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As the moon is tidal locked, she is always showing the same side turned toward Earth.
How could I give her a little rotation, allowing us to see the other side, without destroying the earth's current ecosystem?
For how long will it turn? At what frequency do I have to repeat the process?

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    $\begingroup$ Note that if (somehow or other!) you got the moon to spin, that would not, in itself, cause any harm to Earth. It would make very little difference on Earth (it might affect tides very slightly). Obviously though, if you smash planets in to the Moon, that would rather affect Earth (as in "we may be smashed to pieces by the debris!" :) ) You may enjoy reading Seveneves by Neal Stephenson. $\endgroup$
    – Fattie
    Jul 19, 2017 at 14:06
  • $\begingroup$ @Fattie, That's why our scientist choose to nuke the moon. This way we won't have the side effect of the planetary collision. and it cost far less than their first idea: Create a big ship in the shape of a thumb to rotate the moon. $\endgroup$ Jul 19, 2017 at 14:11

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A big almost tangential impact can do the trick. A quick google search returns, among others, this video.

Something bigger than Apophis would set it on a slow rotation. A dwarf planet impacting the Moon would set it on a pretty fast rotation. Tidal forces would then lock it again in few millenia, and likely with a different side facing us.

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  • $\begingroup$ With no risk of pushing her outside of our reach? $\endgroup$ Jul 19, 2017 at 11:34
  • $\begingroup$ @DragandDrop, I think to change the orbital velocity of the Moon, an impact would have to be so powerful to actually destroy it $\endgroup$
    – L.Dutch
    Jul 19, 2017 at 11:39
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Repeated glancing impacts by a steady stream of dwarf planets (larger asteroids? Kuiper belt objects?) should do the trick. Needless to say this would risk missing the target every time, and it would certainly make a hot mess (literally!) of the Moon's equator, where the impacts would be directed. I visualize a temporary ring of ejecta around the Moon, too, though whether they would achieve (short-lived) orbit is not clear to me.

I'm not sure how much mass and at what speed you would need. I'm also not sure how much it would take for tidal acceleration to turn things back. Consider that the Moon is pretty far away already, so tidal acceleration is not as strong as it was a couple billions years ago.

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    $\begingroup$ "Repeated glancing impacts by a steady stream of dwarf planets" This project is going to be called 'Dwarf Planet Gatlingun'. $\endgroup$ Jul 19, 2017 at 12:09
  • $\begingroup$ I wonder if, really, there's a mass/speed domain where it WOULD spin the moon, BUT wouldn't just smash it up badly. That is a complex engineering question. $\endgroup$
    – Fattie
    Jul 19, 2017 at 14:07
  • $\begingroup$ @Fattie There's no friction in space, so really just pushing the Moon using a lot of dust specks would do the trick, only much more slowly. Smashing it up (as opposed to scarring it badly) is really not feasible unless you use a really large body. $\endgroup$
    – pablodf76
    Jul 19, 2017 at 14:12
  • $\begingroup$ Nah, if you send a HUGE amount of tiny specs tangentially at a point on the moon's equator, it would very likely just .... grind it down, it would cut a hole in it, like a water-cutter. Exactly as I said, "mass/speed domain where it WOULD spin the moon, BUT wouldn't just smash it up badly" $\endgroup$
    – Fattie
    Jul 19, 2017 at 14:15
  • $\begingroup$ @Fattie I was thinking not all the dust specks hitting the same spot. :P $\endgroup$
    – pablodf76
    Jul 19, 2017 at 14:16

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