Provided by: predict_2.2.3-4build2_amd64 
NAME
predict - Track and predict passes of satellites in Earth orbit
SYNOPSIS
predict [-u tle_update_source] [-t tlefile] [-q qthfile] [-a serial_port] [-a1 serial_port] [-n
network_port] [-f sat_name starting_date/time ending_date/time] [-p sat_name starting_date/time] [-o
output_file] [-s] [-east] [-west] [-north] [-south]
DESCRIPTION
PREDICT is a multi-user satellite tracking and orbital prediction program written under the Linux
operating system by John A. Magliacane, KD2BD. PREDICT is free software. 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 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 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 current 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 PREDICT 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 program is run. Latitude is normally expressed in
degrees north with latitudes south of the equator expressed in negative degrees. Longitude is normally
expressed in degrees west with eastern longitudes expressed in negative degrees. This behavior can be
modified by passing the -east or -south commmand line switches to PREDICT.
Latitudes and longitudes may be either entered in decimal degrees, or in degrees, minutes, seconds (DMS)
format. 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 satellites in the program's database. Keplerian
orbital data is available from a variety of sources, including http://www.celestrak.com/,
http://www.space-track.org/, and http://www.amsat.org/.
PROGRAM OPERATION
The start-up screen of PREDICT 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 previous passes to help to confirm or
identify past observations.
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
calculations are started and prediction information is displayed on the screen.
The date and time in UTC, along with the satellite's elevation 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. If spacecraft attitude parameters (ALAT,
ALON) are included in PREDICT's transponder database file, then spacecraft antenna squint angles are
displayed instead of orbit numbers in the orbital prediction output.
An asterisk (*) displayed to the right of the orbit number or squint angle 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 Satellite (UARS) are visible to the naked eye.
If no symbol appears to the right of each line, then the satellite 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 directory. 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 underscore (_) 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 provides the option of breaking out of visual orbital prediction 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 geostationary 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 prediction 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 in real-time using
PREDICT's Single Satellite Tracking Mode (main menu option [T]), or simultaneously as a group of 24 using
the program's Multi-Satellite Tracking Mode (main menu option [M]). The positions of the Sun and Moon
are also displayed 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, a wealth of information related to tracking a spacecraft and
communicating through its transponder is displayed. The current date and time is displayed along with
the satellite's sub-satellite 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 modulo 256 orbital phase of the satellite, the eclipse depth, the spacecraft
antenna squint angle, and orbital model in use, as well as the current orbit number are also displayed.
The date and time for the next AOS is also provided.
Additionally, if the satellite is currently in range of the ground station, the amount of Doppler shift
experienced on uplink and downlink frequencies, path loss, propagation delay, and echo times are also
displayed. The expected time of LOS is also provided.
Uplink and downlink frequencies are held in PREDICT's transponder database file predict.db located under
$HOME/.predict. A default file is provided with PREDICT.
Transponders may be selected by pressing the SPACE BAR. The passband of the transponder may be tuned in
1 kHz increments by pressing the < and > keys. 100 Hz tuning is possible using the , and . keys. (These
are simply the < and > keys without the SHIFT key.)
If no transponder information is available, the data displayed on the tracking screen is abbreviated.
The features available in the Single Satellite Tracking Mode make it possible to accurately determine the
proper uplink frequency to yield a given downlink frequency, or vice versa. For example, if one wishes
to communicate with a station heard on 435.85200 MHz via FO-29, then 435.85200 MHz can be selected via
the keyboard as an RX frequency using the tuning keys while tracking FO-29, and the corresponding ground
station TX frequency will be displayed by PREDICT.
Obviously, an accurate system clock and up-to-date orbital data are required for the best tuning
accuracy.
If a sound card 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 coordinates in real-time. Announcements such as:
"This is PREDICT. Satellite is at fifty six degrees azimuth and forty five degrees elevation, and is
approaching. Satellite is currently visible."
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 satellites in very high
orbits, such as the AMC-6 geostationary satellite (35780 km). Voice announcements are performed as
background processes so as not to interfere with tracking calculations as the announcements are made.
Alarms and special announcements are made when the satellite being tracked enters into or out of eclipse.
Regular announcements can be forced by pressing the 'T' key in Single 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 heading, elevation, sub-satellite point latitude (in degrees North)
and longitude (in degrees West) positions are provided, 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 indicates 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 sunlight
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 lettering. 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 geostationary
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 especially valuable to spacecraft designers and satellite ground station controllers who
must monitor spacecraft power budgets or thermal conditions on-board their spacecraft due to sunlight and
eclipse periods. It can even be used to predict the optimum times for astronauts to perform extra-
vehicular activities in space. Solar illumination predictions may be logged to a file in the same manner
that orbital predictions may be logged (by pressing L).
SOLAR AND LUNAR ORBITAL PREDICTIONS
In addition to making orbital predictions of spacecraft, PREDICT can also predict transits of the Sun
and the Moon. Lunar predictions are initiated by selecting [L] from PREDICT's Main Menu. Solar
predictions are selected through Main Menu option [O].
When making solar and lunar orbital predictions, PREDICT provides azimuth and elevation headings, the
right ascension, declination, Greenwich Hour Angle (GHA), radial velocity, and normalized distance
(range) to the Sun or Moon. Declination and Greenwich Hour Angle correspond to the latitude and
longitude of the object's sub-satellite point above the Earth's surface. The radial velocity corresponds
to the speed and direction the object is traveling toward (+) or away (-) from the ground station, and is
expressed in meters per second. When the radial distance of the Moon is close to zero, the amount of
Doppler shift experienced in Moonbounce communications is minimal. The normalized distance corresponds
to the object's actual distance to the ground station divided its average distance. In practice, the
normalized distance can range from about 0.945 to 1.055 for the Moon, and about 0.983 to 1.017 for the
Sun.
Note that the effects of atmospherics are ignored in determining the elevation angles for the Sun and
Moon. Furthermore, the data provided by PREDICT corresponds to the object's center, and not the upper or
lower limb, as is sometimes done when predicting the rising and setting times of these celestial objects.
OPERATION UNDER THE X-WINDOW SYSTEM
PREDICT may be run under the X-Window System by invoking it through the xpredict script contained with
this software. xpredict can invoke rxvt, xterm, Eterm, gnome-terminal, 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 predict.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 beach_house.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 beach_house.qth
or
predict -q beach_house.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/predict.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. PREDICT then quietly exits without displaying
anything to the screen, thereby eliminating the need for entering the program and selecting the
appropriate menu options. This option is invoked using the -u command line switch as follows:
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 follows:
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 -qr www.celestrak.com/NORAD/elements/amateur.txt -O amateur.txt
wget -qr www.celestrak.com/NORAD/elements/visual.txt -O visual.txt
wget -qr 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
PREDICT is compatible with serial port antenna rotator interfaces conforming to the EasyComm 2 protocol
standard. This includes the PIC/TRACK interface developed by Vicenzo Mezzalira, IW3FOL
<http://digilander.iol.it/iw3fol/pictrack.html>, TAPR's EasyTrak Jr. (currently under development), and
Suding Associates Incorporated's Dish Controllers <http://www.ultimatecharger.com/Dish_Controllers.html>.
The FODTRACK rotator interface is supported through the use of Luc Langehegermann's (LX1GT) fodtrack
utility written for and included with PREDICT.
Using any of these hardware interfaces, PREDICT can automatically control the position of AZ/EL antenna
rotators, and keep antennas accurately pointed toward a satellite being tracked by PREDICT. In
operation, tracking data from PREDICT is directed to the specified serial port using the -a command line
option. For example:
predict -a /dev/ttyS0
will send AZ/EL 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 using
9600 baud, 8-data bits, 1-stop bit, no parity, and no handshaking. Data is sent to the interface if the
azimuth or elevation headings change by one degree or more. For interfaces requiring keepalive updates
at least once per second whether the AZ/EL headings have changed or not (such as the ones by SAI), the
-a1 option may be used:
predict -a1 /dev/ttyS0
ADDITIONAL OPTIONS
The -f command-line option, when followed by a satellite name or object number and starting date/time,
allows PREDICT 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 location 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 January 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 and longitude of the satellite's
sub-satellite point at the time specified, the slant range to the satellite 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 produced. 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 following 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 produces an output consisting of the date/time in Unix
format, 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 provided 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 communicating 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 PREDICT. 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
distribution of PREDICT as a guide. The sample program has comments to explain how each component
operates. It is useful 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 command 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 satellites in PREDICT's orbital database may be added,
modified, 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 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.
NEAT TRICKS
In addition to tracking and predicting passes of satellites, PREDICT may also be used to generate a NASA
two-line Keplerian element data set from data entered via keyboard. For example, let's say you're
listening to Space Shuttle audio re-broadcasts via WA3NAN and Keplerian elements 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 (Keyboard 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 signals 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 communication with a
satellite in such a position is not possible 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 communications 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 predict/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.db Satellite transponder database file ~/.predict/predict.qth Default ground station location information
SEE ALSO
predict-g1yhh(1)
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 <benscosm@iol.it>. SGP4/SDP4 code was derived from Pacsal routines written by Dr. T.S. Kelso, and converted to 'C' by Neoklis Kyriazis, 5B4AZ. See the CREDITS file for additional information.