This demo shows how a satellite moves around the earth and moon under the gravities. We assume that the satellite, the earth, and the moon are in the same plane. We also assume there is no friction and the earch and moon are prefectly round.
y1 and y2 are the positions of the satellite relative to the earch and
moon. The earth resides on (-miu, 0) and the moon resides on (1-miu, 0)
always. The constant miu is defined as
Mass_of_Moon / (Mass_of_Moon + Mass_of_Earth) = 0.012129.
The trajectory of the satellite is a periodic curve and the period is around 6.192169.
This demo is based on the example 10.6 in "Introduction of Computation Method", by Cuiwei Xu, 1985, Higher Education Press.