Here is a screen shot from NY2O of the ground track from GSAT-6A (43241, 2018-027A). What kind of orbit can make this wave shaped ground track?
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3$\begingroup$ Quite similar to Mars's retrograde motion. $\endgroup$– ugorenMay 14, 2018 at 12:27
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$\begingroup$ I want to ask the question "is it possible to get a 'straight line' orbit from this elliptical orbit" but have no idea how to begin phrasing it. $\endgroup$– Magic Octopus UrnJun 21, 2018 at 16:28
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1$\begingroup$ @MagicOctopusUrn if the orbital plane is also the Earth's equatorial plane, I think pretty-much yes. If it's not, I think pretty-much no, but why not ask? And in addition to a 'straight line' you could ask about any great circle orbit or an orbit parallel to lines of longitude or lines of latitude. Ask about all of them, it should be answerable in one post. $\endgroup$– uhohJun 21, 2018 at 16:53
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1$\begingroup$ @uhoh that would've been my guess; I think I'll keep my vague question answered by a vague comment :P. Thanks again good sir! $\endgroup$– Magic Octopus UrnJun 21, 2018 at 17:59
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1 Answer
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An elliptical one. The Wikipedia page you link gives a signfiicantly different apogee and perigee and a period of 20.8 hours. So, on average, it moves West to East a bit faster than the Earth does, but at apogee it's moving more slowly and the Earth overtakes it a bit (which are the "S-bends" in the track). It swings a little North of the equatorial plane while approaching the Earth, and a bit South while receding. At the moment of the above screenshot it is close to perigee.
Each full cycle of the wave pattern is an orbit, so after roughly six orbits (120 hours) when the Earth has turned five times beneath it, it will get back to the same longitude. This fits with the apparent size of the wave pattern on the map, which is credibly about 4 time zones.
answered May 13, 2018 at 9:13
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2$\begingroup$ The Earth turns west to east! So that's the descending node you've found. $\endgroup$ May 13, 2018 at 10:24
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8$\begingroup$ Ha! Indeed it does. I think that it used to turn the other way, but I guess they changed it in the early 1960's to make launching from Florida easier. ;-) $\endgroup$– uhohMay 13, 2018 at 10:26
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4$\begingroup$ Terrific, concise answer. If I could, I'd give, 2, possibly 2.7 upvotes. $\endgroup$ May 13, 2018 at 15:18
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2$\begingroup$ @ChrisR See the wikipedia page linked in the question -- they lost contact before the final orbit-lifting burn. $\endgroup$ May 14, 2018 at 7:37