Ion Propulsion

Today we’re going to put our scientific eye-on-propulsion.  (See what I did there?)

I don’t know about you, but when I see a nice blue-colored flame coming from ANYTHING, my immediate response is as follows:

WICKED

So today, in honor (or honour, as Ben would say) of the successful Hayabusa mission, I’m going to give you a VERY brief, VERY simple explanation on Ion Propulsion technology.

So the first thing you’ve gotta know about Ion Propulsion, is that it’s OLD.

Ion thrusters have been in constant use on Russian satellites since the 1970s, so they’re not anything new, per-se, but their more recent implementations are much more exciting than the old ones.

Does anyone have any questions? Remember, there are no stupid questions…

So Jacob, if ion thrusters are so old, then why don’t I see any jets powered by ion thrusters?

Thank you for that stupid question, anonymous-person.  First, a “jet” by definition is an aircraft powered by a “jet engine”, which is not an “ion propulsion” engine… duh…

Secondly, ion propulsion is SLOWWWWW.

A typical full-scale ion thruster may only produce 100 to 1000 milli-Newtons of thrust.  So for the most part, ion thrusters have only been used in satellites for station-keeping (orientation changes and small altitude changes).  Compare this to the Pratt and Whitney F135 Axial-Flow, Dual-Spool, Afterburning Turbofan engine which produces 191 kilo-Newtons of thrust, almost 200,000 times more thrust than an ion propulsion engine.  There is no way on Earth that you could get something as big as a jet or a spacecraft moving with only 1 Newton of thrust.

Luckily, Ion propulsion engines aren’t typically used on Earth ;-)

The true advantage to an Ion propulsion engine lies in something called its Specific Impulse.  Specific Impulse is a measure of how much force is created given a certain amount of propellant.  You could think of it as a fuel-efficiency for rockets and other propellant-based forms of propulsion.

Rocket engines typically see specific impulses on the order of 200-500 seconds, (btw, don’t worry about the units, just understand that a higher specific impulse is better) while Ion thrusters have demonstrated specific impulses as high as 30,000 seconds.

So for spacecraft, what this means is that you can carry minuscule amounts of fuel, and go a looong way with it.  Unfortunately, because of the low thrust, it might take a while to accelerate to an decent speed in the first place.


Author’s Artistic Representation of an Ion Thruster in action

OK Jacob, we get it… Ion thrusters are old and slow, whatever… What makes them cool?

Well, I was going to draw you another turtle picture, BUT NOT ANYMORE!

Sheesh…  Anyway…

Ion propulsion is COOL because it derives it’s propulsive force from an electrical power source. This is great in space because solar panels provide a pretty reliable source of electrical energy.  So if you have an engine that uses very little propellant, and can be powered by the sun, you can theoretically design a spacecraft that could be propelled for hundreds of years on very little propellant.

Wasn’t this article supposed to be about how Ion Propulsion worked?  Who is this guy?

I’VE HAD A LONG WEEK ALRIGHT!?!?

*Awkward pause*

Different ion thruster designs vary in how exactly they create their propulsive force and the specific propellants they use, but the basic idea behind them all is this…

  1. Take a lightweight, gaseous particle like xenon
  2. Give it an electrical charge, either by rubbing it on your head, or bombarding it with electrons from an adjacent hot filament, whichever fits your engine design best
  3. Now place that charged particle into an electromagnetic field
  4. The electromagnetic field will impart a force onto the particle, and if aligned properly, the particle will be accelerated out of the engine.
  5. Due to the Newtons Third Law, since the spacecraft has imparted some force to the particle, the particle in-turn imparts some force to the space craft (equal-and-opposite reaction), and therefore accelerates the craft.

The blue lines represent the lines of magnetic flux, and the force imparted on the Xe ion would be out-of-the-screen, into your face.

Did you follow that?  If you happen to know anything about these engines, you’ll know that I’ve skipped over a lot of details, so feel free to discuss the details with me in the comments.

So basically, you can think of the way that an Ion thruster works by imagining yourself on a frictionless(!) skateboard, tearing off bits of clothing and throwing them behind you to make yourself move… You’re not going to go very fast.  And on Earth, due to air resistance, you probably won’t move at all… but in space, you’ll slowly accelerate until you’re naked, and continue at that velocity until the end of the universe.

Luckily, we engineers know how to take something that barely works, and turn it into something actually useful.  So how do you make a weak, not-very-powerful engine into something useful?  By using 4 to 500 of them at a time!

Newer deep-space probes like Dawn carry three or more ion thrusters, but future missions plan to use upwards of 500 smaller ion thrusters in an array to attempt to provide thrust on the same order of magnitude as rocket engines.  Combine this with a nuclear power source, and we may just have found our path to the stars…

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5 Responses to Ion Propulsion

  1. Amy E.No Gravatar 15 June, 2010 at 4:06 pm #

    totally awesome! though i wish you wouldn’t have listened to your dumb question-asker and given us more turtle renderings.

  2. BrianNo Gravatar 16 July, 2012 at 9:54 pm #

    Hey! I just read your article, learned a lot and was entertained! That’s pretty rare! I might have to read more…

  3. Carlos BarreraNo Gravatar 19 September, 2014 at 3:50 pm #

    Technology Submission – Novel Rotary-Turbo-InFlow Tech – Featured Development

    GEARTURBINE PROJECT
    Atypical InFlow Thermodynamic
    Technology Proposal Submission
    Novel Fueled Motor Engine Atypical Type

    *State of the art Innovative concept Top system Higher efficient percent.
    Have similar system of the Aeolipile Heron Steam device from Alexandria 10-70 AD. -New Form-Function Motor-Engine Device. Next Step, Epic Design Change, Broken-Seal Revelation. -Desirable Power-Plant Innovation.

    YouTube; * Atypical New • GEARTURBINE / Retrodynamic = DextroRPM VS LevoInFlow + Ying Yang Thrust Way Type – Non Waste Looses

    -This innovative concept consists of hull and core where are held all 8 bteps of the work-flow which make the concept functional. The core has several gears and turbines which are responsible for these 8 steps (5 of them are dedicated to the turbo stages). The first step is fuel compression, followed by 2 cold turbo levels. The fourth step is where the fuel starts burning – combustion stage, which creates thrust for the next, 5th step – thrust step, which provides power to the planetary gears and turbines and moves the system. This step is followed by two hot turbo steps and the circle is enclosed by the final 8th step – bigger turbine. All this motion in a retrodynamic circumstance effect, wich is plus higher RPM speed by self motion. The Reaction at front of the action.

    *8-X/Y Thermodynamic CYCLE – Way Steps:
    1)1-Compression / bigger
    2)2-Turbo 1 cold
    3)2-Turbo 2 cold
    4)2-Combustion – circular motion flames / opposites
    5)2-Thrust – single turbo & planetary gears / ying yang
    6)2-Turbo 2 hot
    7)2-Turbo 1 hot
    8)1-Turbine / bigger

    -With Retrodynamic Dextrogiro vs Levogiro Phenomenon Effect. / Rotor-RPM VS InFlow / front to front; “Collision-Interaction Type” – inflow vs blades-gear-move. Technical unique dynamic innovative motion mode. [Retrodynamic Reaction = When the inflow have more velocity the rotor have more RPM Acceleration, with high (XY Position) Momentum] Which the internal flow (and rotor) duplicate its speed, when activated being in a rotor (and inflow) with [inverse] opposite Turns. The Reaction at front of the action. A very strong Novel torque power concept.

    -Non waste parasitic looses for; friction, cooling, lubrication & combustion.
    -Shape-Mass + Rotary-Motion = Inertia-Dynamic / Form-Function Wide [Flat] Cylindrical shape + positive dynamic rotary mass = continue Inertia positive tendency motion. Kinetic Rotating Mass.

    -Combustion 2Two continue circular [Rockets] flames. [ying yang] opposite one to the other. – With 2TWO very long distance INFLOW [inside propulsion] CONDUITS. -4 TURBOS Rotary Total Thrust-Power Regeneration Power System. -Mechanical direct 2two [Small] Planetary Gears at polar position. -Like the Ying Yang Symbol/Concept. -Wide out the Rotor circumference were have much more lever [HIGH Torque] POWER THRUST. -No blade erosion by sand & very low heat target signature profile. -3 points of power thrust; 1-flow way, 2-gear, 3-turbine. *Patent; Dic. 1991 IMPI Mexico #197187 All Rights Reserved. Carlos Barrera.

  4. Carlos BarreraNo Gravatar 2 November, 2015 at 6:31 pm #

    Technology Submission – State of the Art – Novel InFlow Tech – Featured Project Development;|/ ·1; Rotary-Turbo-InFlow Tech / – GEARTURBINE PROJECT Have the similar basic system of the Aeolipilie Heron Steam Turbine device from Alexandria 10-70 AD * With Retrodynamic = DextroRPM VS LevoInFlow + Ying Yang Way Power Type – Non Waste Looses *8X/Y Thermodynamic CYCLE Way Steps. Higher efficient percent. No blade erosion by sand & very low heat target signature Pat:197187IMPI MX Dic1991 Atypical Motor Engine Type /·2; Imploturbocompressor; One Moving Part System Excellence Design – The InFlow Interaction comes from Macro-Flow and goes to Micro-Flow by Implossion – Only One Compression Step; Inflow, Compression and outflow at one simple circular dynamic motion / New Concept. To see a Imploturbocompressor animation, is possible on a simple way, just to check an Hurricane Satellite view, and is the same implo inflow way nature.

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  1. Episode 130 | Old Lander On The Moon | Science... sort of - 4 April, 2012

    […] live long enough to take advantage of ion thrusters (which he’s written about before on the Paleocave blog), Ryan wants to know what this means for TIE fighters, and Ben finally understands the aerodynamics […]

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