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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 12/31/2012 6:29:04 PM , Rating: 1
quote:
The electricity is then used to ionize molecules of xenon and a cathode to accelerate them electrostatically.

I was wondering if, besides boosting the speed of a space craft, the motor could also be used as a means to communicate with earth, e.g. via the heat signature from the rocket motor.




By james007 on 12/31/2012 7:51:43 PM , Rating: 2
I don't see how that would be of any help.

A heat-signature is really just light, whose spectral distribution reflects the temperature of whatever heated surface is emitting it. Trying to communicate by modulating the temperature of the engine exhaust would, I would expect, offer no advantages over using normal electromagnetic-based technology that is specifically designed for communication (ie, radio).
James H


By StevoLincolnite on 12/31/2012 10:57:29 PM , Rating: 3
It won't really "boost" the speed over your regular chemical rockets as the amount of thrust they produce is relatively small.

The advantage however is that where Chemical rockets will boost for minuets/hours an ION engine would be able to boost for days/months. - Perfect for a long voyage as it will gather up speed the entire trip.
Combine it with Nuclear and it may even last a century provided you have enough Xenon.


By Bad-Karma on 1/1/2013 6:02:36 AM , Rating: 2
Actually, you'd only be speeding up through the first half of your trip, then the craft would turn around and begin decelerating for the second half.


By Samus on 1/1/2013 2:25:24 PM , Rating: 1
There is no 'deceleration' in space. Once you approach a cruising speed, no additional propulsion is required to maintain that speed.

The ion drive could constantly keep accelerating long after any other propulsion source is spent, theoretically push a craft close to the speed of light (after many, many years...)


By Alexvrb on 1/1/2013 8:45:50 PM , Rating: 3
So... no gravity well? Once you're past a certain point, that issue vanishes... but then again after a certain point the solar winds will also cease to aid you. More importantly, is your craft guaranteed to have perfectly even heat radiation? Is space is a perfect vacuum? The deceleration might be almost negligible, but it exists.

Anyway, the "turn around" part of his post indicated that he was talking about a mission to a specific destination, like Mars. If you just keep on accelerating... it makes for a rough landing. Now for deep space exploration, you wouldn't need to turn around and fire the engine the other way, of course.


By Bad-Karma on 1/2/2013 1:51:36 AM , Rating: 3
So as the vehicle approaches its destination, there is no slowing down???? Would be amazing to use your theory to put something into orbit around a distant body......

2nd-- Yes, there is a normal expectation of deceleration in space, be it microscopic dust particles in your path or gravitational pulls, it does happen. Even a radiat source striking the surface of the craft can have an effect similar to a crook's radiometer and impede velocity.

It is just over a much longer period of time.


By FaaR on 1/1/2013 7:22:41 AM , Rating: 2
quote:
It won't really "boost" the speed over your regular chemical rockets

Well, uh actually they do, as the ion drive is - as Tiffany's article states - a lot more efficient than a chemical rocket engine or cold gas thruster. Since a probe can't carry much fuel with it, this difference in efficiency would let the ion drive build up more velocity over time - perhaps a lot more, depending on the length of the trip.


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.


By DarkUltra on 1/1/2013 8:36:58 PM , Rating: 2
Another important property is the speed of the ions. A rocket engine can only efficiently speed up to a certain velocity, while the ion drive keeps accelerating the spaceship. Or have I misunderstood?


By SlyNine on 1/2/2013 5:04:31 AM , Rating: 2
Speed is only relative.. It's the push of one object from another that matters. In space I could be going 10,000 mph (relative to object A). but If I push off an equally sized body at 10mph, we will move away from each other at that 10mph. So I will be going 10,005 and it would be going 9,995. But that's only relative to object A. If Object B is moving the same speed as me, after I push off each will be moving 5mph, but in opposite directions. How fast is any object going, well that just depends on what object you're basing the speeds off of.

That's why we can only see so far in space, about 13 billion light years. Because after that space is moving away from us at faster than light speeds. But you cannot really say how fast we are moving or how fast that part of space is moving.

Its the force of the separation. Not the same thing as thrusting air out the back of a jet, because in that case speed is not just "relative". There is, in affect a 0 mph when talking about jets on earth. Not with rockets in space, until we start hitting near the speed of light its all relative.


By half_duplex on 1/2/2013 2:01:21 PM , Rating: 2
Actually... I read a while back that there were efforts to collect the particles ionized for propulsion well behind the engine, in the vapor trail if you will.

This would make the NEXT more green!!


twins
By ipay on 1/1/2013 7:09:03 PM , Rating: 2
How about twin ion engines? And perhaps one solar panel for each engine.




RE: twins
By Visual on 1/2/2013 5:11:48 AM , Rating: 2
Oh, those are solar panels? Gotta wonder how that is working out on the dark side... ;-)


RE: twins
By ipay on 1/2/2013 5:57:55 AM , Rating: 3
If you only knew the power of the dark side... =)


Nit picking
By HoosierEngineer5 on 1/1/2013 1:24:39 PM , Rating: 2
"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."

The thrust actually occurs when the ionized Xenon atoms are electostatically accelerated (force = mass times acceleration).




RE: Nit picking
By Gondor on 1/1/2013 1:38:52 PM , Rating: 2
quote:
30 million-newton-seconds of total impulse


You missed this one - the actual unit is "newton-second". "Million-" is not a part of the unit (but "mega-" would be).

Then again countries like Burma and United States haven't adopted SI unit system just yet so it's easier to understand why Tiffany might be unfamiliar with its intricacies.


RE: Nit picking
By HoosierEngineer5 on 1/2/2013 9:56:00 AM , Rating: 2
True, but I was trying to point out the fundamental difference between a regular rocket engine which generates thrust from an expanding gas, and the Ion Thruster which seems to generate thrust directly by accelerating individual charged particles through a voltage gradient. Probably verly little thrust is developed due to the plasma expanding (but probably more than one would expect, since the particles are charged and would repel one another). An explanation of this would interest me more than most of this article has).


Distance traveled?
By half_duplex on 1/2/2013 2:02:23 PM , Rating: 2
Does anyone know just how far this 40K hours would get just the engine it self in space?




RE: Distance traveled?
By JediJeb on 1/2/2013 4:20:11 PM , Rating: 2
Need to know the Thrust, Mass, and Relative Velocity of the ions to figure how far you would have traveled for a given time of engine operation. Acceleration would not even be a constant since the mass would be getting less over time while the thrust should remain constant. Mass loss and acceleration I believe would be linear(not sure since it has been a very long time since I did those equations) and velocity would increase in more of a quadratic curve than a linear one.


Comparison to Dawn Spacecraft
By docinct on 1/1/2013 8:36:11 AM , Rating: 2
The article strangely fails to mention the Dawn Spacecraft which is powered by Xenon Ion Propulsion engines. Their projected lifespan matches the 45000 hours of NEXT.
As pointed out the accumulated action of the ion engines is more efficient than liquid fuel (Dawn added 9,600 mph to its launch speed) on equivalent of 16 gals of fuel.
As to comment on turning around to reduce speed, if you do it right the speed of the spacecraft closely matches the target speed when the craft arrives, thus conserving fuel. (Coasting for a while also helps conserve fuel).




Ion is cool.. but
By Dfere on 1/1/2013 12:36:30 PM , Rating: 2
It doesn't provide enough thrust to get the flaming dark matter sword up out of earth's gravity well, nor the torso nor shield. Luckily, the arms and legs have their own motors.




Basic Physics?
By timothyd97402 on 1/1/2013 3:58:38 PM , Rating: 2
A very simplified version of how the math is done:

Assuming initial speed of zero, you accelerate constantly for the first half of your trip, finally reaching a speed of say 100,000 miles per hour. You flip over and then decelerate at a constant rate until at the end of your trip you reach a speed of zero.

Simple algebra here kids. Your average speed for the whole trip is half of your maximum speed at the halfway point or 50,000 miles per hour. What do they teach in school these days?

Now, this example is not entirely accurate as there is always the acceleration of gravity from the Sun and the Planets affecting your actual direction and speed (vector). Also since we are burning fuel during this hypothetical trip, the mass we are moving is less as time goes on, so we get more acceleration from a given amount of fuel at the end of the trip than we did at the beginning.

While the thrust, and therefore acceleration, of an Ion Drive is very low, there is little/no friction in space so your speed just continues to build up because an Ion Drive is so efficient that it can burn continuously on very little fuel. Great for long trips in open space, useless for getting off planet, haven't done the math for a trip to the moon.




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