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ESA Moves Forward on New Electric Engine
museumpeace writes to tell us the ESA is reporting that they have confirmed the principle behind a new space thruster. Plasma Double Layers, first discovered by Australian researchers Christine Charles and Rod Boswell, may help to develop a new electric engine that gives more thrust than traditional engines while still maintaining efficiency. From the article: "In essence, a plasma double layer is the electrostatic equivalent of a waterfall. Just as water molecules pick up energy as they fall between the two different heights, so electrically charged particles pick up energy as they travel through the layers of different electrical properties."
My work here is dung.
Because these are very low thrust engines, they can't hold a candle to gravitational forces. Where they shine in interplanetary and stationkeeping (orbit and orientation) applications.
-everphilski-
Would the article submitter PLEASE not call ion engines "traditional thrusters"?
Now back to thrusting my girlfriend traditionally.
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I can't wait to put one of these bad-boys in my Civic!
In essence, a plasma double layer is the electrostatic equivalent of a waterfall. Just as water molecules pick up energy as they fall between the two different heights...
Water molecules do not pick up energy as they fall. There potential energy is simply converted into kinetic energy. However, they had the energy all along in the form of potential energy.
Energy source for the SSME is combustion (Hydrogen and Oxygen)
4 3.html ... even 10*5 times more thrust is only 5 newtons (read: not much). Scale it up to a SSME sized engine and your talking maybe 25-50 newtons. SSME thrust is measured in MILLIONS of newtons.
Energy source for this engine is electricity, or rather an energy potential... solar cells, nuclear power plant, etc.
Two different concepts. Two different ballparks. While the article states that this method will deliver "many times more thrust" than ESA's "SMART-1" thruster (70 mN, thats mili-newtons) http://www.aoe.vt.edu/~cdhall/Space/archives/0003
So basically, different tech that won't scale to drive a vehicle out of a gravity well. But it is useful for orbital/stationkeeping/interplanetary maneuvers if you have the time.
-everphilski-
Read about this on the BBC article, with diagram This morning... Sounds like it's greatest use will be in deep space missions. It still hold potential for other use if we can find a more efficient way to use it.
-Khyras
The real question is: How do these thrusters stack up to MPDTs (Magnetoplasmadynamic thrusters)? The article is light on technical details like Isp, engine life, potential design issues, fuels, etc. MPDT is a great upcoming technology. But if this new tech can best it by having a shorter development track and equivalent performance, then let's leapfrog the MPDT technology altogether! :-)
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The ion engines rely on the same principle of accelerating propellant through its electromagnetic properties. Plasma is an ionic gas, and propellant is gas too. The only difference I could imagine is that the method of ionization itself produces thrust. Is this indeed the source of higher energy efficiency? The description of two levels sounds like two varying magnetic fields which cause magnetically charged particles (plasma) to accelerate, and the divergence sounds like magnetism applied to aerodynamics. Perhaps this is another source of higher efficiency. If so, this really is groundbreaking.
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You must be new here.
I think that's the point of the design. The ions can be accelerated without the need for being attracted by cathode plates or wire mesh at the back, as is done now.
I would hesitate to call this a "very low thrust" engine, since 100kw is somewhere around 140 horsepower.
Thrust is not measured in kilowatts (or horsepower, or any unit of power). It's measured in units of force, like Newtons.
I'd say you're comparing apples to oranges, but it's even worse than that. How is force related to energy? By the equation Energy = Force * Exhaust Velocity. The higher your exhaust velocity is (and on mass-efficient rockets like these, it's huge), the lower your thrust is for the same energy input. Other posters have already pointed out how many orders of magnitude more power typical chemical rockets use, but those huge ratios actually *understate* how much more thrust they produce.
The principle was popular in particle accelerators for a while - I worked at Daresbury some time back, which was a 20 MeV tandem accelerator. It's cheap and easy. A variant, only with reversed electrical fields, was used in old-fashioned thermionic valves. In that configuration, they were termed deflection grids. CRTs use the same technology to steer electrons towards the correct place on the screen.
Not sure why anyone would need to prove the idea would work in space, since we already use the technology in vaccuum and we already know tandem accelerators can produce greater acceleration than a single grid.
I would be much more interested in knowing if it were practical to ionize oxygen then use this technique to improve the oxygen/nitrogen ratio in the engine. If you could, it would improve engine efficiency and may help in reducing the complexity of the engine electronics and mechanics.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
That's what Bussard Hydrogen collectors are for.
(Astronomers are, as a rule, mystified by plasma-dynamic events, leading them to talk about "hot gases", "stellar plumes", "galactic jets", "magnetars", "dark matter", "dark energy", and worse. For most, their only exposure to anything like plasma in school was an unphysical mathematical construct called MHD, so they are worse off than if they'd skipped class. (Hawking is often quoted, with no trace of irony, saying "the greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.") For those of us even a little more familiar with real plasma effects, astronomical press releases are no end of hilarity.)
Plasma double layers aren't mysterious. They develop naturally as the diffuse particles containing ions tend toward equilibrium. Variation in composition, ionicity, and density in a diffuse plasma gather at boundary layers between regions, making the space between the boundaries much more uniform, and concentrating mass, electric fields, and current flow. Highly-stressed double layers tend to explode; on the sun they call it a "coronal mass ejection". On another star it may be called lots of things.
In one of those plasma ball toys, you can see double-layer tubes connecting the electrode in the center with the transparent ball. You see them because the current density is high enough to put the plasma it runs through in "glow-discharge" mode, exactly as in a neon sign or St. Elmo's Fire. The other two modes are "invisible" and "arcing". The former is common throughout the universe (and detectable only indirectly, as you might imagine) such as between the earth and the sun, between star systems, and even between galaxies. The latter is what you see in a lightning bolt, on the surface of the sun, or in one of those spotlights they used to use at movie premieres. Astronomical glow-discharge events (with the exception of earth's polar aurorae) are usually confused with "shock waves".
The most beautiful astronomical glow-discharging double-layer structure I know of is M2-9 in Ophiucus. "In this image, neutral oxygen is shown in red, once-ionized nitrogen in green, and twice-ionized oxygen in blue."
to the Variable specific impulse magnetoplasma rocket?
What I'm thinking about is that this "new" Ion engine has a higher thrust and/or a higher specific impusle than a standard Ion engine (like the one on Deep Space 1.) But how does it actually rate against the VASIMR style engine and does it have the flexibility of it? (That is, can it adjust it's SI/Thrust depending on the situation - orbital maneauvering vs. cruising.)
Bill
It's my Sig and you can't have it. Mine! All Mine!
Gonna nitpick here: one-over-r-squared ( 1/r^2 ) forces do NOT decrease exponentially with increasing distance. They decrease in proportion to ... one-over-r-squared.
You can be an atheist and still not want to succumb to some weird cross-over sheep disease -- AC
What "weightlessness" really is: the pressure gradients within your body are too small for your nervous system to measure. In fact, only on the ground are you feeling a net force close to zero: gravity minus the force of the ground pushing back on you (which is the ground minus the amount of gravity required to keep you on the surface in a circle as the planet spins). In space, you're missing the ground pushing back: only gravity is pulling on you, and nothing is pushing back.
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Cassini has to fire its main engines once every 400 days in order to flush corrosion from the cat beds that might clog the lines otherwise... This has never been much of a problem to do as small maneuvers can be planned without messing up the interplanetary trajectory.
Actually for interplanetary missions chemical rockets are far less risky than low thrust systems. This is because chemical rockets instantly change you from one safe trajectory to another.. low thrust engines make this change over several days and as a reult there are often periods where if the engine fails the spacecraft would be left on an unstable orbit that is likely to crash into something or be thrown into an escape trajectory. JIMO and Dawn both had major problems trying to design trajectories that always left enough time to recover from possible engine failures without crashing.
It all comes down to control authority... bigger thrust gives you more control authority and you can much more easily recover from unexpected trajectory perturbations.
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