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\______/ |_| \_\ |______/ |___| |_| VERSION 1.2
ORBIT: An orbit prediction program
for Atari ST computers.
By: Harrie F.A. de Leeuw, PA3CVX,
Papaverstraat 24,
5271 RB Sint-Michielsgestel,
The Netherlands,
Sept. 1986.
Preface:
With the help of this program it is possible to predict the
position of satellites in an elliptical orbit. This program is
primary intended for radio amateurs that communicate via amateur
satellites, such as the OSCARs. It is also possible to use this
program to track weather satellites or for instance a space
shuttle.
For a given time, (and your position) the program computes:
-- The direction to which to point the antenna. Azimuth
and elevation.
(azimuth = angle between north and the position of the
satellite; elevation = angle between the horizon and the
position of the satellite)
-- The doppler shift. Owing to the high velocity of the
satellite, the frequency of the receiver (or
transmitter) differs a little from nominal. This
frequency difference is computed.
-- The heigth of the satellite above the earth.
-- The distance between you and the satellite.
-- The position of the satellite in terms of degrees north
and west.
General remarks:
-- This is public domain software. You can copy it as often as
you want. There is only one restriction: leave the program
unchanged! Especially you are not allowed to change the name of
the author.
-- I have written this program for my pleasure in the first
place. That is why some functions are a little overdone, (like
sizing the info windows) but I wanted to learn to program a
window, that can be controlled totally. And I enjoyed it!
-- This program uses the classical Keplerian set of elements as
its input. This numbers can be found in several HAM magazines.
(The Netherlands: ELECTRON issued by VERON). To get reliable
output use up-to-date elements!
-- The basic calculation-algorithm of this program was written
by Tom Clark, W3IWI, and published in 'Orbit' March/April 1981.
-- This program has been written in Modula 2.
Files on disk:
ORBIT.PRG is the main program.
In the subdirectory (folder) ORBIT.DAT the following files should
be found:
-ORBIT.RSC This is the resource file. Must be available!
-ORBIT.PIC Picture file. Must be available!
-STATION.ORB Information of the station. When the program
can not find this file, you are forced to
create this file.
-xxxxxxx.SAT Satellite information files.
In the folder DOCUMENT.ORB the documentation of the program can be
found (ORBIT.DOC). To be able to read this file the program
1ST-Word of GST is included (1ST_WORD.PRG and 1ST_WORD.RSC).
In the subdirectory (folder) SOURCE.ORB the source files of
'Orbit' can be found:
-In the folder DEF the definition modules can be found.
-In the folder MOD the implementation modules and the source
of the main program can be found.
-In the folder RCS_SHP the following files can be found:
-ORBIT.DEF Definition file used by the resource
construction set.
-ORBIT.I Output from resource construction set,
used in the module OGEMGlobal.
-EARTH.SHP Shape file (Earth) used by the shape and
icon editor.
-EARTHD.ICN Output from shape and icon editor. This
icon file is used by the resource
construction.
-ORB1.SHP Shape file (First part of ORBIT shape).
-ORB1D.ICN Icon file (First part of ORBIT shape).
-ORB2.SHP Shape file (Second part of ORBIT shape).
-ORB2D.ICN Icon file (Second part of ORBIT shape).
-ATTENTI.SHP Shape file (Attention symbol).
-ATTENTID.ICN Icon file (Attention symbol).
REMARK: The SOURCE.ORB folder is ment for those who want to see
how things are done in this program. These files are not
necessary to run the program.
The Menu bar:
Desk:
-About 'Orbit'
Selecting this menu item gives the version number and
the name of the author.
-Desk Accessories
File:
-Load Satellite
Load satellite information from disk.
-Save Satellite
Save current active satellite data on disk.
-New Satellite
After the selection of this menu item, a dialog box
appears. This dialog box can be filled up with data of a
new satellite. These new data become the current active
ones.
-Change Satellite
Selecting this menu item, it is possible to change data
of an already existing satellite data file on disk.
This function only changes the data on disk. If you
want to use the new data, this data must be loaded using
the 'Load Satellite' option.
-Delete Satellite
Delete a satellite file from disk.
-Change Station
Change the station data. The new data are stored on disk
and will be used in the computations.
Remark: The longitude must be given in degrees west of
Greenwich. For instance: Hamburg (W-Germany) lies 350
degrees west. (not 10 degrees!)
-Quit
Exits the program, back to GEM Desktop.
Compute:
-Set Start/Stop/Step
Sets the starttime, endtime and timestep, which will be
used in the computations when 'Start Scan' is selected.
Enter time and date in UTC (=Greenwich Mean Time).
-Start Scan
Compute satellite position from starttime to endtime,
which are defined with 'Set Start/Stop/Step'. Output
times are in UTC. Hitting any key on the keyboard will
stop the computations.
-Track Real Time
Compute satellite position at the system time and date
(converted to UTC). Hitting any key on the keyboard
will stop the computations.
REMARK:
The last 100 computations are saved in a buffer. Using the
window's vertical slider it is possible to browse through
this data. The usual window controls apply here.
Output:
-Screen Text
Output on screen as a table.
-Screen Graphics
Output on screen on a map of the world. The position of
the satellite is marked with a cross.
-Printer
The output will be printed.
REMARK:
It is only possible to change the output mode, when the
output window is closed.
Info:
-Scan Parameters Settings
Gives information about the currently active scan
parameters.
-Satellite Parameters
Gives information about the currently active satellite.
-Station Parameters
Gives information about the currently active station.
REMARK:
The info windows can be controlled according to the usual
rules.
Time/Date:
-Set System Time/Date
Utility to set the system time and date. Use local time
here.
Precision of REALs:
Because of the poor precision of REALs, the point of time for
which a computation is done may slightly differ from the time
you expected. This is also the reason why, sometimes, the
Keppler equations can not be solved. In the next version
this problem will be solved. The REALs which are critical
will be substituted by LONGREALs. At this time the
implementation of LONGREALs is not present.
Harrie F.A. de Leeuw, PA3CVX,
Papaverstraat 24,
5271 RB Sint-Michielsgestel,
The Netherlands,
Sept. 1986.