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Revolutionary Ion Thruster To Be Tested On International Space Station (abc.net.au)
Three Australian researchers have developed "an ion thruster that could replace the current chemical-based rocket propulsion technology, which requires huge volumes of fuel to be loaded onto a spacecraft." Slashdot reader theweatherelectric shares this article from the ABC News:
An Australian-designed rocket propulsion system is heading to the International Space Station for a year-long experiment that ultimately could revolutionize space travel. The technology could be used to power a return trip to Mars without refuelling, and use recycled space junk for the fuel... It will be placed in a module outside the ISS, powered, as Dr Neumann describes, by an extension cord from the station. "What we'll be doing with our system is running it for as long as we can, hopefully for the entire year on the space station to measure how much force it's producing for how long."
In the early 2000s "it was basically a machine the size of a fist that spat ions from a very hot plasma ball through a magnetic nozzle at a very high velocity," and the researchers are now hoping to achieve the same effect by recycling the magnesium in space junk.
In the early 2000s "it was basically a machine the size of a fist that spat ions from a very hot plasma ball through a magnetic nozzle at a very high velocity," and the researchers are now hoping to achieve the same effect by recycling the magnesium in space junk.
No it isn't. TLDR, read atomic rockets, n00b. Or, since you won't be reading it : high specific impulse ion drives have existed in various test forms for years. They are easy to make and they all have high efficiency, albeit some designs are more reliable than others. The problem with all of them is the nasty equation KE = 1/2 m * V^2. That means the higher the exhaust velocity (and thus specific impulse which is the fuel efficiency), energy required goes up with the square of exhaust velocity.
Plenty of ion thruster designs, including VASIMR, have reasonable energy efficiency. The problem is that you still have to pay the bill even if the efficiency were 100%. You still have to supply as much electrical power as the kinetic energy of the escaping propellant.
This is a big problem. Even the most exotic nuclear power generator designs anyone has drawn up, the nuclear generator is a heavy ass piece of equipment being propelled by barely any resulting thrust from the ion drive. It means that you might have great specific impulse but trips to Mars still take months. What you need is also high thrust. That's why the best engine for space travel that currently is feasible is still plain old nuclear-thermal. You only get an ISP of about 1000 (compare to 15k for this particular thruster), but you get thousands of times more thrust. You can complete your Mars injection burn in about half an hour instead of having to run the engine for months. That in turn increases efficiency because there is always 1 optimal point to do your engine burns at.
For those interested, there is a lengthy and interesting interview with Dr Neumann about this on The Space Show. http://thespaceshow.com/show/0...
http://descanso.jpl.nasa.gov/S... is as good a summary as any about NASA's current ion engines, while the APL paper by Neumann, Bilek and McKenzie for the http://scitation.aip.org/conte... has information about the Neumann Drive.
Short version is that xenon drives vary in specific impulse and power efficiency depending on the power levels, while Neumann Drives vary in specific impulse and power efficiency depending on the fuel used, while the power level affects how many pulses per seconds. Higher power levels appear to cause faster wear of the grid in Gridded Ion Thrusters, or the chamber in the case of Hall Effect Thrusters, as well as needing more investment in Power Processing Units and so on. Additionally, there is the issue of tankage, regulators and so on for dealing with the xenon itself, which means it's not a straight 1:1 comparison. That said ...
TLDR : Magnesium in a Neumann Drive runs about 9 uN/watt and 11 000s specific impulse. A NSTAR running at ~1000 watts input has about 32 uN/watt and 2850s of specific impulse.
Thanks for chiming in and linking the paper, and my apologies for exposing yourself to the comment environment here, which has become rather toxic concerning space issues of late. The fact that the press coverage comes across as "hype-y" doesn't help any.
While I think your premise of using space junk is... let's say "optimistic", in the anywhere-close-to-near-term timeframe.... the engine concept itself seems quite sound and interesting. I can't read the paper (not going to shell out $30 for it... not your fault I know, the publishing world is terrible), but - how sensitive is it to the geometry of the cathode? Is your concept that things would be melted down and cast (or extruded, or any other mechanism) into your desired geometry? I assume that at present you're doing something like feeding in wire off a spool to act as the cathode?
Everybody point at the libertarian and laugh.
It's press coverage - it's going to be hypey, and thats just the world we live in. As indeed is toxic comment environments :)
While running on space junk would be nice, it doesnt need to happen for the drives to be useful. If you're rocking 11 000s of specific impulse, then it's simple enough to bring a shipment of cathodes up from earth, transfer to a SEP tug and take them to where they are needed. The fact they are solid, and therefore dont need to be kept at the correct temperature and pressure helps a lot.
Cathode geometry is something we need to do more science on. At the moment, we've been working with one inch diameter circular cathodes, and the 'star' erosion pattern appears to be a thing. Yes, we're definitely looking at cast/extruded cathodes. We've got some ideas about how to move cathodes forward, and thats on the 'to do' list for the model thats going up to the ISS.
We know how Zubrin feels about VASIMR. There's also good reason to disagree with him. For example, his nuclear reactor criticism? He himself proposes building a powerful nuclear reactor to power colonies on Mars, so he's not self-consistent. His power density figures aren't anywhere close to realistic. He talks like 50W/kg is some sort of unachievably optimistic goal, when in reality ATK Ultraflex solar arrays already get 150W/kg (and MegaFlex 200W/kg), figures that have been going up significantly with time; high power nuclear designs for future space missions are measured in kilowatts per kilogram. His complaints about the funding that's gone to VASIMR versus other things are unfair, as VASIMR hasn't received all that much funding - certainly not enough to develop a nuclear reactor as he mentions. And nobody is going to develop a power system for VASIMR without having first validated the propulsion system (something Zubrin apparently doesn't want them to do). He tries to portray its various ion drive competitors as better, without mentioning that the primary reason for choosing VASIMR is its high peak thrust levels. Lastly, Zubrin's dismissal of the dangers of in-transit radiation is not shared by most researchers.
Everybody point at the libertarian and laugh.
It's a stupid comparison that's not to Zubrin's credit. The reason that no powerful space nuclear reactors have been developed is because there hasn't been any demand for them. Nuclear reactor power to weight ratios don't scale up linearly, they scale up vastly higher than linearly. Figures of 1000W/kg aren't just some sort of out-of-a-hat fantasy numbers, they're based on the very real work in the field. More to the point, even solar is already in the low hundreds of watts per kilogram, so again, Zubrin's acting like 10W/kg is the state of the art and 50W/kg overoptimistic is beyond absurd.
Everybody point at the libertarian and laugh.