This spaceflightnow article says near the end that the Falcon 9 2nd stage will leave SES-9 in an elliptical, inclined transfer orbit. This article says that this is a super-synchronous orbit, and that the original plan was for a sub-synchronous orbit with apogee of only 26,000km which would have then left SES-9 with a 93 day "climb" to geostationary.

I'm a little overwhenlmed by acronyms so I've left them out. but first of all what exactly do these represent: "GTO", "GSO", and "GEO".

But the main part of my question is how will SES-9 reach its target geostationary orbit from the inclined elliptical orbit described in the first article? I found this in GitHub which points to the image below, but that's clearly for a different initial condition.

enter image description here

Image linked from here in reference to a different transfer orbit strategy.

  • $\begingroup$ This is a follow-up question to this one. $\endgroup$ – uhoh Feb 24 '16 at 16:49
  • $\begingroup$ Excellent @TildalWave - I will give that a thorough read. $\endgroup$ – uhoh Feb 24 '16 at 18:57

GEO and GSO are synonyms for geostationary (earth) orbit. They are orbits that are in the equatorial plane at an altitude that has a $24$ hour period so that the satellite appears to stay at one point in the sky. Many communications satellites are placed in one of these orbits and SES-9 is going to one at $108.2^\circ$ East longitude. GTO is geostationary transfer orbit. It is typically an orbit with a low perigee (a few hundred km), an apogee at about 42000 km, close to the altitude of GEO, and some inclination. The satellite carries a rocket to circularize the orbit. It fires the rocket when the satellite is at apogee, raising perigee and cancelling the inclination. If the initial apogee is not at synchronous altitude, that needs to be corrected as well by firings. Supersynchronous orbits have the apogee higher than 42000 km, so it must be lowered. If the launch rocket has enough performance to provide an orbit like that, it can reduce the fuel consumption of the satellite by reducing the fuel needed to cancel the inclination.

  • $\begingroup$ Does geosynchronous orbit have its own acronym? $\endgroup$ – uhoh Feb 24 '16 at 16:52
  • $\begingroup$ Geosynchronous or geostationary are two expansions of the G in GEO and GSO. $\endgroup$ – Ross Millikan Feb 24 '16 at 16:54
  • $\begingroup$ Since those two words mean different things, we should be careful. It's why I wrote what exactly in italics. Also, "The satellite carries a rocket..." to circularize and cancel inclination is not false, but it's not really an explanation. $\endgroup$ – uhoh Feb 24 '16 at 17:01
  • $\begingroup$ Each satellite has an orbit raising plan, which is updated as things go along. It includes when to fire the rocket, where it should be pointed, and for what duration. From a classic GTO you only need firings at apogee. To a first approximation, you can just take the velocity vector you want for GEO, subtract the velocity vector you have at apogee, and that is the $\Delta v$ vector you need to apply. You can do that in one step or break it into a number of steps. $\endgroup$ – Ross Millikan Feb 24 '16 at 17:08
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    $\begingroup$ Actually, there is only one GEO. Satellites placed in it differ in phase (longitude over Earth) but they are all at the same (equatorial) inclination, the same altitude, the same (lack of) eccentricity. Meanwhile, GSO may differ in inclination (how far north/south the satellite goes), phase (over which longitude the satellite moves) and argument of periapsis (at which time the satellite crosses the equator). $\endgroup$ – SF. Feb 24 '16 at 19:44

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