Eric's Beijing Diary

Just saw the news. The Chinese unmanned moonship "Chang'e" has successfully entered the earth-moon transfer orbit. The regimen they have designed for this thing is impressive. They put it into orbit around the earth, and then set up a series of ever increasing concentric circles to bring the apogee to a point where the craft can switch to an earth moon orbit. The obvious intent of this is to save fuel. They are playing the earth's gravity off against the moon's gravity until they can make the exchange. This is really an ingenious plan. They don't say why they did it this way, but it seems to me the reason is obvious. Once a satellite is in orbit, it doesn't need fuel. The moon has been traveling around the earth for many years without using any fuel. So by keeping the craft in an ever increasing earth orbit until it is able to make the short jump to the moons orbit, they can get the craft to the moon with very little fuel. It's a much longer trip that way, but who cares? Most of the journey is being powered by the following simple words of wisdom by Isaac Newton:

Every body is attracted to every other by a force that is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them.