
Why Do Lunar Satellites Eventually Crash into the Moon? [video] - ColinWright
https://www.youtube.com/watch?v=EadClM4Y45A
======
mabbo
Even after watching the video I didn't really get it. One of the comments made
it more clear though:

On Earth, the orbits decay because the satellite hits the atmosphere and slows
down, losing energy to drag. On the moon, satellites don't lose energy, but
their orbits change. The perturbations of the gravity field cause the
satellite to be moving faster but lower on one side of the orbit and higher
and slower on the other side. Taken far enough, the low side is lower than the
mountain the satellite slams into.

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gshubert17
Mass concentrations ("mascons") perturb orbits of lunar satellites. The Lunar
Orbiter is in a special "frozen" orbit in which the various perturbations
cancel each other, with the tradeoff that this eccentric orbit is not optimal
for photography.

EDIT: The auto-generated transcript feature enables one to read enough to
decide whether or not to watch the video.

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colechristensen
TL;DW from the video

>Spacecraft orbiting the Earth have remained in space since the 1950's and may
last for centuries more, but spacecraft orbiting close to the moon can crash
within weeks. The reason for this is the lunar gravity field is lumpy, with
geological features making the smooth orbits of space probes distort until
they hit the surface.

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antognini
One of my favorite papers asks the opposite question: Why do Earth satellites
stay up?

[https://arxiv.org/abs/1309.5244](https://arxiv.org/abs/1309.5244)

It turns out that the orbit of most satellites would be unstable were it not
for the quadrupole moment of the Earth's gravitational field which detunes
certain orbital resonances.

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zwerdlds
GRACE is/was the Earth-centric counterpart. I believe there may be a more
modern variant as well.

[https://www.nasa.gov/mission_pages/Grace/overview/index.html](https://www.nasa.gov/mission_pages/Grace/overview/index.html)

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geocrasher
Somehow I knew before clicking that this was going to be a Scott Manley video.
I love that guys channel, it's always so good. Even his less good stuff is
still good!

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HNLurker2
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baybal2
That's the guy who does quick time stuff at Apple

