I have read for calculating azimuth and elevation from the Earth we use north east up reference frame. What reference frame is used for satellite to measure azimuth and elevation on the Earth? And which axis is taken as boresight axis for satellite?
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What does this mean: "What reference frame is used for satellite to measure azimuth and elevation on earth ?" – Organic Marble Dec 11 '19 at 17:04
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From the reference frame of the satellite, the earth spins next to (below? above?) it, and the universe rotates around it. It's generally not useful to use the reference frame of a satellite for any purpose, and especially not an azimuth taken from that reference frame as, for a non-tumbling satellite (one that always maintains orientation relative to the Earth, such as to keep an antenna pointed "down") in LEO, the azimuth to the sun goes through a full 360 degrees every 90 minutes... so the answer is... "The azimuth conventions are whatever the people communicating agree on at the moment." – Ghedipunk Dec 11 '19 at 18:55
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There are exceptions, of course, when a satellite needs to keep track of more than just where the Earth is and where its station keeping thrusters are pointing... For example, observatories need to keep their cameras pointed at the target, then either reorient so that their radios can work properly, or keep their directional antennas pointed towards their ground station(s)... (Hubble is an example of the first, SDO an example of the second, and SOHO sits in a place where the azimuth matters, but there isn't much need to change any orientation) – Ghedipunk Dec 11 '19 at 18:58