The Chinese are hoping to land a lunar lander called 'Chang'e-4' on the far side of the Moon. It was (supposedly) inserted into lunar orbit with a rocket burn yesterday. The successful execution of this maneuver was publicly announced. https://spacenews.com/change-4-spacecraft-enters-lunar-orbit-ahead-of-first-ever-far-side-landing/ But the always-interesting Jonathan McDowell alerts us to a deepening mystery by retweeting this: https://twitter.com/coastal8049/status/1073142174466764800 Ever since around the time of the lunar orbit insertion burn, amateur space trackers can no longer hear the Chang'e. Details in this blog: https://skyriddles.wordpress.com/2018/12/13/eating-static-from-the-moon/ The blog's author suggests three possibilities: "What could be going on? 1. Nothing, the mission is proceeding normally and they just decided to turn the beacon off and/or have changed their standard operating procedures. 2. Chang'e 4 is emitting signals on a frequency that is not coordinated with the ITU. [International Telecommunications Union] 3. Something happened during or after the LOI [lunar orbit insertion] that now prevents the beacon from operating or effectively radiating toward Earth and China is figuring out how to resolve the issue before reacting publicly." Time will tell.
It's starting to look like the Chang'e-4 signal has been reacquired. But mystery remains. Its lunar orbit appears to be in a plane perpendicular to the Earth such that the vehicle's signal isn't cut off by going behind the Moon. It can be heard for its entire orbit. That's not a bad orbit for landing something on the far side of the Moon since the orbit should be stationary relative to the 'fixed' stars as the Moon rotates below it (yes, the Moon rotates, again relative to the 'fixed' stars). But... that's not the plan the Chinese announced, which was an energy-efficient insertion burn that would have produced an orbit edge-on to the Earth, and it would have taken a huge delta-V to achieve an orbit 90 degrees to that. So suspicion was raised that another vehicle might be emitting on Chang'e's frequency. But the new orbit isn't consistent with the communications satellite the Chinese have in orbit around the Moon to communicate with Chang'e when it's hidden on the far side of the Moon. So right now it isn't clear what is going on. https://skyriddles.wordpress.com/2018/12/14/x-marks-the-orbit/#more-396
