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Tiny Ion Engine Runs On Water

timothy posted 1 year,14 days | from the instant-ice-tea-doubles-the-range dept.

Space 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."

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103 comments

No, it runs on sunlight. (5, Informative)

Anonymous Coward | 1 year,14 days | (#44279667)

n/t

Re:No, it runs on sunlight. (4, Insightful)

Anonymous Coward | 1 year,14 days | (#44279863)

That answer is just as dumb.

It runs on both.

It always needs a propellant and a energy source.

Re:No, it runs on sunlight. (2, Insightful)

Anonymous Coward | 1 year,14 days | (#44279895)

The propellant used is incidental, as evidenced by the ion drives that run on xenon, for example. The difference here is that the engine can use something easily found in space, i.e. water. It's no small achievement, but the headline is disingenuous to say the least.

Re:No, it runs on sunlight. (4, Informative)

K. S. Kyosuke (729550) | 1 year,14 days | (#44279917)

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.

Re:No, it runs on sunlight. (0)

fisted (2295862) | 1 year,14 days | (#44280999)

Now that your post is +5 Informative, would you mind adding some information regarding those ,,*very* good reasons''?

Re:No, it runs on sunlight. (3, Informative)

Anonymous Coward | 1 year,14 days | (#44281539)

Ease of ionization, mass to charge ratio (something favoring both being xenon), cost, size and ease of storage, scalability of storage (two things apparently favored by water over xenon), long term impact on accelerating grids, ...

Re:No, it runs on sunlight. (1, Interesting)

Anonymous Coward | 1 year,14 days | (#44279981)

Can you define "easily found" as regards to water in space? Are you telling me there's a 5 gallon jug of pure water just waiting to be used as propellant? Is there also a canister of xenon? That's also found in space.

Re:No, it runs on sunlight. (1)

SJHillman (1966756) | 1 year,14 days | (#44280085)

Re:No, it runs on sunlight. (4, Funny)

interval1066 (668936) | 1 year,14 days | (#44280149)

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.

Re:No, it runs on sunlight. (1)

Anonymous Coward | 1 year,14 days | (#44280289)

Dune is at best soft sci-fi.

Re:No, it runs on sunlight. (1)

cellocgw (617879) | 1 year,13 days | (#44286001)

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. (0)

Anonymous Coward | 1 year,14 days | (#44281319)

Most Fremen (like all of them) have never even taken a bath and you expect them to build space ships?

Re:No, it runs on sunlight. (4, Funny)

The Mighty Buzzard (878441) | 1 year,14 days | (#44281599)

Dunno about rocket scientists but they sound like damned fine sysadmin material.

Re:No, it runs on sunlight. (2)

Noughmad (1044096) | 1 year,13 days | (#44286177)

Arrakis used to have plenty of water, unfortunately all those damn Fremen kept collecting it and hiding it in caves.

Re:No, it runs on sunlight. (1)

K. S. Kyosuke (729550) | 1 year,13 days | (#44293805)

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.

Re:No, it runs on sunlight. (0)

Anonymous Coward | 1 year,14 days | (#44280353)

And to you something that's billions of light years away falls under "easily found" in the context of this story? As opposed to the Pacific Ocean for example?

Re:No, it runs on sunlight. (2)

SJHillman (1966756) | 1 year,14 days | (#44280485)

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.

Re:No, it runs on sunlight. (2)

symbolset (646467) | 1 year,14 days | (#44280735)

One asteroid we know of has 200 quadrillion metric tons of the stuff. Is that both enough and close enough for you? Yes, the Pacific Ocean has more, but it is rather more inconveniently located at the bottom of a deep gravity well.

Re:No, it runs on sunlight. (-1)

Anonymous Coward | 1 year,14 days | (#44280761)

The Pacific is also rather conveniently located where everything is. Space is rather inconveniently empty. There's no infrastructure there, and again, I doubt the water is just waiting for you in a jug. Is it pure? There's no impurities in space? How lucky for us! All the stuff is just pre-made for us, all arranged neatly!

"Gravity well" is also a strong indicator you got your world-view from sci-fi, ie, it's not based in reality. But I already know you are a Level II Space Nutter, maybe even Level III.

Re:No, it runs on sunlight. (0)

icebike (68054) | 1 year,14 days | (#44280909)

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. (4, Interesting)

symbolset (646467) | 1 year,14 days | (#44281303)

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.

Re:No, it runs on sunlight. (-1)

Anonymous Coward | 1 year,14 days | (#44281845)

Wow! Such imagination! I read all those sci-fi novels too in the '80s! Robert L Forward in the house! Hahahaha!!! Oh you're so naive and so cute. Don't ever change.

Re:No, it runs on sunlight. (1)

symbolset (646467) | 1 year,14 days | (#44281961)

I think these are well documented properly referenced well known facts. If you think there is some flight of imaginary fancy posed here then please be specific and point to it so I can educate you about the specific scientific ways that you are wrong. You're using the emotional appeal, but you're WAY too deep in a /. thread for anybody to see it but you and me.

Re:No, it runs on sunlight. (2)

evilviper (135110) | 1 year,14 days | (#44282373)

Ceres [...] 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

But when we start mining the ice there, what will we do with all the Woolly Mammoth skeletons we did up?

Re:No, it runs on sunlight. (1)

evilviper (135110) | 1 year,14 days | (#44282383)

*dig*

Re:No, it runs on sunlight. (1)

CHIT2ME (2667601) | 1 year,13 days | (#44290405)

"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." No, No, No! We will crack the nut for Man's exploration of the solar system and the stars when we can protect Man from the hellish radiation which dwells there!

Re:No, it runs on sunlight. (1)

kermidge (2221646) | 1 year,13 days | (#44292217)

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. (-1)

Anonymous Coward | 1 year,14 days | (#44281379)

Yup, I suspect people like symbolset don't bother to actually think things through in terms of practical engineering and reality, they just like repeating pleasant-sounding fantasies to themselves. Sort of like a religion. I think most religious people know there's no invisible man in the sky you can talk to, they just go to church to talk to friends and do something together, then they go home knowing full well it's all nonsense. I'm guessing symbolset here does the same, he comes here hoping to find other people to exchange sci-fi with, then he goes on in real life knowing full well it'll never happen.

Re:No, it runs on sunlight. (3, Insightful)

Teancum (67324) | 1 year,14 days | (#44281689)

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.

Re:No, it runs on sunlight. (0)

Anonymous Coward | 1 year,13 days | (#44286103)

And you think a tiny ion engine designed to move a small payload in space will have enough power to lift that load off a large asteroid?

Re:No, it runs on sunlight. (0)

Anonymous Coward | 1 year,13 days | (#44285329)

Well, there's a teapot half way between earth and Mars, at least. Should give an extra few miles.

Re:No, it runs on sunlight. (0)

Anonymous Coward | 1 year,14 days | (#44281479)

something easily found in space

Even for the brightest rocket scientists, the only thing easily found in space is nothing.

Re:No, it runs on sunlight. (1)

The Cat (19816) | 1 year,13 days | (#44282683)

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!"

Re:No, it runs on sunlight. (0)

Anonymous Coward | 1 year,13 days | (#44285277)

Sure you need a propellant, but a more accurate definition of "runs on" is "what the energy source is", otherwise we may as well say a car runs on iron and rubber because those are all in propelling a car.

Re:No, it runs on sunlight. (1)

spectral7 (2030164) | 1 year,14 days | (#44280625)

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.

Re:No, it runs on sunlight. (2)

icebike (68054) | 1 year,14 days | (#44280929)

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.

Re:No, it runs on sunlight. (1)

Anonymous Coward | 1 year,14 days | (#44281001)

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"...

Re:No, it runs on sunlight. (1)

Hognoxious (631665) | 1 year,14 days | (#44282265)

It runs on water about as much as a steam engine does.

Re:No, it runs on sunlight. (1)

The Cat (19816) | 1 year,13 days | (#44282677)

There's one in every FUCKING thread.

University of Michigan (-1)

Anonymous Coward | 1 year,14 days | (#44279681)

Perhaps those studying at the University of Michigan could use those ion engines to make Michigan a habitable place, and (along with those from Wisconsin, Boston, and Pennsylvania) stop moving to California where they drive rents up, wages down, and clutter up our beaches and roads with their unwelcome dumbfuckery.

-- Ethanol-fueled

I'm sure there is a drought in space joke somewher (4, Interesting)

tloh (451585) | 1 year,14 days | (#44279699)

.....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 (4, Interesting)

K. S. Kyosuke (729550) | 1 year,14 days | (#44279869)

I'd be also interested in knowing that. Xenon really is the almost ideal propellant: low ionization energy, heavy ions, completely inert, good density... Water might be slightly nasty, especially if the oxygen ions will come into contact with something reactive. But I do hope that these guys pull it off. I've been a space propulsion junkie since the age of ten or so. Stuff like this makes me tickled pink.

Re:I'm sure there is a drought in space joke somew (5, Interesting)

M0HCN (2981905) | 1 year,14 days | (#44280095)

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 (3, Interesting)

symbolset (646467) | 1 year,14 days | (#44280815)

Exhaust velocity is 20,000 Km/hr and propellant is half the mass of the craft so it should be on the order of Dawn Mission's 10,000 KPH delta V. If it works at all. These ion engines can theoretically run on a wide variety of propellants like xenon, argon or iodine but since water is so common in space it would be nice if it were effective. Ultimately that means one might refuel in transit, or we might shoot fuel at one with a rail gun. Further out there is less solar energy for the solar cells but we can laser illuminate them. Radio is a problem because of power laws, but space to space laser comm fixes that, with satellite to ground radio relays.

Re:I'm sure there is a drought in space joke somew (1)

Teancum (67324) | 1 year,14 days | (#44281729)

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 going to be anywhere near where these nanocube vehicles are going to be operating at.

One of the huge things that is being worked on right now is trying to refuel satellites where their propellant has been depleted. At the moment, even otherwise functioning satellites have to be shut down when that happens, so finding a propellant that is easy to transport and transfer can make a huge difference.... especially when those satellites cost billions of dollars just to build.

Re:I'm sure there is a drought in space joke somew (4, Interesting)

symbolset (646467) | 1 year,14 days | (#44281859)

The main asteroid belt is beyond Mars, but it's also the closest space that water ice can remain on a body after all these billions of years. Ceres is a gift. It is a fuel depot for interplanetary exploration. It is a potential habitat. It is a gateway to the stars. 200 quadrillion metric tons of water in a low-g environment close enough to the sun for solar cells to work. What more could you ask for? Somebody to exploit it for you? Just wait and they'll come along but they will charge market rates for the effort and then some margin.

Re:I'm sure there is a drought in space joke somew (5, Insightful)

real-modo (1460457) | 1 year,14 days | (#44282217)

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".

Re:I'm sure there is a drought in space joke somew (1)

tlambert (566799) | 1 year,14 days | (#44282365)

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]

Re:I'm sure there is a drought in space joke somew (1)

symbolset (646467) | 1 year,14 days | (#44282467)

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 refer you to one...

Re:I'm sure there is a drought in space joke somew (0)

The Cat (19816) | 1 year,13 days | (#44282695)

Don't you just being lectured by a know-it-all neckbearded arrogant condescending talking penis?

You want to know why people don't give a fuck about science and don't ever want to talk about it? Assmunches like this.

Re:I'm sure there is a drought in space joke somew (1)

tibman (623933) | 1 year,13 days | (#44289767)

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.

Re:I'm sure there is a drought in space joke somew (1)

Teancum (67324) | 1 year,13 days | (#44286923)

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. Moving into space would be easy in comparison to some of their efforts.

While I'm impressed with Ceres as a world, and I'd agree that its water resources are something that would be worth using, there are sources of water which are much more accessible and can use solar-powered ion engines in the meantime. I would imagine that some Thorium reactors might also be used, but nuclear engineering in a microgravity environment is something that hasn't had much engineering development effort to perfect. Some pebble reactors and some other interesting designs might work, but it would take some effort to get them build and even designed in the first place. Nothing which breaks physics like an FTL ship, but it does require some real engineering in a completely different design domain. I'll also note that the Moon and possibly Mercury would be excellent places to obtain Uranium and Thorium, and there certainly would be some other potential sources for those materials with Apollo-class asteroids.

Re:I'm sure there is a drought in space joke somew (1)

mrax (1825176) | 1 year,14 days | (#44282465)

Actually, unmanned craft can reach outer planets by using gravity slingshots around inner planets. (Cassini probe for example) Esentially, you would first aim for Venus where you have enough solar power and use it's gravity to change course and gain some dV towards the outer planets.

Re:I'm sure there is a drought in space joke somew (1)

Teancum (67324) | 1 year,13 days | (#44286771)

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.

Re:I'm sure there is a drought in space joke somew (1)

Nilsie (2984011) | 1 year,14 days | (#44282149)

So i suppose Deuterium is would be an interesting candidate to regular water.

Re:I'm sure there is a drought in space joke somew (1)

Nilsie (2984011) | 1 year,14 days | (#44282169)

To be more clear, heavy water made from Deuterium as opposed to regular Hydrygen.

Re:I'm sure there is a drought in space joke somew (-1)

Anonymous Coward | 1 year,14 days | (#44280125)

Stuff like this makes me tickled pink.

You poor thing! Is there medication for that?

Re:I'm sure there is a drought in space joke somew (0)

Anonymous Coward | 1 year,13 days | (#44283081)

It's okay, they're using Monster de-oxygenated water ;-)

Re:I'm sure there is a drought in space joke somew (0)

Anonymous Coward | 1 year,13 days | (#44285447)

I read TFA and then the Kickstarter page, This is not an ion thruster in any way (and the guys at Discovery can hand in their geek cards). This is a type of electrothermal thruster, which works on the exact same principle as a chemical rocket except that the propellant is heated by an electric supply instead of a chemical reaction.

I don't have much literature on this exact engine type, but it is almost identical to the (lower specific impulse) resistojet so I'll use that as an analogy. (Resistojects heat propellant with a simple resistor while this one uses electromagnetic waves -- i.e., it's a microwave oven.)

Any fluid can be used as a propellant in these sorts of engines, as long as it doesn't excessively corrode the engine itself. A resistojet normally uses hydrazine propellant because catalytic decomposition will preheat it and thus improve efficiency; this engine seems to use water over hydrazine mostly because hydrazine isn't as common in the solar system and to a lesser extent because it is safer and more stable in the long term. The toxicity of many rocket propellants is also not to be underestimated (to the extent that the Soviets had to change change their original launch trajectories for something less inhabited).

Xenon is indeed a good propellant for ion engines. Both Hall effect and electrostatic ion thrusters, the two flight proven types, use it. But as I said before, this is not actually an ion thruster. The ideal propellant for a thermal rocket (e.g. this one) is helium, since it has a low atomic mass and is a noble gas. (Molecule formation in the exhaust reduces the temperature, and thus specific impulse. Also, molecules are less spherical than atoms and tend to start rotating from collisions, which further consumes energy that could have been directional thrust.) Helium isn't actually used in spacecraft propulsion because it isn't storable (cryogenically stored & leaks all over the place) and low density means big tanks (= high launch drag & high tank mass).

If you want to know more, I'd recommend a trip to your local library. Ask for "Rocket propulsion elements" by Sutton & Biblarz. (If they don't have it, ask for an interlibrary loan.) Only chapter 17 is really about electric propulsion but you'll need a general background in rockets as well.

But I do hope that these guys pull it off. I've been a space propulsion junkie since the age of ten or so. Stuff like this makes me tickled pink.

It's even worse for me...

Re:I'm sure there is a drought in space joke somew (0)

Anonymous Coward | 1 year,13 days | (#44285559)

I, the above AC, stand corrected on this not being an ion thruster in any way. They do ionize the propellant after heating it, I fail reading comprehension, so I'll hand in my geek card instead.

The rest is accurate.

Back Up (1)

ThatsNotPudding (1045640) | 1 year,13 days | (#44286697)

Stuff like this makes me tickled pink.

You're standing too close to the exhaust!

Re:I'm sure there is a drought in space joke somew (0)

Anonymous Coward | 1 year,14 days | (#44280005)

The article mentions that Xenon storage requires large tanks to store, which is impractical for a tiny cubesat. Water has no such downside. Xenon is also expensive, water is... well, not so much.

Re:I'm sure there is a drought in space joke somew (1)

mspohr (589790) | 1 year,14 days | (#44280157)

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.

Re:I'm sure there is a drought in space joke somew (0)

jd2112 (1535857) | 1 year,14 days | (#44281409)

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...

Re:I'm sure there is a drought in space joke somew (1)

able1234au (995975) | 1 year,14 days | (#44281797)

Ya make one small mistake and they never let you forget it!

Re: I'm sure there is a drought in space joke some (2)

fermion (181285) | 1 year,14 days | (#44280255)

A cubesat is a kilogram or so. Adding a cold gas thruster with a solar panel could give it limited attitude control and not break the mass budget. I don't know how you build interplanetary telemetry and control in a kilogram so that an ion thruster can get to mars and transmit data. the solar panels necessary for a jupiter mission are massive and much more limited than a nuclear option. A big benefit of the ion engine is a reduction in the fuel that has to be lifted. And the fuel must be easy to ionize, which seems to currently argon, not water. Of course any test bed to see how things actually work is space is great. We can theorize all we want but won't know until we try

Better than Jesus... (5, Funny)

ElectroVaping (2983501) | 1 year,14 days | (#44279711)

Jesus could only walk on water this thing runs on water. That is no small feat...

Re:Better than Jesus... (4, Funny)

M0j0_j0j0 (1250800) | 1 year,14 days | (#44279865)

Ye, but can this thing turn water into wine, ye Jesus wins!

Re:Better than Jesus... (2)

Argon (6783) | 1 year,14 days | (#44282493)

But, this does turn water into a _whine_ when expelling it but it's just that you can't hear it in space :-).

Re:Better than Jesus... (1)

sjames (1099) | 1 year,14 days | (#44279961)

Honestly, we have no idea how big Jesus' feet were.

Re:Better than Jesus... (1)

SJHillman (1966756) | 1 year,14 days | (#44280093)

Jesus was actually a juvenile sasquatch. He had to fake his death because the hair started coming in as he reached sasquatch puberty.

Re:Better than Jesus... (1)

Whiteox (919863) | 1 year,13 days | (#44282673)

You mean "That is no small feet" don't you?

Re:Better than Jesus... (1)

brianerst (549609) | 1 year,13 days | (#44286977)

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...

cxx stl string c_str() no go mo jo (0, Offtopic)

Anonymous Coward | 1 year,14 days | (#44279729)

Next line fails so I did the belower code. Do you know why?

//char *strPtr = (char*)(rawDataStr.substr(0, colonIx).c_str());
#pragma meme("for some reaosn, char *strPtr = (char*)(rawDataStr.substr(0, 1).c_str()); does not pt strPtr to first char of rawDataStr")

// I might want to run it through in the debugger to see what is going on with that

string xStr = rawDataStr.substr(0, colonIx);
char *strPtr = (char*)xStr.c_str();
char *endPtr = NULL;
decodeType = strtoul(strPtr, &endPtr, 10);
if (endPtr == strPtr) {  // could not convert (bogus number)
    decodeType = UINT32_MAX;
}

I await for your wisdom.

Re:cxx stl string c_str() no go mo jo (0)

Anonymous Coward | 1 year,14 days | (#44280021)

Use Java and take a load off. Everything just works -- everywhere.

Re:cxx stl string c_str() no go mo jo (1)

Whiteox (919863) | 1 year,13 days | (#44282681)

Nothing wrong with B.A.S.I.C.
Otherwise alter the arry +- 1 and try that.

Extremely misleading and dishonest headline (1, Informative)

Anonymous Coward | 1 year,14 days | (#44279747)

The submitter should be ashamed of itself.

holy cow! (1)

Anonymous Coward | 1 year,14 days | (#44279937)

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? (2, Informative)

Anonymous Coward | 1 year,14 days | (#44280057)

Summary makes no mention of the CAT [kickstarter.com] kickstarter campaign for this thing.

So this is how we get sample from other planets. (1)

Ralph Ostrander (2846785) | 1 year,14 days | (#44280167)

And bring them back a conventional robot cold go get the sample conventional thruster put it in orbit and this thing collect it and bring it back. I will then call it wall-e

Why is water better than Xe? (5, Interesting)

Anonymous Coward | 1 year,14 days | (#44280303)

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.

Re:Why is water better than Xe? (2)

MichaelSmith (789609) | 1 year,14 days | (#44280379)

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 interesting to do the calculations.

Re:Why is water better than Xe? (1)

symbolset (646467) | 1 year,14 days | (#44280871)

Once our robots start mining Ceres we will have more water on orbit than we know what to do with. Ceres has 200 quadrillion metric tons of the stuff in a convenient concentrated form and low g environment. More than all the fresh water on Earth. We might have to start worrying about free space being polluted with too much water. Argon and xenon might work better but the supply on orbit will always be rare. It would be nice if water works. That is why water is better than Xe: Eventually you might be able to top up here and there.

Re:Why is water better than Xe? (0)

Anonymous Coward | 1 year,14 days | (#44281019)

My God... The shock you're going to experience when none of what you are talking will ever happen is going to be rough. I hope you have good health insurance. In the meantime I guess you can go back to reading Known Space novels. Look, Ceres has a police station on it! Are you going to be a space policeman when you grow up?

Re:Why is water better than Xe? (2)

symbolset (646467) | 1 year,14 days | (#44281357)

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.

If your goal was to troll the howto out of me, then well done! Mission accomplished.

Re:Why is water better than Xe? (1)

Teancum (67324) | 1 year,14 days | (#44281743)

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.

Re:Why is water better than Xe? (1)

symbolset (646467) | 1 year,14 days | (#44281893)

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.

Re:Why is water better than Xe? (0)

Anonymous Coward | 1 year,14 days | (#44282179)

As a non-idiot AC, I disagree entirely. You've spent more energy in responding to the troll than the troll used in the first place, while calling attention to the troll, which is exactly what the troll wants.

Re:Why is water better than Xe? (2)

c0lo (1497653) | 1 year,14 days | (#44282227)

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).

Accelerate ions to relativistic speed? (0)

Anonymous Coward | 1 year,13 days | (#44285883)

If we find a way to accelerate the ions to the point we get increased relativistic mass, does that also aid us in not having to carry as much fuel (or is the relativistic mass not useful for propulsion effects?)

Yaaaawn (0)

Cyberax (705495) | 1 year,14 days | (#44280705)

Ok, yet another ion thruster. This time it uses water. So?

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.

Re:Yaaaawn (0)

Anonymous Coward | 1 year,14 days | (#44281121)

Technically, getting to LEO cheaply is a solved problem, at least on paper. However, scaling them is prohibitively expensive because of the marginal cost of money. The sum of construction costs plus launch costs divided by expected launches underestimates the true economic cost.

To understand the true economic cost, consider paying for 20 years of cable TV right now, properly discounted for future value. That underestimates the cost to _you_ because the 1st dollar is much cheaper to you then the 10,000th dollar at any instant in time.

And that's assuming perfect assessment of risk and return on the investment, by the way.

So the true economic cost of the initialize investment for construction grows much faster than the nominal dollar amount.

Re:Yaaaawn (1)

Teancum (67324) | 1 year,14 days | (#44281771)

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 simply increasing the reuse of existing components instead of throwing millions of dollars worth of hardware away into the oceans of the Earth on every launch. There are dozens of different approaches to doing that, but it mostly boils down to people just trying one or two of those ideas and getting it done.

Re:Yaaaawn (1)

FooAtWFU (699187) | 1 year,14 days | (#44281137)

This solves the problem of getting to LEO cheaply enough by using a miniature, lightweight tank. That's why it's a big deal. (Or at least a medium deal.)

And forget the interstellar-space angle for a moment, too: anyone for a decent picture of Pluto?

This + Space Gun (0)

Anonymous Coward | 1 year,14 days | (#44280823)

If you ruggedized this enough you could probably get it to the point where it could be fired out of a HARP-style space gun or a railgun. Then it could fly on it's own power once out of the atmosphere. No rocket needed!

How long until TIE Fighters (1)

davydagger (2566757) | 1 year,14 days | (#44281717)

How long until we have high altitude bombers with these Tiny Ion Engines(TIE) get lasers?

Please don't... (0)

silvermorph (943906) | 1 year,14 days | (#44281867)

Please don't make water into a fuel. I need water for other things.

Engines running on water? I'll take 4... (0)

Anonymous Coward | 1 year,13 days | (#44286007)

...One for each wheel on my car. Thanks.

A more practical use (1)

Hentes (2461350) | 1 year,13 days | (#44287611)

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 (1)

gzuckier (1155781) | 1 year,13 days | (#44291477)

My dad had an engine which ran on water.
I think it was called an outboard motor.

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