The family speeds through space in the Jupiter 2, looking for familiar stars so they can chart a course for Alpha Centauri. Smith would prefer to go to Earth, and fights with Don over the astrogator, breaking it and causing the ship to fly out of control. Don manages to repair the instrument and stabilize the ship. Smith, however, continues to use every tactic he can to get back to earth. He blackmails John, and when that does not work, he takes matters into his own inept hands. In doing so, he mistakenly jettisons the ship’s entire fuel supply.
The Jupiter 2, no longer having enough fuel to reach Alpha Centauri or Earth, cannot find any other place to land. However, John remembers that there is a refueling barge nearby, so they stop and refuel. The radar picks up a few strange blips but no one really pays them any mind. Don thinks he may have seen a figure moving around outside, but he’s not really sure.
The ship once again sets course for Alpha Centauri. Smith tricks Penny into altering the controls to set course for Earth again, even though John has told them it is far too dangerous.
Smith is happy until he sees a green lady floating outside his window. Sadly, no one else saw her, and no one will believe him. Will stays up with Smith in case she comes back. She does indeed come back, but Will does not see her. The Robot does see her and translates her message as a love song for Smith. The song is interrupted as the Jupiter 2 heads for a collision course with the Earth’s sun. John and Don manage a “near miss” and save the ship. Seeing as how they have enough fuel, and that it’s closer, they decide to go to Earth after all. Everyone is excited, especially Doctor Smith.
That night, the green lady returns and hypnotizes Smith with her song. He comes out of the Jupiter 2 in a spacesuit to cavort with her. As it turns out, the green lady is really after the ship’s fuel, deutronium, which her species consumes. When the Robinsons discover what has happened to Dr. Smith, they alter course and save him. In so doing, they lose their chance of landing on Earth, and are once again lost in space.
- We get to hear how truly noisy the gate was, as Dr. Smith takes the lift to the lower level, while singing, "We're going back to Earth..." For some reason, they didn't overdub his voice here, to cover the physical noise of the gate sliding. They almost always overdubbed dialog during gate openings/closings, or the actors simply avoided speaking while it was in motion.
- The Alpha Control F-12 fuel barge and the landing sequence would later be reused in The Haunted Lighthouse - although the vessel would be a manned 'Lighthouse ship' of a different role. The vessels were apparently designed as interstellar 'fueling stations' for future colonization missions (in the same way that the 'Lighthouse ships' were designed as 'weather/mapping information stations'). Oddly, the station contains only fuel and nothing else in terms of spare parts or supplies or even a transceiver to communicate back to Earth. It is presumed that Alpha Control simply shot these stations out into space without ever wanting to keep track of them.
- This is the first time the Jupiter 2 has been in direct contact with Alpha Control since The Reluctant Stowaway. John Robinson, according to The Alpha Control Reference Manual, deposited a copy of the ship's log on the fuel barge which was found and detailed by an Alpha Control ship, and some more of the circumstances causing the loss of the ship became clear.
- The following episode produces some contradictions with the ending of this one, namely in the amount of fuel the Jupiter 2 has on board and how they were able to reach the following automated planet but not able to get to Earth (due to lack of fuel for maneuvering). If they did not have enough fuel for a course change, it seems impossible they could land and take off in the following episode The Ghost Planet.
- The mysterious green girl, unnamed in this episode, returns in The Girl from the Green Dimension, where we learn she is called Athena. Her catchphrase is the famous 'Handsome, pretty, handsome, Dooktur Smith!'
- There is some discrepancy about when exactly this episode is set (the time having been established midway through the first series as 1998). The Alpha Control announcer mentions that the ship was lost over a year ago. This makes the time as the end of 1998, 1999, or early 2000, but the vagueness of time references in the first season (it is not clear whether Return from Outer Space shows Christmas/New year 1997/8 or Christmas/New year 1998-9), make time continuity sketchy at best.
- There are animals capable of surviving in cold and vacuum, at least for a limited period. Tardigrades, a primitive form of anthropod, exist here on Earth and have survived the vacuum of low Earth orbit with no bad effects. A higher order, more complex animal like a human, especially one lacking an exoskeleton, would not last more than a couple of minutes under the conditions of interstellar space.
- We discover another species in the LiS Universe that eats deutronium fuel, the eponymous flora in "Attack of the Monster Plants."
- When discussing the lower-than-expected level of fuel in the barge, Prof. Robinson states that if there had been a leak, the fuel would still be moving past the barge. In fact, given that the fuel has been established to be a liquid, then at the low pressure of space it would almost certainly volatilize upon its escape due to the vacuum and blow out and away from the barge. Newton's laws of motion would then require the barge to move in the opposite direction, slowly but surely pushing it off-station, possibly by tens of thousands of miles even at a modest velocity of 1 ft/sec. The barge also must be heated or incredibly well insulated in order to keep the contents from freezing. Perhaps the first reason is the explanation why Athena's people hang around it - just to keep warm!
- Although getting scale and size right was never a strong point of the series, one can estimate the amount of fuel on the barge from its size relative to that of the Jupiter 2 which appears to be about 60-70 feet in diameter and perhaps 30 feet high at most. The barge has a "life saver" shape perhaps twice as high as the Jupiter with a diameter that's also about twice that of the Robinson's ship. A crude but reasonable upper limit guess for the volume of the barge would be 200,000 cubic feet or enough volume to hold over a million gallons. Since it's a quarter low that means Athena's people must have consumed about 250,000 gallons of it.
- The family does not spot an enormous glowing red ball of space dust until seconds before they are about to smash into it.
- If Earth is only 4 days away, why don't they head on back there, drop Smith off (it would be a relief to be rid of him), make needed repairs, and also gather needed supplies?
- Although Alpha Control manages to locate and contact the Jupiter 2, they in no way attempt to help them.
- This episode features a rare overhead shot of the Jupiter II as the fuel cells are jettisoned by Dr Smith.
- Telescopic photos of nebulae from NASA provide a realistic backdrop for the exterior view of outer space.
- This is the first of several background incidental music scores from regular Star Trek man, Alexander Courage.
- Will puts Don’s space gear away by opening the mysterious hatch between the glide tube and the freezing tubes. Maybe if Will had searched a bit more closely, he may have found a more useful item for their travels; like a Space Pod!! Nope, you won’t find that one till next season!
- Vitina Marcus plays the Girl from the Green Mist. She was also known for playing many Native-American roles on television, but is in fact Italian-Sicilian-American.
- Jonathan Harris’ space helmet has the back part cut out of it due to his claustrophobia.
- Don and Dr Smith fight each other for control of the astrogator. [Go Don, give it to that weakling Smith!] A split second before the spaceship careers out of control, watch the Robot as it prematurely lurches back away from the men.
- The Robot accuses Dr Smith of lying, who promptly removes its power pack, causing the automaton to slump over in typically de-activated state. Shortly after, the Robot is seen in erect posture. Smith walks away, but in the next shot, the Robot is now slumped over even greater than before.
- After Dr Smith changes course, we see the Jupiter II turn and exit from the screen top right. The spaceship goes into shadow near the end of the shot. What would cause that in space? Perhaps a miniature model J-2 being shot in a TV studio, flying away from a light source?
- When Dr Smith is discovered out in space with the girl of the green mist, the Robot exits the glide tube elevator and walks around to the rear of the astrogator. You can clearly see Bob May’s feet, using the Robot’s “bermuda shorts”.
- When Don rescues Smith from his spacewalk and brings him back inside the spaceship, the inner hatch door opens and Don and Smith enter without their space helmets.
- Dr. Smith attempts to change the Jupiter II’s flight path back to Earth instead of Alpha Centauri by grabbing the astrogator. He pulls the astrogator's control stick out causing the ship to go flying wildly through space. The simple solution? Don puts the control stick back in! Of course, it’s obviously just a simple click clack mechanism!!
- John maintains the Jupiter II’s destination as Alpha Centauri, but meekly gives in to Smith’s demands; promising him he will change course for Earth, only if Smith has the true coordinates. Surely they could be re-calculated later with help from the Robot?
- Dr Smith is somehow able to use his magnetic ring to change the Jupiter II’s course to Earth, even though the astrogator is locked.
- Why the hell is there a switch on the Jupiter II control panel that triggers the release of the deutronium cells?
- How is it that Penny has suddenly become a space navigator, capable of plotting co-ordinates without any problem, or more incredibly, not spotted by the “professionals” on the flight deck?
- Frustration abounds as Will fail to notice the green lady, as he faces away from the viewport. Even when Dr Smith emits his high pitched yelp, Will doesn’t immediately turn around; he just asks him what’s the matter?…
- As sound cannot travel in a vacuum, plus the apparent lack of communication device strapped to the green girl whilst floating in space, it seems unlikely for either Dr Smith or the Robot to hear anything that she says.
- The Robot tells Smith that he sees the green lady, but that she does not compute. Then suddenly it launches into a detailed diatribe saying that her language is a mathematical progression, to which he can now suddenly translate!
- The Jupiter II encounters the fuel barge just in time. Amazing how the fuelling station is shaped to fit the Robinson's vessel perfectly. All Alpha Control's space ships must be saucer shaped…
- At one point Don says they are "on the edge of the Siribidus Galaxy." The closest galaxy to ours, Canis Major, is 25,000 light years away, meaning that even traveling at the speed of light it would take 25,000 years to get there. Moreover, if Earth is only "4 days away" then they must be very close to Earth. So the Jupiter 2 can't possibly be at the edge of another galaxy. It has to be somewhere in our galaxy, the Milky Way. Later when they miss Earth they are suddenly "exiting the galaxy headed for outer space." What is more likely meant is they are leaving the solar system. But they are already in outer space.
- After entering the solar system, Don says that their spaceship will pass by Uranus and Arcturus to reach Earth. Uranus, a planet in our solar system is about 2 billion miles away whilst Arcturus is a colossal star over 200 trillion miles away. Not only that, but they are approaching Earth by way of the sun, which means they should get to Earth well before they would ever come close to Uranus, since Earth's orbit is much closer to the sun than that of Uranus. Hmm, back to flight school, Major...
- How does Dr Smith manage to suit up and exit the air lock to join the green lady without being noticed by the men? That’s twice in the one episode they’ve missed secret visits on the flight deck! Maybe they’re busy in that other room, secretly building a Space Pod…
- Uh oh, here comes the Sun!!! During close encounters with Earth’s extremely hot star, it is standard regulations for all personnel to remain in their Alpha Control issued pyjamas and dressing gowns!
Dr Smith: “There is more than one way to skin a cat, dear boy” Robot: “There are exactly 37 ways” Smith: “And I’ve used them all!”
Dr Smith” [in high sing song voice to the green lady] – “I’m coming”
Dr Smith: [singing] “We’re going back to Earth, to wonderful, wonderful earth! A ball, I recall, as the best part of all, in all the universe!”
John: “I suggest we all go to bed after we eat. We’re gonna have a busy day tomorrow. Don and I have important maneuvering to do just before midnight” (!!!) [at least that explains why they never notice anyone that visits the control room – too busy maneuvering...]
Alpha Control voice: “You're exiting the galaxy headed for outer space. Good Luck".
Will: “Where are we going now, sir?” John: “We'll know when we get there, son. We'll know when we get there”
- "You bloated blimp!"
- "You clumsy clump!
- "You clanking clot!"
- "You are a deplorable dummy!"
- "You lily-livered, lead-lined lummox!"
- "You scurrilous scatterbrain!"
- "You blithering booby!"
- "Oh, the pain! The pain!"
- Dr. Smith tells The Robot that his "green lady" has green hair and green eyes, however, Lorelei's hair (if she has any) cannot be seen and her eyes are brown.
- Marta Kristen as Judy Robinson* Billy Mumy as Will Robinson* Angela Cartwright as Penny Robinson* Jonathan Harris as Dr. Zachary Smith