Scientists know that the telescope can become a telescope because it must realize the basic function of observing targets in different directions, and the signals collected by the main mirror must be effectively collected. Arecibo uses the similarity between a sphere and a paraboloid to look at different directions, and then uses a worrying line feed or a complex Gregory feed cabin to collect signals. Although the Gregory feed cabin works well, as mentioned above, this cargo is really too heavy, reaching several hundred tons. Whether it is an engineer or not, I guess it should be used for hoisting with corresponding technical difficulties. So some people think, when we are doing FAST, can we make the mirror into a paraboloid and converge it into one point at a time, without wire feed and bulky Gregory feed cabin? On the other hand, we can't make a fixed paraboloid at a time, so we can't observe celestial bodies in different directions, so we can try to make this paraboloid move.