In contrast, Lozano's microthruster design adds little to a satellite's overall weight. The microchip is composed of several layers of porous metal, the top layer of which is textured with 500 evenly spaced metallic tips. The bottom of the chip contains a small reservoir of liquid—a "liquid plasma" of free-floating ions that is key to the operation of the device.
To explain how the thruster works, Lozano invokes the analogy of a tree: Water from the ground is pulled up a tree through a succession of smaller and smaller pores, first in the roots, then up the trunk, and finally through the leaves, where sunshine evaporates the water as gas. Lozano's microthruster works by a similar capillary action: Each layer of metal contains smaller and smaller pores, which passively suck the ionic liquid up through the chip, to the tops of the metallic tips.
The group engineered a gold-coated plate over the chip, then applied a voltage, generating an electric field between the plate and the thruster's tips. In response, beams of ions escaped the tips, creating a thrust. The researchers found that an array of 500 tips produces 50 micronewtons of force—an amount of thrust that, on Earth, could only support a small shred of paper. But in zero-gravity space, this tiny force would be enough to propel a two-pound satellite.
Lozano and co-author Dan Courtney also found that very small increases in voltage generated a big increase in force among the thruster’s 500 tips, a promising result in terms of energy efficiency.
"It means you have a lot of control with your voltage," Lozano says. "You don't have to increase a lot of voltage to attain higher current. It's a very small, modest increase."