To the best of my knowledge the key idea of the Tundra and Molniya orbits is that they are elliptical orbits at non-zero inclination that remain in the same ground track. Obviously, for practical reasons, the orbital period of those orbits are then chosen to synchronise to the solar day rather than the siderial day as is mentioned in this article. Please, re-check and modify articles.
--IndigoMind 10:41, 18 May 2006 (UTC)
The article is correct. Since the earth rotates once per sidereal day relative to inertial space, that is the necessary orbital period to create a repeating ground track. Kemperb 00:01, 17 May 2007 (UTC)
what's special about that angle?
- Could it just be a coincidence that Plesetsk Cosmodrome is at 63° North, from where due East launches reach a 63° orbital inclination with no pricey orbital inclination change maneuver required? (sdsds - talk) 18:57, 26 June 2009 (UTC)
This inclination has a special property: perturbations from the earth's equatorial bulge don't cause any long-term changes in the argument of perigee. That's the angle measured within the orbit plane from the S->N equator crossing to the perigee. At any other inclination the argument of perigee slowly changes and with it the apogee latitude. The Molniya and Tundra orbits are designed to serve high latitudes so you want the argument of perigee to remain at 270 degrees (for the northern hemisphere) or 90 degrees (for the southern hemisphere).
Sirius chose the tundra orbit so that users in the continental US, especially the north central states, could see higher elevation angles than are possible from geostationary orbits over the equator. This reduces the number of terrestrial repeaters needed to provide good coverage in urban canyons. Because they're not stationary (that's possible only over the equator), continuous service requires multiple tundra satellites. They also move in the user's sky, but this isn't a problem because satellite radio uses small, hemispherical antennas that don't have to be pointed. Karn (talk) 10:52, 22 September 2009 (UTC)
Geosynchronicity and Earth asymmetry
I can't find reference to Molnya orbit taking advantage of an axial asymmetry of the planet. http://en.cnki.com.cn/Article_en/CJFDTOTAL-JBXG199001013.htm I remember reading that such asymmetry was a big advantage in keeping synchrony at smaller energy cost. I can barely find some reference to the Pacific - Atlantic asymmetry! — Preceding unsigned comment added by Spamhog (talk • contribs) 13:56, 10 January 2013 (UTC)