posted on Jan, 4 2019 @ 04:37 AM
Well, all the bluster about landing/no-landing aside, the Chinese have actually accomplished something equally interesting with this mission. Prior
to the landing of the Chang'e 4 probe, the Chinese established the Chang'e 4 Communications Relay Satellite in a "Halo Orbit" around Earth's L2
Lagrange Point. The unstable orbit is established in such a way to be 'around' the L2 point, not exactly 'on' the L2 point. This allows the
communications relay satellite to stay above the Moon's horizon so it has a line of sight to Earth while at the same time having a line of sight to
the Chang'e 4 probe on the far side of the Moon.
It's quite an accomplishment, and frankly not one which, to the best of my knowledge, even the USA has been successful at establishing to date. The
USA has established craft at Lagrange points before (mainly for Sun observation), but not the L2 point behind the Moon. And I don't believe any of
these were "Halo Orbits", but rather stationary.
I think many people here realize the far side of the Moon isn't really "Dark" (as some often refer to it). It get's as much sun as the side which
faces Earth due to its rotation, but that 'far' side never faces Earth so communications to craft on the far side of the Moon was not possible until
the craft re-emerged above the Moon's horizon and could establish comms with line of sight to Earth. For the early Apollo missions as an example,
there was a comms blackout as the LEM transited the far side of the Moon. Any object on the far side surface would be in a similar comms blackout,
but permanently (or at least until an orbiting satellite picked up the data and relayed it)...until now. Now, China can have real-time comms with
their probe on far side of the Moon.
I thought this might be interesting for some of you.