Differential Evolution Aids Space Travel

January 29, 2008

Sophisticated mathematics that simulates evolutionary change may soon help guide spacecraft to distant comets, planets, and other destinations.

University of Missouri engineers have proposed that a mathematical approach called "differential evolution" be a key planning tool. The mathematics "helps you figure out trajectory, size up the spacecraft, how much fuel is needed, what kind of launch vehicles are needed . . . all answers you need to get before going into the mission details," aerospace engineer Craig Kluever told MSNBC.

Today's mission planners use a variety of tools, including a design-driven approach in which experienced analysts make their best guesses at trajectories before doing the actual calculations. Kluever suggested that NASA add differential evolution to their toolbox. "It's not going to be a replacement, but you can look at a problem from a different angle," he said.

The underlying algorithm "mutates" solutions and then tests them against other potential solutions. The best solutions remain in use until they are supplanted.

Applying this approach to calculate spacecraft trajectories is "not new,” said Aaron Olds, a former Missouri graduate student who worked with Kluever, “but it's catching on."

Kluever and Olds tested their algorithm against four mission scenarios—including the 1997 Cassini mission to Saturn, which involved swing-bys of Earth, Venus, and Jupiter, as well as deep space maneuvers. "The Cassini results were very close to what was actually flown," Kluever noted. "A lot of event times and flybys were right on the same day or just off by one day."

Olds proposed the algorithm for "missions that require a little more computational power," such as the International Rosetta mission that will chase down a comet and put a lander on its surface by 2014. Rosetta's complex trajectory has already included two swing-bys of Earth and one of Mars, with a final Earth swing-by in 2009.

Source: MSNBC, Jan. 9, 2008; University of Missouri, Nov. 16, 2007.