Oh, Say Can You See

The 4th of July in the U.S. is almost always celebrated with a fireworks display, ideally with proper supervision by responsible adults.  Here’s a display up in the sky that’s definitely overseen by responsible rocket scientists, captured via telescope in Betzdorf, Luxembourg.

We recently got word a new satellite has come into service at ASTRA. Launched in April, the ASTRA 1KR satellite underwent a rigorous in-orbit testing before arriving on-station at 19.2° East, which it shares with several other satellites. Ever wonder what that looks like? We’ve got the video.

If you’re an amateur astronomist, you can try this at home. If the skies are dark enough and you have a telescope, you can spot some of the satellites in the Clarke Orbit, a.k.a. the geostationary ring, 36,000 kilometers (23,600 miles) above the Earth.

Most geostationary satellites are really geosynchronous. For radio and television broadcasting, this is essential. With mean motions between 0.9 to 1.1 revolutions per day, these satellites drift across a 45-square-kilometer “box” before corrections are made by spacecraft controllers on the ground via on-board thrusters. Anomalies in the Earth’s gravitational field causes this “drift,” as atmospheric drag is irrelevent at this altitude. The Moon’s gravitational pull provides an out-of-plane force as well, gradually increasing the orbital inclination towards that of the Moon around the Earth (which itself varies between 18 and 29 degrees).

So the satellite’s track tends to resemble a figure-eight track. In the ASTRA 1KR video, we get to see a small portion of this eventual figure-eight. Allowed to go on unchecked, a satellite’s orbit becomes more inclined. Some satellites are purposefully directed towards an inclined orbit, thus providing better coverage of the polar regions. Antarctic research stations rely on these satellites for communications.

Unlike objects in low Earth orbit, geostationary satellites are visible throughout every night of the year, entering the Earth’s shadow for up to 70 minutes per day. During the same period the satellite tends to brighten over several days, twice a year (equinox, +/- one week), when the satellites’ orientation toward the Sun causes “flares,” the most spectacular of which comprise the Iridium system (check this site for predictions). Two line elements can be obtained for nearly all these satellites via Dr. T.S. Kelso’s site.

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