NASA's Ion Thruster Sets Continuous Operation Record 165
cylonlover writes "NASA's Evolutionary Xenon Thruster (NEXT) ion engine has set a new world record by clocking 43,000 hours of continuous operation at NASA's Glenn Research Center's Electric Propulsion Laboratory. The seven-kilowatt thruster is intended to propel future NASA deep space probes on missions where chemical rockets aren't a practical option. The NEXT is one of NASA's latest generation of engines. With a power output of seven kilowatts, it's over twice as powerful as the ones used aboard the unmanned Dawn space probe, yet it is simpler in design, lighter and more efficient, and is also designed for very high endurance. Its current record of 43,000 hours is the equivalent of nearly five years of continuous operation while consuming only 770 kg (1697.5 lbs) of xenon propellant. The NEXT engine (PDF) would provide 30 million newton-seconds of total impulse to a spacecraft. What this means in simple terms is that the NEXT engine can make a spacecraft go (eventually) very far and very fast."
If I am doing the math right (Score:5, Interesting)
This ion thruster placed on Voyager 1 would have taken it up to 37 km/s over 5 years compared to the 17km/s it is going now. Not part of my calculations is that Voyager 1 would have been slightly lighter due to the reduced fuel load. i don't have exact enough numbers to do the calc, but it would have likely been in the low 40's km/s.
Re:If I am doing the math right (Score:5, Informative)
Just realized how careless I was. My calcs assume acceleration from propulsion only. Voyager 1 took up much less fuel but is going at a pretty good clip due to gravitational assists. So the comparison is not apples-to-apples. Voyager 1 has used about 80 kg of mass to get to its current speed, but a good part of that was due to energy from being placed in orbit and from a slingshot around Jupiter.
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Only problem is coming up with a multi-kilowatt electrical source that far out in space. Voyager's RTGs were only a few hundred watts, I believe.
Re:If I am doing the math right (Score:5, Interesting)
Agreed. You can get a lot of energy from solar in the inner solar system, but ion engines are about long durations, and you're not going to be spending that much time in the inner solar system. I guess you could launch it towards the sun and do a slingshot around it. That will let you pick up a lot more velocity due to spending more time where your panels are effective, but it obviously adds a lot more distance to your trip as well.
You could just use a much larger RTG, or perhaps even a reactor. Not sure how that works out in terms of mass trade-off vs just using a conventional rocket.
Re:If I am doing the math right (Score:4, Informative)
You would think that launching towards the sun would help; so did I. After hours of playing Kerbal Space Program, I've learned that in order to even get to the sun, you have to negate then Earth's velocity in order to fall close enough to the sun to get a boost, and you'd have to get pretty close to get a boost. Not sure if the time and energy expended doing a sun flyby (not to mention having to add extra solar shielding) would provide enough of an advantage for extra-solar trips.
Even gravitational boosts from other planets are tricky. You have to make sure you're coming from behind in order to get a boost since it allows you to fall into the planet while it's still traveling away from you, giving you more speed longer. If you intercept in front of it, the planet basically stops you in your tracks and pulls your towards itself, killing your momentum.
Re:If I am doing the math right (Score:5, Informative)
Umm, no. Maximum energy gain for a gravitational assist is a slingshot maneuver where you narrowly miss a head on collision with the planet, you will then be whipped around on a parabolic path and depart in the opposite direction with twice the planet's velocity added to your own. The "gravitational tugboat" maneuver you describe is great for minor boosts and course corrections, but is unlikely to be used for speed unless a slingshot maneuver is incompatible with reaching the desired destination.
http://en.wikipedia.org/wiki/Gravity_assist [wikipedia.org]
As for a solar slingshot, yeah it's pretty pointless for in-system travel - it's hard to get close (not to mention survive the passing), and since it's basically the "stationary point" for the solar system you can't steal much speed from it, so once you reach your starting distance you'll have roughly* the same velocity as when you started with. Unless you just want to briefly go really fast for some reason, or are on an interstellar vessel seeking a gravity assist on your way to somewhere else in the galaxy, the sun is pretty useless for gravity boosts.
* You won't leave a solar slingshot with exactly the same velocity because the sun itself is orbiting the solar-system's barycenter, typically between about 1/2 and 1 solar-diameter from the sun's center and constantly moving as the orbiting of the outer planets shift the system's center of mass. So there will be some velocity transfer, just not enough to be actually useful.
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Huh, I hadn't thought of that. That could make a solar slingshot useful for interstellar launches at least, assuming we could shield against the massive radiation of a near solar approach. Actually getting there shouldn't be too difficult, a partial slingshot around a convenient planet to eliminate virtually all angular momentum and drop like a rock into a very close approach. Of course given the much higher return velocity it'd probably be extremely difficult to recover the energy thus discarded, but wi
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Unfortunately, current generation electric propulsion isn't high thrust to weight and hence, c
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Yup, realized that. I was referring only to spending more time in the inner solar system - as long as your thrust was directed along your velocity vector any speed you pick up on the way towards the sun will translate directly into speed on the way out.
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Sorry, I'm replying to negate my accidental Overrated mod... meant to be : Funny+1 :)
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Ya, I did that once. Then I found out the shitty part.
Sure, you can go blazing around the sun like doing your own recreation of the big bang, and zing back 1000 years. You can't go forward using the same method.
It'll only be another 1960 years until I'm born. You people won't have found how to leave this miserable rock for a couple hundred more years. That whole "whee, we're just outside the atmosphere" thing and "oohh, we have a RC car on the next planet", w
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I'd give you mine, but I'm pretty sure it's in a eccentric orbit around Sol. Somewhere around the orbits of Sol 6 and Sol 9 (Saturn and Pluto, in Earth terms). All the odds of hitting one of their little probes, and I managed to hit two on the last trip. I won't admit which ones, since they'll probably try to sue me.
If they ever do manage to find my repulsors or the part of the hull they were attached to, I believe one is still stuck in the side. If you get there first, can you give the crew who are p
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Purely a political problem. Suitable and inexpensive reactor designs have existed for decades.
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Also not included in your calcs is the velocity "lost" due to escaping from the sun's gravity well.
The funny thing is that higher initial speed (or, more on the note of continuous acceleration, comparatively short acceleration deep inside the gravity well) actually diminishes the effects of the speed loss. Do the math yourself. If you accelerate to the local parabolic speed, your speed in the infinity is going to be zero. If you accelerate to local parabolic speed plus, say, 3 km/s, your speed in the infinity is going to be significantly higher than those 3 km/s. You don't even need to integrate anything
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Only problem is coming up with a multi-kilowatt electrical source that far out in space
SAFE-30 [wikipedia.org] nuclear reactor. In fact the Jupiter Icy Moons Orbiter [wikipedia.org] (JIMO) was planned to use nuclear-electric propulsion to explore the moons of Jupiter but it was cancelled. Another possibility if you want to stay in the inner planets i.e. not go further than Mars is to use a gigantic solar panel array. The 8 ISS solar arrays generate 84 kW.
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Mind my laymen's explanation, which could be completely wrong. My understanding was that chemical rockets have a maxed velocity because the energy departed from burning fuel is based on the the relatively slow speed that the matter leaves the rocket based on the temperature of exhaust. Ion-thrusters sho
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The exhaust velocity on an ion thruster is nowhere near that of a partical accelerator. According to a 1996 NASA document I found, the exhaust velocity of an ion thruster is 31.5 kilometers per second, while particle accelerators are very close to the speed of light. The speed record is 0.999999999976c, which is roughly ten thousand times faster than the ion thruster exhaust velocity. That's not to say that thruster exhaust velocity is the speed limit, since the thruster exhaust velocity is relative to the
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Ion thrusters (Score:4, Interesting)
Re:Ion thrusters (Score:4, Informative)
Re:Ion thrusters (Score:5, Informative)
The simple concept that we now have "Ion Thrusters" is extremely cool to me.
OK, brace yourself for techno-orgasm.
The first recorded successful firing of ion thrusters in space was onboard the Soviet Zond 2 probe. 8th December 1965.
Yes, fifty years ago.
That particular installation was experimental, but ion engines were widely used in subsequent Soviet probes. Mainly developed at the Kurchatov Institute.
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> The first recorded successful firing of ion thrusters in space was onboard the Soviet Zond 2 probe. 8th December 1965.
Thanks for the information, I knew that it was Russians who worked first in this field, but I didn't know that this was *that* early.
As there was discussion about Voyager 1, it's interesting to remind ourself that it was launched in 1977..
Re:Ion thrusters (Score:5, Funny)
And first put on a small one man fighter called the Twin Ion Engine fighter in 1977.
Re:Ion thrusters (Score:5, Funny)
And first put on a small one man fighter called the Twin Ion Engine fighter in 1977.
But it was short range only, and couldn't operate far from base.
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Unless it had gotten lost, been part of a convoy or something.
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Only "Now"? They've been in use for decades in various probes and satellites...
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Warp Drive? It's only around the corner once you've reached Orbital Science See? [google.com]
Um, they used what? (Score:1)
while consuming only 770 kg (1697.5 lbs) of xenon propellant.
Last I heard, xenon was a gas, and that sure sounds like an awful lot of it - how much is left (on our planet)?
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My first thought as well.
Wikipedia's first hit:
"Extraction of a liter of xenon from the atmosphere requires 220 watt-hours of energy.[52] Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m3"
Sounds like we have some scaling issues before this engine puts us on mars on a regular basis.
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What I don't understand is why you would measure "production" of a gas as a unit of volume. And if you're going to do that, why wouldn't you include the pressure as well? Doesn't this tell us basically nothing, or is there some sort of standard I don't know about?
Re:Um, they used what? (Score:4, Informative)
is there some sort of standard I don't know about?
Yes. Standard temperature and pressure [wikipedia.org].
the IUPAC's definition is a temperature of 273.15 Kelvin (0 C) and a pressure of 100 kilopascals, though there's a bunch of other standards to choose from.
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If a pressure is not given, assume STP. At least, according to IUPAC. Though like many unit cock ups in the past, assumptions can get you in all sorts of trouble. however if it was given in m^3 then it's going to be reasonably safe to assume STP, then you just use the ideal gas law to work out quantity - Xenon is reasonably close to one.
Re:Um, they used what? (Score:5, Informative)
Less power than running a dungeon in world of warcraft using a decent gaming rig. doubly so, if you run dual cards.
total power usage of gaming rig under load - ~400 watts
Time to run a dungeon - between 45 min - 1 1/12 hours.
300 - 600 watt hours
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Xenon doesn't have a whole lot of uses here on earth. It's an inert (noble) gas. Ion engines aren't terribly useful for moving living beings around as they wouldn't accelerate an object (and it's life support systems) out of LEO and to Mars before the occupants either starved or died of cancer. Chemical rockets aren't as efficient, but at least they can get you to Mars in under 9 months. A very loose analogy would be crossing the Atlantic in an open 8' rowboat vs flying across in a jet powered 747.
Re:Um, they used what? (Score:5, Informative)
lots and lots and lots. just expensive to separate as it is widely distributed.
Xenon is a trace gas in Earth's atmosphere, occurring at 87±1 parts per billion (nL/L)
(wikipedia is fun)
being heavy it doesn't escape the atmosphere.
It is very dense as a liquid, stores compactly, and can used as a heatsink for the engine.
for fun:
770kg of xenon is 130641 L at STP
it is 252 L at xenon boiling point (as liquid)
it is also ~2% of total xenon production (in 1998)
Re:Um, they used what? (Score:4, Informative)
Re:Um, they used what? (Score:5, Informative)
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Xenon makes up about 87 parts per billion of the Earth's atmosphere.
The dry mass of the Earth's atmosphere is approximately 5.14 quadrillion tonnes.
That comes to about 447 million tonnes of Xenon.
Xenon is also a waste product from nuclear fission.
Re:Um, they used what? (Score:4, Interesting)
Last I heard, xenon was a gas, and that sure sounds like an awful lot of it - how much is left (on our planet)?
Seriously man.. 770kg shouldnt sound like "an awful lot of it" when you are asking about how much we have "on our planet." You do know how massive the atmosphere is, right?
Extracting a liter of xenon from the atmosphere requires 798000 joules of energy, and 770 kg of xenon is 131804 liters. So thats 104388768000 joules of energy.
(yes, I am shooting for "oh noes big number")
Thats equivalent to under 3 minutes of output of the typical (average American) coal plant that puts out 667MW.
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The hassle of recovery of the gas is entirely based on cost. Helium is routinely recovered and recompressed in research labs and institutions, usually centrally because of the high cost and scarcity - the helium compressor at my university consumes 0.125 MW, by far the single biggest energy sink on the campus, when a critical volume has been recollected ready for purification and reliquification. It's still cheaper doing it this way than just buying more in.
Xenon is relatively easy to extract from the air,
Re: Um, they used what? (Score:2)
Why would isotopic purification increase the efficiency by a factor of 2?
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If I had to guess, the isotopic version is probably missing or has an extra ion (or two or three), which makes it easier for the ion engine to accelerate it using the same power output. The mass difference is probably negilible, but you could accelerate the same mass using less power (say, 3.5kw instead of 7kw)
Re: Um, they used what? (Score:2)
I'm a mass spec guy, so I certainly agree that different masses will focus differently. But in the ion drive schematics I see online, I don't see where there is a focussing step. The plasma is made, then just accelerated across a planar electrostatic voltage drop. No focussing needed. I'm also not seeing a x2 increase just from a slightly better ability to focus even if that did matter.
Re:Um, they used what? (Score:4, Informative)
For the engine they probably store it as a liquid. Significantly below the transition point. On Earth that's not much of a problem, and in space not much of one either...unless you get near the sun. 165K seems to be cool enough.
Quote from Wikipedia:
Xenon is the preferred propellant for ion propulsion of spacecraft because of its low ionization potential per atomic weight, and its ability to be stored as a liquid at near room temperature (under high pressure) yet be easily converted back into a gas to
Note, however, that ion engines can theoretically work with any atom. Personally, I think they should be designed to use some common heavy element, like iron, and to accelerate the ions maximally. This, however, is an eventual design goal, not something to aim for in the next decade or so.
Turn To Slide 6 For Recent Updates (Score:2)
Xenon? (Score:2)
Re:Xenon? (Score:4, Funny)
I thought to use something as fuel in an ion thruster, it has to be able to ionize? Xenon is about as inert as it gets and really isn't useful for anything because nothing reacts with it in any way. In fact, wasn't hydrogen or something the typical fuel for an ion thruster? Can one of the hundred or so ion thruster engineers that are likely here on slashdot (lol) explain it to us?
http://en.wikipedia.org/wiki/Ion_thruster [wikipedia.org]
http://en.wikipedia.org/wiki/Xenon [wikipedia.org]
You figure out the rest.
Re:Xenon? (Score:5, Informative)
In a chemical sense, yes Xenon is inert and doesn't like to ionize. However, in the case of an ion thruster, the ionization is accomplished using high voltages - very easy to do.
Xenon is preferred because it's non-toxic, comparatively easy to handle, and has a 'heavy' nucleus -- meaning that you can more easily give each atom more of a push, resulting in higher thrust. You could use ions of any atom you like, though. Hydrogen's got the lightest nucleus there is, so it's not much use, not to mention being a royal pain to handle.
The Russians started out with, iirc, cesium and mercury thrusters. But of course these are really nasty substances and you really don't want to be around them if you can help it.
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Mercury is nasty? Given what's typically used in rocket propulsion, mercury is nothing to worry about. I still have a few grams of mercury stored for experiments, and still have a mercury thermometer or two. Why wouldn't I want to be around it? It's stored in sealed glass containers, in secure storage.
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Versus a ton of Xenon doing no environmental damage at all.
There's a potential hazard as all that gas will probably slump straight down (being really heavy by comparison with nitrogen and oxygen molecules) and present a risk of anoxia for every living thing in the immediate area. Yes, it would dissipate fairly quickly but the immediate vicinity would be temporarily quite hazardous. Compare with what happens when a crater lake belches carbon dioxide (admittedly in much larger quantities) that can kill substantial numbers of people. CO2 isn't as dense as Xe (which wo
Re:Xenon? (Score:5, Informative)
Xenon is easy to ionise - it's a large, diffuse atom with the outer electrons far from the nucleus. It's also inert and heavy, giving you a non-toxic, non-corrosive fuel with a high mass/charge ratio; ideal for an ion thruster.
If only it were cheaper to buy!
It's also not true that "nothing reacts with it". The lower end of group 18 does react with strong oxidisers and you can form (and isolate) crystals of XeO4 and so on. The closest to being truly "noble" gasses are helium and neon.
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Let me reiterate: Those particles will often be hitting your magnetic scoop at relatively high fractions of c, far faster than what you're going to get from your engine.
I've constantly used 0.1c as a number for speed, so I'll continue with that here. I've also used the explicit example of traveling 0.1c and expelling the particles at 0.2c. You are telling me that 0.1c is greater than 0.5c, and that 0.2c is smaller than 0.1c.
I think you are full of shit and looking for an arguement about nothing, and you are willing to lie to feel smart because you heard about "Bremsstrahlung" once, and it makes you feel smarter to work it into as many conversations as possible.
Hydrogen stacks up really well (Score:2)
Actually you're probably better stripping off the electrons than trying to add them. A naive ion thruster consists of two high-voltage electrodes - the positive electrode strips off some electrons from colliding neutral atoms, which then get powerfully attracted to the negative electrode while applying an equal-but-opposite force to the thruster itself (See "lifters", a fun hovering ion-drive you can build in your garage, assuming you're competent to play with tens of thousands of volts)
The critical evalua
Ion Thrusters (Score:2)
Useful, and yet... (Score:2)
The fact that it has a high specific impulse is good, if one were traveling though very empty space. But, the gravitational slingshots and interplanetary highways require short bursts of high energy, at very specific times, rather than high efficiency.
Still, though, the problem which neither of these addresses, and that none of the solutions I have seen so far address, is the collision with other masses.
Sounds like a good delivery platform for FOCAL (Score:2)
The FOCAL [centauri-dreams.org] mission might benefit from this kind of tech, seeing as it involves getting a telescope 550AUs out from the Sun and using the sun as a lens.
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Most likely this thing was not aboard any ship or probe or any other object in outer space. This thing is being developed, so it is likely attached to some instruments in a lab where they can monitor it continually and make sure there aren't any problems. Likely they shut it down periodically to look for any problems, signs of breakdown or other signs that this cannot be scaled up for any reason.
So how far and how fast are irrelevant. There are enough numbers in the summary that you can do your own calculat
Re:Given that we aren't actually simpletons... (Score:5, Insightful)
Likely they shut it down periodically to look for any problems, signs of breakdown or other signs that this cannot be scaled up for any reason.
.
Not. It was 43,000 hours of continuous operation.
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Yes. But it was on a test stand, so that *IF* problems developed, they could shut it down to fix the problem. Think of it as a debugging run.
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If they shut them down how could it be claimed to be continuous operation? You do know that continuous means "uninterrupted", right?
Re:Given that we aren't actually simpletons... (Score:5, Funny)
Maybe they mean "continuous" operation the way ISP's mean "unlimited" bandwidth?
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Ahhh, I remember when AT&T Worldnet screwed that up for everyone. They gave "unlimited" and would periodically bump their users offline. Those of us who had our machines automatically reconnect and notify us of our new IP were apparently a pain. "Unlimited" became "Unlimited, yet limited to x hours per month" and if you did stay connected all month, it was something like a $5,000 charge for the extra time, even if you barely transferred anything.
I almost preferred the per minute billing. I couldn't
Re:Given that we aren't actually simpletons... (Score:5, Funny)
My calculations would say it probably went at a speed of around 0km/second, placing it now around 0km from Earth after 5 years.
Re:Given that we aren't actually simpletons... (Score:5, Funny)
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My maths are 0.00074295 km from the Earth. :)
Re:Cool... (Score:4, Interesting)
Although acceleration is not the same as speed, AC is right. Even if you assume the probe's weight is negligible, you begin to run into issues with thrust to weight of fuel. Over the five years cited in this story, the ion thruster consisting of fuel only would get you to 75km/s, or about a 14,000 year flight to alpha centauri. Scaling up doesn't help much as the ion thruster has to accelerate a larger mass.
Re:Cool... (Score:5, Informative)
I keep hoping, but interstellar is extremely difficult. It won't happen in our lifetimes. To get to Alpha Centauri in just 70 years requires acceleration to near 0.1c. That takes way more energy than we can currently give our probes. Thinking that a gravity assist can help significantly with that is like thinking you can make your car go significantly faster by having a person stand beside the road and blow air at your back as you pass.
Maybe we could eventually swing something on the order of 700 years. But just 70 years is really pushing the longevity of our current designs. Plutonium doesn't last long enough. In any case, how to make a probe last 700 years is only half the problem. Keeping a project alive, relevant data fresh on current media, and people trained for such a length of time would be the other half. 700 years is an awful long time for circumstance to scuttle the project. Can NASA or any other agency last that long? Can the US?
Barring catastrophe, we will eventually do it.
Re:Cool... (Score:4, Interesting)
> Thinking that a gravity assist can help significantly ...
http://en.wikipedia.org/wiki/Gravity_assist [wikipedia.org]
Right. Most folks, even amateur space enthusiasts like us, don't really understand the gravity "slingshot" and how it works. Some have the idea that you can just accelerate like a demon toward a given planet or moon, whip around it and somehow gain all sorts of new velocity. That's not so.
What you will gain is part of the orbital velocity of the object that you're "slingshotting" around. Nice boost and it makes a difference -- our space probes use it all the time -- but it's not some magical means by which you can accelerate to C-fractional speeds.
Re:Cool... (Score:4, Insightful)
To get to Alpha Centauri in just 70 years requires acceleration to near 0.1c.
And then to actually stop there to land on a planet requires deceleration by nearly 0.1c.
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A few years of economic difficulties and some populist loudmouths talking about draconian cuts, and boom! There she goes.
Re:Cool... (Score:4, Interesting)
Trying to work a project for 700 years would also inevitably land you in the position of launching something that is 300 years newer that would pass your 300 year old probe long before it got to it's destination, because propulsion tech is 300 years better.
I mean, 700 years ago was 150 years before Copernicus created his heliocentric model of the solar system, and was lambasted for it. Now we've got probes on their way out of the solar system that he was mostly correct about.
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This is somewhat disingenuous. Physics is physics and rocket technology hasn't improved much since the Centaur (hydrogen rocket) engine in the mid-1960s because they're already getting close to the theoretical maximum energy from chemical rockets. This is sort of like saying we shouldn't develop spoons and forks at the turn of the last millennium because by 1935 we'll have developed the spork. Cutlery has been a mature technology for about two thousand years now, and you can't really improve on it. Short of
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This is somewhat disingenuous. Physics is physics and rocket technology hasn't improved much since the Centaur (hydrogen rocket) engine in the mid-1960s because they're already getting close to the theoretical maximum energy from chemical rockets. This is sort of like saying we shouldn't develop spoons and forks at the turn of the last millennium because by 1935 we'll have developed the spork. Cutlery has been a mature technology for about two thousand years now, and you can't really improve on it. Short of FTL travel we're looking at scramjets and multigenerational probes.
Cutlery has changed significantly, even in the 700 year period we were discussing:
Slate article [slate.com]
I'm not sure how it affects your argument, but perhaps you should try to find an example of something that hasn't changed significantly in the past 700 years.
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Because new ideas never happen, right?
There probably was once someone who said that the telephone could never be improved, because a human can only talk so fast. Then digital communications happened.
Just because you and I can't think of it, doesn't mean it won't happen.
Re:Cool... (Score:4, Insightful)
The christian church (in various forms) has been around for millenia awaiting the return of their messiah. That is quite a bit of longevity. Perhaps we should convert NASA to a religion, then there will be no problem having someone wait a few hundred years for the return of their white metallic savior.
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>> Barring catastrophe, we will eventually do it.
And where did you pick that up ? On the last 50 tv shows/sci-fi movies that you looked .. ?
You could just as easily say we're all dead. Both statements are dellusional, unfortunately influenced by above mentioned that influenced you to think this way.
Offtopic, but relevant in some sort of abstract way: Then people wonder why media can influence people opinion (to give a green light) when it comes to bombing 20 countries in 10 years.
And my personal opini
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I really doubt that "we", i.e., the stay-at-homes, will ever do it. The only way to have a project last for 700 years is to inspire true commitment. A colony ship might work, but but the time they got there, they wouldn't be interested in living on a planet, and this would need to be planned for. (And by planned for, I don't mean rig things to coerce them.)
The other possibility that I see is that an AI could be designed that WOULD maintain focus for that long and longer.
OTOH, if we don't choose to remain
Re:Cool... (Score:4, Interesting)
Re:Cool... (Score:4, Informative)
For a more earthly comparison, it would take about 8.6 seconds to drive across Kansas at that speed.
http://en.wikipedia.org/wiki/Kansas [wikipedia.org]
Re:Cool... (Score:5, Funny)
That's still a lot of time to spend in Kansas.
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But it's still a lot better than the 8.6 hours it takes to drive across it.
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Hoo, clever! What, no Wizard of Oz reference? Those are always so insightful.
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Isn't this where your Bussard collectors come in. Now, I understand that there's not likely to be a lot of Xenon in interstellar space, but it's possible that once NEXT is producing plenty of data, we can figure out how to get something working with hydrogen.
Re:Why no ion thrusters on satellites? (Score:4, Informative)
They are used on satellites. http://en.wikipedia.org/wiki/Ion_thruster#Operational_missions [wikipedia.org]
But is it valuable? (Score:2)
Sure, it's not the cheapest reaction mass, but at 220 Watt-hour/liter it's not exactly terribly expensive to extract from the atmosphere, and it is well suited to ion-drive use.
What I wonder is is it actually a particularly valuable substance (usefulness as opposed to price) for anything else, or can we go ahead and use up the planet's supply* as spacecraft "fuel" in good conscience. From what I can tell it's used primarily for lighting, radiation detectors, and as a general anesthetic (How does that work?
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That would be pretty pointless though - pushing directly away from the planet you're orbiting just changes your orbital eccentricity, without significantly changing your orbital energy. Meaning that when you reach the opposite side of your orbit you'll be even closer to the planet than you were before. And since you'd have to be pretty close to begin with for a significant portion of your exhaust to collide with the planet that probably means you've just executed a de-orbiting maneuver. And actually, sin
Re:Cool (Score:5, Funny)
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Nah, we'll need to give them a bit more thrust before they become useful. Considering the fighter itself has no life support, the pilot will be dead before he gets to above walking pace if we use the current model.
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Hardly, if both sides had such low-power ion-drives the defenders couldn't even get off the surface and would be sitting ducks. As long the rebels could avoid the moon's point-defense systems they could just eject annoying droids at sensitive targets until the whole place came crumbling down.