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Molniya-orbit communication satellites work well for ground locations near the poles. These high eccentricity, highly inclined orbits, with a period of 12 hours, “loiter” for about 6 hours over the poles.

A trio of 3 satellites can provide continuous coverage.

enter image description here

https://en.wikipedia.org/wiki/Molniya_orbit

Unlike geostationary satellites (GSO) which remain over a fixed geographic location, Molniya satellites have a moving ground track. This has two consequences:

  1. For Molniya reception, a tracking antenna is needed. By comparison, GSO satellites can be received with a fixed dish
  2. A Molniya antenna needs to break communication and re-acquire the next satellite 6 times a day.

Parabolic dishes have a primary axis which is aligned in the direction of the signal source. Parabolic dishes need to be aimed at (and track) the satellite of interest.

Spherical dishes have no inherent axis. The axis is determined by the location of the receiver antenna. In the sketch below, A and B are the location of focal points for objects 1 and 2 respectively.

enter image description here

An example is the Arecibo telescope. This dish could not be pointed, so a spherical design was used for the reflector dish, with mobile receiving antennae (illustrated below)

Two antennae (pointing at different locations in the sky) are illustrated: the spike and the sphere.

enter image description here National Geographic

A fixed spherical receiving dish for a trio of Molniya satellites, with a trio of mobile antennae, could potentially provide continuous reception without re-acquisition delay. Is this a reasonable design? Ever been done?

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  • $\begingroup$ Wouldn't it be 4 reacquisitions per day? If the loiter time is six hours, why the extra two switchovers? $\endgroup$
    – Darth Pseudonym
    Nov 15 at 22:25
  • $\begingroup$ Molniya satellites are always described in trios. The higher they are, the slower their angular speed. Maybe that makes tracking and re-acquisition easier ??? 3 satellites each making 2 passes a day makes for 6 reacquisitions. $\endgroup$
    – Woody
    Nov 15 at 23:31

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