[TowerTalk] Off topic quesiton

[jimlux]

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)