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Microthrusters For Small Satellites
An anonymous reader writes "A research team led by Paulo Lozano at MIT's Space Propulsion Lab and Microsystems Technology Lab have shown off a microthruster array capable of powering small satellites. The tiny, flat design could obviate the need for bulky propellant tanks. '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.'"
How large, in zero-gravity, is a 2 pound satellite?
"zero-gravity" is usually used synonymously to mean effective weightlessness, neglecting tidal effects.
So, yes, there is plenty of gravity acting upon satellites in orbits, but they are in free fall, so there isn't a significant gravitational force experienced by the components of the satellite due to their accelerating reference frame. Thanks to our somewhat sloppy terminology, this is zero-gravity.