Mars Odyssey: how close to sun-synchronous? Options

[Doug M.]

I've noticed that almost every report on Mars Odyssey that mentions its orbit points out that it is "nearly sun-synchronous", so that it passes over the same spot on Mars' surface at the same local time. (It's a slightly retrograde polar orbit, with an inclination of 93 degrees.) According to NASA, successive ground tracks are separated in longitude by approximately 29.5 degrees and the entire ground track nearly repeats every two sols. This is handy from a science POV, since it means that THEMIS can take pictures of the same features with the same lighting over and over.

That "nearly" makes me thoughtful, though. Mars Odyssey has been orbiting Mars for over 12 years now -- more than 50,000 orbits. If that "nearly" means it's off sun-synchronicity by just a fraction of a second per orbit, its ground track would shift quite noticeably over time.

Probably not a big deal, especially given that Odyssey has adjusted its orbit a bunch of times, most recently in the summer of 2012 to catch the MSL landing. Still, it left me curious. Does anyone know just how close to sun-synchronicity Odyssey is? Brief googling has not turned up a clear answer.

thanks in advance,


Doug M.