NOTE: This spoiler was sent in by Tesseractgirl
The movie opens with some exposition about how the space program used to use chimps and the most famous of these “Space Chimps” is Ham. We then realize that the narrator for this is a ringmaster at a circus who introduces Ham III, the grandson of the famous Ham. Ham III (who I will refer to as Ham as he is for the rest of the movie) is the “monkey cannonball” and works in the circus getting shot out of the cannon every night. Ham is shot out of the cannon very high in the sky and tries to grab the moon. He starts to show off when he falls and begins to tell himself that he needs to keep his chin down and arms out when he lands. (Important later) He misses the target when he lands and falls into a drum set for the band. He gives a thumbs up to let everyone know that he’s ok.
The next scene is about a remote vehicle that the space program has sent out to explore planets being sucked into a wormhole and landing on an alien planet. The planet is very colorful with bi-pedal aliens in a village. We meet Zartog who is the curmudgeon of the village who everyone hates. The remote vehicle crash-lands onto his house right behind him. The vehicle starts to try to “probe” him, but then it plays a message with information about earth, including a scene of Las Vegas and Zartog is in awe. He wants his planet to be like earth. Then the vehicle changes from a “ship” into a kind of mobile suit with arms to grab things. (Kind of like the one from the first Alien movie). Zartog starts to terrorize the village, sticking them in this liquid (I forgot what they call it) that freezes them solid to make them obey him.
Then we return to Earth at the space program as three scientists are explaining to the Senator about how they lost the probe in a wormhole and that they cannot send a human into the wormhole because it might kill him. They agree that the best thing to do would be to send the chimps up instead. The scientists take the senator to see their chimps, and the Senator says that this screw up was so big and expensive that they need to save face with some good publicity. He sees a picture of the original Ham and says that they need that chimp. The scientists explain that Ham I has been dead for over thirty years, but that he has a grandson.
We flash back to Ham III at the circus in his trailer with Houston, a chimp who knew his grandfather and who is like a father to Ham now. The caretaker of the chimps from the space program comes to the circus to take Ham back to the center, but Ham doesn’t want to go, and pushes her out of the trailer. Houston tells Ham that he is missing an opportunity to do a lot more with his life and really be something, but Ham doesn’t care. Of course, it doesn’t matter what Ham wants, because his trailer is lifted by helicopter and taken to the space station.
Ham is put in a room with the other chimps: Titan (a strong military type who really knows his job), Luna (the required love interest), and Comet (a technical wizard who was responsible for getting the chimps to have a chance to go into space by hacking into the space program’s computers and putting up a picture of the chimps.). They are all excited to meet Ham, but all Ham can think about is getting back to the circus. He sees his chance when Luna explains to him that they (the chimps) will be demonstrating some jet packs in a few days. Ham’s face lights up and he decides to go through with the training. It is also revealed that only three chimps can actually go on the mission, and Comet will have to stay home.
There is a training montage where we basically learn that Ham is a natural at this, and that to go through the wormhole the chimps will face upwards of 10 G’s. (Ham is able to do this easily while the other’s pass out.)
On the day of the test, Ham forgets all about the controls for the jet pack, and causes a bunch of rockets to crash into each other like dominoes. The Senator is furious over this, and vows that if the chimp mission into the wormhole is not successful he will turn the space program into a “paint your own plate” store.
Before the chimps are launched into space Comet gives Luna a radio made from a banana (which Ham quips is a “bananaberry”). He says that they should be able to use it even after they are through the wormhole.
The three chimps, Titan, Luna, and Ham finally get into space. As foreshadowed earlier, they hit 10 Gs going through the wormhole, and everyone but Ham passes out, and he is forced to take the controls to crash land on the planet.
After the crash, Ham opens the hatch and goes outside. Luna follows him and is initially upset about how Ham is doing so many dangerous things, but she is finally overcome with the fact that they are on a new planet.
In the meantime, we get to see what Zartog has been up to. He has been very busy freezing people, and using them to decorate his Vegas rip off mansion. On of his cronies points out that they are building his palace at the base of a huge volcano that is filled with that liquid that will freeze everything solid. But Zartog states that he has already figured out how to divert the flow to the village below before the volcano is scheduled to erupt on “Triple Sun-day”. (The day when the planet’s three suns align). One of Zartog’s general’s report that another “metal beast” (what they call the ships) has landed, and it is bigger than the one that Zartog is now controlling. After Zartog dips the original general for insinuating that Zartog is not powerful, he commands a bunch of guys to go and get the new metal beast.
Luna and Ham continue to explore the world, and Ham’s knowledge of the circus proves useful when Luna wants to touch a flower and Ham tells her about a clown at the circus who had a box with a flower just like the one they are looking at but his box opened up to have a snake jump out at you. Luna dismisses this and touches the flower anyway, and the flower promptly turns into a huge snake like creature with a huge toothy mouth. Several more creatures pop up from the ground, and Luna and Ham are done for when the creatures suddenly run away. Luna and Ham turn around to see a huge army coming at them with alien people on foot and some riding these flying creatures that resemble ocean rays. They run for it while some of the aliens capture the ship with Titan still on it.
Luna and Ham run into a jungle, where Ham teaches Luna to use her instincts and swing on vines to escape. Of course, the vines are really more kinds of snake creatures. But they continue swinging because the flying ray alien riders are still after them. They manage to get away by handing a snake vine to the rider guys, but then they discover that they swung themselves over the edge of a very high cliff and are going to fall. Ham gives Luna the “chin down, arms out, opposable thumbs in” speech and they both land. Ham lies still for a bit after falling, but is revealed to be all right after Luna runs over and starts to cry about how she needs him.
The space station scientists exposit that the ship with the chimps did go through the wormhole, but they cannot get a signal to know exactly where it is. Comet and Houston realize that they cannot get a signal on the bananaberry, but Comet figures out that with more power he can get them to work to a point where he can hear everything that Luna and Ham are doing on the planet, but they cannot hear them. The space program scientists also explain that the ship is programmed to automatically return to earth in 24 hours. This means that Luna and Ham need to get back to the ship by then or they will be stranded on the alien planet forever.
Titan finally wakes up and meets Zartog. Zartog wants to dip him immediately, but Titan is smart enough to realize that he has had the training to know how to work the “metal beast” that Zartog is using to control his planet. Titan basically hints around that there is much more the suit is capable of and that he can teach Zartog. Zartog realizes this is a much better idea than just freezing him right away, and gives Titan a reprieve.
Luna and Ham meanwhile, meet a little alien whose head lights up like a light bulb when she is scared. They nickname her Kilowatt, and she agrees to lead them to their ship. She also explains how Zartog whipped out her village. She tells them that the journey is dangerous, and there are monsters.
They run into a group of aliens that look like gummy bears. There is a cute scene were the gummy aliens group together to form a gummy Ham and Ham and his gummy alter ego dance together. Of course, the fun is cut short when Zartog’s men attack again, but the gummy men form themselves into a giant hamster wheel and wheel them to safety.
They approach the cave that they must go through that Kilowatt tells them has a dangerous monster in it. The monster looks like a giant tadpole with a huge toothy mouth, and they have to run from it. Since Kilowatt is terrified, her head starts to glow and the monster can easily see them. While the monster is stuck in between two rocks, Ham tells Kilowatt how to calm down so her head will stop glowing. It works, and with her newfound bravery, Kilowatt goes to distract the monster so that Ham and Luna can escape and she is eaten by the monster.
Ham and Luna fall out of the cave and into the “Cloud of Id”. There is a mockery of a psychiatrist’s office, where Luna is like the doctor, and Ham is the patient. Ham reveals that he has always been insecure living in the shadow of his grandfather, and that he has never really thanked Houston for all that he has done. Houston and Comet listen in and Houston is touched.
Ham and Luna make it to Zartog’s mansion. Zartog captures all three of the chimps and is about to dip them when Titan tricks him again telling him that he can be more powerful if he pushes a bunch of buttons. This turns out to be an ejector seat and it flings Zartog from the machine, giving the chimps all the time they need to get back to their ship before it leaves.
But as they are in the ship, Ham sees Zartog, back in the probe, dunking people left and right. He feels bad, and decides to stay. Luna says she’ll stay with him. Titan says that they are crazy, and will be stuck on the planet forever. We see Ham and Luna watch the ship take off, presumably with Titan on it, but Titan stays to help them.
After a big fight scene where Kilowatt reveals herself to be alive (the monster doesn’t chew she tells us) Zartog is dipped into the freezing liquid and is frozen solid. The chimps are happy that they helped save everyone, but sad that they are not going home.
At the space program, Comet and Houston figure out a way to get more power into their radio so that Luna and Ham and Titan can hear them. They fly around the building with the jet packs and finally get the bananaberry to work. They explain to the space chimps how to build a new rocket home out of the probe. They figure out that they can use the force of the volcano that is about to explode to propel them into space.
All of the aliens on the planet help in gratitude for being saved. (The chimps even “unfroze” them by breaking the freeze off with a hammer). Right before they are about to take off, Comet tells them that they will need a nose cone. Ham comes up with the idea to use the frozen Zartog.
The volcano explodes and the chimps are in space again headed back for the wormhole. Ham is again the only one to stay awake during the massive Gs in the wormhole, and it’s up to him to land the ship.
Ham manages to crash the ship with Luna’s help when she wakes up, right in the middle of a press conference where the Senator is announcing that the space program is now a paint your own plate store. But the Senator is made to look the fool when the chimps land safe, are all alive, and are heroes. They also make the space program look like heroes for training them.
Ham and Luna confess their love for each other, and then all the chimps stand in front of the crashed ship looking heroic.