  orbital  "clock"  that describes a satellite's orbital
       position with respect to perigee.  Orbital  Phase  may  be
       modulo 256, or modulo 360, and is sometimes referred to as
       mean anomaly when speaking of amateur radio satellites  in
       elliptical   orbits,  such  as  the  Phase  3  satellites.
       Orbital phase is zero at perigee.

Path Loss:
       The apparent attenuation a radio signal  undergoes  as  it
       travels  a  given distance. This attenuation is the result
       of the dispersion radio waves experience as they propagate
       between  transmitter and receiver using antennas of finite
       gain. Free space path  loss  is  technically  an  oxymoron
       since free space is loss free.

Perigee:
       Point  in a satellite's orbit when the satellite is at its
       closest distance to the earth's surface.

Nodal Period:
       A satellite orbital parameter specifying the time  between
       successive ascending nodes.

Slant Range:
       The  straight line distance between the ground station and
       the satellite at a given time.

Sub-Satellite Point:
       The latitude and longitude specifying the location on  the
       Earth that is directly below the satellite.


ADDITIONAL INFORMATION
       Detailed  information  on  the  operation of PREDICT's UDP
       socket-based interface as well as sample code for  writing
       your  own  client  applications  is  available in the pre-
       dict/clients/samples subdirectory.   The  latest  news  is
       available  through  the official PREDICT software web page
       located at: <http://www.qsl.net/kd2bd/predict.html>.

FILES
       ~/.predict/predict.tle
              Default database of orbital data

       ~/.predict/predict.qth
              Default ground station location information

AUTHORS
       PREDICT  was  written  by  John   A.   Magliacane,   KD2BD
       <kd2bd@amsat.org>.  The socket server code was contributed
       by Ivan Galysh,  KD4HBO  <galysh@juno.nrl.navy.mil>.   The
       PIC/TRACK  serial port antenna rotator controller code was
       contributed   by   Vittorio   Benvenuti,    I3VFJ    <ben-
       scosm@iol.it>.



KD2BD Software           23 October 2001               PREDICT(1)
