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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.'"
Do we have satellites in zero-gravity? Hmmm.
How large, in zero-gravity, is a 2 pound satellite?
http://en.wikipedia.org/wiki/United_States_customary_units#Units_of_mass
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.
Depends on the application. Day to day when I'm buying lunch meat not really, but if it's a technical issue or article then yes, it would be a problem. Technical and scientific articles have a much greater need for correctness. Getting these things wrong can lead to significant and expensive problems.
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
while (sig==sig) sig=!sig;
There are three factors that are important for any propulsion system:
1) Thrust - check
2) Wheight - probably very low, hopefully not too important
3) Specific impulse - how much fuel do you need to get that thrust? The higher the velocity of the exhaust, the less fuel you need for a given thrust. And that is exactly what is missing from all sources. Who knows what they had to compromise with in order to scale the whole thing down?
Thank you for being the first person to post something useful and constructive on the thread. Shame I had to scroll through the usual pedantic know-it-all minutiae about units and mass and weight to get to it.
I swear, /. is going severely downhill in the quality of discussion these days.
Drill baby drill - on Mars
All satellites need station keeping thrusters to maintain a stable orbit. Because the Earth is shaped like an oblate spheroid, orbits are not stable. There is a particular amount of thrust needed per pound of satellite to maintain the orbit. Their calculations probably assumed some typical orbit and the station keeping thrust needed.
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.
if you had a sense of humour, you'd be familiar with the sound a 2 pound satellite makes over your head (even in a low earth orbit)
You can't handle the truth.