I actually agree with the other reviews here. This episode is a mess, almost at bad as "The Questing Beast" although its free of cheap sentiment. What's to like? Not much but Dr. Smith's green, curly hair and strength is chuckle-worthy!!! The Hippies are awful, like left-overs from on of the 60's Beach Party Movies.
And yes, were cheated out of a Jupiter 2 lift off at the end.
Not as funny as the writer thought it was, it bores but in a terrible way.
Even the usually spot-on Robot is given NO funny lines!

That one just gave me a headache.

My sensors indicate this will easily be one of the weirdest LIS episodes you will ever see. Dr. Smith gets even creepier when he sprouts a funky hairdo and muscles (and becomes the lust interest of a hot blond). The girls occasionally appear on-screen, say some odd things, and then exit stage left. Space hippies on space choppers spew random goofy dialog. The Robot is perpetually confused and learns he can't trust his sensors. And all of that is in the part of this episode that makes sense! If you like corny and campy humor in a disjointed plot, this is for you. Danger Will Robinson! Special Effects: Uh, can anyone say 6th grade theater? Very funny stuff.
Plot: Well, sort of.
Acting: Gut wrenching and mesmerizing. And that's just the Robot!
Action: Air punches and those famous LIS transition explosions! Yes!!!

This episode was downright painful to watch. I'm guessing it came out after Easy Rider.