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ESA and ANU makes a 10 times more effective ion-engine

Posted by: Voyager4D - Thu Jan 12, 2006 9:21 am
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ESA and ANU makes a 10 times more effective ion-engine 
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Post    Posted on: Fri Jan 13, 2006 9:49 pm
This new electric drive should make for a better interstellar precursor probe. An NTR heavy interplanetary probe to test Mars-Ship tech could deploy a fast ion probe using this drive and its own pile once in-space nuclear electric power is perfected. With an NTR boost and years of ion acceleration--we would have a true extra-solar probe.


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Post    Posted on: Sun Jan 15, 2006 3:26 am
I had a look at the SP-100 lithium cooled fast spectrum nuclear reactor used in the auxiliary power system in this conceptual design =>http://trs.nis.nasa.gov/archive/00000662/01/tp212691.pdf

The specific power and lifetime appear to be pretty limited, there is 3 percent burnup after 5 years of generating 375kWe in 12 tonnes of powerplant (missing the 60 tonnes of shielding!!) That works out as 30watts per kg. After minimal shielding, thruster mass and efficiency are are figured, you might get ~15 watts per kg being converted into kinetic energy. That would be a total of 2.4GJ/kg of powerplant and thruster.

With no payload the maximum delta V occurs at about 55km/sec with a fixed exhaust speed (almost anywhere)around 40Km/sec, over half of the mass then being propellant. You can do a little better if you have the ISP increase with time instead of being fixed. A fixed exhaust speed of 210km/sec only allows a delta V of 19km/sec.
If this is a representative power system, then even though I've ignored the influence of e.g. propellant tankage, 210Km/sec is probably not optimal for extra-solar power sources in the near-term, even with a modest efficiency increase.


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Post    Posted on: Sun Jan 15, 2006 9:17 am
Hello, nihiadrem,

the design the article causing this thread is talking about is atest-design in alab. A test-design for and in a lab can't be considered to be representative and this one at least has been constructed simply to test the new approach. So it can't be considered to be adjusted to avehicle, a payload or something like that.

If and once the new design is going to be used by a vehicle it will be adjusted that vehicle. In so far the article is talking about something which I personally would call a prototype. So I wouldn't wonder if efficiency etc. can be optimized, improved, increased.

Again this has to do with the Synopsis Technology-thread. The ion engine tested and using the new design never will be allocated to a vehicle. The tested engine is an allocation of components, fuel etc. itself and this allocation will be going to be modified - or altered perhaps - to achieve improvements which enable it to be used by vehicles carrying payloads and being significanly advantageous compared to engines like that of Smart-1. Something like that is behind what has been said nearly at the end of the article.

So I don't think the test-engine to be representative no way.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


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Post    Posted on: Sun Jan 15, 2006 6:06 pm
Ekke, my argument has nothing to do with the state of development of the thruster itself but only the velocity they are talking about and how compatible it is with currently forseeable (i.e. not currently existing) space power. I don't doubt that even this ion engine can tolerate lower exhaust speeds which might be useful, the electronics driving it could be changed. Incidentally the 30kV thing is fairly odd, it's *exactly* the potential drop you need to get 210km/sec with ideal Xenon ionization, so unless the ionization isn't appropriate or uniform (reducing the efficiency) the previous 5kV notwithstanding it is a suspicious number. [EDIT] I had stupidly forgot about extraneous currents also lowering efficiency, so the 30kV thing I thought was suspicious probably isn't.


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Post    Posted on: Sun Jan 15, 2006 9:56 pm
Andy Hill wrote:
ISince thrust is dependant on exhause velocity, a higher velocity gives more thrust per ion making the engine more efficient. Ignoring the power used for the moment this means that you get more thrust per kg of propellant and an engine having the same throughput of ions as SMART-1 would have a lot more thrust.

Getting back to the power being consumed, it does not necessarily follow that having a much higher voltage requires much more power, that said there is no such thing as a free lunch and there is likely to be an increase in power consumed, a 10 fold increase in voltage might allow a smaller drive current to be used so power need not rise by the same amount. Also some of that power is used to generate the ions in the first place and since we are talking about the same amount of ions being produced this should not alter.

I'm not sure you need to generate Megawatts of power to get enough accelleration from an ion engine to be able to use it on a manned craft. While it is never going to push you back in your chair a few kilograms could work OK.


Sorry to butt in, but that's not quite correct. Modern ion engines consume only a fraction of their power for ionisation. Most goes into acceleration. You can calculate the power needed by multiplying thhrust, exhaust velocity, and efficiency (which is typically around 60% for SPTs and >85% for gridded ion thrusters). Another way to get the power is to multiply the so-called beam current (ion charge times number of ions expelled per second) with the acceleration voltage. One important thing to note is that for a given plasma stream, the ionisation power is always the same (ideally), whereas beam power is directly proportional to the acceleration voltage applied. At the same time, the impulse (and thereby the thrust) of a constant mass stream scales linearly with exhaust velocity, that's proportional to the square root of power input. So, this new design will allow to use very little propellant but will use theoretically about sixteen times as much power per newton of thrust as an SPT engine like on SMART-1. In practice, thanks to better efficiency, I guess it'll be more like ten times as much.

This is actually why it's so hard to build a decent electric-propulsion spaceship: You're always power limited, so in many cases the cost and mass used for power generation (nearly) outweighs the savings from lower fuel consumption - or at least programme managers don't like to take a risk for the remaining bargain.

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Post    Posted on: Mon Jan 16, 2006 12:01 am
Max Lange wrote:
this new design will allow to use very little propellant but will use theoretically about sixteen times as much power per newton of thrust as an SPT engine like on SMART-1. In practice, thanks to better efficiency, I guess it'll be more like ten times as much.

This is actually why it's so hard to build a decent electric-propulsion spaceship: You're always power limited, so in many cases the cost and mass used for power generation (nearly) outweighs the savings from lower fuel consumption - or at least programme managers don't like to take a risk for the remaining bargain.


So I guess this new type of engine will be limited to probes around the inner solar system and possibly satellite station keeping then, pity. With such a huge power requirement its never going to be scaled up to give a lot of thrust. I'm not sure whether this is an improvement or not over the original engine designs it seems to me that they have improved the efficiency but have created a much bigger problem with the power needed.

If I remember correctly Pratt & Whitney were designing an Ion engine with a thrust of 1 Newton a while back I cant see anyone building anything much bigger for quite some time. The couple of orders of magnitude necessary for a manned craft is still only possible in the movies. :(

PS Dont worry about Butting in, if I'm wrong about something I dont mind being corrected and the more people posting the more interesting the discussion becomes. :)

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Post    Posted on: Wed Jan 25, 2006 6:07 pm
An engine is only as good as its power/fuel source. NTR is the way to go.


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