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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."
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-
Imagine probe. Ok now imagine proe with nicely size Nuclear reactor in place of the big propellant tanks.
Now imagine voyager rebuilt with this technology and having the ability 30 years later to still apply thrust vectors.
Understand now? current thrusters are more volatile and are a crap shoot every time they fire them, espically on deep space probes that have not fired the engines in 15 years.
This has less chances of freezing up, only one valve to worry about and no nasty easy leaking hydrogen. This is something that is really cool for probes and long term missions.
Do not look at laser with remaining good eye.
Hmm, 100 kW. not bad for an electric thruster, but still only 134 horsepower. When compared with the Space Shuttle main engine's 12,000,000 horsepower, that isn't very much.
Ewige Blumenkraft.
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-
The plasma thruster is designed to deliver low amounts of thrust over long periods of time with low fuel consuption. They are best suited to use on interplanetary probes and that kind of thing, not for reaching escape veolcity.
One of the most interesting things about this new thruster (developed here at the ANU) is that by using the double layer the need for any metal parts coming in contact with the plasma is reduced. This greatly increases relabily through reduced erosion of the thruster.
See: http://prl.anu.edu.au/SP3/research/HDLT for more info
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
Actually, hydrazine chemical rockets these days are pretty much a solved problem. Cassini's main engine is not substantially different from the Apollo lander's main engine; IIRC, they're hypergolic hydrazine thrusters using helium to pressurise the tanks (and blow the hydrazine out). They're reliable and can cope with long periods of inactivity.
Of course, they're still chemical rockets, which inherently suck. But they're not nearly as shoddy as you make out.
Every time they fire the thrusters on a probe they hold their breath because the risk of not firing is higher than they like. espically on thrusters that need to be on off on off on off wait 5 years on off on off wait 3 years.... etc.. the more you use it the more you have failures. This setup reduces the failure potential significantly and offers a HUGE advantage of a long thrust period if you need it. Imagine a probe that after hitting the Heliopause that can point it's self in the direction of travel and then kick in the thrusters until all fuel is spent.. this would give it a nice kick to get going out there much faster. heck a voyager probe redesigned with these engines could pass voyager in 1/2 the time it took voyager to get where it is now. There is a huge increase in the amount of thrust (time) compared to the chemical setups.
rnted when you are out of argon you are done, but it takes much less argon to give you X grams of thrust than it does in a chemical rocket. (chem rockets certianly have a much bigger kick in the pants for a shorter amount of time though)
Do not look at laser with remaining good eye.
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.
1 HP = 747 Watts = 747 (1 Joule per Second)
Therefore, assuming no air-resistance, a 1hp rocket engine could lift 76 kilograms at one meter per second (3.6 km/hr).
Horsepower is merely a useful term to use because it's large, and it's more commonly used that kWatts. Although really, watts make more sense. I believe Europeans use kWatts to describe engines as well.
1kW = ~1.4hp.
Ok, a few more answers to your question that I haven't seen yet:
The plasma drive is good because it's efficient. A chemical rocket is terribly inefficient, so you have to carry a lot more fuel then you'd like to for a given amount of ability to thrust.
We already have an ion drive that's very efficient, but it's got a *very* low rate of thrust - essentially, it can't accelerate quickly. It's got great mileage, but you it'll take you 10 minutes to go from 25 to 75. The new drive still has great mileage. It's slightly bigger, but you can go from 25 to 75 in only 2.5 minutes (or whatever). To carry the analogy a bit further, a chemical rocket has *terrible* mileage, but you can get to 75 in about 2 seconds...
Low mileage is great - it means your intersteller probe (or interplanetary probe) can get some really high speeds built up. It just takes a while to get there. However, it doesn't have enuf thrust to get you out of a gravity well - great mileage, but you can't drive up a hill.
It's a pat on the back for an ion drive that gives many more times the thrust of the old model, which means your probe can do things like turn quicker, get up to speed quicker, and make emergency adjustments a little better (altho if we calculate that badly, you can probably kiss your probe goodbye). Not revolutionary, but a big step.
The fact that it uses electricity is convenient for a lot of reasons; ion drives are really cool. More information here:
http://en.wikipedia.org/wiki/Ion_drive
--LWM
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.
ion engine accelerates propelland through ELECTRIC MESHES. the principle is similar to CRT, except you have many cathodes and many annodes (they are both meshes, in reality)
... double layer (sorry, but that's what they are called) in the plasma that need to be accelerated out, saving the mesh but now you need to have some containment for the plasma: magnetically trapped electrons. (the meshes served as a electrostatic trap in ion engines)
double layer creates a
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)
(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."
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.
"There are a dozen opinions on a matter until you know the truth. Then there is only one." - CS Lewis (paraprhase)
The problem with propulsion in space is that not only do you have to worry about energy efficiency, you almost always need to worry about mass efficiency. i.e. how much mass you need to shoot out the back of your spacecraft to make its forward velocity increase by a certain amount. In fact, in the long term for spacecraft that orbit the Earth or operate anywhere near the Sun, mass efficiency is the ONLY thing that matters. You can constantly get energy from the Sun via solar cells, or from a long-lived nuclear power supply onboard, but once you use up propellant mass, it's gone. The idea behind ion thrusters and this new propulsion design is to impart as much kinetic energy as possible to the spacecraft while ejecting as little mass as possible. (It can be shown that this mass efficiency is proportional to the exhaust velocity of the reaction mass - this is why so much research is being done into ion thrusters, since their exhaust gas velocity is far higher than that of a chemical engine.)
retrorocket.o not found, launch anyway?
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.
There are 10 types of people in this world, those who can count in binary and those who can't.
Of course you need a big rocket to get the thing off the planet. But then why not use an ion engine? Those long coasting times you get with a chemical rocket are a perfect opportunity to use something that produces low thrust over a long period of time -- like an ion engine.
p rometheus.html1 .htmp r99_2.htm
The engine itself MAY be heavier, but the advantage of ion engines is that they give you a given delta-v with much less reaction mass then chemical engines (ie they are much more efficient), so long as you don't need high acceleration. So your total mass is way less.
NASA seems fairly excited about using these things to explore deep space:
http://www.nasa.gov/vision/universe/features/nep_
http://science.nasa.gov/headlines/y2000/ast15jun_
http://nmp.jpl.nasa.gov/ds1/tech/sep.html
http://science.nasa.gov/newhome/headlines/prop06a
From one of those:
Some proposed mission concepts considering ion propulsion include the Comet Nucleus Sampler Return (CNSR), the Saturn Ring Observer, the Titan Explorer, the Neptune Orbiter, and the Europa Lander.
Neptune... sounds pretty Voyagerish. Except Voyager didn't have the fuel to stop and orbit, only to pass by.
An ion engine lets you carry MORE payload AND get there faster. It even lets you do something more than float on past when you do get there.