Astronomy and Astrophysics – Astronomy
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dda....39.1502m&link_type=abstract
American Astronomical Society, DDA meeting #39, #15.02
Astronomy and Astrophysics
Astronomy
Scientific paper
At present there is a "constellation" of 66 active Iridium communications satellites and nine spares, all moving along in nearly-circular orbits at an altitude of approximately 780 km above Earth's surface. The Iridium satellites are arrayed into six orbit planes tilted 86.4 degrees to the celestial equator and spaced at equal intervals of right ascension around it. Each orbit plane contains eleven active satellites spaced at equal intervals of true argument of latitude.
Each Iridium satellite has three highly-reflective, mirror-like antennas, called "Main Mission Antennas" (MMAs), which are tilted down 40 degrees from the vertical axis of the spacecraft and spaced 120 degrees apart. Should an Earth-fixed observer be looking in the direction of one of these antennas and see the reflection of the Sun through it, he or she will observe, for a few fleeting seconds, a bright flare of sunlight that can exceed visual magnitude -8. Such a solar reflection, called an "Iridium flare," typically happens several times a day to any Earth-fixed location, although several days may go by with no Iridium flare visible to a given Earth-fixed observer.
The attitude of each Iridium satellite is maintained on-orbit according to the following control law: "long axis down, MMA #1 forward." Since this control law dictates the precise orientation in space of each MMA at all times, it is possible to predict Iridium flares, given also that the dynamicist has in hand the current orbital elements of each Iridium satellite.
Therefore, as part of my poster presentation, I will show how to make Iridium flare predictions using the algorithms that I have developed for this purpose. I will predict the Iridium flares, if any, that can be seen from Boulder, Colorado, during each night of the DDA 2008 meeting.
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