How Hard Would It Be to Keep the Moon from Floating Away?

Heh, not particularly accurate. The moon won&#x27;t “eventually escape entirely”. It&#x27;s orbit will keep increasing till the solar day = lunar month. At which points the tides stop and there&#x27;s no more energy to increase the moon&#x27;s orbit.<p>The fun part is because vacuum is not perfect and the incredibly small effects of gravitational waves the orbit will start decreasing.... till it hits the Roche limit and becomes a ring!<p>All that ignores the sun expanding and consuming the inner planets.

It might be marginally more feasible to build an enormous space tether (<a href="https:&#x2F;&#x2F;www-istp.gsfc.nasa.gov&#x2F;Education&#x2F;wtether.html" rel="nofollow">https:&#x2F;&#x2F;www-istp.gsfc.nasa.gov&#x2F;Education&#x2F;wtether.html</a>). By dragging it through Earth&#x27;s magnetic field (which extends out past the moon on the &quot;downstream&quot; side of the solar wind), you could: 1) generate large quantities of electricity, which would be extracted by orbital energy 2) use that electricity in some useful way to further slow momentum (like powering some of the ion engines they talk about in the article).<p>Anyone with a stronger physics background want to do the math and tell me why this won&#x27;t work (or at least be marginally better than the proposal in the article?)

Sci-fi has covered pretty much &quot;everything&quot;, so it&#x27;s not a surprise that there was a TV series in the 1970&#x27;s that had this exact premise:<p><i>In the opening episode, set in the year 1999, nuclear waste stored on the Moon&#x27;s far side explodes, knocking the Moon out of orbit and sending it, as well as the 311 inhabitants of Moonbase Alpha, hurtling uncontrollably into space.</i><p>I never could bring myself to watch it, because the premise was just too absurd.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Space:_1999" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Space:_1999</a>

Until I saw this title, this wasn&#x27;t really something I was worried about.<p>But now I&#x27;m worried.<p>On a more serious note the moon will stop drifting away once it&#x27;s orbital period matches the length of an earth day.<p>It&#x27;s like a kind of &quot;friction&quot; where the daily rotation of the Earth tries to speed up the monthly rotation of the moon.

can someone explain:<p>&gt;They’re also the most efficient type of space propulsion, maxing out around 80% efficiency. The most powerful use about 100 kW of power and are capable of generating about 5N of force (about 1 pound).<p>How can 80% efficiency get you just 1 pound of force if you put in 100 kW of power? This seems many orders of magnitude off!