Engineers test an idea for a new hovering rover
A levitating vehicle might someday explore the moon, asteroids, and other airless planetary surfaces

Date:
December 21, 2021
Source:
Massachusetts Institute of Technology
Summary:
MIT aerospace engineers are testing a concept for a hovering rover
that levitates by harnessing the moon's natural charge. The design
uses tiny ion beams to charge up the vehicle and the surface
underneath, with little power needed. Such an ion boost could
be strong enough to levitate a 2-pound vehicle on the moon and
large asteroids.



FULL STORY ========================================================================== Aerospace engineers at MIT are testing a new concept for a hovering
rover that levitates by harnessing the moon's natural charge.


========================================================================== Because they lack an atmosphere, the moon and other airless bodies such
as asteroids can build up an electric field through direct exposure
to the sun and surrounding plasma. On the moon, this surface charge
is strong enough to levitate dust more than 1 meter above the ground,
much the way static electricity can cause a person's hair to stand on end.

Engineers at NASA and elsewhere have recently proposed harnessing this
natural surface charge to levitate a glider with wings made of Mylar,
a material that naturally holds the same charge as surfaces on airless
bodies. They reasoned that the similarly charged surfaces should repel
each other, with a force that lofts the glider off the ground. But such
a design would likely be limited to small asteroids, as larger planetary
bodies would have a stronger, counteracting gravitational pull.

The MIT team's levitating rover could potentially get around this size limitation. The concept, which resembles a retro-style, disc-shaped flying saucer, uses tiny ion beams to both charge up the vehicle and boost the surface's natural charge. The overall effect is designed to generate a relatively large repulsive force between the vehicle and the ground, in
a way that requires very little power. In an initial feasibility study,
the researchers show that such an ion boost should be strong enough
to levitate a small, 2-pound vehicle on the moon and large asteroids
like Psyche.

"We think of using this like the Hayabusa missions that were
launched by the Japanese space agency," says lead author Oliver
Jia-Richards, a graduate student in MIT's Department of Aeronautics
and Astronautics. "That spacecraft operated around a small asteroid and deployed small rovers to its surface.

Similarly, we think a future mission could send out small hovering rovers
to explore the surface of the moon and other asteroids." The team's
results appear in the current issue of the Journal of Spacecraft and
Rockets. Jia-Richards' co-authors are Paulo Lozano, the M. Alema'n-Velasco Professor of Aeronautics and Astronautics and director of MIT's Space Propulsion Lab; and former visiting student Sebastian Hampl, now at
McGill University.



========================================================================== Ionic force The team's levitating design relies on the use of
miniature ion thrusters, called ionic-liquid ion sources. These small, microfabricated nozzles are connected to a reservoir containing ionic
liquid in the form of room- temperature molten salt. When a voltage is
applied, the liquid's ions are charged and emitted as a beam through
the nozzles with a certain force.

Lozano's team has pioneered the development of ionic thrusters and has
used them mainly to propel and physically maneuver small satellites
in space.

Recently, Lozano had seen research showing the levitating effect
of the moon's charged surface on lunar dust. He also considered the electrostatic glider design by NASA and wondered: Could a rover fitted
with ion thrusters produce enough repulsive, electrostatic force to hover
on the moon and larger asteroids? To test the idea, the team initially
modeled a small, disk-shaped rover with ion thrusters that charged up
the vehicle alone. They modeled the thrusters to beam negatively charged
ions out from the vehicle, which effectively gave the vehicle a positive charge, similar to the moon's positively charged surface.

But they found this was not enough to get the vehicle off the ground.

"Then we thought, what if we transfer our own charge to the surface to supplement its natural charge?" Jia-Richards says.



==========================================================================
By pointing additional thrusters at the ground and beaming out positive
ions to amplify the surface's charge, the team reasoned that the boost
could produce a bigger force against the rover, enough to levitate it
off the ground. They drew up a simple mathematical model for the scenario
and found that, in principle, it could work.

Based on this simple model, the team predicted that a small rover,
weighing about two pounds, could achieve levitation of about one
centimeter off the ground, on a large asteroid such as Psyche, using a 10-kilovolt ion source. To get a similar liftoff on the moon, the same
rover would need a 50-kilovolt source.

"This kind of ionic design uses very little power to generate a lot
of voltage," Lozano explains. "The power needed is so small, you
could do this almost for free." In suspension To be sure the model
represented what could happen in a real environment in space, they ran
a simple scenario in Lozano's lab. The researchers manufactured a small hexagonal test vehicle weighing about 60 grams and measuring about the
size of a person's palm. They installed one ion thruster pointing up,
and four pointing down, and then suspended the vehicle over an aluminum
surface from two springs calibrated to counteract Earth's gravitational
force. The entire setup was placed within a vacuum chamber to simulate
the airless environment of the moon and asteroids.

The researchers also suspended a tungsten rod from the experiment's
springs, and used its displacement to measure how much force the thrusters produced each time they were fired. They applied various voltages to
the thrusters and measured the resulting forces, which they then used
to calculate the height the vehicle alone could have levitated. They
found these experimental results matched with predictions of the same
scenario from their model, giving them confidence that its predictions
for hovering a rover on Psyche and the moon were realistic.

The current model is designed to predict the conditions required to
simply achieve levitation, which happened to be about 1 centimeter off
the ground for a 2-pound vehicle. The ion thrusters could generate more
force with larger voltage to lift a vehicle higher off the ground. But Jia-Richards says the model would need revising, as it doesn't account
for how the emitted ions would behave at higher altitudes.

"In principle, with better modeling, we could levitate to much higher
heights," he says.

In that case, Lozano says future missions to the moon and asteroids could deploy rovers that use ion thrusters to safely hover and maneuver over
unknown, uneven terrain.

"With a levitating rover, you don't have to worry about wheels or moving parts," Lozano says. "An asteroid's terrain could be totally uneven, and
as long as you had a controlled mechanism to keep your rover floating,
then you could go over very rough, unexplored terrain, without having to
dodge the asteroid physically." This research was supported, in part,
by NASA.

========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Jennifer
Chu. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Illustration_of_hovering_rover_that_could_levitate_by_harnessing_the
moon's_natural_charge ========================================================================== Journal Reference:
1. Oliver Jia-Richards, Sebastian K. Hampl, Paulo
C. Lozano. Electrostatic
Levitation on Atmosphere-Less Planetary Bodies with Ionic-Liquid
Ion Sources. Journal of Spacecraft and Rockets, 2021; 58 (6):
1694 DOI: 10.2514/1.A35001 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211221102805.htm

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