Title and Author - SF short about the Moon being fake.

[airbolt]

The short story i'm looking for goes like this.

Astronauts training for a Moon Orbit are training in a mechanical simulator . Essentially they fly many simulated missions in a huge stage set. When the simulator capsule goes behind the moon , the windows shut to simulate it. The moon is a huge prop and only modelled on the light side - it resembles a tennis Ball cut in half from the other side.

NASA are not telling the astonauts when the real mission is. They dont know if they are flying for real or a sim. Then on one simulation , the windows on the capsule fail to close and the astronauts see the " back" of the moon as hollow - they go completely mad!

Anyone recognise it?

[Tom Braider]

"Ideas die hard" by Isaac Asimov

[airbolt]

thank you!!!!! :)