Slashdot Mirror
Tiny Ion Engine Runs On Water
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."
n/t
.....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?
Stay sentient. Don't drink bad milk.
Jesus could only walk on water this thing runs on water. That is no small feat...
Next line fails so I did the belower code. Do you know why?
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// I might want to run it through in the debugger to see what is going on with that
// could not convert (bogus number)
#pragma meme("for some reaosn, char *strPtr = (char*)(rawDataStr.substr(0, 1).c_str()); does not pt strPtr to first char of rawDataStr")
string xStr = rawDataStr.substr(0, colonIx);
char *strPtr = (char*)xStr.c_str();
char *endPtr = NULL;
decodeType = strtoul(strPtr, &endPtr, 10);
if (endPtr == strPtr) {
decodeType = UINT32_MAX;
}
I await for your wisdom.
The submitter should be ashamed of itself.
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.
Ezekiel 23:20
I am seriously impressed and wish I had more than a few cents in my bank account with which to back this.
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.
Summary makes no mention of the CAT kickstarter campaign for this thing.
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.
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.
I don't read your sig. Why are you reading mine?
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
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
"She's a scientist and a lesbian. She's not going to let it slide." Orphan Black
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.
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/ We have missions that use ion thrusters to move across the Solar system: http://en.wikipedia.org/wiki/Dawn_Mission
Low-thrust propulsion is basically a solved problem. What is yet unsolved is getting to the LEO cheaply enough.
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.
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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!
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...
Any insufficiently advanced magic is indistinguishable from technology.
How long until we have high altitude bombers with these Tiny Ion Engines(TIE) get lasers?
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.
Ya make one small mistake and they never let you forget it!
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.
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Please don't make water into a fuel. I need water for other things.
So i suppose Deuterium is would be an interesting candidate to regular water.
To be more clear, heavy water made from Deuterium as opposed to regular Hydrygen.
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".
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
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.
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...
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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.
It's okay, they're using Monster de-oxygenated water ;-)
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...
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.
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?)
...One for each wheel on my car. Thanks.
You're standing too close to the exhaust!
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.
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.
Instead of interplanetary travel, how about using these thrusters to deorbit the cubesats at their end of life so they don't become spacejunk?
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.
http://soylentnews.org/~tibman
My dad had an engine which ran on water.
I think it was called an outboard motor.
Star Trek transporters are just 3d printers.
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 released.)
Launch cost is based on the volume taken up and/or the mass (there is limited space available and limited mass capability, so you have to fit within both constraints)
They're intended for quick'n'dirty development. The reason they're so cheap is that there's no guarantee of delivery in any desired orbital plane, no interfacing with the launcher (except in the physical sense of being loaded into a carrier), and comms with them is your problem from the outset. They're expected to be entirely self-contained and be able to sort themselves out once they discover they're free-floating.
(They're also cheap because 99% of them are prototypes made with COTS gear and duct tape, not subjected to any kind of space/launch qualification except those the maker decides to run. For any other type of launch there are dozens of prototypes made, plus flight spares and virtually _everything_ down to screw level is custom made and space rated over hundred of tests (space rating an instrument such as an ion detector takes several months in a vacuum chamber over extreme temperature excursions and costs hundreds of thousands of dollars. Launch rating requires similar tests on high powered vibration tables more than easily capable of turning your insides to jelly should you be silly enough to sit on one while running (There's one in the same building as I am and everyone knows when it's in use). On top of that there are ultra-precision requirements for everything, to ensure that it all assembles correctly - but that doesn't always stop things being installed backwards (eg gyro sensors on a Proton, the parachute dispensing sensor on New Horizons or the swapping of camera assemblies between spirit and opportunity despite precautions being taken at every step of the way to prevent exactly that occurance) because all the engineering in the world is no use if it doesn't include "design for assembly".)
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 out to Ceres and get the water that lays on the ground in the measure of 200 quadrillion metric tons. The crust of Ceres will of course have the remains of all the platinum group metals that Near Earth Asteroids will since it is the queen of the Asteroid belt and has gathered a coating of asteroids for the last few billion years. On the surface of Ceres iron is more common even than silicon, and uranium is abundant.
In a few months NASA Dawn mission will image Ceres, and the commercial space race will begin in earnest. Ceres is a really, really big deal that changes everything we thought we knew about resources in space. Also: I wouldn't put long money in gold, silver, platinum and other such metals now. Those have been my faves, but not now.
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