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RocketStar tests fusion-enhanced in-space propulsion process
- api 2y agoI’ve seen a few papers on using electrostatic fusion (Farnsworth fusor type designs) for propulsion. Electrostatic confinement is not a method that’s ever come close to overunity but that’s not the point. The power source would be fission or solar. The idea is to use a driven fusion reaction to accelerate propellant to achieve even higher iSP than pure ion drives.
- pfdietz 2y ago"During the tests the process was seen to create the ionizing radiation and improve the base propulsion unit’s thrust by 50%, said RocketStar." It does not say that the fusion increased the unit's thrust by 50%. If you shoot protons into a gas containing boron, you will see some fusion. But the problem is not achieving fusion, it's achieving significant fusion. In this case, I'm betting almost all the extra heating is just due to the injected protons depositing energy, not due to the fusion they might be inducing. If the gas being hit is only partially ionized then energy loss of the protons to additional ionization will slow them down very rapidly, and very little fusion will occur. This is why just slamming nuclei into a solid target can't possibly reach breakeven.
- ricardobeat 2y ago> I’m betting almost all the extra heating is just due to the injected protons depositing energy And their team over at HPEPL / Georgia Institute of Technology wouldn’t have noticed that basic fact because…? If simply injecting tiny amounts of boron (or anything else) into the exhaust to get burnt improved performance by 50% this would have been ubiquitous by now. Afterburners were invented in the 1940s after all.
- sidewndr46 2y agoIt does work: https://en.wikipedia.org/wiki/Zip_fuel https://en.wikipedia.org/wiki/Zip_fuel
- pfdietz 2y agoThis is a completely different thing.
- pfdietz 2y ago> And their team over at HPEPL / Georgia Institute of Technology wouldn’t have noticed that basic fact because…? Who says they didn't notice? Nowhere did they say the heating was due to fusion. Read carefully what they wrote, not what they left unstated and allowed you to wishfully assume. The heating would not be due to tiny amounts of boron, but rather due to the energetic protons slowing down, depositing energy. This would happen even in the absence of boron or of any nuclear reactions.
- ricardobeat 2y agoQuoting from their website: “This fusion process, like an afterburner in a jet engine, transforms boron into high-energy carbon, which rapidly decays into three alpha particles. The result? A remarkable 50% improvement in thrust compared to our FireStar™ Foundation thruster.” “We've witnessed fusion reactions occur in our lab and the result is a 50% jump in thrust performance”
- cryptonector 2y agoThat's not quite the quote we'd like to see.
- cryptonector 2y agoIndeed, I suspect one could get much more than a 50% boost from fusion, so maybe they're not getting much heating from fusion. It's a nice idea though, a Fansworth-style fusor to heat propellant.
- pfdietz 2y agoI think it's an idea that clearly doesn't work. Ideas that don't work can't be "nice".
- twic 2y agoOkay firstly, how are they getting fusion? You need a lot of energy to overcome the Coulomb barrier for boron - apparently at least 148 keV [1]. For a proton to have that much kinetic energy it needs to be going at 5340 km/s [2]. "The exhaust velocity of a [pulsed plasma thruster] is of the order of tens of km/s" [3]. So what gives? I'm guessing that exhaust velocity figure is for heavy ions, but are protons really that much faster? Secondly, how are they turning the fusion into thrust? Causing fusion in the exhaust stream after it's left the motor will make it hotter, but how does that heat couple to the vehicle? In a pulsed plasma thruster, thrust is produced from the reaction against the acceleration of the plasma by the magnetic field. How does fusion affect that? [1] https://www.nature.com/articles/s42005-023-01135-x https://www.nature.com/articles/s42005-023-01135-x [2] https://www.omnicalculator.com/physics/relativistic-ke https://www.omnicalculator.com/physics/relativistic-ke [3] https://en.wikipedia.org/wiki/Pulsed_plasma_thruster https://en.wikipedia.org/wiki/Pulsed_plasma_thruster
- Gravityloss 2y agoVery odd. How could they then reach any fusion if they have a hundredth of the needed velocity (50 km/s instead of 5000 km/s)? If they still detected alpha particles... I get 1600 km/s from a naive calculation, still a factor of 30 off: https://www.wolframalpha.com/input?i=sqrt%282*150+kev+%2F+%28boron+atomic+mass%29%29 https://www.wolframalpha.com/input?i=sqrt%282*150+kev+%2F+%2...
- ben_w 2y agoAlthough I don't know the specifics of this thruster — the phrase "generates high speed protons through the ionization of water vapor" sounds like the reporter/press release writer didn't understand what the scientists told them — it's very easy to get protons up to 148 keV in a lot of different ways. There's a specific kind of fusion reactor which gets done as a highschool science-faire project every so often, similar voltage level: https://www.popularmechanics.com/science/energy/a34312754/12-year-old-builds-working-fusion-reactor-world-record/ https://www.popularmechanics.com/science/energy/a34312754/12...
- cryptonector 2y ago
- bragarian 2y ago[flagged]
- Sporktacular 2y agoHow much of a performance improvement from fusion in return for spicy exhaust?
- krunck 2y agoSo how radioactive will the thruster become? If used for human spaceflight it's going to end up in the same place where people will be.
- mcswell 2y agoSpace is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. I assume this is for interplanetary (or perhaps lunar) travel.
- mr_toad 2y agoIt’s an Ion engine used for satellite maneuvering. I doubt the radiation is a significant concern.
- ben_w 2y ago> During the tests the process was seen to create the ionizing radiation and improve the base propulsion unit’s thrust by 50%, said RocketStar. A 50% boost is both impressive and, given my memory of Farnsworth fusor discussions, surprising.
- pfdietz 2y agoIt's only impressive if the boost is due to fusion, not due to the protons just heating the gas by depositing their own energy.
- ben_w 2y agoThat would make a lot more sense, yes.
- XorNot 2y agoI don't think this is inconsistent though? The goal is to optimize the Isp you get from your fuel, not to get more energy out of the process then you put in necessarily - i.e. in space you can harvest solar power all you want, but if you don't have reaction mass then you can't give yourself momentum which is what you need to get around. So efficiently using the reaction mass you have is worth it, even if you put in more energy then you get out.
- ben_w 2y agoIndeed, but my surprise is due to how far away Farnsworth fusors seemed to be from useful for anything besides being a switchable source of (ironically given this article is about aneutronic p-B11) neutron radiation.
- baking 2y agoThe only thing I can figure is that this beam-target fusion except that the proton beam is their primary thruster so that any protons that don't fuse are not wasted. Still not sure how they get a 50% increase from fusion with boron but I assume that is merely optimistic.
- NegativeLatency 2y agoSo potentially is this like, get to mars quicker or does it make missions to outer planets feasible?
- baq 2y agoResearch missions up to Jupiter will benefit, perhaps Saturn with a really big ass solar array. Other than that, station keeping for Earth orbit, so longer lived birds translate to perhaps cheaper sat services.
- cryptonector 2y agoYou could run a propellant-cooled fission reactor to power the fusor to get the extra ISP. When you get to your destination and finish decelerating you toss the fission reactor overboard so you don't have to deal with its remaining heat.
- rbanffy 2y agoRemember you can replace solar panels with RTGs if you need consistent power further from the Sun.
- _joel 2y agoSure, most are when it's at that distance from the Sun. Looking forward to seeing Dragonfly sport it's RTG https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=DRAGONFLY https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id...
- rbanffy 2y agoQuicker to Mars also means less shielding for the same radiation exposure and, therefore, more payload.
- jmward01 2y agoThis sounds exciting, but I don't have a practical example in my head to understand the potential value here. 50% increase in ISP is great but is fuel mass the limiting factor on this type of engine or is it energy production? It would be great to get a simple example of utility here by possibly comparing existing uses to something with this modification. Anyone have a good example?
- cryptonector 2y agoThe problem with this, I suppose, must be the power plant needed to produce the electric power needed to drive the fusor. My guess is that for a deep space ship one would need a propellant-cooled fission reactor, while for a thruster for orbit management a solar/battery/capacitor system might suffice (but with very short run times). For a deep space system there would be challenges. Shutting down the fission reactor would require continuing to use propellant as coolant long after the fusor stops working -that or a massive radiator-, and either way the net ISP would be driven down. And then the fission reactor would have to stay shut down for quite some time. Though if you jettison the fission reactor when propellant runs out then there are no such problems! For orbit management thrusting though this might yield a very weight-efficient system!
- sjburt 2y agoFuel mass is very much the limiting factor. "Electric" or "ion" propulsion of this general type are used on satellites for things like orbit raising or orbit maintenance. They don't provide very much thrust, but they provide a very high ISP (often 10x what would be possible for a chemical reaction propellant), which typically translates to a longer lifespan for a vehicle or the ability to carry less reaction mass and more payload.
- sigmoid10 2y agoThey don't increase ISP, they increase thrust. This is also something you can do with an ordinary afterburner: Trade ISP for thrust. For space electric propulsion this seems reasonable, since ISP is usually extremely high, but thrust is ridiculously low. It's ok for keeping satellites in orbit, but even a 50% increase means we're not going to send humans anywhere with that any time soon. Additionally, their fusion idea works a bit differently by not directly using the energy created from fusion, which makes the 50% claim seem rather wild. I would wait for a peer reviewed paper or an actual flight test before getting excited about any of this. Small companies promising revolutionary space drives that end up as vaporware are quite common nowadays, because there are lots of simple minded venture capitalists out there who dream of funding the next SpaceX despite having no clue about physics.
- jessriedel 2y ago> Adam Hecht, professor of nuclear engineering at the University of New Mexico said, “RocketStar has not just incrementally improved a propulsion system, but taken a leap forward by applying a novel concept, creating a fusion-fission reaction in the exhaust. What fission is taking place? Is this just referring to the fission of the excited isomer Carbon-12 (into three alpha particles)? Isn't that like, extremely short-lived? Aren't all fusion reactions "fission-fusion" in this trivial sense?
- Tuna-Fish 2y agoThere are fusion reactions that result in larger atoms. B-P fusion results in 3 alphas, so it's fusion-fission.
- jessriedel 2y ago> There are fusion reactions that result in larger atoms Do you mean “smaller”? I thought the defining characteristic was that the atomic number was increasing. > B-P fusion results in 3 alphas, so it's fusion-fission. You’re saying the “fission” part comes because one of the inputs, Boron-11, is larger than the outputs, the alphas?
- jessriedel 2y ago(My brother is a plasma physics postdoc at LLNL and he says he's never heard of anyone refer to p-B as a "fusion-fission" reaction. So it still seems weird to me.)
- TheDudeMan 2y agoIf this is really fusion, is it not a possible avenue for a fusion power plant here on Earth?
- cyberax 2y agoNo. It's not energy-positive, fusion provides less powe than is put in. Instead it's a way to produce very energetic exhaust, resulting in better fuel economy.
- actionfromafar 2y agoWasn't it worse fuel economy (lower ISP) but higher thrust?
- cryptonector 2y agoNo, this would be heating the propellant to higher temperatures than chemical reactions can get -- in principle one could get much more than 50% extra ISP for the same propellant mass. In rocketry/satellites/deep space propellant mass is a big deal -- anything you can do to reduce the amount you need without having to gain even more mass in other ways is a big win.
- deleted 2y ago[deleted]
- rbanffy 2y agoThat image on the top of the article doesn’t inspire much trust.
- crustaceansoup 2y agoFor about the last year or so I've been getting pushed fishy articles on another nuclear propulsion company, Pulsar Fusion, via Google Now and elsewhere. AI-generated-reading articles on nobody websites. Something strange about all of this.
- neilv 2y agoIf it weren't attributed to the company, I would've guessed generative AI.
- rbanffy 2y agoI looks A LOT like an AI generated image.