Zarkov's rocket ship is a homemade rocket, invented by Dr. Hans Zarkov. Zarkov was criticized by his colleagues for thinking that he could build a rocket that would fly to other planets, but it turns out that he was right the whole time. The ship makes it to the planet Mongo on its first try.
Zarkov's rocket is filled with gauges and dials, and there's a big contraption in the middle that sparks. There is comfortable seating for three. Oxygen is provided from a tank situated near the main control bank. The oxygen must be turned on by hand, during flight. ("Chapter 101: The Planet of Peril")
In flight, Dale Arden says that the rocket ship is "rushing away from the Earth at the speed of light", but she is probably exaggerating. ("The Amazing Interplanetary Adventures of Flash Gordon) On the way back from Mongo, a radio announcer makes a more reasonable estimate, saying that the craft is "moving toward the Earth at the incredible speed of at least 1200 miles an hour." ("Flash Gordon's Trip to Mars)
It's possible to open the hatch of the ship during spaceflight, for example, to throw a time bomb out of the ship before it explodes, but care must be taken, because it's very windy outside. ("Chapter 113: Rocketing to Earth")
To land the ship, occupants must engage a powerful counter-magnet at the proper moment. If the counter-magnet isn't used correctly, the ship will be smashed to scrap. In the comic strip and The Amazing Interplanetary Adventures of Flash Gordon, they don't engage the counter-magnet, and the ship is smashed to scrap. ("Chapter 101: The Planet of Peril") Retarding rockets can also be used for the same purpose. ("Flash Gordon's Trip to Mars")
The ship is equipped with a telescope, which operates like a submarine periscope. It's not always possible to know exactly where the ship will land; in fact, it's possible to land without being sure which continent you're on. Flash, Dale, and Zarkov are pleasantly surprised to discover that they've landed in the United States when they open the rocket's door. Given that uncertainty, it's a remarkable coincidence that they happened to land right in front of Ming's palace in Chapter 101: The Planet of Peril.
By the time Flash, Dale and Zarkov make a return visit to Mongo in a bid to combat the so-called Purple Death being spread by Ming's death dust, Zarkov has made several alterations to his rocket ship, no doubt after having been inspired by Ming's own rocket ships. The most obvious difference is the addition of a weapon on the ship's nose for offense. For defence, Zarkov has fitted his ship with a Transparency Screen, which renders it (and its occupants) completely invisible for limited periods of time. The door is no longer a standard one on hinges with a regular door handle, but is a more robust, dual-layered mechanism operated by a lever. The interior of his ship is much larger, and no longer has an oxygen tank which needs to be manually turned on and off. Finally, Zarkov's ship is also now fitted with a bed, useful if one of the occupants should faint or wants a sleep during a long flight.