Engines powered by chemical fuel? How passé. For the spacecraft with truly modern flair, an ion thruster is the only way to go. Such a system might not provide powerful and dramatic bursts of speed, but space agencies around the world are recognizing the benefits of its slow-and-steady approach, which is just what's needed for cruising between planets.
Ion propulsion works by electrically charging, or ionizing, a gas and accelerating the resulting ions to propel a spacecraft. The concept was conceived more than 50 years ago, and the first spacecraft to use the technology was Deep Space 1 in 1998. Since then ... there have only been a few other noncommercial spacecrafts that have used ion propulsion [Technology Review].
However, the technology has a clear advantage over chemical propulsion when it comes to long distance missions, because a very small amount of gas can carry a spacecraft a long way. Astronautics expert Alexander Bruccoleri explains that with chemical propulsion,
"You are limited in what you can bring to space because you have to carry a rocket that is mostly fuel" [Technology Review].
Now, a European Space Agency (ESA) probe will use four ion thrusters to scoot all the way to Mercury, the planet nearest to the sun. That mission won't launch until 2014, but ESA officials say the $37 million propulsion system will be the most efficient yet, and will also be the most ambitious test of the technology to date. The Mercury probe will be launched by a conventional rocket, and will continue to use chemical propulsion until it's out of Earth orbit. When it begins its six-year cruise to Mercury, though, its ion thrusters will kick in. The system will draw electricity from solar panels; as the xenon ions
pass through the electrified grids they accelerate to up to 50km a second (31 miles per second) and shoot from the rear in a parallel beam. On Earth, at sea level, the thrust would be just enough to lift a pound coin. In space, however, the same thrust will create a much much bigger lift [Telegraph].
Meanwhile, NASA is developing new ion engines under the NASA Evolutionary Xenon Thruster (NEXT) program, and has also partnered with Ad Astra Rocket Company. That agreement paves the way for Ad Astra's VASIMR system
to be fired in space, attached to the International Space Station, if further ground-based tests are successful.... If flight testing on the space station goes according to plan, Ad Astra hopes to win a NASA contract to use VASIMR to provide the periodic boosts needed to keep the ISS in its orbit [New Scientist].
Ion thrusters have been suggested for a possible manned expedition to Mars, although such missions are in doubt following a presidential panel's declaration that NASA's human spaceflight program is on an “unsustainable trajectory.” But it isn't clear how the panel's recommendations will affect NASA's space-faring plans. It may be worth noting that ion thrusters got an appreciative nod from NASA's new administrator, Charles Bolden, during his Senate confirmation hearings, when Bolden called lawmakers' attention to an ion engine that
can enable trips to Mars in "39 days instead of 8 to 11 months" [New Scientist].
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