Aeronautical engineers at MIT are testing the concept of a lunar rover that floats on the Moon’s surface by harnessing the electrical charge it generates. In the absence of an atmosphere, the surface of the Moon and similar celestial bodies can build up an electric charge through direct exposure to sunlight. On the Moon, the resulting electric field can be strong enough to lift the fine dust on its surface to heights of more than a metre. MIT researchers have used this phenomenon to move their planned lunar rover.
The lunar rover is shaped like a classic flying saucer and uses ion beams to charge the vehicle and also to amplify the electric field on the surface. This provides an economical way to maintain a repulsive force between the lunar rover and the surface. The researchers calculated that an ion propulsion system using this principle should be powerful enough to float a small vehicle weighing less than a kilogram on the Moon or a small planet like Psyche.
The small-scale ion thrusters of the lunar rover designed by the research team are attached to a fuel tank containing room-temperature molten salt. When the tank is energised, ions are ejected from the liquid in the form of a jet of radiation through the thruster nozzles. According to the researchers’ tests, a 10-kilovolt power source would be needed to lift a rover weighing about one kilogram to within a centimetre of the surface of Psyche. On the Moon, this would require 50 kilovolts.
For practical testing, the research team created a 60-gram test sample in the shape of a palm-sized hexagon. Two of the ion thrusters were mounted upwards and four were mounted towards the surface. The prototype was then placed in a vacuum chamber, suspended on two springs to simulate the lower gravity and lack of atmosphere on the surface of a small planet. The researchers also attached a tungsten rod to the springs to measure the thrust of the ion thrusters. During the experiment, the prototype performed as expected, and the results suggest that a similar device could even lift off from the surface on the Moon.
The propulsion system could theoretically be capable of lifting such a device much higher, but these tests have not yet given researchers a clear answer as to how the lunar rover would behave at higher altitudes, but the concept is very promising in several respects: it could easily float over various surface obstacles and, due to the complete absence of moving parts, would probably require orders of magnitude less maintenance than its wheeled counterparts. MIT’s research is partly funded by NASA.