1A sample TLE entry for the International Space Station looks like
2this:
3
4ISS (ZARYA)
51 25544U 98067A   01286.44085648  .00059265  00000-0  81723-3 0  5959
62 25544  51.6394 213.7002 0007838 194.2620 314.2054 15.56596996165535
7
8Each line in satfile must begin with a satellite ID number (e.g. 25544
9for the ISS).  Each ID must exist in the associated TLE file.
10
11Valid additional keywords are "align", "altcirc", "color", "font",
12"fontsize", "image", "position", "spacing", "thickness", "trail",
13"trail_output", and "transparent".  The usage for most of these is
14identical to the usage for arc and marker files.  In addition, a
15string to be plotted with the marker may be enclosed in either double
16quotes (""), or braces ({}).  If a string is not supplied, the marker
17will take the name of the satellite supplied in the TLE file.
18
19The "altcirc" keyword draws altitude circles on the surface of the
20earth.  The format is "altcirc=angle", where a circle is drawn
21bounding the area where the satellite is greater than angle degrees
22above the horizon.  For example, altcirc=0 draws a circle bounding the
23region where the satellite is above the horizon, while altcirc=45
24draws a circle bounding the region where the satellite is more than 45
25degrees above the horizon.  This may be specified more than once.
26
27The "trail" keyword is used to specify an orbit trail.  The format
28must be "trail={ground|orbit,start_time,end_time,interval}", where the
29start and end times and interval are each in minutes.  The start and
30end times are relative to the time of the calculation.  When using the
31-projection option, trail will always be "ground".
32
33The "trail_output" keyword outputs the satellite's position to a text
34file, using the same time interval specified by "trail".  If the
35"trail" option is not also present, "trail_output" has no effect.
36
37A few sample entries are given below:
38
3925544
40This draws a marker with the string "ISS (ZARYA)" for the
41International Space Station.
42
4325544 "The Space Station"
44This draws a marker with the string "The Space Station" for the
45International Space Station.
46
4725544 "" image=iss.png transparent={0,0,0} altcirc=0
48This draws iss.png at the current position of the International Space
49Station.  No text string is drawn.  A curve containing the area where
50the International Space Station is above the horizon is drawn.
51
5225544 "" image=iss.png transparent={0,0,0} altcirc=0 altcirc=45 trail={orbit,-5,10,2}
53As the previous example, but also draw the orbit trail from five
54minutes before to ten minutes past the current time, calculated every
55two minutes.  A second altitude circle bounding the region where the
56International Space Station is more than 45 degrees above the horizon
57is also drawn.
58
59