Microthrusters For Small Satellites 75
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.'"
Re:Satellites in zero-gravity? (Score:4, Informative)
"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.
Weight vs.s. mass (Score:2, Informative)
Re:Weight vs.s. mass (Score:4, Informative)
http://en.wikipedia.org/wiki/United_States_customary_units#Units_of_mass [wikipedia.org]
The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams by agreement between the U.S., the U.K. and other English-speaking countries in 1959. Other units of mass are defined in terms of it.
The avoirdupois pound is legally defined as a measure of mass[15], but the name pound is also applied to measures of force. For instance, in many contexts, the pound avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force". The slug is another unit of mass derived from pound-force.
Re:I'm in a nitpicking mood. (Score:4, Informative)
Not really - ion propulsion trades "energy squared" for "propellant flow rate". So the large fuel tank (100 kg, say) has been replaced with a much smaller one, around 1 kg, for the same thrust. Here's the trade details:
1. Trading a 350 Isp Hydrazine thruster for a 35,000 Isp ion drive - it uses 1/100th the propellant for the same total impulse (thrust*time)
2. The thrust decreases dramatically typically - but for small satellite station-keeping that doesn't matter
3. The power requirement/N thrust gets ridiculous - from about 3.5KW/N to 350KW/N
Re:Hooray for meaningless "facts"! (Score:4, Informative)
Slashdotters are not rocket scientists... (Score:2, Informative)
In the torque-free environment of space, any amount of force will overcome inertia in an appreciable way. Gravity gradients, solar pressure, lunar and solar gravitational influences, atmospheric drag.
All they're saying is that 50 microNewtons is about the right size for small satellites, regardless of how many pounds-force that satellite might be at sea level. More than likely this is intended for attitude control maneuvers rather than orbit changes, but even in the latter case, small thrusts for long periods in space can be used.
And yes, I am an aerospace engineer.