Thousands of years later, an immoral archeologist named Professor Rudolph Karloff uses a special gas to awaken the mummy in what seemed to be an undead state. The Ancient Astronaut is then forced to do his bidding, but once the villain is captured by the Super Friends, the Ancient Astronaut escapes in his spaceship, presumably returning to his homeworld.
Little is known about the physiological makeup of the Ancient Astronauts. They apparently had what humans would consider Superhuman Strength and durability. Little can be told about their physical appearance either, since the Mummy of Nazca was covered in mummy wrap.
Their technology was far more advanced then humans even of the 20th century. Nazca's spacecraft for example, was a rocket presumably capable of interstellar space travel. This isn't nessasarilly true though, as it is possible that the ship is designed to function for thousands of years, and it can take that long to travel such interstellar distances.
That being the case, there would most likely be some on-board suspended animation device. It's also possible that Ancient Astronauts have long life-spans, making it possible for them to survive the journey. In an instance like that one would assume there is some sort of atmospheric recycling system on board, so that the Ancient Astronaut doesn't run out of air. That is assuming the Ancient Astronauts are not self sustaining and actually do need to breathe.