powerfull new ion engine

[dragon]

Not exactly new but still a deffinite step in the right direction. Still imagine once they're able to hook up a nuclear power to an ion engine.

A new design for an ion engine promises up to 10 times the fuel-efficiency of existing electric propulsion engines, according to tests by the European Space Agency. The new thruster could be used to propel craft into interstellar space, or to power a crewed mission to Mars, ESA says.

Ion engines work by using an electric field to accelerate a beam of positively charged particles – ions – away from the spacecraft, thereby providing propulsion. Existing models, such as the engine used in ESA’s Moon mission, SMART-1, extract the ions from a reservoir and expel them in a single process.

Tests on a prototype called the Dual-Stage 4-Grid (DS4G) thruster, at ESA’s Electric Propulsion Laboratory in the Netherlands showed that DS4G’s two-step process produces an ion exhaust plume that travelled at 210 kilometres per second – more than 10 times faster than possible with the engine in SMART-1, and four times faster than the latest prototype ion engine designs. This would mean a spacecraft could carry much more weight for a given amount of fuel, or it could go further, faster.

“Crewed or heavyweight robotic missions to Mars become a distinct possibility. And there’s even talk of interstellar missions [beyond the solar system],” says Orson Sutherland of the Australian National University in Canberra, who led the team that built the engine, in a project coordinated by Roger Walker of ESA's advanced concepts team in the Netherlands.

Collision erosion
The conventional ion engine contains three grids perforated with thousands of millimetre-wide holes. These grids are attached to a chamber containing the charged particles.

The first grid operates at thousands of volts, while the second is kept at a low voltage. This voltage difference creates an electric field, which extracts the ions from the fuel reservoir and accelerates them out into space in one step. The third grid acts to stop electrons flying back into the ion beam.

Ideally, the voltage difference between the first two grids should be as high as possible, to maximise the speed at which the ions are expelled, and also the fuel efficiency of the engine. But when the difference approaches 5000 volts, ions collide with the second grid, and start to erode it.

The new design incorporates four grids. First, the ions are extracted from the reservoir using two closely spaced grids that both operate at an intermediate voltage of 3000 V to 5000 V.

Acceleration comes in the second stage, when the extracted ions are channelled between the second and third grids, across which a very high voltage is applied. The final, low-voltage stage, between the third and fourth grids, prevents electrons from the exhaust plume from flying backwards.

Mars and back
This system allows voltage differences of up to 30,000 V between the two grid sets, producing much faster ion exhaust plumes than previously possible, and without damage to the engine.

Given sufficient electrical power, a cluster of DS4G engines could take a crew to Mars and back, says ESA. Alternatively, the design could be used to slash the time of longer missions to Pluto, or the Kuiper belt.

But given the extensive testing required of a new ion engine design, it could be a decade before DS4G engines make their debut in a space mission, Sutherland

link

[Koolaidkirby]

Excellent news, with this, TIE fighters become more and more plausible.

and I love hearing about major steps in the right direction like this.

[Kanastrous]

It would be very funny to take some TIE models into Lightwave or whatever, and create a space-combat scene where they move they move the way actual ion engines would move them...

[GrandMasterTerwynn]

It would be very funny to take some TIE models into Lightwave or whatever, and create a space-combat scene where they move they move the way actual ion engines would move them...

It'd have to be time-compressed. Very, very time compressed. Ion engines are useful because they can deliver a steady thrust over long, long periods of time. Days, weeks, months. Except that an individual ion has very low mass, so the thrust they produce is absolutely miniscule. But over the long term, an ion engine will outpace a rocket, due to the fact that an ion engine can run for so long.

[Fingolfin_Noldor]

They would need to find some way to increase the thrust by either increasing the density of ions, along with more voltage. One way I guess will be a nuclear reactor.

[Kanastrous]

It would be very funny to take some TIE models into Lightwave or whatever, and create a space-combat scene where they move they move the way actual ion engines would move them...

It'd have to be time-compressed. Very, very time compressed. Ion engines are useful because they can deliver a steady thrust over long, long periods of time. Days, weeks, months. Except that an individual ion has very low mass, so the thrust they produce is absolutely miniscule. But over the long term, an ion engine will outpace a rocket, due to the fact that an ion engine can run for so long.

That's kind of the idea; the whooshy-zappy VFX/SFX, over a ship drifting along at miniscule acceleration...

...maybe not so funny, as I had thought.

[dragon]

Ion engines have a high specific impulse. And with our current technology its hard to get something with a high Isp and high thrust. Current Ion engines on the drawing board will get about 1/10 of a G at best. Sure thats good enough to go to Mars and back with a manned mission but for deep space such as Jupiter or further you would need something like the ICAN II which is a long way off.

Thers also the gas-dynamic mirror engine fast

and the Variable Specific Impulse Magnetoplasma Rocket (VASIMR)
link

If I remember right, which I have a bad memory , a NASA white paper said the therotical max for a ion engine might be high as 1G but the power requirements would be very high.

[His Divine Shadow]

Ion engines cannot be high thrust; it is a physical impossibility in their design. If you add more ions to the stream, they will repel each other and share the energy, ruining the efficiency, and if you crank up the voltage, you'll get electrical arcing across the engine, ruining its operation entirely.

High thrust ion engines are purely fictional. But, you don't need high thrust for the kind of applications which ion engines are made for: sending robots to other planets, since they can easily take their sweet time to get up to speed. Thus, advances in the technology are certainly useful.

Manned missions will need higher thrust, so manned missions will need a completely different kind of engine. They probably won't get the fuel efficiency of an ion engine, meaning they must carry more propellant per payload mass than the ion one, but that's the trade off you have to make in almost every case.

I believe Saxton made SW ion engines work by being two stage, first generate the ions in a normal way, then as they are going out run them through an accelerator to make each ion approach velocities nearing the speed of light.

[Sikon]

Personally I dislike the way most news articles talk about ion engines, not because such are technically wrong but just since such leave out context unfamiliar to many of their readers.

With an ion engine being just one component of a propulsion system, its limits are affected by the limits of its electrical power supply.

Have an ion engine mounted on a craft with a 1 kW power supply, and it will have low thrust. Have an array of ten of those ion engines or a single bigger ion engine mounted on a craft with a 10 kW power supply, and it will have 10 times the thrust at the same specific impulse. It's like a light bulb powered by a small battery versus light bulbs powered by a large generator. For overall capabilities, the power supply matters as much as the type of device using it.

In general, for any electrically-powered rocket engine or thruster:

Thrust = 2 * η * P_input / V_exhaust

where P_input is the input electrical power, η is efficiency (the fraction of input electrical energy that becomes the directed kinetic energy of exhaust), and V_exhaust is exhaust velocity.

At a given efficiency, thrust goes up with increased power. At constant power, obtainable thrust is inversely proportional to exhaust velocity. Ten times the exhaust velocity means each kilowatt of input power can handle accelerating only 1% the mass per second to that velocity. Kinetic energy goes up with velocity squared.

Too high specific impulse is actually suboptimal when engine power is limited, if thrust and acceleration were to fall so low that obtainable velocity in the mission timeframe dropped from that as the primary limiting factor. Of course, before that point, too low specific impulse undesirably consumes too much propellant and would cause expenditure of all propellant onboard before reaching the optimal velocity. A good detailed illustration of optimal specific impulse for a power-limited transport is here.

Considering the preceding, some thrusters are designed to be capable of variable specific impulse, to be adjusted as appropriate.

This formula depends not at all upon the particular type of electrically-powered thruster chosen, whether an ion engine or not, provided such can handle P_input, except to the degree that choice affects η and V_exhaust.

The basic formula above would also be valid for a MPD thruster, hall thruster, a pulsed inductive thruster, or, for that matter, technically even an electrically-powered slingshot ... any electrically-powered thruster ... although obviously V_exhaust, η, and the practicality or impracticality of having a bunch of those handling a given amount of power would vary greatly.

As an example, consider the Deep Space 1 craft. A lightweight probe, it had small solar panels that gave up to 1860 watts of power to its ion engine, so P_input = 1860 W. Its ion engine could obtain meanwhile 3035 sec ISP, an exhaust velocity of 29.8 km/s, so V_exhaust = 29800 m/s. Efficiency was 60%, so η = 0.6.

Substituting those values into the formula, one determines that *any* electrically-powered engine with that exhaust velocity and that efficiency operating off 1860 watts of power gets 0.075 newtons of thrust.

And 0.075 N is exactly the measured figure for it shown within here at that throttle level, illustrating the accuracy of the formula (although that was known anyway, with the formula being a derivation based on KE = 0.5mv^2 and ρ = mv).

A force of 0.075 newtons accelerating the half-ton spacecraft causes slow acceleration since that's a force a fraction as much as the weight of a golfball on earth.

Fundamentally, Deep Space 1's ion engine was low thrust because:

• 1. For the ion engine (like any other electrically-powered thruster that could have been installed on that probe), input power was limited by the output of the small solar panels.
• 2. At a given power level, thrust is inversely proportional to exhaust velocity. The nice high exhaust velocity of that ion engine makes it fuel efficient but also means it consumes a relatively high amount of power per mN of thrust. Thrust is then particularly low for the limited amount of power.

Of course, it's also technically accurate to say its ion engine thrust was limited by the amount of voltage and so on, but input voltage & current was most fundamentally limited by the power supply in the first place, making the ion engine used be designed to be small and capable only of handling around the 2 kW supplied.

It was fine for the probe to have low thrust since that was sufficient for its mission; it was going to take months in travel anyway, so there was no real need for extreme thrust.

As a random example illustration, consider instead if there was a 7500-kg dry-weight nuclear-electric-propulsion vehicle with 1 MW of onboard power. With 500 times the power, it would be possible to obtain 500 times the thrust if at the same efficiency and specific impulse. Actually, in the case illustrated in the document, a design goal was 5000 sec or more Isp, and, at 67% efficiency, thrust would be 26 N or less. That's an example of up to 350 times the thrust of the DS1 probe, corresponding to up to around 20 times the acceleration after adjusting for the mass difference.

That's an illustration of the same basic thruster technology except scaled up to take advantage of a different power supply.

Of course, even 26 newtons is not superficially a lot of thrust for such a craft: like 6 pounds of force and causing 0.0004 g acceleration in this case.

Extremely high thrust (like 1g or more) at the same time as simultaneously extremely high exhaust velocity (like hundreds of thousands of m/s or more) requires truly enormous amounts of power relative to mass. That ordinarily means not solar-electric and not even nuclear-electric propulsion but a different method, such as the Orion Project proposal having a ship with literally terawatts of power from nuclear bombs detonating behind a pusher plate, way more energy than any onboard power plant and generator could have handled internally. The ICAN II discussed a little in the other thread, for example, is a smaller-scale lower-power version of similar principles.

However, there are a lot of applications for which low thrust is sufficient, like today's interplanetary probes. Sci-fi depicting ion engines as high thrust is just typical sillyness. But solar panels (or nuclear reactors) generating electricity to power ion engines can work as a more fuel-efficient method than chemical rocket engines, accelerating slowly but obtaining more delta v.

[dragon]

Very nice summary Sikion, so do you work in this field?

[Sikon]

Very nice summary Sikion, so do you work in this field?

Thanks but no.

[dragon]

Very nice summary Sikion, so do you work in this field?

Thanks but no.

Sol where did you learn all of that.

[Sikon]

So where did you learn all of that.

While this might go to PMs, one more reply in the thread won't hurt.

While not in the aerospace industry, I'm used to similar considerations in mechanical engineering, in this case seeing the indirect consequences of basic physics for momentum & KE, and I always had an interest in space.