Zombies of the Stratosphere (1952 serial film)

This 1952 Republic serial involves a plot where Martians decide to remove Earth from it's orbit (sending Earth spiraling into Space) so Mars can be positioned to take it's place. Both tasks are to be completed with Hydrogen Bombs. The 12 chapter serial film was latter spliced into the feature film 'Missile Monsters'.

Plot
Larry Martin (Judd Holdren), a leader in the Inter-Planetary Patrol, detects a rocket coming to Earth. He takes to the air in his jet-powered rocket suit and helmet to investigate and discovers Martian invaders, led by Marex (Lane Bradford). Since Mars is now orbiting too far from the Sun and its ecology has been dying, the Martian invaders want to swap Earth's and Mars' orbits, so Mars will then be closer to the Sun. They plan on achieving this by using hydrogen bomb plans stolen from Earth scientists to cause the two planets' orbits to swap, using specifically placed atomic explosions on both worlds. Martin also learns the Martians have Earth accomplices in the forms of the traitorous Dr. Harding (Stanley Waxman), and two gangsters, Roth (John Crawford) and Shane (Ray Boyle), who bedevil him and his associates, Sue Davis (Aline Towne) and Bob Wilson (Wilson Wood).

The Martians set up a base in an underground cave that can only be reached from underwater, where they begin constructing their bomb; and make a remotely-controlled robot to supplement their human associates in acquiring supplies and funds to complete the project. Eventually, Larry and his comrades gain the upper hand: Marex kills Harding when he attempts to surrender, Roth and Shane are killed when Larry turns the robot against them, and the Martians are brought down in flames in their rocket ship after a furious stratosphere raygun battle with Larry in his own spacecraft. Marex's Martian aide, Narab (Leonard Nimoy) survives the crash and tells Larry where to find the underwater cave with the activated bomb in it. Larry arrives in time to defuse the bomb just seconds before it would have exploded.