IN JANUARY 2019, when a Chinese spacecraft called Chang'e 4 visited the Moon, the mission broke new ground, figuratively speaking, by landing on the far side of that orb, which is perpetually invisible from Earth and thus also out of direct radio contact. This meant communications had to be relayed by a satellite which had been cunningly located for the purpose at a place where the interaction of the gravitational fields of Earth and Moon meant it could orbit a point in empty space.
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