With the eight years of intermittent cruising needed to catch up with Ceres, traditional propulsion would be impractical in the extreme. Like that bunny that just keeps on going, Deep Space 1’s engine has been thrusting intermittently for more than 375 days, and has only used just over half its fuel.

Ion engines work by ionizing a propellant gas in a discharge chamber and accelerating them out the back of the spacecraft through a set of two electrically charged grids to a speed of over 78,000 miles (125,525 kilometers) per hour. This creates a small but highly efficient amount of thrust. In the vacuum of space, where there’s virtually no resistance, a small amount is all that’s needed to cruise around the solar system -- given enough time and patience. Ultimately, ion propulsion allows spacecraft to reach higher speeds than does chemical propulsion.

"I’m pleased that the success of DS1 has been recognized and that the mission has made a difference so quickly," he said. "I’m confident that many other missions will use SEP and the other technologies on DS1 in years to come."

John Brophy, head of the SEP team at JPL that will oversee the system’s use on Dawn, takes that sentiment a step further. "In my opinion, most of the missions that JPL will fly in the future will use SEP," he said.

It will fall to Brophy and his crew to mitigate a sticky wicket problem with DS1’s ion-propulsion engine that caused a major bump in the road in the mission’s early phase. Namely, the darned thing wouldn’t turn on.

Turns out a tiny flake of debris, probably from the launch vehicle, apparently got caught between the two grids of the ion accelerator system, causing what amounted to a short every time engineers attempted to turn on the engine. That debris was eventually cleared, much to everyone’s relief, by alternately heating and cooling the grids by turning the engine to face first toward, then away, from the Sun.

Since then, the system has worked perfectly and has now accumulated more than 9,000 hours of operation.

Russell has been proposing predecessors to his Dawn Discovery mission since 1994, with SEP at the heart of each incarnation. That first year, titled Diana and using an ion engine with six thrusters, the destination target was our Moon and Wilson-Harrington, believed to be either a dormant comet or a "transition object" that is in the process of changing from a comet to an asteroid. Verdict: SEP was too high risk.

In 1996, Russell pitched the Main Belt Asteroid Rendezvous, or MBAR, to visit Vesta. Again SEP was deemed too high a risk. Another MBAR proposal in 1998, evaluated after DS1 had begun validating ion propulsion, was deemed only a moderate risk, but still was turned down.

SEP’s use in the 2000 Dawn proposal, featuring only three thrusters, was deemed low risk -- a key factor in NASA’s decision to choose the project as one of three proposals for the next mission within the Discovery Program of lower cost, highly focused, rapid-development scientific spacecraft. Partners include UCLA, JPL, the German Aerospace Center (DLR) and Orbital Sciences Corporation of Dulles, Virginia.

A phase-2 feasibility study is set for later this year, with Gavit coordinating the effort. An announcement of the final choice is expected by the end of the year.

Gavit, who came onboard the project in January, has been riding a steep learning curve about the science goals and is enthusiastic about what she has learned to date. As she put it, "The more I learn about the mission, the more I realize just how exciting it is. Think of it -- we’re going to be observing pristine materials that will take us all the way back to the very start of the solar system."