Main Engine Cut Off

I wrote about this mission in an earlier post. Initially, we thought that this satellite was perhaps a new SDS and would be launched into HEO (a 63-degree inclined 'Molniya orbit'). Subsequent observations of a fuel vent by the Centaur upper stage seen from the western USA four hours after launch did not seem to fit this, and made us speculate whether the payload perhaps was something new and went into a 58 degree inclined MEO (see the discussion at the bottom of this previous post).

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The orbit of USA 310 is decidedly odd. There have never been classified launches in such an orbit before. One commercial object was launched in a somewhat similar orbit (the orbital inclination is lower), the first (and only) of an ill-fated commercial communications network in MEO: ICO F2 (2001-026A) launched in 2001.