Walking on the Moon is no small feat. Apollo spacesuits weighed about 180 pounds (82 kg), which essentially equaled the full body weight of the average astronaut. Even in the Moon’s lower gravity, exploring in these suits was hard work.

Even before Apollo 11’s successful landing, NASA was considering how astronauts on later missions could get around the Moon more efficiently. But before they planned to use lunar rovers, NASA was seriously considering using Lunar Flying Units, or LFUs, to jet the astronauts around.

How do you fly on the Moon?

In early 1969, NASA issued contracts to two competing groups to conduct seven-month studies exploring the feasibility of LFUs. The plan was to run the units on leftover fuel from Apollo’s landing craft, the Lunar Module (LM).

The contracts’ recipients were Bell Aerosystems Company and North American Rockwell, both of which had already done work for Apollo. Bell had designed the Lunar Landing Research Vehicle used to train astronauts to land safely on the Moon, as well as the LM’s ascent rocket, which carried astronauts back to the Command/Service Module (CSM) after surface exploration was complete. North American (which after a 1967 acquisition became North American Rockwell) had built the CSM, Apollo’s “mothership” responsible for carrying the crew to and from the Moon.

Both companies had also already dabbled in the idea of flying machines. By 1961, Bell had developed a “rocket belt,” which it originally marketed, unsuccessfully, to the U.S. Army (its 5 gallons (19 liters) of fuel only offered 20 seconds of flight time). And in 1964, North American Aviation had developed a proposal for a flying platform that allowed an astronaut to traverse the lunar surface while standing upright, carrying a payload of tools, samples, or even his crewmate on an attachable tray.