In an effort to increase the dismal television ratings for their space launches, NASA decides to send an ordinary man into space, and Homer is chosen for the task.
The powers that be at NASA, distraught over low television ratings for their space launches, decide to improve them by putting a private citizen on their next space shuttle. After receiving an angry phone call from Homer, they decide he is their man.
- The story opens at the nuclear power plant where all the employees are assembled for the Employee of the Month ceremony. Homer has never been given the award and thinks today is his day, since all of his coworkers have been given it and it's written into their contracts. Burns and Smithers give the award to an inanimate carbon rod instead.
While watching television, Homer is flipping channels and when the batteries fall out of the remote, the TV is stuck on a station broadcasting a NASA space launch. Homer panics and Bart voices his objections but they are unable to change the channel. Bart finally pulls the plug on the TV.
At NASA, a group of promotion agents are meeting and lamenting their low ratings; the public just isn't interested in space missions. One scientist floats the idea of telling the public that all the monkeys they shot into space came back at genius-level intelligence but it's quickly dismissed. Another scientist shows the NASA director some of the more popular shows on television (chiefly Home Improvement and Married With Children) and the room gets an idea: they'll recruit an average American man to become an astronaut. While the contemplate a lengthy and expensive search -- at the taxpayer's expense -- Homer suddenly calls them and berates them for showing boring NASA missions on TV and also demanding to know why he can't get any Tang drink mix. When he flushes the toilet while still on the phone, the NASA reps realize they've found their man. They find Homer at Moe's Bar with Barney Gumble and ask if Barney wants to join NASA. He enthusiastically agrees, prompting Homer to beg them to take him too. One of the NASA guys hits them both with a sap, knocking them out cold.
Homer and his family travel to NASA HQ (presumably near Houston) for Homer's training. A press conference is held where the media are very skeptical of NASA's new promotional stunt. When Homer fields a question about the scariness of traveling into space, he replies that the only danger is if they land on the "planet of the apes." Homer suddenly realizes that the apes' world was actually Earth and yells about it in a parody of Charlton Heston. Barney suddenly groans and passes out.
When Homer shows up at the training facility he finds that Barney has already arrived and is suddenly in better shape since he quit drinking and started the demanding exercise regimen. Barney proves to be superior to Homer in every test of the training and is chosen. When a bottle of champagne is popped to celebrate and Barney takes a sip, he instantly returns to his disheveled alcoholic state, grabs a jetpack and launches himself drunkenly into the air, despite the champagne being non-alcoholic. He crashes and is run over by a truck. Homer becomes the winner by default.
Homer becomes nervous about the launch but Marge talks him into going as an example to their children and because he shouldn't throw away a big chance to do something important. Homer and two astronauts Buzz Aldrin (doing his own voice) and Race Banyon, are shot into outer space, ostensibly on a mission to study the effects of weightlessness on ants. On board, Homer opens a bag of potato chips which fly out in every direction. Banyon complains that the chips will clog the shuttle's instruments. Homer tells them he'll handle the problem and floats through the cabin, eating the chips before they can cause trouble. However, he loses control and smashes head first into a small aquarium containing the ants. They fly out in all directions, even behind the control panels, shorting out their instruments.
Back on Earth, Homer's family watch as the news broadcasts show the trouble aboard the shuttle. When newscaster Kent Brockman sees the live camera feed, he assumes the ants are giant and have taken over the craft. He immediately declares that the ants will come to Earth and conquer it, adding that a public figure like himself can help them enslave humanity. He later retracts his statement, saying he was hasty in coming to his conclusions.
On the shuttle, at the suggestion of guest musician James Taylor, a plan is formed to deal with the ants and potato chips. The crew and Homer will blow the hatch of the craft allowing the air to be sucked out of the cabin, which should take the ants and chips along with it. The maneuver is successful until Homer, having not strapped himself to his seat, is sucked out too. The astronauts haul him back in but the latch and the door cannot be secured. Banyon, in a fit of rage, tells Homer he's going to beat him. Homer grabs the nearest object to use as a bludgeon, a carbon rod handle. When he swings it to hit Banyon, it lodges in the door's latch. Banyon tells Homer that it might just be enough to close the hatch before re-entry.
The shuttle crew steer themselves back toward Earth. The rod holds and they make it, crashing into the roof of building hosting a reporters convention. Homer emerges from the craft, holding the rod victoriously. However, he is not given a hero's welcome; the public flocks to the rod, which is given a ticker tape parade. Homer laments that he wasn't recognized as a hero but Lisa gives him a pep talk, saying that he's one of a select few who have traveled into space.
The final shot of the episode is of the Space Child of 2001: A Space Odyssey, in a likeness of Homer, floating toward Earth. It's hit on the head by a Fox satellite and yells "D'OH!!".