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I read somewhere that Israel launched satellites in retrograde orbit. America also has some satellites in retrograde orbit.

I am new to this concept, so I am curious:

    1. What are the benefits/objectives of retrograde orbit? What could the objectives be that a prograde orbit would not fulfill?
    2. More power is required to keep the satellite in retrograde orbit (and to launch it there in the first place), right?
    3. Do natural satellites ever orbit in retrograde? What factors influence whether a satellite is in retrograde or prograde orbit (i.e. distance from primary)?

Thank you.

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  • $\begingroup$ Welcome to Space Exploration! Please note that our Q&A works best by splitting individual questions into separate posts. If they are directly related and don't deviate much from the main question that you have (i.e. you have subquestions), then that might work OK since it wouldn't break the narrative in answers. But if you require in-depth answers on distinct questions, they should really be asked individually too. Rule of thumb is, that if you can't think of a single sentence title ending with a questionmark that would reflect what the question inquires about, you're asking too many. ;) $\endgroup$ – TildalWave Dec 27 '13 at 16:05
  • $\begingroup$ Also, now that I wanted to edit out your case against closure from the question itself (please do that), I can't help but wonder, did answers to that question you link to answer any of your questions here? If not, please describe in your own question why not. Just stating that you think it's not a duplicate because you extend it isn't really helpful. Thanks! $\endgroup$ – TildalWave Dec 27 '13 at 16:08
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1) Good question, I can't think of any off the top of my head. Maybe if you needed to snap photos of the Earth really quickly (and you had cameras that could take good photos considering the speed of the satellite relative to the Earth) it would make sense, but most imaging satellites are launched into polar orbits, meaning the orbit makes a right angle with the equator, or it's slightly prograde or slightly retrograde. Polar orbits ensure you can cover every bit of the globe.

I believe the reason Israel launches to retrograde orbits from its own launch sites is for safety concerns. There are a lot of inhabited areas underneath a trajectory for a rocket going to a prograde orbit, but for retrograde you just have the Mediterranean. Given high tensions in that region, launching prograde could easily be misinterpreted as an attack.

2) More power is required to launch into a retrograde orbit because you have to go against the Earth's rotation. When launching into a prograde orbit, the Earth's rotation gives you a little benefit, so you can use a little less propellant getting to orbit. For retrograde, you need to work against that boost, which, of course, requires more propellant.

It does not require more power to keep the satellite in retrograde orbit. Although I suppose if it's in a fairly low orbit it might be more affected by atmospheric drag since the relative velocity of the atmosphere against the satellite will be higher in a retrograde orbit, but I would venture to guess that the difference would not be significant, probably not even by one order of magnitude.

3) Yes, one of Saturn's moons orbits retrograde: http://en.wikipedia.org/wiki/Phoebe_(moon)#Orbital_characteristics

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    $\begingroup$ Difference between a ballistic missile launch and satellite launch, is really where it lands. :) Also, Shavit launcher is basically a derivative of the Jericho missile. $\endgroup$ – geoffc Dec 27 '13 at 15:58
  • $\begingroup$ +1 so if a planet has several moons, only the outermost moons could have a retrograde orbit? Since Phoebe isn't the outermost moon, are Saturn's outermost moons in retrograde or prograde? Generally, the further the moon is away from the primary, the more eccentric its orbit? Thanks $\endgroup$ – Emi Matro Dec 27 '13 at 16:10
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    $\begingroup$ @user436158 Could you please first split your question into the three distinct ones that you have? To answer your question here in the comments, no. Their orbital period doesn't have anything to do with their inclination. Phoebe is likely a captured asteroid. $\endgroup$ – TildalWave Dec 27 '13 at 16:13
  • $\begingroup$ @EmiMatro moons were just found around jupiter, but not at all as you state. The innermost are almost exclusively prograde and the outermost, retrograde (except for the oddball I linked). There's far more to moons than human-launched objects, including billions of years. $\endgroup$ – Magic Octopus Urn Jul 19 '18 at 12:46

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