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(SeattlePI)   Okay, folks, that's as far and as long as we can imagine thrusting through space ... So, let's pack it in   (seattlepi.com) divider line 9
    More: Interesting, NASA, jabs  
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11608 clicks; posted to Main » on 26 Jun 2013 at 6:10 PM (1 year ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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2013-06-26 06:25:01 PM
7 votes:
What they didn't mention in TFA is that they're really shutting down the experiment because the device they used to monitor it can only operate for five years.  That's the problem when you use ionic pentameter.
2013-06-26 11:16:33 PM
1 votes:

Lochsteppe: debug: It doesn't really seem like that kind of life span would actually be necessary.  Once you're in zero G wouldn't inertia pretty much keep you going?  You would just need thrusters for course changes, right?

TFA talks about its use for scooting around the solar system, mining asteroids for crystals to make Sinibombs & such.  Doesn't sound like they plan to use it for a straight shot to the next star system right away.


Run, coward!!!
2013-06-26 07:46:58 PM
1 votes:

DubtodaIll: Build a track long enough and theoretically there's almost no limit to the speed you can reach, escape velocity would be easily attainable.


You'd need to run the track in a vacuum tunnel all the way to the upper atmosphere, because hitting denser air at 11.2km/s (or faster to compensate for the frictional loss) will probably do very bad things to your craft. We had the Stardust reenter at 12.4km/s, but it got to decelerate in the upper atmosphere and was going much slower by the time it got to denser air.

DubtodaIll: The article didn't mention what kind if fuel the ion engine use but I'm just guessing its considerably lighter than rocket fuel which is why it would be optimal for the mag lev track.


Ion engines are powered by electricity (from whatever source you like) and typically use Xenon as reaction mass.
2013-06-26 07:31:55 PM
1 votes:

Ishkur: JesseL: With a 1000Kg starting mass and 230Kg final mass, plugging the numbers into the Rocket Equation yields something more like 333,500 km/s for the final velocity.

That's faster than the speed of light.

You may have misplaced a decimal or something.


As mentioned, it's a classical equation as applied to relativistic velocities.   It's going to be inaccurate because the equation doesn't know that c is the speed limit and that mass and energy (and therefore achievable velocity) all behave in odd ways near the limit.
2013-06-26 07:01:28 PM
1 votes:

Flatus: It doesn't matter if they test it for five thousand years, this Administration doesn't give a crap about space exploration and we're not going anywhere meaningful for a long, long time.


Are you QA's new alt because everyone has ignored him? or a politics tab troll that got lost?
2013-06-26 06:34:38 PM
1 votes:

debug: It doesn't really seem like that kind of life span would actually be necessary.  Once you're in zero G wouldn't inertia pretty much keep you going?  You would just need thrusters for course changes, right?


This type of an engine is designed to take advantage of exactly what you mentioned.  Just a few points to correct and inform:

1.  zero G (which doesn't really exist) has nothing to do with your ability to continue at a constant velocity indefinitely, the reason you can do that is due to conservation of momentum ("an object in motion will tend to stay in motion unless something acts upon it")  On Earth the thing that 'acts upon something' is friction due to atmospheric drag, or an object getting in the way (like the Earth itself).  The reason this works in space is due to the lack of an atmosphere and thus effectively no drag.  (In reality, there is some, but it might as well not exist for our purposes so we will just say 'no drag')

2.  These engine don't just work for a long time, they are VERY efficient.   Of course, due to With that in mind, the reason these engines are of interest isn't that you can get something somewhere eventually, but that they can get you there faster because they can convert more energy into thrust for a given amount of fuel.   Take 10kg of rocket fuel, and 10kg of fuel for these engines and these engines will produce more energy from those 10kg than the rocket.  More energy converted into useful thrust = faster (eventually)   It also means you can take advantage of a lot of things which wouldn't happen if you had to wait a long time for your spaceship to arrive at it's destination.   It also means you can have your spaceship go somewhere, and THEN go somewhere else.   With traditional rockets, we mostly just consider it a one way trip.
2013-06-26 06:22:36 PM
1 votes:
It doesn't matter if they test it for five thousand years, this Administration doesn't give a crap about space exploration and we're not going anywhere meaningful for a long, long time.
2013-06-26 06:22:31 PM
1 votes:

debug: It doesn't really seem like that kind of life span would actually be necessary.  Once you're in zero G wouldn't inertia pretty much keep you going?  You would just need thrusters for course changes, right?


Ion thrusters are ridiculously low thrust.  The only reason you use them is because they're high efficiency (so you can carry less fuel), but you have to fire them up over loooooong time periods to get any kind of actual velocity going.

So five years is probably not completely out of the ballpark, I wouldn't think.  Depends what you're planning to do of course.
2013-06-26 06:22:08 PM
1 votes:

debug: It doesn't really seem like that kind of life span would actually be necessary.  Once you're in zero G wouldn't inertia pretty much keep you going?  You would just need thrusters for course changes, right?


It's for constant acceleration. Would you rather inertia carry you slowly or constantly gain velocity so when you cut it off the inertia carries you more quickly?

UberDave: Someone do the math.  I'm hastily (and probably incorrectly) getting 30,000 k/s for that thrust and run time given 1000kg in mass (770 for fuel plus me rounding it up).  I thought it would be way faster.


With such puny thrust, a NEXT-based ion drive would need to run for 10,000 hours - just over a year - to reach a suitable speed for space travel. Dawn, a NASA probe that's powered by previous-generation NSTAR ion thrusters, accelerated from 0 to 60 mph in four days. As a corollary, ion thrusters only work at all because of the near-vacuum of space; if there was any friction at all, like here on Earth, an ion drive would be useless. The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph).
 
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