if you took a ride in any of the rockets, at the apex you'd see firsthand the earth is flat with no curvature. You need to be more than 1-1/2 earth radius altitude before the earth is visible edge-to-edge in your line of sight. At that distance, it may reveal itself to be a donut shape, or a cucumber shape, or maybe even round and flat. The moon looks round and flat, doesn't it?