Defender II (Atari 2600)

Alien marauders are attacking your planet. They're kidnapping resident humanoids and turning them into mutants! You pilot your ship along the planet surface, blasting away. But first you go for the Landers - the most treacherous of the aliens. You race to the nearest Stargate and whoosh! You experience that eerie - time warp - feeling as you're transported to the other side of the planet. Only you, with the help of the Stargate, can save the planet against attack!