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NASA's NEXT engine  (Source: nasa.gov)
NEXT is a seven-kilowatt thruster that receives electrical power from solar panels or a nuclear power source

NASA's Evolutionary Xenon Thruster (NEXT) ion engine has broken the record for hours of continuous operation.

The NEXT ion thruster has clocked 43,000 hours of continuous operation at NASA's Glenn Research Center's Electric Propulsion Laboratory, breaking the overall record. The 43,000 hours is equivalent to nearly five years of continuous operation.

NEXT is a seven-kilowatt thruster that receives electrical power from solar panels or a nuclear power source instead of burning fuel. The electricity is then used to ionize molecules of xenon and a cathode to accelerate them electrostatically. When the molecules come out of the engine, they create thrust.

For the entire 43,000 hours of continuous operation, NEXT only consumed 770 kg of xenon propellant. The engine would offer 30 million-newton-seconds of total impulse to a spacecraft.

The NEXT ion engine is meant to send spacecraft into deep space missions further and faster with more efficiency than engines that burn fuel.

Making more efficient spacecraft has been an important goal in the space industry. For instance, SpaceX, a private California-based space transport company that was the first of its kind to send a spacecraft to the International Space Station (ISS) this year, recently showed off its Grasshopper project for reusable rockets. The Grasshopper Project is a Falcon first stage with a landing gear that's capable of taking off and landing vertically. It does this by shooting into orbit, turning around, restarting the engine, heading back to the launch site, changing its direction and deploying the landing gear. The end result is a vertical landing.

Source: NASA



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By drycrust3 on 1/1/2013 1:47:42 PM , Rating: 2
I think part of the way it works is based on the "Relativity" idea that as you accelerate something up towards the speed of light you add to the mass of the object, so with ions, which have a mass of next to nothing (but, importantly, not nothing), as you accelerate them their mass goes up. Say you happened to increase the mass of the ions by 10%, that's 10% less fuel than you'd otherwise need to carry.


By maugrimtr on 1/2/2013 10:55:31 AM , Rating: 3
Hang on, this is still back in Newtonian physics - Newton's 3rd law of motion. The spacecraft ejects the propellant at force. The propellant exerts an equal but opposite force on the spacecraft, i.e. the spacecraft moves in the opposite direction to the propellant's velocity.

The only difference from a chemical rocket is efficiency. Chemical rockets waste stacks of energy generating heat, and you can only store limited amounts of energy chemically. Ion propulsion is far more efficient but it produces very little thrust. It's the idea of having them on for months or even years (instead of minutes for normal rockets) to build up velocity with relatively little propellent needed (less weight!) that is attractive.


By Gurthang on 1/2/2013 12:14:04 PM , Rating: 2
Nope.

The simplest way to think about the efficency of ion thrusters versus chemical rockets is that a chemical rocket gets its thrust from a chemical reaction of the propellants thus the propellant is both energy source and the mass used to accelerate the ship. With ion drive the energy source can be any source of electricity which can come from far more compact sources like nuclear fission or from outside via solar/beamed power. Also ion drive acellerates the "probellant" far more than any chemical rocket so the space ship gets more acceleration from a given mass of propellent. So the spaceship can be lighter or at least devote less mass to thrust/manuvering or be able to accelerate more or longer.

The downside is that the various ion drive ideas don't push very hard without mindbogglingly huge amounts of electricity. Which makes them impractical at this time to launch anything.


By theapparition on 1/3/2013 12:36:54 PM , Rating: 2
Just for reference, this article indicates that over 5 years, this Ion engine:
quote:
For the entire 43,000 hours of continuous operation, NEXT only consumed 770 kg of xenon propellant. The engine would offer 30 million-newton-seconds of total impulse to a spacecraft.


The Saturn V first stage, in 168 seconds of burn produced 1193 million-newton seconds of impulse. In less than 3 minutes, produced 40X what the ion engine was capable in 5 years.

Granted it weighs much more, and wastes a lot of fuel, etc. But it's just a quick look at the relative performance difference between the technologies.


By ameriman on 1/15/2013 3:10:32 PM , Rating: 2
Your example is a difference of scale and size, not technology.
An ion drive the size of a Saturn V would generate a lot of thrust

The ion drives have an ISP of 3100, over ten times the propulsive efficiency
of the Saturn's F-1 engine.


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