His discovery of the belts named after him was pretty critical for the manned and unmanned space missions, especially the Apollo series. With their locations and intensities calculated out, all equipment is hardned against the radiation and spacecraft have trajectories to fly through their weak points.
According to Dr. Phil Plait of Bad Astronomy, the Moon-Landing Hoaxers will use the Van Allen Belts as proof that the the landings were faked since all astronauts would’ve died of radiation poisoning as they traversed through it. Rather odd they believe in what probes report from space while they just handed you the rope to hang them with in the argument. As I stated earlier, thanks to Dr. Van Allen (and the numerous other scientists involved), the belts were mapped out along with their radiation levels. Thus, the Apollo spacecraft only travelled through the weakest points so the astronauts were exposed to the equivalent to a couple chest x-rays.