The rocket changes from a Polaris missile to an ICBM when launched at the start of the show.
The spaceship seen on the ground on Venus doesn't look anything like the capsule seen earlier in flight.
When Crane is on Venus he and Nelson speak to each other via radio in a normal conversation. At is minimum distance from Earth, it would take a radio signal a little over 2 minutes each way to communicate.
When the missile is launched there is stock footage of a Polaris missile shown. The Polaris had a diameter of around 54 inches, far too small to accommodate the extra roomy capsule used by the astronauts.
When the alien first talks to Capt. Crane, it tells him that they are from "the double planet Centaur." This makes no sense; the actor presumably was supposed to say the "double star."