Synopsis by Hal Erickson
With the Jupiter 2 still unable to take flight, the Robinsons place their hopes on a small two-person "space raft" constructed by John (Guy Williams) and Don (Mark Goddard). It is hoped that this vehicle will enable at least two of the space travelers to return to Earth and seek help. But when the raft is commandeered by Will (Bill Mumy) and Dr. Smith (Jonathan Harris), it ends up landing several million miles short of its goal! The "reactor core" in this episode is actually a familiar prop from another Irwin Allen TV project, Voyage to the Bottom of the Sea.