The ever ready ion thruster

"Crewed or heavyweight robotic missions to Mars become a distinct possibility. And there’s even talk of interstellar missions." Those words were spoken by Orson Sutherland of the Australian National University in Canberra in January of 2006, who led the team that built the advanced Dual Stage 4 Grid (DS4G) ion engine in a project coordinated by Roger Walker of the European Space Agency's advanced concepts team in the Netherlands.

ESA's earlier Smart 1 mission to the moon, launched in September of 2003 and designed to impact the moon in a controlled crash landing was also powered by an ion thruster. The trip to the moon took almost exactly three years, compared to the two and a half days it took the Apollo astronauts to get there in a conventionally fueled rocket, but the mission was a great success for it proved that ion thrusters work and it returned valuable data for ESA's future lunar missions.

Ion engines are a form of electric propulsion and work by accelerating a beam of positively charged particles, or ions, away from a spacecraft using an electric field. They are far more fuel efficient than liquid fueled conventional rockets and are increasingly used on long range space missions, where their ability to maintain thrust for long periods of time ultimately pays off in much higher velocities. Ion thrusters can run on a few hundred grams of propellant per day. Ion thrusters push their exhaust about ten times faster (1998) than chemical rocket engine exhaust. NASA probe Deep Space 1's ion engine used less than 159 pounds of fuel in over 16,000 hours of operation. In mid-August of 2001, its Xenon ion engines set a new record by completing 200 days of continuous thrusting.

The image below, taken from the Electrostatic Propulsion page of the home site of the Associated Plasma Laboratory (LAP) of the National Space Institute (INPE) in São José dos Campos, SP, Brazil, is of an ion micro attitude thruster planned for future INPE satellite projects.

The DS4G has dramatically improved performance over previous ion engine designs. The new engine is over ten times more fuel efficient than the Smart 1 engine design. Using the same amount of fuel as Smart 1, a probe using the DS4G would be able to leave the solar system altogether. Exhaust plumes of 210,000 m/s were achieved, over four times faster than then current state of the art ion engine designs.

Already the news is almost a year and a half old. The numbers can only improve.