bjorgan
commented
7 years ago Some sources (e.g. http://lfvn.astronomer.ru/report/0000019/7_summary.htm, http://www.astronomer.ru/data/0128/ESAclassification_Issue17.pdf and possibly a journal paper cited by the above (https://link.springer.com/article/10.1023/A:1013399804776, can't access it even through NTNU)) indicate the following definition:
- Mean motion between 0.9 and 1.1 (also mentioned in http://www.satobs.org/geosats.html)
- Eccentricity below 0.2 (some places 0.1?)
- Inclination below 70 degrees (some places 20 degrees?)
Should find a more proper source, but at least mean motion parameter might at first glance seem to be consistent with satellites in geostationary.txt.
... are probably "wrong".
predict_is_geostationary()returns false on e.g. ELEKTRO-L 1 (37344) and INSAT-3A (27714), though they are geostationary. This results in weird behavior like a LOS or AOS occurring 180 days in the future, since the algorithms are allowed to step to a time so far away from the epoch that numerical inaccuracies allow AOS to happen.Geostationary satellites never have mean motion set exactly to 1.002701 revolution per day (or do they), but the question is what is reasonably true and what is the correct definition. We have a list over geostationary TLEs, what is the threshold mean motion for these? What could it be true in the future? What satellites are reasonably geostationary over the period the TLE is valid? How exact is the mean motion-parameter?
EDIT: Could be related to geostationary vs geosynchronous, not sure. The value in the function corresponds to the strict definition of a geostationary satellite. Keeping the "bug" mark, but could be that we just need to extend with another function for checking whether a satellite is geosynchronous, need to check.
EDIT 2: Very strict definition of geostationary satellites also require something about the inclination and other parameters.
~I don't think we have any use for the strict definition. This function is used mainly for avoiding long iterations in predict_next_aos and similar, which was also its original purpose in Predict.~ Strict definition is required, since the satellite has to move with the direction of Earth's rotation. Could technically have a TLE with mean motion set to one rotation per sidereal day, but completely different direction.