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NASA, DARPA will test nuclear engine for future Mars missions
- wkat4242 4y agoNice, at least this doesn't seem like one of those horrible 60s designs that spewed radiation everywhere by basically detonating a small nuclear bomb against a pusher plate. I think nuclear propulsion is there only way forward for interplanetary colonisation because we've long reached the limits of chemical. And ion is too slow.
- Scalene2 4y agoNERVA in the 1960s operated under a similar principal to the one just announced. Orion (what you're describing) was not the only proposal in the 1960s. As for nuclear propulsion being the only way forward, I doubt that, I suspect that chemical will be more cost efficient for a lot of the trips, especially for unmanned cargo trips.
- NegativeLatency 4y agoProbably easier to generate chemical fuel on the moon/mars too then to refine nuclear fuel, although if you could carry enough nuclear fuel in the first place maybe that would be moot.
- Kim_Bruning 4y agoNuclear rockets are a bit funny: they have a separate fuel (something that produces heat, like U-235, Thorium, etc) and propellant (something that gets heated and pushed out the back, like Hydrogen, Nitrogen, etc) . I think the idea is to carry a lifetime supply of nuclear fuel. Nuclear rockets aren't necessarily super particular about what propellant they use in conjunction with that fuel, so you can probably easily either directly scoop or otherwise easily refine/distill usable propellants anywhere you can find gas or something that is liquefiable.
- comprambler 4y agoGood video on the NERVA project. https://www.youtube.com/watch?v=eDNX65d-FBY https://www.youtube.com/watch?v=eDNX65d-FBY
- NegativeLatency 4y agoThis was excellent
- kneebonian 4y agoSo I've been working on a sci-fi book that involves interplanetary governance, and one of the things I've realized is that if one wanted to have a civilization that worked on an interplanetary scale nuclear is probably the only way to go for meaningful power production. Chemical means, based on carbon products that we've used up till now, would be very rare on remote planets, solar wouldn't work because planets could be various distances from a star they orbit, or could have different atmospheric, or magnetospheric conditions that would make that impractical, wind suffers a similar issue. The only power source that could be guaranteed to work at the large scale, both in terms of space and time, reliably, and is likely to be available is nuclear power. With your other options being the quantum vacuum energy or anti-matter, but both fall more into the fiction part of sci-fi right now than the science part. it was just a fun interesting little thought exercise. I'd love to hear if anyone has a criticism of the reading though.
- blisterpeanuts 4y agoIsaac Arthur on YouTube has some interesting commentary on antimatter, and other advanced proposed propulsion systems. It seems that for the moment, at least, antimatter is strictly in the realm of science fiction, until some very difficult problems are solved.
- gpm 4y agoNaively I'd expect that you would need fusion specifically. Uranium isn't plentiful unless you're on a rocky planet, and isn't very high energy density compared to hydrogen. Hydrogen is everywhere by comparison. The other reasonable option might be solar power near stars, and forwarding the power on to your ships/distant planets using some form of directed energy (lasers, lenses, etc).
- blisterpeanuts 4y agoIt sounds like you’re referring to nuclear pulse propulsion, a proposed method of reaching Mars from the Earth’s surface in 2 weeks.[1] I’m not sure what’s “horrible” about it. Research was halted because of the Test Ban Treaty, but if a safe way could be found to get the nuclear material into orbit, why not try it? 2 weeks is far better than 45 days which is what Nasa estimates nuclear thermal propulsion would achieve. Zero gravity and space radiation are deadly to humans, and the more exposure we can cut, the better. 1. https://en.m.wikipedia.org/wiki/Nuclear_pulse_propulsion https://en.m.wikipedia.org/wiki/Nuclear_pulse_propulsion
- wkat4242 4y agoIn the 60s we were much too cavalier about nuclear pollution. Barfing out nuclear isotopes everywhere is just not feasible. The whole spacecraft would get polluted with it. The same attitude also gave us the Russian RORSATs, many nuclear reactor cores are still in a parking orbit and will come down at some point in the future. I don't think the launch issue is the main problem: after all the nuclear thermal system also requires nuclear materials in orbit.
- midoridensha 4y agoIt's horrible because it'll pollute outer space with deadly radiation! /s
- photochemsyn 4y agoApparently a nuclear drive could half the transit time to Mars for astronauts, which has the additional benefit of less hard radiation exposure (assuming the nuclear reactor doesn't have any issues in transit). There were projects to develop nuclear thermal designs at the Nevada Test Site (Area 25, 'Jackass Flats') run by Los Alamos, 1955-1973. They had three designs (Kiwi, Phoebee, Pewee), all using highly-enriched uranium (bomb grade, as with nuclear engine reactors). I think these have longer lifetimes and are more efficient, but the new NASA report makes a point of using low-enriched designs this time around. https://en.wikipedia.org/wiki/Project_Rover https://en.wikipedia.org/wiki/Project_Rover I can't imagine it would be plausible to launch something like that without first testing it at a DOE/NNSA facility of some kind however, which might be a little problematic, as blowing up a nuclear reactor during a rocket test would be bad optics.
- xattt 4y agoGiven the increased speeds, how does arrival at the destination work? I assume the rocket is rotated 180° and fired. Is the plume the rocket flies through radioactive?
- photochemsyn 4y agoThere are some other options like aerobraking in the thin Martian atmosphere, and the gravity of Mars helps capture the vehicle at the other end, so not that much braking thrust is needed, and it's going to be fired at some complex angle: https://marspedia.org/Earth-Mars_Transfer_Trajectory https://marspedia.org/Earth-Mars_Transfer_Trajectory https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit These types of rockets ideally shouldn't produce much radiation, as the working fluid (propellant) is just heated up by passage through the reactor, although I don't know if there's a primary coolant loop and a heat exchange or if it's just basically the primary coolant being blown out to space, in which case maybe there'd be some 3H-tritium formed? Probably not much of a concern, though it might be for a Earth-based test firing.
- woooooo 4y agoI don't think the rocket flies through the plume? It's in vacuum and just keeps going, faster than the rocket and ahead of it?
- 1bent 4y agoSounds like the system in Heinlein's Rocket Ship Galileo
- protokultur 4y agoKerbal Space Program right again
- OhNoNotAgain_99 4y ago[dead]
- geijoenr 4y agoDefinitely a common sense step in the right direction. Humans going anywhere beyond the moon using chemical propulsion seems quite problematic due to all the unsolved issues related to radiation and micro-gravity. Now talking speculative fiction, the real breakthrough will come if we figure out a way to induce acceleration without an action-reaction process. Just an energy source, and no propellant. Being able to sustain 1g for a few months on a heavy spacecraft means interstellar travel (proxima centaury) would be within grasp.
- eddsh1994 4y agoHow does your initial point of 1g for a few months on a heavy spacecraft lead to traveling 4.246 light years? Genuine question!
- gpm 4y agoIt would take 6 years to get there (earth time) or 3.6 years (spacecraft time) if you could have constant 1G acceleration (in the opposite direction for the second half of the journey). https://cosmicreflections.skythisweek.info/2019/09/04/space-travel-under-constant-1g-acceleration/ https://cosmicreflections.skythisweek.info/2019/09/04/space-...
- geijoenr 4y agoWith a spacecraft big enough to live in, we are talking of a time frame not too different from the one from the age of exploration by sea. I have no doubt many people would want to take such a trip even if it takes 10 years to get back to earth. Unmanned spacecrafts would be able to go much faster, sustaining more dramatic accelerations. So getting cargo and robots there for support would be way faster.
- eddsh1994 4y agoThis takes you to 0.99C, how feasible is that (thinking materials more than anything)
- 4y ago
- allenrb 4y agoPersonally I am excited to see this, but I wonder if the optics will kill it? People get upset enough about reactors that don’t move and live inside huge structures of reinforced concrete. Can we convince this segment of the population that launching a small device (with necessarily less shielding) is safe? Even the most reliable launch vehicles (Falcon 9, Atlas V) are probably not more than ~99% likely to succeed. Can the payload be made safe in the event that it fails to make orbit?
- nradov 4y agoNASA has already used multiple radioisotope thermoelectric generators in space probes without many people getting upset. An RTG recently went to Mars. So this new engine doesn't seem like much of a stretch from a political and public relations standpoint. https://inl.gov/mars-2020/ https://inl.gov/mars-2020/
- idlewords 4y agoThis reply deserves more upvotes; NASA routinely launches big hunks of plutonium, and a nuclear thermal reactor at launch (before it's been turned on) is far less radioactive.
- ETH_start 4y agoThe key point that needs to be related to the public is that the reactor is turned off while in Earth's atmosphere, and a reactor poses very little danger when it's turned off.
- nordsieck 4y ago> Even the most reliable launch vehicles (Falcon 9, Atlas V) are probably not more than ~99% likely to succeed. Falcon 9 is it at this point. All of the remaining stock of Atlas Vs and Ariane 5s have been sold. Of course Vulcan and Ariane 6 will come online soon; buy they don't have anywhere close to the safety record that Falcon 9 does. I'm not a statistician, but I wouldn't be surprised if Falcon 9 had better than 99% chance of success. It has more than a 150 long success streak. And no rockets in the current configuration have ever failed. > Can we convince this segment of the population that launching a small device (with necessarily less shielding) is safe? This isn't obviously no to me. NASA has launched a bunch of RTGs in the past. Those have the same sort of safety concerns in the event of a failed launch. Probably less material, though.
- le-mark 4y ago> NASA and DOE are working another commercial design effort to advance higher temperature fission fuels and reactor designs as part of a nuclear thermal propulsion engine. These design efforts are still under development to support a longer-range goal for increased engine performance and will not be used for the DRACO engine. Anyone have info on how they’re improving on NERVA?
- credit_guy 4y agoIt looks like they are aiming for core temperature of "close to 3000K" [1]. Nerva reached only about 2300K. [1] https://inl.gov/article/space-the-next-frontier-requires-innovation-in-nuclear-fuel-design-and-testing/ https://inl.gov/article/space-the-next-frontier-requires-inn...
- deleted 4y ago[deleted]
- perihelions 4y agoI think the differences are less dramatic than that. You're conflating the nuclear fuel internal temperature (inl.gov link) with hydrogen exhaust temperature (NERVA / 2,300 K). There should be a sizable temperature gradient between those two.
- idlewords 4y agoExactly. The temperature limit for the exhaust (and therefore the specific impulse) is set by the materials used to make the engine. You can run a reactor as hot as you want, but it will want to vaporize itself and the spacecraft around it.
- idlewords 4y agoThere's a big effort to use low-enriched uranium in next generation nuclear thermal designs instead of the highly enriched fuel used in NERVA.
- coenhyde 4y agoCan we develop a nuclear salt water rocket already? https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket Scott Manley video on the subject: https://www.youtube.com/watch?v=cvZjhWE-3zM https://www.youtube.com/watch?v=cvZjhWE-3zM Basically a controlled thermo nuclear reaction blasting out the back. "One design would generate 13 meganewtons of thrust at 66 km/s exhaust velocity (or 6,730 seconds ISP compared to ~4.5 km/s (450 s ISP) exhaust velocity for the best chemical rockets of today)." You certainly wouldn't want to use this to take off from Earth. But we could use it for deep space travel.
- JoeAltmaier 4y agoUse for heavy lifting? Depends on efficiency. If it 'burned' its fuel completely, then maybe not as dirty as imagined. Further the oceans already contain dissolved uranium salts. Returning them to the ocean is 'net neutral' in a sense. Especially if we harvested them from there to begin with!
- deleted 4y ago[deleted]
- philipkglass 4y agoThe dirty part is the fission products, not the unspent uranium. You wouldn't want to launch a nuclear salt water rocket from the surface even if it achieved 100% fuel burnup. https://en.wikipedia.org/wiki/Nuclear_fission_product https://en.wikipedia.org/wiki/Nuclear_fission_product
- kerpotgh 4y ago[dead]
- AtlasBarfed 4y agoPractically all the nuclear propulsion designs are ideally launched from space. You want to get the "fallout" as far from the Allen Belts as you can from what I remember reading of General Atomics's Project Orion. Since nuclear rockets are far more practical for all major interplanetary travel, that's why a moon base or captured asteroid habitat will be the first real step to a "space civ". Of course I'm nutso enough to think that SpaceX should launch antimatter collection arrays in orbit to grab it from the solar wind, right now. Getting to Mars otherwise is really just a big marketing exercise. It now kinda seems unrealistic that most sci fi interstellar empires have lots of planet based settlements (well, the ones that have to deal with gravity). Gravity wells are a huge PITA once a reasonably closed-loop space civ gets moving. A nice asteroid belt seems a lot more valuable or a planet with a crapton of low-gravity moons, than a planet with 1G gravity well you have to spend millions to escape. On the moon, you could probably setup maglev launch or assisted launch with just solar panels. Alas, our delicate earth-adapted physiology.
- dtgriscom 4y agoIs a nuclear thermal engine expected to have a higher specific impulse than current-day ion thrusters, or is the benefit a higher absolute thrust?
- idlewords 4y agoIon thrusters have a much higher specific impulse, but nuclear thermal engines are high thrust and have about twice the specific impulse of chemical rockets. There's a concept called 'Bimodal Nuclear Thermal Propulsion' where you use the reactor for nuclear thermal propulsion when you need high thrust, and as a low-thrust, high specific impulse nuclear electric rocket the rest of the time.
- 66666xxx 4y agothey always come with something new www.nasa.xxx