Lunatron (1963)

In an October 1963 paper, William Escher, with the Future Projects Office at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, wrote about the "Lunatron," an electromagnetic accelerator that would take advantage of the moon's lack of an atmosphere and low gravity to launch payloads to Earth, across the Solar System, and beyond. The name Lunatron recalls synchrotron electromagnetic accelerators used in particle physics.

A cargo capsule or manned spacecraft would ride the electromagnetic Lunatron track attached to a trolley. Escher proposed that a Lunatron be used to speed low-acceleration electric-propulsion spacecraft out of cislunar space on planetary exploration missions. In defending the need for new space transportation methods, he argued that

it is not enough to seek marked improvements in propulsion system types with which we are already familiar. New and unexplored kinds of propulsion must be conceived and objectively evaluated and then - with time - reevaluated. It may indeed turn out that when interplanetary flight is a fully routine endeavor, the modes of propulsion then in use could hold some real surprises. . .from the perspective of today.

The concept of launching cargoes and passengers off the moon using an electromagnetic track originated with Arthur C. Clarke, who first wrote about it in 1950 in the pages of the Journal of the British Interplanetary Society. The 1954 book The Exploration of the Moon, written by Clarke and illustrated by artist R.A. Smith, depicted such a device (image above). Eight years later (April 1962), Clarke published "Maelstrom II," a science fiction story based on the concept. Escher explained that he was unaware of Clarke's priority when he began his Lunatron work. After learning of it, however, he engaged in a "helpful correspondence" with the British author and spaceflight thinker.

Escher noted a limitation on the Lunatron's speed: "the centripetal acceleration resulting from the circular path imposed on the spacecraft as it is retained upon being accelerated to above circular velocity on the Moon-fixed track." As they passed lunar orbital speed (1.7 kilometers per second), trolley and payload would tend to rise away from the track. Lunar escape speed is, however, 2.4 kilometers per second, so they would need to be held down so acceleration could continue.

As the Lunatrom continued to accelerate the trolley, passengers would feel "down" shift by up to 180°, from toward the moon's center to directly away from it. Escher proposed that they "be mounted in swivel support systems to compensate for this effect." The faster the trolley moved, the more acceleration the passengers would feel in the new "down" direction. In effect, the Lunatron would become a centrifuge and the payload would become its gondola.

Escher calculated that, for a 50-to-500-kilometer-long Lunatron for launching cargoes and passengers from the moon to the Earth, acceleration would top out at a tolerable eight times the pull of Earth's gravity. However, for larger systems - such as the 870-kilometer Lunatron for throwing payloads out of the Solar System - acceleration could reach 60 Earth gravities.

The MSFC engineer proposed siting the Lunatron for launching beyond the Solar System at the center of the moon's Farside hemisphere. Launching there at local midnight would take advantage of the orbital speeds of the moon around the Earth and the Earth around the Sun, slashing the velocity the Lunatron would need to provide from 42.5 kilometers per second to just 12 kilometers per second. This would in turn limit the acceleration to which its passengers would be subjected.

Building a long Lunatron track, Escher wrote, would constitute "an almost overwhelmingly large construction job," with "extensive cuts. . .through mountains [and] fills or bridge structures. . .across low areas." He maintained that the magnitude of the construction task, combined with the large amount of electricity needed to accelerate payloads, would mean that the Lunatron would probably not become available until "well after the start of colonization of the Moon."

"On the Utility of the Moon in Space Transportation: the Lunatron Concept," William J. D. Escher, Engineering Problems of Manned Interplanetary Exploration, pp. 102-112; paper presented in Palo Alto, California, September 30-October 1, 1963.