A "clipper", as I understand it, is orbiting a planet to repeatedly flyby one of its moons. Mariner 10 orbited the Sun to fly by Mercury 3 times. Should clippers in general use retrograde orbits in order to get more frequent flybys (or "clips")? Or are instead slower flybys prefered?

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    $\begingroup$ I guess that would depend on the types of observations you want to make and what scientific equipment you have on board $\endgroup$ – neelsg Jun 22 '15 at 8:59

The purpose of most missions are to study planetary bodies in detail, taking images, using radar or lasers for ranging and mapping, using gravimetric instruments to measure composition, etc. All these types of activities benefit from slower relative movement between the spacecraft the the body being studied.

There may be some mission profiles where more frequent flybys would be better than longer lasting flybys, although I can't think of any at the moment. Of course it may be that fuel limitations would mean that only a retrograde orbit is possible, in which case you take what you can get.

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  • $\begingroup$ But slow encounters means rare encounters. The probe would drift along with the moon for a while and then never come back, much like the Spitzer space telescope falls behind Earth's orbit around the Sun. A "clipper" would still fly by its target moon at low speed compared with pure flyby missions like Voyager and New Horizons. $\endgroup$ – LocalFluff Jun 23 '15 at 7:56
  • $\begingroup$ I'm assuming you are going to get multiple flybys prograde or retrograde @LocalFluff. If a prograde orbit gets you one shot but the retrograde gives you many then the retrograde is likely the one to go for. $\endgroup$ – GdD Jun 23 '15 at 8:17

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