Tiny Ion Engine Runs On Water 103
symbolset writes "Discovery News is covering a project by two engineers from the University of Michigan to pair cubesats with tiny ion engines for inexpensive interplanetary exploration. The tiny plasma drive called the CubeSat Ambipolar Thruster (CAT) will ionize water and use it as propellant with power provided by solar cells. In addition to scaling down the size of ion engines they hope to bring down the whole cost of development and launch to under $200,000."
No, it runs on sunlight. (Score:5, Informative)
Re:No, it runs on sunlight. (Score:4, Insightful)
That answer is just as dumb.
It runs on both.
It always needs a propellant and a energy source.
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Re:No, it runs on sunlight. (Score:5, Informative)
The propellant used is incidental, as evidenced by the ion drives that run on xenon, for example.
Actually, there are *very* good reasons for why specific kinds of engines run on specific kinds of propellants. "Incidental" is hardly the word I'd use.
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It's definitely out there, in decent quantities.
http://news.nationalgeographic.com/news/2011/07/110726-most-massive-water-cloud-quasar-black-hole-space-science/ [nationalgeographic.com]
Re:No, it runs on sunlight. (Score:5, Funny)
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Dune is at best soft sci-fi.
Well of course it is, duh! Sand is soft. You want hard SciFi, try Podkayne of Mars. Ooops, not *that* kind of hard?
Re:No, it runs on sunlight. (Score:5, Funny)
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Arrakis used to have plenty of water, unfortunately all those damn Fremen kept collecting it and hiding it in caves.
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As I recall, it's actually the sand worms (or rather their younger form - sand trout) that sequestered water and effectively terraformed the planet's surface so that it'd be suitable for adult sand worms, for whom water is poisonous.
http://en.wikipedia.org/wiki/Sandworm_(Dune)#Sandworm_life_cycle [wikipedia.org]
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You'd think that the Fremen with all their technology would find a way to scoop it up and funnel it down to Arrakis then.
This is a common trope in SF: You take an advanced planet X and resource Y and say that Y is rare there. There are two alternatives. Either the natives completely ignore the masses of resource Y right over their heads, or they skip them completely and go interstellar to find something that could more easily be obtained locally.
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The point that they've found a cloud of the stuff billions of times the size of the Earth is a decent indicator it will exist in smaller, but still vast, quantities elsewhere. It's unlikely there's just one big cloud of water in all the universe.
The Pacific Ocean is a poor example because the poster I was responding to specified space, which generally means "not caught in a planet's gravity". The cloud I referenced is free-floating in space.
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And besides all that pure water sitting around in the universe, I suppose the GP also thinks we have all that sunlight with which to ionize the water.
Until, that is, you get out to the Oort cloud where all the water is. Then all of a sudden you need every ounce of electricity you can possibly generate just to melt the water.
So both elements needed in ionized water drive fail you exactly when you need it most.
Re:No, it runs on sunlight. (Score:5, Interesting)
Until, that is, you get out to the Oort cloud where all the water is.
Ceres [wikipedia.org] was the first asteroid discovered and is now classed as a "minor planet". It is a main belt asteroid between Mars and Jupiter. It has a diameter of about 1000 km, and is believed to have a mantle composed almost entirely of water ice that makes up one third of the body's mass. 200 quadrillion metric tons of water ice should be more than sufficient, as it's more than all the fresh water on Earth and ionizing that much water to plasma would take more energy than we have until fusion is worked out. For scale, these interplanetary cubesats would launch with 1.5 kg of water for propellant, or 1/1*10^20 of that. The water ice should be relatively pure as it was gravitically distilled during the formation of the body. Ceres may even have liquid water still. It is a main asteroid belt object near enough to the sun that solar energy is effective for solar water distillation and solar cells. It has an equatorial surface gravity of 0.03g, and an escape velocity of 500 m/s. On the surface it has a thin coat of iron and silicon rich minerals that would also be useful. It is believed to own 1/3rd the mass of the entire main asteroid belt, or just over 1% of the mass of the Moon, 0.01% the mass of the entire Oort cloud all in one convenient low gravity place close enough to the sun for solar cells to work. How much more water the Oort cloud has than Ceres is irrelevant if Ceres has more than we can use in a more convenient place.
In just over 18 months, February 2015, the NASA Dawn [wikipedia.org] mission will arrive there and survey Ceres. NASA Dawn uses an ion engine also, and its delta-V is not very different from that proposed for these cubesats.
On the energy thing: Solar cells are perhaps misnamed because of their historical use. It turns out they convert energy quite well if you point a laser at them. Even better as the laser can be tuned to the maximum conversion frequency of the cell. As the energy of lasers don't diminish as much over distance as other methods it is quite possible to power the "solar cells" of distant craft by pointing lasers at them from closer to the sun where insolation is higher using solar cells as energy input. We think of lasers as a thing that has perfect collimation that makes them useless for powering solar cells but in fact at interplanetary distances past the utility of the sun's energy the beam will be larger than the craft. Our deep space craft need not run out of "solar" energy ever while we care to illuminate them with space-based lasers to the limit of their capacity, even to interstellar space. This is much preferable to carrying the energy with the craft even with nuclear fission fuels. Maybe one day we'll make a craft that goes out to the Oort cloud, eats a comet to refuel on its way to the stars. But that's in the distant future. For now the Oort cloud is off the table.
Because filters exist you can even still use communication lasers on a different frequency from your power lasers. Communication lasers don't suffer from physics as much as radio transmissions do, as long as you use space based relays in Earth orbit with radio ground comms. The Earth's atmosphere plays hob with communication lasers. You still have periods twice a year when you can't talk to the thing, and can't send it power. If you have power and comm relays on Ceres this drops to once in 800 years when both Earth and Ceres are conjoined.
Ionizing the water is part of the process of the engine converting it to plasma, so ordinary water is the input - not some special "ionized" water.
In short, if water works as an ion engine propellant then we've cracked the nut for Man's exploration of the solar system and the stars. Your issue about having to go out to the Oort cloud for water is, of course, ridiculous.
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But when we start mining the ice there, what will we do with all the Woolly Mammoth skeletons we did up?
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*dig*
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Nicely done, thanks. Those with a strong engineering background can dig it, 'cuz it's piecework all the way. Nothing fancy at all. Take a bit of doing but once established it'd make a handy place for water and its components.
Didn't look at the delta-v chart yet, but I suspect Ceres is also well-placed for general solar system maneuvering; easy to get to, easy to leave, centrally located. Sunward is easy; can use light sails for steering.
Re:No, it runs on sunlight. (Score:4, Insightful)
The Pacific Ocean is something very inconvenient for a spacecraft in Geo-synchronous orbit. In fact, it is much, much easier to grab something from the Moon or from an asteroid or comet than it is to get that same bucket of water from the Pacific Ocean. In fact, it would be easier and "cheaper" (assuming the infrastructure was in place) to mine the ice caps of Mars than it would be to get water from the Pacific Ocean.
A really good diagram that shows some delta-v budgets for moving stuff around the solar system can be found here: http://upload.wikimedia.org/wikipedia/commons/7/74/Delta-Vs_for_inner_Solar_System.svg [wikimedia.org]
The gravity well is something that is not just from science fiction, but something that has to do with real-life physics. Or are you one of those who thinks the Apollo Moon landings happened in a Burbank studio? I suppose NASA has never sent anything above the "sky" either, not even a communications satellite? Without real people doing real things in space, you would likely be dead. I'm not exaggerating.
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So let me ask you the real question on everyone's mind: When you go to a party where there are a lot of attractive women, do you announce your arrival with something like "Hi everyone! I'm a gigantic dick!"
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Water is the fuel, sunlight is merely a power source. The solar arrays could be replaced with whatever power source you want - RTG, fission reactor, Li-ion battery, etc.
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Water is the fuel, sunlight is merely a power source. The solar arrays could be replaced with whatever power source you want - RTG, fission reactor, Li-ion battery, etc.
A fuel, by definition, supplies power. Water supplies none. Therefore it is not a fuel.
Water is merely a propellant.
You don't get to use the word "merely" in relation to a power source. That's totally backwards.
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Propellants often react or change in some way to provide energy. They don't have to, and technically propellant is correct here, but I'd avoid the whole thing by going with "reaction mass"...
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It runs on water about as much as a steam engine does.
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There's one in every FUCKING thread.
I'm sure there is a drought in space joke somewher (Score:5, Interesting)
.....but more practically: how much thrust/impulse/whatever would you be able squeeze out of an amount of water that can be carried by a tiny cubesat? The article implicitly compares it favorably to current Xenon/Krypton based systems, but made no effort to explain why. Any slashdoter willing to work out the math?
Re:I'm sure there is a drought in space joke somew (Score:5, Interesting)
Re:I'm sure there is a drought in space joke somew (Score:5, Interesting)
Thats true, but the issue in a cubesat is going to be all about total propellant mass fraction (The fraction of the vehicle mass at launch made of of stuff you can sling out the back at high speed), so while Xe is a better reaction mass if you have the space for the tank, it may well be that in this particular use case the higher storage density (and thus the ability to fit more of it into a tiny tank) actually trumps the heavier ion.
Space propulsion is all about propellant mass fraction and exhaust velocity, as those two numbers define how much delta V you can get out of your available fuel.
The problem with light ions in this situation is that the momentum transferred is simply the product of exhaust mass and exhaust velocity, the energy required to produce that exhaust velocity is 1/2 mv^2, thus a heavier ion travelling more slowly requires less energy input to the accelerator for a given amount of momentum transfer then a light ion moving fast.
However if you have surplus electrical power, and are not too concerned about producing large accelerations (even by ion drive standards), and can solve the corrosion and thermal management problems, it might actually be a reasonable tradeoff.
All space propulsion is tradeoffs between energy/reaction mass/specific impulse/acceleration, there are no really right answers here, and having another validated tool in the box is always going to be useful.
Re:I'm sure there is a drought in space joke somew (Score:4, Interesting)
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Further out there is less solar energy for the solar cells but we can laser illuminate them.
Solar energy production only really becomes an issue when you get beyond Mars.... about the orbit of Jupiter or so (perhaps a little closer to the Sun depending on your solar array size and efficiency). There is still a whole lot of Solar System much closer that can be used for all kinds of activities, including 99.9% of all satellites that are currently in use or for that matter have ever been used. Exploration of the outer Solar System definitely requires some alternate energy sources, but that isn't go
Re:I'm sure there is a drought in space joke somew (Score:5, Interesting)
Re:I'm sure there is a drought in space joke somew (Score:5, Insightful)
It is a potential habitat. It is a gateway to the stars.
...and here you reveal your true colours.
Ceres is not a potential habitat.
Assume you can develop a shelter with adequate shielding from cosmic rays and solar storms, adequate insulation, pressure containment, etc. (Despite the fact that we don't know what "adequate" is, or exactly what's in "etc".) And assume you can transport inhabitants there, all the while keeeping them healthy. Fine. One teeny little failure in one annoying little subsystem, lasting a mere minute, and every inhabitant is dead. What are the odds of zero operation failures in a lifetime? Never happened in any city here on Earth. Or even any inhabited building.
Another thing. If you could build machines reliable enough to transport people safely around the solar system (and you actually wanted to have people live off Earth), why would you bother with a habitat on an asteroid? Stick with what works: the spaceship. Iain Banks had this right.
Ceres is not a gateway to the stars.
Nothing is. The stars are too far away. You'll never live long enough to learn anything from sending a physical mass to any star with Earth-like, habitable zone planets; your city won't exist long enough. Your civilization likely won't last long enough. (The Fermi paradox is no paradox at all. It's a demonstration of how far apart stars are, and how hostile and unrewarding the intervening space is...and perhaps of the rationality of other intelligent life.)
So what are we left with? Ceres is a potentially useful source of reaction mass/propellant, if anyone ever discovers a valid reason to send physical masses past geosynchronous orbit. (I'll believe mining asteroids could be profitable when I discover a pressing ubiqitous and essential materials problem for which all solutions require one particular element, and the element is both in short supply here on Earth and abundant on an asteroid near Ceres. To date, though, there are substitutes and alternatives for pretty much everything that might start to get short in the next century, so don't hold your breath.)
I can see a point to mini ion drives. They're potentially handy for sending things out to geosynchronous orbit and doing stuff there and in LEO. And I can see a point to operating telescopes with good resolving power out "in space". But I can't see why they'd need to be very far away from Earth. And even for purposes of scientific experimentation, I can't see a point to sending physical mass much past the outer part of the Oort cloud.
If you want to get a semi-knowledgeable public interested in this stuff, don't use words and phrases like 'habitat', 'gateway to the stars' or 'profit' when talking about this stuff. They scream "space cadet".
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It is a potential habitat. It is a gateway to the stars.
...and here you reveal your true colours.
Ceres is not a potential habitat.
Assume you can develop a shelter with adequate shielding from cosmic rays and solar storms, adequate insulation, pressure containment, etc. (Despite the fact that we don't know what "adequate" is, or exactly what's in "etc".) And assume you can transport inhabitants there, all the while keeeping them healthy. Fine.
You mean like a buttload of water? Or this? http://tech.slashdot.org/story/08/11/04/171242/experimental-magnetic-shield-against-cosmic-rays [slashdot.org]
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Like tlambert said, I'm pretty sure that 500km of water is an adequate radiation shield. I wasn't even discussing human habitation anyway - we can get the water off without ever setting foot there but of course eventually we will when we can get there quick enough to not kill the passengers.
As for my civilization, I've high hopes and like you, low bets.
I think I'll leave the rest of your psychosis alone. I'm sure it makes sense to you. Maybe you should share it with an interested professional. I could
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When i think of life-support i always think about submarines and the ISS. Subs go down for months at a time and failure is very news worthy. I don't see why a habitat cannot be built on Ceres. The ISS would die without constant resupply though. There is no environment to work with there : / Solar power is about the only thing they get.
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That somebody is likely going to be Planetary Resources, or some other similar company who is going to get involved with asteroid mining. I would suspect that when Rio Tinto gets involved is when you will see serious money being put on the line for asteroid mining (they make IBM seem like a small start-up company). Rio Tinto also has the cash reserves necessary to build a mining colony in space if necessary, and certainly have mining operations in some rather inhospitable locations around the world. Movi
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Asteroids which come near Earth are Planetary Resources' focus. They hope to capture one and exploit its minerals. That is an easy mission: catch what comes to you. Some of these Near Earth Asteroids still contain some captured water content, but an asteroid that has frequented Earth's orbit for a long time will not have them in great pure degree because those boil off - so a great deal of energy and technology must be spent to convert fractions of rock to water. Far more than would be spent to just go
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How many spacecraft have actually gone beyond the orbit of Mars? You can count them on two hands, out of tens of thousands of spacecraft that have been sent into space. Yes, unmanned spacecraft can reach the outer planets and have, but they are exceptional spacecraft that would need to be designed for that specific kind of a mission.
I'm just saying that for 99.9% of all spacecraft that will ever be built, it isn't a problem.
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Back Up (Score:2)
You're standing too close to the exhaust!
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I know it's a drag, but if you actually take the time to read the Kickstarter page, you will see that they have worked out the math. Furthermore, these are actual rocket scientists so they should be better than the average slashdotter.
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I know it's a drag, but if you actually take the time to read the Kickstarter page, you will see that they have worked out the math. Furthermore, these are actual rocket scientists so they should be better than the average slashdotter.
Assuming they didn't mess up a Imperial/Metric conversion in there somewhere...
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Ya make one small mistake and they never let you forget it!
Re: I'm sure there is a drought in space joke some (Score:3)
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Correction:
A cubesat is made up of one or more 10x10x10cm blocks AT LAUNCH.
Mass is entirely dependent on how those blocks are filled up.
Flying configuration is entirely dependent on how they're designed to pack. Quite a few of them unfold quite large solar panels and linear antennas once released into orbit - and you're not constrained to ONE block, just the block-based configuration (Many larger cubesats are made up of 3 blocks. OTOH some cubesats may disperse into a bunch of smaller devices once releas
Better than Jesus... (Score:5, Funny)
Re:Better than Jesus... (Score:5, Funny)
Ye, but can this thing turn water into wine, ye Jesus wins!
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But, this does turn water into a _whine_ when expelling it but it's just that you can't hear it in space :-).
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Honestly, we have no idea how big Jesus' feet were.
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Jesus was actually a juvenile sasquatch. He had to fake his death because the hair started coming in as he reached sasquatch puberty.
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You mean "That is no small feet" don't you?
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Come now - it's far easier to run on water than walk on water. Heck, the basilisk [wikipedia.org] can run on water. Jesus not only walked on water, but he just stood there too and helped pull another guy (Peter) out of the water when he started to sink. Granted, Peter did manage to walk on the water for a little while, so it's not just a Jesus thing...
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Nothing wrong with B.A.S.I.C.
Otherwise alter the arry +- 1 and try that.
Extremely misleading and dishonest headline (Score:1, Informative)
The submitter should be ashamed of itself.
holy cow! (Score:1)
I am seriously impressed and wish I had more than a few cents in my bank account with which to back this.
No mention of the kickstarter? (Score:2, Informative)
Summary makes no mention of the CAT [kickstarter.com] kickstarter campaign for this thing.
So this is how we get sample from other planets. (Score:1)
Why is water better than Xe? (Score:5, Interesting)
As has been previously mentioned, the key question of space propulsion is how much thrust can you get for a given mass of propellant? The usual measure of this is Isp, which is thrust per weight flow rate of propellant. While it seems unlikely that water will beat Xe due to having lower mass per ion, it does have several key advantages, which are not really in the article except the first one:
1. Smaller storage tank can be used for liquid water as opposed to a gas. This is especially important if you're trying to piggyback with another satellite.
2. Gas will leak out over time, requiring more expensive hardware to contain it. You need something able to handle the expansion and contraction associated with sunlight, plus the very high pressure. That's a lot of seals, and getting seals that won't degrade in space is not that trivial- it's a harsh environment, especially from a radiation standpoint.
3. This is just something that occurred to me, but a large fraction of the weight on a spacecraft is a radiator, because the only way to get rid of heat in space is radiative heat transfer, which is much less efficient than convection. (and if you are generating power and thrusting, you are making heat) If you utilized the water as the working fluid in the radiator, you might be able to simplify another subsystem. I don't know if they actually did this.
So in summary:
It is unlikely that water produces a more efficient propulsion system, but it may well produce a simpler, cheaper, and easier to transport one.
Disclaimer: No actual math was done for the writing of this post. If you have math to prove me wrong, please do so.
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Say I want to fly to Saturn and land on Titan. I could build a big vehicle (think Discovery from 2001) and fit it out with a number of fission reactors and a huge array of ion engines. It would have water tanks surrounding the crew compartments for radiation shielding. The mission would include a visit to a small Saturn moon with a known source of water ice so that more reaction mass could be collected. The article doesn't have numbers for the specific impulse of these ion engines but it would certainly be
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Look, I get that you are an Evangelical or some other type of Luddite who would like to discourage space exploration. The "space nutter" thing was a dead giveaway. My puzzle isn't how to get to the stars, but why you think you're going to get anywhere talking to me of all people. All you're doing is encouraging me write a howto on the necessary path using readily available off-the-shelf technology. If your goal is to prevent this then you have not served it here. You would have done better to stay mute
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Ignore the AC idiot. He is really being a troll and are clueless about reality or the state of current technology. So much is happening in space that you really can't keep track of it all any more, even if you do that full time. I'm just talking new ideas and discoveries that merit entries in scientific journals, much less keeping track of launches and actual stuff that is happening in space.
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Thanks.
Regrettably the AC idiots need to be dealt with. Leaving their illiterate posts unanswered implies that they have merit and they will sell that.
Of course I don't take them to heart. If I can distract them from the real engineers and called their lie I've done the little bit that I can do. It's little enough, but it's what I have.
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3. This is just something that occurred to me, but a large fraction of the weight on a spacecraft is a radiator, because the only way to get rid of heat in space is radiative heat transfer, which is much less efficient than convection. (and if you are generating power and thrusting, you are making heat) If you utilized the water as the working fluid in the radiator, you might be able to simplify another subsystem. I don't know if they actually did this.
So in summary: It is unlikely that water produces a more efficient propulsion system, but it may well produce a simpler, cheaper, and easier to transport one. Disclaimer: No actual math was done for the writing of this post. If you have math to prove me wrong, please do so.
Re: radiative heat transfer. I don't think that the power used by a cubesat can provide heating challenges, especially if the said cubesat is to run on solar panels (heaps of surface relative to the delivered power). So much so that keeping the water from freezing may be the actual problem (given the quite high specific heat of water/ice, it would be a pity if needed to waste energy in melting the fuel first).
Yaaaawn (Score:1)
It's no big deal, right now we have ion engines that can successfully work for years: http://www.theregister.co.uk/2013/06/28/nasa_to_shut_down_long_running_next_ion_propulsion_test/ [theregister.co.uk] We have missions that use ion thrusters to move across the Solar system: http://en.wikipedia.org/wiki/Dawn_Mission [wikipedia.org]
Low-thrust propulsion is basically a solved problem. What is yet unsolved is getting to the LEO cheaply enough.
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Technically, getting to LEO cheaply is a solved problem, at least on paper.
It really hasn't been an easily solved problem getting to LEO, technically speaking. There are some fanciful ideas and dreamers who come up with crazy things like space elevators or thermal-laser launch systems, but as a practical matter those haven't really been built for actual payloads.
There are a number of companies who are working on trying to find an actual solution to launch actual payloads on the cheap. The #1 thing that everybody (across the space hardware industry) is looking at right now is sim
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And forget the interstellar-space angle for a moment, too: anyone for a decent picture of Pluto?
How long until TIE Fighters (Score:2)
A more practical use (Score:2)
Instead of interplanetary travel, how about using these thrusters to deorbit the cubesats at their end of life so they don't become spacejunk?
this ain't new (Score:1)
My dad had an engine which ran on water.
I think it was called an outboard motor.