Macintosh satellite tracking software - Re: Newbie with questions

Philip Chien (
Sat, 21 Dec 1996 02:43:50 -0500

Wilfred Whiteside ( said:

>I discovered the hobby of satellite observation just two weeks ago and just
>joined SeeSat.  I am a Macintosh user (in an IBM world) but have the
>capability to run IBM software in slow motion.

No need to do that.  It's a nice that Macintosh users do have the
capability to run PC software when necessary (which doesn't exist in
reverse) but not one you need to use for satellite tracking.

>Is there any software out
>there that can sift out satellite passes based on proximity to easily seen
>stars and planets?  I need this capability to see faint satellites with

Absolutely!  I highly recommend Bill Bard's OrbiTrack.  It's available via
the AMSAT Web site - look under software.  It's
shareware, inexpensive, and the author is a member of the Seasat community.

OrbiTrack has the capability to generate pseudo orbital elements based on
known orbital parmeters and passes over known locations and the capability
to rotate orbits due to launch delays - especially useful in the case of
the space shuttle.  You can track dozens (hundreds? thousands?) of
satellites simultanously in real-time.  What's especially appealing is
OrbiTrack has an output mode which generates data files compatible with the
Voyager astronomy planetarium simulator. (a commercial program from Carina

The combination of these two packages is an *extremely* powerful tool.
When I was hunting (successfully) for the classified DoD-1 satellite (22518
1992 86B) OrbiTrack generated the predicted elements, and Voyager showed me
the path it would take through the stars.

During one especially good pass Sean Sullivan took a photograph of DoD-1.
I asked a friend to digitize the data and ultimately converted the data in
to a light curve, showing the satellite's rotation rate (exactly what Sean
and I had predicted two weeks before the satellite's launch!)  Sean was
rather amused when I told him that a government scanner was used to do the
digitizing!  I overlayed the digitized image with the Voyager plot for a
quite accurate match of the predicted pass vs. the observed results.

And I might mention that the only IBM in the operation was the one used to
scan the image.

>I do not know how to convert the X,Y,Z coordinates of
>a satellite to elevation, azimuth coordinates.

You will very rarely get a satellite's instantaneous position expressed as
an orthoganal reference frame.  However there is a popular(?) format used
by NASA and others which describes a satellite's orbit in terms of its
cartesian coordinates, and velocities in each of the orthogonal directions.
Typically it's called M50 (for Mean 1950).  The M50 format is a more
accurate technical means for describing the satellite's position and
velocity, while the six classic Keplerain elements are more useful for
describing a satellite's orbit.    The M50 format is not time dependent
which is more useful for many applications. The program VEC2TLE converts
M50 in to two line element format.  VEC2TLE is an MS DOS program, so I
suppose you could use a PC Emulator to run it.

Here's a sample output in both M50 and the more typical two line elements
and verbose formats.

Ken Ernandes <> said:

Below is the nominal OMS-2 State Vector for STS-81.  Launch is currently
scheduled for 12-JAN-97 / 09:27 UTC.  Since this is a Mir docking mission,
this vector is only valid for a very short launch window.  This file may be
read by VEC2TLE version 9648 to add/update the corresponding Keplerian
elements to a designated text file.  However, you will need to provide the
above launch date and time.

Satellite Name:         STS-81
Catalog Number:         99981
Epoch MET:                  0.02972340278
                           0/00:42:48.102 MET
EFG E:                          7279322.1 ft
    F:                         20466405.0 ft
    G:                         -2758933.7 ft
    Edot:                   -14307.430647 ft/s
    Fdot:                     2437.145137 ft/s
    Gdot:                   -19670.908986 ft/s
ndot/2 (drag):              0.00002150149 rev/day^2
nddt/6:                       0.00000E+00 rev/day^3
Bstar:                        8.51679E-06 1/Earth Radii
Elset #:                                1
Rev @ Epoch:                1.52567183472

The catalog number (99981) is temporary; a permanent catalog number will be
assigned upon launch of STS-81.

The following Keplerian elements were computed by VEC2TLE from this vector
and the scheduled launch time, using a 0.1 drag multiplier:

1 99981U          97012.42347340  .00002150  00000-0  85168-5 0    17
2 99981  51.6542 149.0440 0033456 202.4709 346.7641 15.85048334    11

Satellite: STS-81
Catalog number: 99981
Epoch time:      97012.42347340
Element set:       1
Inclination:       51.6542 deg
RA of node:       149.0440 deg
Eccentricity:    0.0033456
Arg of perigee:   202.4709 deg
Mean anomaly:     346.7641 deg
Mean motion:   15.85048334 rev/day
Decay rate:    2.15015e-05 rev/day^2
Epoch rev:               1
Checksum:              278

VEC2TLE may be downloaded from: /amsat/software/PC/util

Philip Chien, KC4YER
Earth News - space writer and consultant
note new E-mail address -