This huge golden cannon was designed by the villainous Moonlander General Lunaris to aid in his plan to lead the armed forces on the Moon to attack and conquer the Earth; the simple concept of the device was that passengers would climb into the large shell-shaped space capsule and be shot off by the cannon into space in the direction of Earth.
Lunaris was eventually forced to abandon this line of research in his efforts to develop space travel, as all his tests concurred that "no living thing" could survive the pressures involved in the blast. His plans of space war were able to go forward without the Cannon when he managed to nick the plans of the Spear of Selene from Della Duck in 2019, but he kept the large machine in his personal hangar, where Donald Duck later managed to use it to flee from Lunaris's grasp, defying the supposed lethality of the process — although it is worth noting that Lunaris's tests were conducted with Moonlander physiology in mind, whereas Donald is an Earther, and quite a tough one at that.
It is, of course, a reference to the method used in Jules Verne's seminal anticipation novel De la Terre à la Lune by Earth men to get to the Moon, making it a sly joke that it is here an inhabitant of the Moon who developed the technology for the opposite journey. The claims about no living things being able to survive the pressure also poke light fun at the fact that, while more or less plausible at the time the novel was written, the process as described by Verne is now understood to be impossible for human beings to survive.