On 1/21/19 9:57 AM, k7lxc--- via TowerTalk wrote:
Howdy, TowerTalkians --
The recent Chinese moon landing on the dark side has me wondering how they
communicate from back there. Since we're talking line of sight frequencies with no
atmospheric scattering or repeater relay capabilities, what's going on? Inquiring minds
want to know. Tnx!
Relay satellite in a halo orbit at L2. L2 is on the far side of the
Moon, about 450 million km from Earth (the Moon is around 385 million km
from Earth)
https://en.wikipedia.org/wiki/Halo_orbit
Although we talk about it as a round circular orbit in a plane, in
reality the orbit is more like the edge of a Pringles potato chip. It's
not planar. There's a whole family of stable orbits that look like 3D
lissajous figures.
For what it's worth, there's also Moon libration, and some tall
mountains near the Lunar south pole.. if you land there, you're
technically on the far side, but the mountain is high enough to see over
the edge, helped a bit by diffraction. There's also schemes to use
diffraction from within Aitken Basin for comm without a relay (perhaps
in an emergency, if your relay satellite dies)
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