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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 109
    More: Interesting, NASA, jabs  
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11605 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 05:08:12 PM
i.imgur.com
"I do believe that he said thrusting."
"You are correct. He then said pack it in."
"Heh."
 
2013-06-26 06:14:22 PM
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?
 
2013-06-26 06:14:25 PM
/ Approves

netdna.shebudgets.com
 
2013-06-26 06:14:53 PM
FTA: "...can provide 30 million-newton-seconds of total impulse to the spacecraft."

images.sodahead.com
 
2013-06-26 06:15:07 PM
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.
 
2013-06-26 06:15:12 PM
Get me two of those...
 
2013-06-26 06:15:20 PM
Ahm givin' 'err ahll she's goht cap'n!
 
2013-06-26 06:18:52 PM
One thing not mentioned, or if it was I missed it, did it have to be refueled, or is that on one "tank" or whatever?
 
2013-06-26 06:19:12 PM
upload.wikimedia.org

If only we had two of them...
 
2013-06-26 06:19:44 PM

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.
 
2013-06-26 06:20:14 PM
Meh, most of my hard-drives have more hours than that thing.  One of my oldest I still use is sitting at over 67,000 hours and climbing.
 
2013-06-26 06:22:06 PM

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.


That's probably right.  These kind of engines are very low thrust, but very high efficiency.  If I ran the numbers right, that's a specific impulse of nearly 4,000s, which is fantastic.  Conventional rocket engines are in the 300-400s range.
 
2013-06-26 06:22:08 PM

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).
 
2013-06-26 06:22:22 PM

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?


The longer you can accelerate the faster you go.
 
2013-06-26 06:22:23 PM
So, its kind of like you're with a gal and she's like "are you done yet?  I'm tired!"

Hail to my ion thrusters.  Yeah baby...
 
2013-06-26 06:22:31 PM

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 06:22:36 PM
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 06:22:47 PM

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?


They don't have a hell of a lot of oomph, they are just stupid efficient. So if you want to go really fast with one you have to run it a long time. Fortunately, it can run a long damn time (obviously), and as far as I know it's about the only engine that will.
 
2013-06-26 06:23:14 PM
On 6 October 2007, Dawn turned on its ion engines and has been thrusting itself through the Asteroid Belt.

/Mind you, it did take a year off to take a lot of nice pictures of the asteroid Vesta
 
2013-06-26 06:23:27 PM

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?


You can continue increasing speed as you burn fuel.
 
2013-06-26 06:25:01 PM
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 06:25:23 PM
So, did we find God?
 
2013-06-26 06:25:44 PM
The pelvic thrust will drive you insane.
 
2013-06-26 06:28:08 PM
Grumpy Cat:
So, did we find God?


What does God need with an ion propulsion engine?
 
2013-06-26 06:28:53 PM

dragonchild: 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.


Boooooo
 
2013-06-26 06:30:29 PM

dragonchild: 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.


userserve-ak.last.fm

//Sees what you did there.
 
2013-06-26 06:34:38 PM

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 06:34:57 PM

dragonchild: 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.


I'm not sure if this comment is really awesome or really awful...
 
2013-06-26 06:36:44 PM
Quick, somebody Pshop up an "Ionic" tag for this story.
 
2013-06-26 06:37:12 PM
That's an article?

*quote*

"good"
 
2013-06-26 06:37:59 PM

bingethinker: Quick, somebody Pshop up an "Ionic" tag for this story.


I had a greenlight back in the days of yore which used that joke
 
2013-06-26 06:38:11 PM

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?


So think about it this way.

You have a car.  It's a fairly pathetic little car with a 1 HP engine.  The good news is that there is no air resistance whatsoever so eventually you can accelerate up to plaid speed, you can go between any point A and any point B by a more or less straight line, and there's no traffic.

You need to get from LA to NYC.  Are you better off accelerating to 25, and holding it there, or accelerating as high as you can get in half the distance, flipping, and then decelerating the rest of the way?
 
2013-06-26 06:38:28 PM

Lochsteppe: Doesn't sound like they plan to use it for a straight shot to the next star system right away.


For actually getting out of the solar system, a gravity assist using Jupiter or (theoretically) a solar flyby is going to impart far more velocity than any possible ion engine.  However, efficient rocketry means we can line up those kinds of slingshots better.
 
2013-06-26 06:39:55 PM

adenosine: dragonchild: 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.

I'm not sure if this comment is really awesome or really awful...


Both?
 
2013-06-26 06:40:51 PM

Lawnchair: For actually getting out of the solar system, a gravity assist using Jupiter or (theoretically) a solar flyby is going to impart far more velocity than any possible ion engine.


Uhhh the maximum velocity a gravity boost can impart is the relative velocity between the spacecraft and the gravitational body.  Planets don't move that fast.
 
2013-06-26 06:41:34 PM

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.


Don't forget that acceleration increases as you use up reaction mass. 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.
 
2013-06-26 06:41:54 PM
Make that between the destination and the gravitational body.
 
2013-06-26 06:47:14 PM
Something smells fishy here.  How do they know how long the next one will run for?  Hmmm?
 
2013-06-26 06:48:18 PM

adenosine: dragonchild: 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.

I'm not sure if this comment is really awesome or really awful...


Awfulsome.
 
2013-06-26 06:48:20 PM

JesseL: 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.

Don't forget that acceleration increases as you use up reaction mass. 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.


Can we quit with the km/s? The speed of light called and asked that you all slow down.

METRES per second, guys.

/
 
2013-06-26 06:49:46 PM

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?


The thruster provides very very little inertia. It takes a ton of time to get up to speed
 
2013-06-26 06:51:08 PM

ProfessorOhki: 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).


Considering that the nearest solar system to ours is Proxima Centauri, which is 4.2 light years away...

So possibly 200,000mph, light year is 5.87849981 × 1012 miles...

I'd say pack a lunch. Maybe a few books.
 
2013-06-26 06:51:21 PM

opiumpoopy: JesseL: 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.

Don't forget that acceleration increases as you use up reaction mass. 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.

Can we quit with the km/s? The speed of light called and asked that you all slow down.

METRES per second, guys.

/


D'oh. Sorry about that.
 
2013-06-26 06:53:26 PM

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?


Not really no. Unless you really want the trip to take the maximum amount of time possible, you thrust for as long as possible for the first half and then reverse thrust for as long as necessary in the second half.
 
2013-06-26 06:57:50 PM
This runtime isn't actually that outlandish.  These types of engines are being put on geosynchronous satellites for station keeping.  GEO sats don't actually stay put exactly where you want them - the earth's gravitational field isn't perfectly uniform, 3rd body perturbations, solar radiation pressure, etc. all combine to mean that you need to regularly fire thrusters to maintain your orbital slot.  The amount of fuel these vehicles can carry to maintain this position is one of the primary limitations on their useful life.

The numbers I've heard indicate that the GEO sats with the ION thrusters fire them for 8 to 12 hours/day.  Combine that with a 15 year expected service life and you see that these engines could possibly exceed this test span - not to mention orbital repositioning burns and enough gas to graveyard it when you're done.
 
2013-06-26 06:59:44 PM

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?


no
 
2013-06-26 07:00:49 PM

JesseL: opiumpoopy: JesseL: 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.

Don't forget that acceleration increases as you use up reaction mass. 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.

Can we quit with the km/s? The speed of light called and asked that you all slow down.

METRES per second, guys.

/

D'oh. Sorry about that.


No, you used the equation correctly and the proper units are km/s (for that expression of it).

It's just that it's a classical mechanics equation - never meant to be used for velocities that high.  It doesn't know about Einstein, so it happily exceeds the speed of light.
 
2013-06-26 07:01:28 PM

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 07:02:31 PM

Cerebral Knievel: 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?


That's not a QA post.  That post implies that it would be worthwhile.
 
2013-06-26 07:02:39 PM
One explination was probably sufficient, but if anyone else would like to explain it again, feel free.

"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") "

That's what I said, inertia.
 
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