Darwinian spacecraft engine to last twice as long

[AcesHigh]

http://www.newscientist.com/article/mg2 ... -long.html

SPACE agencies may one day have Charles Darwin to thank for the longevity of their spacecraft. The life expectancy of a popular type of ion engineMovie Camera has been almost doubled using software that mimics the way natural selection evolves ever fitter designs.

Electrostatic ion engines are becoming popular in space missions. Instead of relying on burning large amounts of heavy liquid propellant for thrust, they use solar power to ionise a small supply of xenon gas. A high voltage applied across a pair of gridded electrodes sends the positively charged ions rushing at high speed towards the negative electrode. Most ions pass through the grid, generating thrust.

However, some ions collide with the grid itself, causing it to gradually wear out, says Cody Farnell, a space flight engineer at Colorado State University in Fort Collins. Simulations suggest grids in a typical NASA engine will last 2.8 years - but Farnell wondered whether changing the grid's design could extend its lifespan.

He used evolution-mimicking software called a genetic algorithm (GA), and started by instructing the algorithm to randomly generate values corresponding to the geometry of the grid and the voltages applied to it. These values can be thought of as analogous to genes.

Each combination of values was then fed into a simulator to give an idea of the grid's performance and its expected lifetime. If the performance was promising, the "genetic material" was subjected to further random changes, or mutation, and this process was repeated until no more improvements were forthcoming.

After 100 generations, the GA spawned a geometry/voltage set that boosted the ion engine grid's lifetime to 5.1 years - at least in the simulator (Journal of Propulsion and Power, DOI: 10.2514/1.44358). Factors optimised included grid hole diameter, hole spacing and the thickness of the grids. The engine could be improved further, says Farnell, by evolving the other parts too.

"After 100 generations, the algorithm spawned a design that almost doubled engine lifetime"

Propulsion engineer Steven Gabriel at the University of Southampton in the UK is developing a triple-gridded ion engine. He says Farnell's work could have major implications if real-world tests of his design match the simulations.

[AcesHigh]

was this the first time such "natural selection" algorythms were used in simulations? If yes, could a similar algorythm be used for the Polywell, for example?

[93143]

Genetic algorithms are quite common in optimization - they take a lot longer than gradient-based methods, but are less likely to get hung up on local minima rather than finding global ones. I don't know why they're making such a big deal of it.

And no, you couldn't do this with Polywell. To do optimization you need a physics model that adequately represents the system and is computationally inexpensive, and to my knowledge no such model of the Polywell is possible with the current level of understanding.

[AcesHigh]

Genetic algorithms are quite common in optimization - they take a lot longer than gradient-based methods, but are less likely to get hung up on local minima rather than finding global ones. I don't know why they're making such a big deal of it.

And no, you couldn't do this with Polywell. To do optimization you need a physics model that adequately represents the system and is computationally inexpensive, and to my knowledge no such model of the Polywell is possible with the current level of understanding.

thanks for the answers. Cant you just imput the basic laws of physics and let the a quantum computer run all the simulations?

(if we had working quantum computers, of course )

[Professor Science]

and a fully functional set of physical laws. We've got some good first order approximations at the present.

I remember one case GA's were used was coming up with a better antennae and the computer popped out what looked to be a 5 years old squiggly line. But it was a very explicit squiggly line.

[krenshala]

I remember one case GA's were used was coming up with a better antennae and the computer popped out what looked to be a 5 years old squiggly line. But it was a very explicit squiggly line.

Ah, but how well did that squiggle work as an antenna? That would have been the deciding factor.

[KitemanSA]

IIRC, those squiggledy lines form the basis of every miniature cell phone in the world today. If your cell DOESN'T have an extendable antenna, it probably has one of those squiggledy ones buried in the case. IIRC.

[icarus]

Wonder if there is way of magnetising the grid so the ions don't collide with it all?

Like a MaGrid kind of thing, but for ion engines.

[Giorgio]

and a fully functional set of physical laws. We've got some good first order approximations at the present.

I remember one case GA's were used was coming up with a better antennae and the computer popped out what looked to be a 5 years old squiggly line. But it was a very explicit squiggly line.

I remembered something similar from nasa, a quick google and I recovered it:
http://www.nasa.gov/centers/ames/news/r ... _55AR.html

Is it the same you are talking about?

Edited:
Here is a better article from another website from google cache:
http://webcache.googleusercontent.com/s ... =firefox-a

[TallDave]

Genetic algorithms are quite common in optimization - they take a lot longer than gradient-based methods, but are less likely to get hung up on local minima rather than finding global ones. I don't know why they're making such a big deal of it.

And no, you couldn't do this with Polywell. To do optimization you need a physics model that adequately represents the system and is computationally inexpensive, and to my knowledge no such model of the Polywell is possible with the current level of understanding.

Agreed, on both counts. A second-generation PW might benefit from such an approach, which I've also seen used elsewhere.

They're making a big deal of it because reporters are morons.

[Aero]

They're making a big deal of it because reporters are morons.

Doubling the ion engine grid's lifetime is news worthy. The "genetic algorithm" slant of the story was kind of kind of mundane, though, IMO.

[Professor Science]

Concerning cell phones, I saw on a NOVA documentary that most cell phones incorporate fractal antennae these days. (also, that article is much more elaborate than the one I saw in science all those moons ago.)