From the start, NASA planned to launch different types of Apollo lunar landing missions. The first would simply be delivering men to the Moon’s surface. Subsequent missions would extend surface operations and turn the focus from a technological mission to a scientific one, as the agency gained confidence in its technology and astronauts. These later scientific flights would demand the astronauts have some way of traveling around the surface, since covering more distance would increase scientific return. NASA began exploring different types of astronaut mobility aids, and one technology proposed by Bell Aerosystems in the wake of Apollo 11’s landing was the one-man lunar flyer, a jet-propelled platform astronauts could use to fly around on the Moon.
Early Lunar Mobility Concepts
Investigations into possible lunar surface mobility vehicles predated the Moon landings, and in some cases even NASA. As early as 1951, engineers at what was then the National Advisory Committee for Aeronautics’ demonstrated mobility using a small, compressed air jet-supported platform in free flight. The key to this design was its use of the user’s balance system, making it a "kinetic balance" or "body motion" system. The same reflexes we use to walk and stand upright were applied to a proof-of-concept demonstration, and the user shifting his weight forwards, backwards, and sideways was enough to maneuver this flying platform.
With the Apollo program already underway in the mid-1960s, lunar mobility studies began fitting in with lunar mission architecture. Engineers at the Marshall Space Flight Center developed the mobile laboratory known as MOLAB in 1964. In 1966, engineers from the Aeronutronic division of the Ford Motor Company presented NASA with a series of worm-inspired roving vehicles. Both of these vehicles were designed to be carried to the Moon stowed in the Lunar Module, and both doubled as a secondary roving habitat and workspace. They were best suited to long duration missions that would see astronauts traveling far from their landing site to explore scientifically and geologically interesting locations.
But intermediate missions would need a shorter range mobility system like Bell's lunar flyer, a minimalistic system that could afford astronauts a way to cover more ground while saving their time, energy, and consumables for science operations.
The winning configuration for the lunar flyer
Lunar Flyer Design Considerations
Foremost in guiding Bell’s investigation into a possible lunar flyer was the vehicle’s practicality. It had to be storable for up to three months before use, since technicians would have to install the flyer in its stowed position inside the Lunar Module well in advance of launch. It would have to be deployed by astronauts wearing gloves and bulky pressure suits. Once deployed, it would ideally be able to make multiple flights, up to 30 per vehicle, covering a total distance of between 10 and 15 miles. And because it would be manned, it would have to be extremely stable in flight with the astronaut in full control of all movement around his axis of pitch, yaw, and roll.
These basic parameters left the door open for Bell Aerosystems to consider a variety of vehicle configurations, with reliability as the guiding factor. Not only did the vehicle in itself have to be reliable, the system would ideally increase the lunar mission’s reliability on the whole. Part of the flyer’s role in extending surface operations was to give astronauts a quick way to return to their Lunar Module in an emergency.
Early versions of the lunar flyer focused on a vehicle with a seat for the astronaut. With a central fuel tank and side mounted outboard engines, this layout minimize the flyer’s overall volume while the short and squat stature increased its structural efficiency and stability in flight. The astronaut could control the vehicle by pivoting and throttling the engines.
Though structurally sound, a sitting layout turned out to be a poor choice from a human factors standpoint. Sitting in a bulky pressure suits proved to be awkward and uncomfortable, and necessitated complicated ingress and egress procedures. To simply the astronaut’s ease of use, Bell looked at standing configurations for the flyer, designs that would allow astronauts to just step onto a platform and begin flying around the Moon.
The standing configuration turned out to have some major advantages in addition to the ease of use. Human legs, for example, are great natural shock absorbers, especially in a reduced gravity environment; this was among the reasons Grumman took seats out of the Lunar Module and had astronauts standing while landing on the Moon. Bell considered a variety of vehicle arrangements for the standing flyer, primarily changing the position of the engines and control terminal relative to the astronaut and varying the method of flight control.
The one man lunar flyer in action
Bell Aerosystems’ Lunar Flyer
The lunar flyer design Bell Aerosystems determined was ideal for short term exploration missions was a single-man standing system. It was the design with the highest score in reliability and practical factors, and was the only design to adhere to NASA’s "three nines" mandate for reliability; it would work perfectly 99.9 percent of the time.
The standing flyer had two throttleable side mounted engines similar to the Lunar Module’s reaction control system engines, that could pivot for directional control. A foreword terminal covered in a multi-layered thermal shield protected the astronaut from the engine exhaust, and allowed him to easily climb onto the platform and start flying. Its four legs were cantilevered; there were no moving parts or sliding joints that risked sticking during use. An optional add-on was a pallet attached in front of the control terminal, for scientific instruments, collected samples, or possibly a second astronaut.
The lunar flyer was designed to be stored, unfueled, outside the Lunar Module, and then unpacked and deployed by the crew once they were safely on the surface. Once it was unloaded and set up, the crew would connect propellant fueling lines to the flyer’s service door on the front of the vehicle from the Lunar Module’s descent stage. With levels monitored by fuel quantity gauges on the astronaut’s control terminal, the flyer would be fueled from the remainder of the LM’s descent engine tanks. Once fueled, the lines would be disconnected and the payload pallet installed.
The astronaut would then unlock the engines and climb onto the rear platform, securing himself with restraining straps just like the ones found inside the Lunar Module. On his terminal would be two hand controllers. The right one would control engine throttle and the left movement around the axes of pitch, yaw, and roll. Safely strapped in, the astronaut would take flight, gaining a unique vantage point above the lunar surface for visual surveys and shortening his time spent traveling from the landing site to a science site and back again.
The first lunar rover as part of the Apollo 15 mission
Rovers Over Flyers
Bell submitted its report on the one-man standing lunar flyer just after Apollo 11 successfully landed on the Moon. Building off this initial mission’s success, the report saw no reason to doubt anything would change the lunar flyer’s standing as a useful land reliable system to assist astronauts on later Apollo flights.
But as we know, NASA never sent a lunar flyer to the Moon. Three months before Bell’s study was completed on April 7, 1969, Wernher von Braun established a Lunar Roving Task Team to consider astronaut surface mobility aids. Von Braun and others on the task force firmly believed a more traditional vehicle would be the best asset on a lunar mission, and shortly after the task force was established, Boeing was awarded a contract to build the rover. Work began in 1970, and proceeded quickly. The first of three lunar rovers reached the Moon with Apollo 15 in 1971, and was considered a complete success.
Sources: “A Brief History of the Lunar Roving Vehicle” by Mike Wright, Bob Jacques, and Savio Morea; “One Man Lunar Flying Vehicle: Final Report” prepared by Bell Aerosystems, Co., 1969.