predict.txt

一个预测卫星方位俯仰的软件

       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.

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.tle file, and replace an
       existing satellite's entry with 2-line Keplerian data  for
       the  new  satellite.   If  this method is chosen, 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.

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 radio communication
       links with satellites when they are within  range  of  the
       groundstation.

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
       The  latest news is available through the official PREDICT
       software        web        page        located         at:
       <http://www.qsl.net/kd2bd/predict.html>.

FILES
       predict.tle
              Default  database of Keplerian orbital data in NASA
              2-line format

       predict.db
              Satellite transponder database file

       predict.qth
              Default ground station location information

AUTHORS
       PREDICT  was  written  by  John   A.   Magliacane,   KD2BD
       <[e-mail]>.  PIC/TRACK code was written by Vittorio
       Benvenuti, I3VFJ <[e-mail]>.




KD2BD Software           02 November 2002        PREDICT (2.2.1d)