The pictures of Rosettas orbit show it doing some straight legs past 67P for the next while.-

Does this mean that at the current distance, the force of 67P's gravity is not really significant, and Rosetta is not really (yet) "in orbit" but rather just flying in the same general direction at the same time?

  • $\begingroup$ possible duplicate of Is this really Rosetta's orbit around 67P? $\endgroup$ Aug 11, 2014 at 23:12
  • $\begingroup$ @MartinSchröder This is not the same question as the one you refer to. The one you are referring to is asking about the accuracy of the reported flight path. This question assumes the answer to the other question is "yes", and asks about whether the first part of that flight path is correctly thought of as "in orbit" or not. It's about the definition of "in orbit". $\endgroup$ Aug 12, 2014 at 8:47

1 Answer 1


Rosetta will shift between different hyperbolic trajectories. This means that it won't move in an ellipse around the comet, but escape it if not repeatedly powered to another hyperbolic trajectory in a series of flybys. Trajectory changes are planned every Wednesday and Sunday. It is not what most ordinary people would think of as an "orbit", hence the confusion.

See from 16:45 in this video of the press conference August 6th.

  • $\begingroup$ So it is fair to say - almost by definition - that it is not "in orbit", because it has a hyperbolic trajectory; that in fact, it is just repeatedly passing by while it happens to be conveniently in the neighborhood? $\endgroup$ Aug 7, 2014 at 12:43
  • 2
    $\begingroup$ Perhaps fair to say that the delta-V between spacecraft and comet will never drop below escape velocity (1.5 ft/s) during any of the flybys. Hence it will never be in a true orbit. $\endgroup$
    – Anthony X
    Aug 7, 2014 at 22:39
  • 1
    $\begingroup$ It will enter a more stable elliptical orbit once comet's mascons are mapped more precisely. IIRC it will reduce semi-major axis 10 fold from what's now roughly 100 km. $\endgroup$
    – TildalWave
    Aug 8, 2014 at 11:33
  • $\begingroup$ @TidalWave Yeah, what is all that "elliptical orbit" talk about? That tiny microgravity comet cannot gravitationally have Rosetta actually orbit it at 100 or 50 km distance. Or what? I suppose the spacecraft will use its engine continuously when it is in (a forced) elliptical orbit. $\endgroup$
    – LocalFluff
    Aug 8, 2014 at 12:53
  • $\begingroup$ @TildalWave Mascon? For the uninitiated please? $\endgroup$
    – Everyone
    Aug 8, 2014 at 13:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.