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If I loosely define "constellation" here as a group of earth satellites where different ones are visible at different times, and you need all or most of them to get round-the-clock coverage, some examples might be: Iridium, Doves, Galileo, Glonass, OG2, QZSS, and GPS.

I'm wondering, were the Molniya's the first practical use of the constellation concept?

note: for this question geosynchronous is fine, but not geostationary. Millitary, commercial, and scientific constellations are all fine.

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    $\begingroup$ Do the orbiting needles count? :) $\endgroup$
    – TildalWave
    Jan 3, 2016 at 14:20
  • $\begingroup$ Yikes!! I'd never heard of that before. Those were heady days indeed! Thanks for bringing it up. One of the references cited in that article caught my attention - "West Ford Needles: Where are They Now?" I didn't realize solar pressure could be so effective for debris way out in MEO. Another question brewing! $\endgroup$
    – uhoh
    Jan 4, 2016 at 16:51

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The earliest communication constellation, as you noted, is likely the Moylniya satellites, which have been active since 1965, and as a constellation since 1968. There were a number of Spy satellites which might be considered constellations in the early 60s, most notably the Corona. Depending on your definition, I would choose one of those two.

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    $\begingroup$ Thank you! Looking for a group of satellites in orbit at the same time so that at least one is always above the horizon, for at least some fixed place on earth. Three Molnya's - with geosynchronous orbits of 12 hours were able to do this - in much of Northern Asia at least one was above the horizon at all times. It looks like the spy satellites were more loners in LEO and didn't work together to keep any given place in continuous observation. $\endgroup$
    – uhoh
    Apr 22, 2016 at 0:55
  • $\begingroup$ I've asked a related question $\endgroup$
    – uhoh
    Apr 22, 2016 at 1:13

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