The problem is, ions that bump into the grid instead of passing through it cause erosion, which limits the average NASA ion engine's lifespan to about 3 years. To extend the engine's lifespan, Cody Farnell, a space flight engineer at the University of Colorado in Fort Collins, used genetic algorithm software to randomly produce values according to the geometry of the grid and the voltages running through it. Genetic algorithms, or software that reenacts evolution, work by sending random sets of geometry/voltage values, akin to genetic material, into a simulator that communicates the grid's efficiency with any given combination, or "mutation." The simulator tests generation after generation for effectiveness until it stops improving. After 100 generations, the software produced a combination of values that increased the ion engine grid's lifespan to 5.1 years in the simulator.