Europeans And Australians Make Space Propulsion Breakthrough

JonClarke · Jan 14, 2006

I was very suprised too, but apparently by using large numbers of junctions, they can collect an almost continuous spectrum. http://www.lbl.gov/msd/PIs/Walukiewicz/02/02_8_Full_Solar_Spectrum.html But even 40-50% is very impresssive and has major implications for a range of space applications. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

JonClarke · Jan 14, 2006

Don't know about G's mike. Like other plasmas thrusters you are talking about 1/1000ths to 1/100ths I suspect. But, as a reminder, this thruster has an exhaust velocity 13 times faster than SMART-1 and 6 times faster than the one on DS-1. I believe it can run on other gases as well, not just extensive xenon. A freind of mine is just about to start a PhD with this team. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

mikeemmert · Jan 14, 2006

<blockquote>In reply to:<hr />I believe it can run on other gases as well, not just extensive xenon.<hr /></blockquote> I noticed in the article that they said the gas didn't touch the grid. Hydrogen has a corrosive effect on the grid, forming hydrides, which are brittle. Hydrogen, with no neutrons, has twice the charge/mass ratio of most other gasses.

spacester · Jan 14, 2006

I find myself in the peculiar position of being the negative voice here. I applaud this recent work but as someone finally brought up, the thrust is still very low. I wrote this elsewhere: This 'breakthrough' does not get us into the solar system any sooner. The problem with ion drives is lack of thrust, the fuel efficiency (specific impulse) is already terrific, so getting even better on that score is not a breakthrough. It does set the stage though. The main reason we can't get high thrust is two-fold: A) We need more power Cap'n! - presumably we'll need nuclear power to provide the energy to create and accelerate the ions. B) Previous designs could not be easily scaled up because of erosion caused by the ions smacking against the perforated plates or wire grids; this design will reduce the erosion and also appears to support higher ion flux density levels. Thus it will have a higher thrust-to-weight ratio and can be scaled up more easily. I'll get excited when the thrust levels get much, much higher than current designs. IIRC the article doesn't even mention thrust values . . . A friend of mine is just about to start a PhD with this team. Very cool. Perhaps I can finally get an answer to a question I've asked from time to time <img src="/images/icons/laugh.gif" /> My (limited) analysis is that the limitation on thrust with an ion thruster is not only the erosion (which I figured someone would solve) but the maximum sustainable flux density. Obviously, you need high power to pack in more ions in the same space and accelerate them at the same value, but assuming that power source is available, am I right that there is some physical phenomena that limits the sustainable propellant mass flow rate? What that phenomena is, I don't know; like I said my analysis is limited. <div class="Discussion_UserSignature"> </div>

mattwr · Jan 14, 2006

A couple of link giving more details of the thruster. http://www.esa.int/gsp/ACT/propulsion/ultra_ion.htm http://www.esa.int/gsp/ACT/propulsion/safe_thruster.htm http://prl.anu.edu.au/SP3/research/SAFEandDS4G Also it seems like one or two people on this thread are confusing this thruster with the Helicon Double Layer Thruster that ESA and ANU are working on. As it says on the ANU page (link above), they are very different thrusters. A link for details of ANU's Helicon Double Layer Thruster is: http://prl.anu.edu.au/020research/130SP3/020research/HDLT/index_html/view

mikejz · Jan 14, 2006

Here's the link I was talking about http://www.entechsolar.com/SpacePaper5.pdf

mlorrey · Jan 14, 2006

It depends upon a few factors. The theoretical maximum efficiency of GaAs, for instance, is 33%. Adding a layer of GaAn (Gallium Antimonide) ups that to 36%. Part of a cells problem is dumping heat, since the solar flux heats up the silicon, or other semiconductor material, and raises its resistance to current. Another problem is that each type of cell material can only convert a specific band of visible light to electricity. Silicon converts a very narrow band, which is why it is so inefficient comparted to GaAs. Quantum Lattices made from tungsten ought to be able to convert at leat 50% of the waste heat on the backside of solar cells to electricity. It does this by an interesting quantum method of extracting as much energy from each quanta of IR as possible. The nanotechnology needed to mass produce this may be applicable to the entire visible spectrum as well as other portions of the EM spectrum.

JonClarke · Jan 14, 2006

I will certainly drop titbits if I can (he has actually posted on these fora once or twice) <img src="/images/icons/smile.gif" /> As I said earlier, the big application of this technology is station keeping, with smaller, longer life, more efficient thrusters. There is commerical interest, which is perhaps why some details are sketchy, like thrust. Any space probe, as opposed to satellite, application is at least 10 years away. Bepi-Columbo is the next ESA probe to use electric propulsion, and that design has been largely frozen. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

mikeemmert · Jan 14, 2006

Dear MattWr; Thank you for the educational and informative links. The DS4G concept is very different to SP3's previous device, the Helicon Double Layer Thruster (HDLT) conceived at the ANU by Dr Christine Charles in 2003, in that it employs accelerating grids to create thrust. "These two technologies are starkly different in their approach, but from SP3's perspective they are complimentary to the overall aim of achieving efficient deep space propulsion" said Professor Rod Boswell, the head of the ANU laboratory. " This answers a question that had been brewing in my brain. I read the Scientific American print article on the Vasimir engine a few years ago. They were very enthusiastic about the variable specific impulse feature. However, if an ion engine can outperform an HDLT or Vasimir engine with regards to ISP, then it would probably be better to use two engine types and optimize the HDLT/Vasimir for high thrust. HDLT and Vasimir are very, very similar. I really don't know enough about plasma engineering to be able to evaluate the pro's and con's of two approaches whose differences are in details. The HDLT article noted that they recieved visitors who had worked on Vasimir. I think details will converge once the proper role of plasma engines is defined. Plasma engines need a gas core nuclear reactor. These require bomb-grade material, which brings up political considerations that the moderators would prefer be discussed in Free Space. OK. Have a nice day <img src="/images/icons/smile.gif" />

mikeemmert · Jan 14, 2006

Thank you, mikejz. Notice that the ray-trace on figure 2 shows different colors being focused on different places. So I guess that they do utilize chromatic abberation to increase efficiency by locating cells optimized for certain colors at the focal point of those colors. But the Boeing design does not allow unused colors to pass through the system. Instead, unused frequencies shine on the radiator, partially defeating it's purpose.

JonClarke · Jan 15, 2006

I believe they had a visit from Chang-Diaz when he was last in Oz. Why do you say you need GCR to power plasma engines? Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

mikeemmert · Jan 15, 2006

RAW HORSEPOWER!!!!!!!!

cuddlyrocket · Jan 15, 2006

"IIRC the article doesn't even mention thrust values . . ." The original ESA article does say: "With an adequate supply of electrical power, a small cluster of larger, high power versions of the new engine design would provide enough thrust to propel a crewed spacecraft to Mars and back." There are figures from the test firings available here. It does say that the thrust per unit area of the aperture is 17 times greater. How this translates into thrust-to-weight ratios needs a better engineer than me! <img src="/images/icons/smile.gif" />

mlorrey · Jan 15, 2006

With Xenon fuel, it has a watts to thrust efficiency of 86 kW per Newton thrust, or 382.5 kW/lbf, with an Isp of 19,000 sec. In comparison, the VASIMR has variable thrust and Isp, it can produce 1000 N with an exhaust velocity of 10 km/s or 100 N at 100 km/s, or 50 N at 300 km/s. All of these points are consuming 10 MW of power from the nuclear power plant, resulting in a range of watts per N ratio of 10 kW/N up to 200 kW/N, depending on the selected Isp. At the 300 km/s exhaust speed, and 50 N thrust, fuel consumption is about .5 g/s. This correlates to an Isp of 25,492 secs. At 100 km/s, it has roughly the same Isp as at 10 km/s. At this point, it is consuming roughly 100 kW/N thrust, which is slightly higher than the ESA proposal. At 10 km/s and 1000 N thrust, fuel consumption is 10 g/s, with an Isp of 10,197 secs. So, the European design seems to be a slightly more efficient middle of the road thruster which is mechanically much more simple. Its drawbacks are primarily the grid electrodes which sit in the plasma stream. This is a huge drawback compared to the electrodeless VASIMR, as plasma-caused erosion of electrodes is the primary limitation on electric thruster lifetime. For this reason, I'd say that the European system may be useful for missions ranging from the Moon to Mars. VASIMR gains the advantage at and beyond Mars where long duration missions are required: going to the asteroid belt, the jovians, and to KBOs and beyond. The European system would be useful for cargo missions, but the high thrust mode of the VASIMR gives an advantage to manned missions that need a shorter trip time.

JonClarke · Jan 15, 2006

"I'd say that the European system may be useful for missions ranging from the Moon to Mars. VASIMR gains the advantage at and beyond Mars where long duration missions are required: going to the asteroid belt" Ion propulsion is already viable for missions to the asteroid belt (Hayabusa, Dawn). It was the propulsion of choice for JIMO. The ANU doule layer thruster has an exhaust velcoity more than 2.5 times that of the NEXIS engine proposed for JIMO. I'd suggest that it is more than suitable for missions well beyond "the moon and mars". VASIMR is a very different system from ion propulsion. It is still has not progressed beyond the lab. The ANU equivalent is the helicon thruster, which has probably comparble performance. It too has progressed only as far as the lab, but is likewise very promising. But don't expect plasma drives to Titan anytime soon. These technologies are very scalable, and the first applications will be for satellite station keeping. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

rlb2 · Jan 15, 2006

According to Dr. Franklin Diaz, the brainchild VASIMR engine, developer you would need 10 megawatts of energy as you pointed out to get to Mars and back with a 25 ton spacecraft . He wanted nuclear power that may have been what killed his work. A nuclear scientist, Dr. Robert Cataldo , that was a part of the sixties development of nuclear rockets must have outflanked him. He didn’t like the idea of nuclear power to make electrical power to run a electrical propulsion system, he wanted nuclear thermal propulsion system. Dr Diaz published an article back in November of 2000 in Scientific America on the results of his tests up to that date. He claimed using solar energy at that time would be too costly and there would be too much mass to carry to Mars and back. That was then - this is now. With solar concentrators developed by Boeing at 250 sols or higher in the image I rendered above there would be a lot less mass to tug along, most of the mass in the concentrator reflector surface would be very thin walled solar reflector. Dr Diaz stated that you would need a solar panels covering 68,000 square meters of solar cells at Mars to produce 10 megawatts of electrical power. Now if you had a solar concentrator as shown above the surface area of the actual solar cells would be only 272 square meters in comparison the solar panels on the space station are 2,500 square meters and quite a bit lower that then the 38 percent efficiency that Boeing is claiming. Now with this new ion drive along with the VASIMR engine, Mars is more reachable than ever in a timelier manner than ever before. Looking down the road a little farther, the more energy we can use the faster you can get to Mars or the moon. For example if this was scaleable as I suggested above then at 250 sol solar concentrator scaled up to produce 200 megawatts of energy then it would need about the same amount of solar cells, 2720 squ <div class="Discussion_UserSignature"> Ron Bennett </div>

mlorrey · Jan 15, 2006

reducing the amount of solar cells you need doesn't help reduce your mass that much, because your concentrator contraptions can weigh at least as much, unless it is truly a gossamer structure.

rlb2 · Jan 15, 2006

It reduces the mass quite a bit. Most of the reflective surface of the parabolic shaped concentrator would be made out of very low mass material, a tab more mass per cubic meter than a solar sails. We are working on different thickness of reflective coatings and determining what types would hold up best in a long space travel. Here is another smaller image of it. <div class="Discussion_UserSignature"> Ron Bennett </div>

mlorrey · Jan 16, 2006

Well, you've got a limitation there, as Silicon is a pretty light material, though Gallium, Arsenic, Indium, and a lot of the other high efficiency cell materials are not so much. What is the watts per kg of the whole structure? Given also that we are talking a pretty large structure to capture 10 MW of solar flux, you'd need to calculate the cost of the additional structure to support it all, even at small accelerations. Another issue you deal with: a gossamer structure is less able to deal with atmospheric braking for orbital insertion. If you ruggedize it, you add more mass. If you stow it for the maneuvers, you lose your power at the time its needed most, at perhilion. Nukes are far more rugged.

rlb2 · Jan 16, 2006

Yes but what kind of mass would you be hauling with nuclear energy? Remember the mass would be appreciably less than the ESA proposed solar array that they earlier planned as a shuttle to Mars and back. The solar concentrator would be much more efficient and much lighter than the one Dr. Diaz envisioned just 5 years ago. <div class="Discussion_UserSignature"> Ron Bennett </div>

mikeemmert · Jan 16, 2006

The solar concentrator contraptions that rib2 proposes are very, very light. Diffraction grating lenses would also be very light. I wish I had the money or pull to follow through on the diffraction grating lens idea. The US government and industry doesn't seem to want to follow up on solar power. The idea of solar power satellites has died completely. The moderators don't seem to want the neccessary discussions about the right kind of nuclear power, which would entail bomb grade uranium, because there are politics involved and we have already seen FLAME WARS here (thanks<img src="/images/icons/rolleyes.gif" />, dude, I'll post a note on Free Space under "Can Bomb Grade Uranium Be Politically Acceptable For Rocket Engines?")

yurkin · Jan 16, 2006

With current technology the best bet is an efficient chemical propulsion engine and solar panels for power. The simplicity of this configuration outweighs everything else. And I would bet it’s the configuration chosen for the first wave of interplanetary spacecraft. Once we start talking about 30 ton starships then we’re talking so far into the future its difficult to say what will be the best approach. There will not doubt be advancements in both solar and nuclear power. But it could just as easily be driven by fusion or some magnetic gravity warp drive. But for raw power you really can’t beat an Orion style nuclear drive.

JonClarke · Jan 16, 2006

"Nukes are far more rugged." Theire radiators aren't. A nuclear electric conversion system generates between 10 and 20 times as much heat as it does electricity. The 10 mW VASIMR that people fancy here would need to shed 100-200 mW of heat. It is very hard to get a good estimate on radiot mass. It depends a lot on operating temperature, materials, cooling liquids (gas, liquid metal are favoured options), and a host of other factors. One system I looked up mentioned about 1.5 m2 and 2kg per kWe. So a 10 mW system would need 15000 m2 and 30 tonnes of radiator. This is black sky technology. One thing is certain though, once your reactor has gone critical you have to keep your radiator deployed or your reactor will overheat. The only way you could do a hot aerobrake is by having a very large unit. Not as difficult as with a large solar array perhaps, but definitely not trivial. You could do a cold areobrake using exospheric drag and multiple passes, but that will work with solar array as well. Jon One t <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

cuddlyrocket · Jan 16, 2006

"The idea of solar power satellites has died completely." That's because they're totally uneconomic. It's much cheaper to build the solar plants in Earth deserts (or actually, on people's roofs), despite the lower solar flux, longer periods of darkness and back-up power and/or storage requirements.

yurkin · Jan 16, 2006

The French can build nice nukes for sure. But I’m not sure I’d want my life support to be run by a French built submarine power plant.

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