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My question could be a little bit surreal, but I was thinking about this:

A hydroeletric plant transform the energy from the water passing through the turbines into electricity. Correct?

If the humans create a machine which instead of water passing through the turbine, the moon pass through a specific turbine, it can generate a lot of energy each day that moon pass through the turbine!

Is it possible?

If it is possible, worth the amount of energy that would be generated?

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... you aren't envisioning a giant tunnel in space that the moon would pass through, are you? Like the crude drawing below?

Moon Turbine

  1. We don't have the materials strong enough to attach it to earth with.
  2. We don't have enough fuel to launch that into space
  3. The turbines would... collide with the surface of the moon to generate electricity?
  4. Even if all this worked, each collision / "passing through" would add orbital velocity to the lunar orbit (attached to earth's surface, it would translate some of earth's rotational energy into lunar orbital energy) and thus we'd lose the moon even faster and you'd need to keep the 'turbine' constantly adjusted for the altitude of each encounter.
  5. The amount of energy you would generate before the Moon gained escape velocity would only be a small fraction of the energy it would take to launch, build in orbit and maintain said Moon Turbine.

Since you asked about total possible energy, if the moon were treated as if it were on a rail (it's not) and the materials could withstand a collision (they can't) you could potentially harness

$2.096x10^{29} Joules$

by slowing the rotation of the Earth down to the angular velocity of the moon. Also probably cause a slew of natural (artificial in this case?) disasters.

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One can consider to harvest power at Gibraltar strait (Moon/Sun energy from tides).
Any turbine to put in space is not feasible and, if not, then soon it will be locked to the motion of the Moon, and then useless.

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  • $\begingroup$ There are also plenty of places other than the Gibraltar Strait where one could do this. $\endgroup$
    – David Richerby
    Commented Apr 25, 2015 at 9:33
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Theoretically it is possible. After all, what law of physics would it violate? However, any energy that we harvested from the moon's orbit would be removed from the moon's potential energy, causing it to move closer to earth. If we harvested enough energy this way, the moon would collide with Earth!

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    $\begingroup$ Actually, if you're using something earth-based to grab energy from the moon, it's going to speed it up and make it recede, not slow and impact. $\endgroup$
    – BowlOfRed
    Commented Apr 24, 2015 at 23:39
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    $\begingroup$ The earth's surface is rotating faster than the moon's orbit. If we harvest the energy from here we will be decreasing the relative motion of the two. This will decrease the earth's rotation, but increase the moon's orbital speed. (And is exactly what happens with tidal energy harvesting). The end point is not a crashed moon but a tidally-locked earth. $\endgroup$
    – BowlOfRed
    Commented Apr 25, 2015 at 0:36
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    $\begingroup$ The question wasn't about harvesting energy from the earth or moon's rotation, but from the moon's orbit. If we were to use the moon to harvest energy from the earth's rotation, the moon would move further from Earth. But if we were to somehow draw energy directly out of the moon's orbit it would move towards Earth. $\endgroup$
    – Sheepman
    Commented Apr 25, 2015 at 2:22
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    $\begingroup$ There is no way to harvest energy from absolute motion, only from the difference in motion between two things. $\endgroup$
    – BowlOfRed
    Commented Apr 25, 2015 at 7:00
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    $\begingroup$ I never suggested anything about harvesting energy from absolute motion. The question was about building a turbine to harvest energy from the orbit of the moon relative to the earth. $\endgroup$
    – Sheepman
    Commented Apr 25, 2015 at 13:54
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Yes it is theoretically possible, as discussed in the other answers and indeed we already do a variation of harvesting a planet's orbital kinetic energy in the space navigation manoeuvre called "gravity assist" or "slingshot" to boost a spacecraft's speed without expending propellant. Here one makes one's spacecraft "collide" with a planet (i.e. make a very close flyby) such that the spacecraft, on rebound, has absorbed some of the planet's orbital kinetic energy. Terry Bollinger's answer to "Where does the extra kinetic energy come from in a gravitational slingshot?" explains this qualitatively in detail. David Hammen's answer to "Maths behind gravity assist" gives you the tools to analyse the situation in detail, but really one can think of the motion states of the interacting bodies before the spacecraft has entered and after it has left the region significantly affected by the slingshotting planet's gravitational field and the problem is no different from any other elastic (energy conserving) collision between two point massses where larger bodies tend to transfer some of their energy to the smaller ones in the collision.

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  • $\begingroup$ I was based on the slingshot theory. haah thank you $\endgroup$
    – Only a Curious Mind
    Commented Apr 27, 2015 at 11:34

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