Ion Thrusters Come of Age for Interplanetary Spacecraft

By Eliza Strickland | September 8, 2009 4:36 pm

Mercury probeEngines 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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Image: ESA. An illustration of the Mercury probe. 

CATEGORIZED UNDER: Feature, Space, Technology
  • Romeo Vitelli

    Is it just me or has ion propulsion been just around the corner since the 1960s?

  • YouRang

    Yep ion thrusters have been just around the corner since the 60s. The problem is: Ion thrusters are the RIGHT tool; whereas Chemical thrusters (and atomic bomb thrusters even more so) are the BIG TOOL (as in Tim tool man Daley’s poster–“Now THAT’s a Tool.” )

  • Carter

    No thruster produces any kind of meaningful ‘lift’ in outer space. Perhaps many readers do not have the benefit of a high school physics course, but I lobby that this should not dissuade Discover Magazine’s blogs from using accurate terminology. In this case, that would be ‘counteract the force of gravity on a pound coin’ instead of ‘lift a pound coin.’ And in the following sentence, it is desirable to point out that the same amount of force is generated but due to the near lack of gravitational forces and matter to produce friction on the spacecraft, acceleration is quite slow but continually increases the velocity of the spacecraft. This would dispel any confusion with the analogy of the pound coin.

  • Mike

    Ion thrusters or even full blown warp drives won’t alone make humanity a space faring race… not in the sense it was once the seafarers that discovered new lands.

    It takes both vision and courage to commit to a long term space effort, something that our current crop of leaders seem far too timid to dare. We are all very busy building military machines, inventing noxious germs in secret labs and basically just conspiring against our common good for any such noble undertaking.

    If there are alien races out there, you can bet they are hoping that the trash stays put, on Earth.

  • Henry Wysmulek

    Nasa might as well pack it’s bags and close the doors under this current president1

  • Dan

    So N years from now, will astronomers in solar systems N light years away be able to detect these various xenon ion trails crisscrossing our solar system?

    Can you imagine their headlines? “Those alien beings bombarding us with bad television now have space travel!”

  • DocM

    The engine Bolden mentioned @Congress that could make a 39 day Mars trip is VASIMR. The author left it open in the last paragraph.

    Also; VASIMR is a plasma rocket, not an ion engine in the sense of NEXT or the others which use electrodes to accelerate the fuel mass. VASIMR uses superconducting magnets to creat fields that accelerate the fuel mass, so no electrode erosion which is a big problem with ion thrusters.

  • Usarian

    I don’t think VASIMR is ION in any way.. no expert, but a big fan of the project. It uses lasers and rf emitters to superheat matter into plasma. Plasma is repelled by all magnetic fields, so really strong magnets are used to contain and compress the plasma and force it out at high velocity. It can’t go as fast as ion engines, but it has a much stonger thrust and doesn’t take years to speed up, and goes significantly faster than chemical thrusters and doesn’t use up the fuels anywhere near as fast. BTW, that 39 day trip to Mars actually IS VASIMR with their most expensive and (unfortunately) least likely configurations, not Ion. VASIMR requires nuclear power to be viable, but a tiny one has been designed to run off the space stations solar power in short bursts for proof of concept basically.


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