Ep 9. Collision of the Planets

An alien civilization dispatches four "social burdens" to a planet whose eccentric orbit threatens their world. These four people can become productive citizens by destroying this world. The aliens warn the "earth colony" there - but the Robinsons need at least a week to get their ship spaceworthy, and the aliens have given them exactly "one half of one diurnal cycle." Compounding the matter is Smith's accidental inhalation of alien fumes that give him the strength of dozens of men - for short periods of time.