It is a flying saucer-style rover that can hover over the surface of the Moon and other surfaces without an atmosphere, such as asteroids. This “flying saucer” would be powered by the electric field built up from direct exposure to the Sun and the surrounding plasma. In the absence of an atmosphere, solar exposure creates a charge capable of levitating dust more than a meter above the lunar surface, an energy that can be harnessed.
The rover would be made of a material called Mylar, which acquires the same charge when struck by sunlight. Small beams of ions would be used to charge the vehicle to increase the natural charge on the surface, thus counteracting gravity. Mylar is polyethylene terephthalate, the material from which mylar shaped balloons for children are made.
“With a levitating rover, you don’t have to worry about wheels or moving parts,” says Paulo Lozano, an aerospace engineer at the Massachusetts Institute of Technology (MIT).
“The terrain of an asteroid could be totally uneven, and as long as we had the mechanism in place to keep the rover hovering, we could traverse uncharted and rugged terrain without having to physically dodge the asteroid.”
Ion thrusters are nothing new, as the German physicist Hermann Julius Oberth (1894-1989) already published the idea in his work Die Rakete zu den Planetenräumen in 1929. The ion thrusters used are called liquid-ion ion sources and use small nozzles that have already been proven to propel satellites into space. The actual fuel is molten salt which, when interacting with the electrical charge, is shot out of the nozzle as a beam. The charge is transferred to the surface to supplement its own natural charge.
Although no prototype has yet been built, mathematical models seem to indicate that it should work, as it would provide enough thrust for the rover to take off from the ground. Newton’s third law takes care of the rest.
However, they have experimented in the laboratory with a small vehicle, the size of the palm of the hand, weighing about 60 grams. In this minirover, ionic-liquid ion sources have been used to create enough electrostatic force for levitation. The necessary force would depend on the size of the planetary body that one wanted to explore.
“This type of ionic design uses very little energy to generate a lot of voltage,” says Lozano. “The energy needed is so small that you could do this almost for free.”
One of the big challenges with the lunar module was getting its weight down as low as possible, and this led to extremely thin and vulnerable walls. The Saturn V itself was getting rid of the stages that it was using after its launch, three in total. In general, for trips to the Moon or any other place in space, weight plays against it, so the vehicles sent are tried to be as light as possible to save energy and/or reduce costs. In this case, in which an ionic-liquid ion source would be used, much of the energy would be obtained naturally.
Analysis of this type of propulsion only shows that levitation is a possibility. For the rover to rise to a respectable height, more models will be needed, the researchers say, although calculations verify the idea.
This “flying saucer” could also explore large asteroids, such as Psyche 16, a rocky place that is difficult to access. Asteroid Psyche 16 has an economic value several tens of times greater than the entire Earth. It was discovered in 1852, measures 226 km in diameter and is located at a distance of 370 million kilometers from our planet, in the asteroid belt between Mars and Jupiter. But what makes it so valuable? It is made exclusively of iron, nickel, and most likely platinum and gold.
“We plan to use it on missions like Hayabusa, which was launched by the Japanese space agency,” says Oliver Jia-Richards, a space technology researcher at NASA and MIT. In this mission, the Hayabusa probe went to the small asteroid Itokawa, using ion propulsion. In the collection of samples, three mini landers —Minerva— of little more than half a kilo of mass were used, but without using this technology.
“That ship operated around a small asteroid and deployed small rovers on its surface. Likewise, we believe a future mission could send small floating rovers to explore the surface of the moon and other asteroids.”
Furthermore, analysis of data from the ion detector experiments on the Apollo missions and the electron reflectometer of the Lunar Prospector mission confirm the presence of suprathermal charges on the Moon, with resulting electric fields on the order of 10 V /m. A field large enough to levitate regolith—in fact, Surveyor landers observed 10-micrometer grains levitating up to a meter in height. It is thought that this surface charge would be responsible for the transport of dust in planetary bodies without an atmosphere and could explain phenomena such as the unusually smooth surface of Atlas.
With this theoretical framework, for now it is just an idea, but with theoretical possibilities supported by objective data.
The study has been published in the Journal of Spacecraft and Rockets, under the title Electrostatic Levitation on Atmosphere-Less Planetary Bodies with Ionic-Liquid Ion Sources . The concept the engineers are up to resembles a flying saucer, a small disk with four legs and the “engine” in the center. On the MIT page itself they have recreated an artistic image of what the curious artifact could be like.
