On October 16, 1997, the United States is gearing up to colonize space. The Jupiter 2, a futuristic saucer-shaped spacecraft, stands on its launchpad undergoing final preparations. Its mission is to take a single family on a five-and-a-half year journey to an Earth-like planet orbiting the star Alpha Centauri.

The Robinson family consists of Professor John Robinson (Guy Williams), his wife Maureen (June Lockhart), and their three children: Judy (Marta Kristen); Penny (Angela Cartwright); and Will (Bill Mumy). The family is accompanied by U.S. Space Corps Major Donald West (Mark Goddard). The Robinsons and Major West are to be cryogenically frozen for the voyage, and they are set to be unfrozen when the spacecraft approaches its destination.

Dr. Zachary Smith (Jonathan Harris), Alpha Control's doctor, is revealed to be a saboteur working on behalf of an unnamed nation, with which he communicated under the code name Aeolis-14-Umbra. After disposing of a guard who catches him aboard the spacecraft, Smith reprograms the Jupiter 2's B-9 environmental control robot (Bob May, voiced by Dick Tufeld) to destroy critical systems on the spaceship eight hours after launch. Smith becomes trapped aboard at launch, however, and his extra weight throws the Jupiter 2 off course, causing it to encounter asteroids. This, plus the robot's rampage, causes the ship to prematurely engage its hyperdrive, and the expedition becomes hopelessly lost in the infinite depths of outer space. Smith's selfish actions and laziness frequently endanger the expedition, but his role assumes less sinister overtones in later parts of the series.
Season 1
The astronaut family of Dr. John Robinson, accompanied by a pilot and a robot, set out in the year 1997 from an overpopulated Earth in the spaceship Jupiter 2 to travel to a planet circling the star Alpha Centauri. The Jupiter 2 mission is sabotaged by Dr. Zachary Smith – an agent for an unnamed foreign government – who slips aboard the spaceship and reprograms the robot to destroy the ship and crew. However, Smith is trapped aboard, and his extra weight alters the craft's flight path and places it directly in the path of a massive meteor storm. Smith manages to save himself by prematurely reviving the crew from suspended animation. The ship survives, but the damage caused by Smith's earlier sabotage of the robot leaves the crew lost in space. The Jupiter 2 crash-lands on an alien world, later identified by Will as Priplanus, where they spend the rest of the season and survive a host of adventures. Smith remains with the crew and acts as a source of comedic cowardice and villainy, exploiting the eternally forgiving nature of Professor Robinson.


Main cast
1967 publicity photo showing cast members Angela Cartwright, Mark Goddard, Marta Kristen, Bob May (Robot), Jonathan Harris, June Lockhart, Guy Williams and Billy Mumy.

    Dr. (Professor) John Robinson (Guy Williams) – The expedition commander and the father of the Robinson children. Robinson is an astrophysicist who also specializes in applied planetary geology.
    Dr. Maureen Robinson (June Lockhart) – A biochemist who is often seen preparing meals, tending the garden, and helping with light construction while adding a voice of compassion.
    Major Don West (Mark Goddard) – The pilot of the Jupiter 2.
    Judy Robinson (Marta Kristen) – The eldest child of the Robinsons.
    Penny Robinson (Angela Cartwright) – The middle child. An imaginative 11-year-old who loves animals and classical music. Early in the series, she acquires a chimpanzee-like alien pet which she names Debbie (in spite of the characters' use of masculine pronouns when referring to it) and is usually referred to as the "bloop" for the sound it makes.[3]
    Will Robinson (Bill Mumy) – The youngest child. A precocious 9-year-old in the first season, he is a child prodigy in electronics and computer technology. In the 2018 TV series he is also very knowledgeable about geography.
    Dr. (Colonel) Zachary Smith (Jonathan Harris) – Acting as Alpha Control's flight surgeon in the first episode, he is later referred to as a "doctor of intergalactic environmental psychology",[4] an expert in cybernetics and an enemy agent. His attempt to sabotage the mission strands him aboard the Jupiter 2.
    The Robot (Bob May, voiced by Dick Tufeld)[5] – A B-9 model environmental control robot who has no given name. The machine was endowed with superhuman strength and futuristic weaponry, and additionally often displays human emotions. The Robot was designed by Robert Kinoshita.[6]