Understand long sentence (no comma)

Solution 1:

You might cut up the sentence into small sentences each containing one idea or two, at most, and connect them through the use of key words and pronouns.

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.

This meant communications had to be relayed by a special satellite;
what was special about it was its location;
it had to be in the vicinity of a point in empty space;
the positioning of the satellite about such a point was cunningly achieved through exploiting the interaction of the gravitational fields of Earth and Moon so that the satellite would orbit the said point.