The Jupiter 2 was a United States spaceship launched by Alpha Control on October 16, 1997 on a five-year mission to a planet in the Alpha Centauri system. At the time of its launch, the Jupiter 2 was considered "the most sophisticated piece of hardware yet devised by the mind of man".
The ship was manned by the Robinson family: John, Maureen, Judy, Penny, and Will, along with pilot Major Don West and an Enviornmental Control Robot. The mission was sabotaged by stowaway Zachary Smith, and the crew became lost in space. ("The Reluctant Stowaway")
The Jupiter 2 was two stories high, with both floors connected via an elevator. Each level was operationally self-contained. ("The Reluctant Stowaway")
There was presumably also a Jupiter 1 (perhaps as an inside joke, in Irwin Allen's film "Five Weeks In A Balloon", which was produced just prior to Lost In Space, as the balloon's name was the Jupiter).
In the original pilot, the ship was called the Gemini 12, but this was changed to the Jupiter 2 ostensibly to avoid confusion or identification with NASA's manned space program. A possibly apocryphal story involves Irwin Allen showing the design of the ship to NASA, who then promptly told him what was wrong with it technically and then he changed the name in a fit of pique.
The original design for the ship had no lower living deck and the crashed ship was to have a large hole in the back hull opposite of the operator controls.
The ship is equipped with a sonic washer to handle routine cleaning jobs such as laundry. But in keeping with the morals and television code of the time, there are no bathrooms, showers, or toilets shown or indicated.
In the episode "Space Creature", the ship is shown to have a third deck below the living quarters that contains the ship's power core.
As is common in mass media science fiction, LIS often uses "fuel" and "propellant" interchangeably. The Jupiter 2 uses "deutronium" as a fuel, a liquid obtained from "concentrating certain radioactive ores" according to Prof. Robinson. The production team was probably thinking of deuterium, an isotope of hydrogen,specifically in the form of heavy water (deuterium oxide) used in fission reactors to slow neutrons, since deuterium itself is a gas under normal conditions. In "The Girl from the Green Dimension" the fuel reserves are accidently jetisoned by Dr. Smith and are shown as collections of cylinders floating in space. The substance used to propel the Jupiter 2 is never revealed.