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posted by janrinok on Saturday May 11, @05:48AM   Printer-friendly

https://gizmodo.com/nasa-pulsed-plasma-rocket-advanced-concept-mars-1851463831

"The future of space travel depends on our ability to reach celestial pit stops faster and more efficiently. As such, NASA is working with a technology development company on a new propulsion system that could drop off humans on Mars in a relatively speedy two months' time rather than the current nine month journey required to reach the Red Planet

[...] The potentially groundbreaking propulsion system is being developed by Arizona-based Howe Industries. To reach high velocities within a shorter period of time, the pulsed plasma rocket would use nuclear fission—the release of energy from atoms splitting apart—to generate packets of plasma for thrust.

[...] It would essentially produce a controlled jet of plasma to help propel the rocket through space. Using the new propulsion system, and in terms of thrust, the rocket could potentially generate up to 22,481 pounds of force (100,000 Newtons) with a specific impulse (Isp) of 5,000 seconds, for remarkably high fuel efficiency"

[...] "The space agency claims that the propulsion system's high efficiency could allow for crewed missions to Mars to be completed within two months. As it stands today with commonly used propulsion systems, a trip to Mars takes around nine months."...


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  • (Score: 1, Funny) by Anonymous Coward on Saturday May 11, @06:30PM (15 children)

    by Anonymous Coward on Saturday May 11, @06:30PM (#1356567)

    Nukular Prupulsion

    • (Score: 5, Informative) by liar on Saturday May 11, @07:12PM (14 children)

      by liar (17039) on Saturday May 11, @07:12PM (#1356572)

      If I understand correctly, the propellant is Teflon...
      "PPTs are generally flown on spacecraft with a surplus of electricity from abundantly available solar energy...Most PPTs use a solid material (normally PTFE, more commonly known as Teflon) for propellant, although very few use liquid or gaseous propellants. The first stage in PPT operation involves an arc of electricity passing through the fuel, causing ablation and sublimation of the fuel. The heat generated by this arc causes the resultant gas to turn into plasma, thereby creating a charged gas cloud. Due to the force of the ablation, the plasma is propelled at low speed between two charged plates (an anode and cathode). Since the plasma is charged, the fuel effectively completes the circuit between the two plates, allowing a current to flow through the plasma. This flow of electrons generates a strong electromagnetic field which then exerts a Lorentz force on the plasma, accelerating the plasma out of the PPT exhaust at high velocity.[1] Its mode of operation is similar to a railgun. The pulsing occurs due to the time needed to recharge the plates following each burst of fuel, and the time between each arc. " https://en.wikipedia.org/wiki/Pulsed_plasma_thruster [wikipedia.org]

      --
      Noli nothis permittere te terere.
      • (Score: 1, Informative) by Anonymous Coward on Sunday May 12, @04:11AM (13 children)

        by Anonymous Coward on Sunday May 12, @04:11AM (#1356620)

        they why did they say "the pulsed plasma rocket would use nuclear fission"

        • (Score: 0) by Anonymous Coward on Sunday May 12, @04:22AM (12 children)

          by Anonymous Coward on Sunday May 12, @04:22AM (#1356622)

          The required electricity is generated by a nuclear reactor.

          • (Score: 2, Insightful) by anubi on Sunday May 12, @08:34AM (11 children)

            by anubi (2828) on Sunday May 12, @08:34AM (#1356632) Journal

            Nuclear power? A SNAP type thermoelectric converter? If this thing is converting a significant amount of thermal energy, there will be significant heat dissipation requirements if using conventional carnot-cycle heat to shaft-work to electricity technology...they gotta have some trick up their sleeve. This ain't no nookly-air sub with the ocean for a heat sink.

            Go critical and it all goes at once! Something capable of this level of energy conversion is highly needed for terrestrial use if it can be made safe and stable.

            https://html.duckduckgo.com/html?q=snap%20nuclear%20power%20converter [duckduckgo.com]

            Just throwing my take out for comment. My understanding won't pass my own bs detector, so it's gotta be something I am not seeing.

            --
            "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
            • (Score: 3, Informative) by turgid on Sunday May 12, @09:45AM (5 children)

              by turgid (4318) Subscriber Badge on Sunday May 12, @09:45AM (#1356638) Journal

              Go critical and it all goes at once!

              This is a poor piece of terminology which people use to scare themselves. Apparently it comes from Enrico Fermi's first public demonstration of the Chicago Pile in the 1940s. By the way, it's interesting to note that the control rods really were suspended on a rope and there was a man with an axe, the Safety Control Rod Axe Man (SCRAM), ready to cut the rope in an emergency.

              When you bring a reactor up yo plot a graph of 1/counts per second against control rod withdrawal. The "counts per second" is effectively neutron flux. The graph is asymptotic (approximately).

              As you withdraw the rods, the negative reactivity of the core is decreasing, i.e. the reactivity is increasing. This means that the rate at which the neutrons from natural fission of the U235 are being absorbed decreases. That means that more of them are available to be moderated and therefore to become thermal and able to induce fission in the U235.

              At a particular point, there are enough neutrons from the induced fission (as opposed to natural fission or radioactive decay) that pulling the rods out further will cause the flux of thermal neutrons to increase. The reactor has now started. It's running on thermal neutrons causing self-induced fission. The reaction is a self-sustaining chain reaction.

              During his demonstration, when Enrico Fermi got to this point, he said, "Gentlemen, we have reached a critical point." That's where the term comes from.

              A reactor is said to be critical when the rate of production of thermal neutrons is exactly balanced by the rate of removal. Neutron flux and therefore power is constant.

              The 1/counts graph intersects the horizontal axis here.

              This says nothing about reactor power. It could be milliwatts. To increase reactor power to something useful, it needs to be brought superctitical by pulling the rods a bit more such that neutron flux can increase, To reduce power, the rods must be pushed to make the core subcritical.

              Prompt critical is the one you want to avoid. Also, I haven't talked about the neutron source.

              • (Score: 2, Insightful) by anubi on Sunday May 12, @09:01PM (4 children)

                by anubi (2828) on Sunday May 12, @09:01PM (#1356705) Journal

                Thanks for the interesting reply.

                Fermi was quite a guy...coming up with all this theoretical work and physically constructing an operating reactor. Like those "Got Talent" shows on TV, some people can do astounding things.

                I remember those analogs to mousetraps using ping-pong balls. Those 1960's nuclear bomb videos.

                I have designed power electronics and have been vexed by thermal issues ... And this one looks to me like a whopper.

                --
                "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
                • (Score: 2, Interesting) by Anonymous Coward on Monday May 13, @12:57AM (1 child)

                  by Anonymous Coward on Monday May 13, @12:57AM (#1356740)

                  I loved that ping-pong-ball video [youtube.com]. It has stuck with me these 50+ years! Back in the 40s and 50s Disney made some outstanding educational videos that they showed in schools for at least several decades (I also remember the one about menstruation [youtube.com]!). They'd show them to us on those 8mm school projectors.

                  I've seen some recent recreations [youtube.com] of the ping-pong-ball reaction on YouTube, but they do it wrong because they use one ping-pong-ball per mousetrap, while the Disney video uses two.

                  • (Score: 1) by anubi on Monday May 13, @10:34PM

                    by anubi (2828) on Monday May 13, @10:34PM (#1356858) Journal

                    Thanks for that.

                    Those brought back a lot of memories.

                    --
                    "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
                • (Score: 3, Informative) by turgid on Monday May 13, @07:16PM (1 child)

                  by turgid (4318) Subscriber Badge on Monday May 13, @07:16PM (#1356834) Journal

                  Go on, ask me about prompt critical.

                  • (Score: 2, Insightful) by anubi on Monday May 13, @10:12PM

                    by anubi (2828) on Monday May 13, @10:12PM (#1356852) Journal

                    Thanks for the exact name of that phenomena!

                    That is my fear of messing around with such things.

                    Seems to me about as risky as welding around an unpurged gasoline tank.

                    --
                    "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
            • (Score: 2, Insightful) by Anonymous Coward on Sunday May 12, @01:40PM (4 children)

              by Anonymous Coward on Sunday May 12, @01:40PM (#1356655)

              As you point out, getting rid of excess heat is an issue and requires radiators. The amount of energy and heat generated depends upon the type and amount of fission material. One reference [nasa.gov]:

              Space nuclear propulsion is a technology that draws energy from fission instead of traditional chemical reactions, thus providing virtually unlimited energy density and opening the door for crewed missions to Mars and deep space science. NASA is looking at two types of nuclear propulsion systems – thermal and electric.

              Nuclear thermal propulsion provides high thrust and twice the propellant efficiency of chemical rockets. The system works by transferring heat from the reactor to a liquid propellant. That heat converts the liquid into a gas, which expands through a nozzle to provide thrust and propel a spacecraft.

              Nuclear electric propulsion systems use propellants much more efficiently than chemical rockets but provide a low amount of thrust. They use a reactor to generate electricity that positively charges gas propellants and pushes the ions out through a thruster, which drives the spacecraft forward.

              With a two-week nighttime on the Moon, nuclear reactors are going to be needed for any sustained base, so there is a lot of effort going into new reactor designs on both the NASA and commercial sides of things.

              • (Score: 2, Insightful) by anubi on Sunday May 12, @09:25PM (3 children)

                by anubi (2828) on Sunday May 12, @09:25PM (#1356707) Journal

                Thanks for the NASA ref.

                Yup. Requires radiators and surface area for emission. Yet more mass. On a rocket. Can't win for losing. There has to be another way than inertial propulsion. If any of this "extraterrestrial" stuff is true, they have to be using something else. Otherwise one simply runs out of things to eject.

                I can easily see nuclear powering a lunar base...but to generate electrical power for thrust on a rocket that has a useful acceleration? I'm stumped. Someone way above my pay grade will have to figure this one out.

                --
                "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
                • (Score: 1, Insightful) by Anonymous Coward on Monday May 13, @12:38AM (2 children)

                  by Anonymous Coward on Monday May 13, @12:38AM (#1356735)

                  This is all pretty new to me as well, but I believe out of the nozzle you get about a 2X gain in ISP over chemical propulsion, but you can carry a lot less mass, so due to the nonlinearity of the rocket equation, plus the fact that you can really crank up the exhaust temperature with a nuclear reactor, the gain over chemical propulsion can be quite significant.

                  • (Score: 4, Informative) by turgid on Monday May 13, @07:42PM (1 child)

                    by turgid (4318) Subscriber Badge on Monday May 13, @07:42PM (#1356838) Journal

                    You certainly can crank up the exhaust temperature but there are considerations. If and when you shut down your reactor (and you will never have infinite propellant) there's still a lot of heat to get rid of.

                    When you shut a reactor down, for example in an emergency, the core goes on generating heat at a rate of approximately 10% of the full power it was just operating at. This is due to radioactive decay of the fission products. This lasts for a long time. In a commercial nuclear reactor, there are legal requirements about the availability of cooling systems in such circumstances.

                    The term "meltdown" is bandied about in the popular media. Homer Simpson even has a Meltdown button on his desk. Real reactors don't have meltdown buttons. Meltdowns are to be avoided.

                    If you have a nuclear reactor that runs at, say, 1GW thermal, and you shut it down, you now have 100MW of heat still to remove. If you don't, several nasty things can happen depending on the design of the reactor.

                    Assuming the induced nuclear fission is stopped (all control rods in), the fuel will increase in temperature until it melts into a puddle which will go through the bottom of the reactor vessel. That's the best case.

                    In a graphite moderated reactor, there's another nasty effect that can happen. As the nuclear fuel ages, plutonium is produced and plutonium-239,241 etc are fissile. Unlike the uranium-235, the plutonium fissions with fast neutrons. As the moderator gets hotter, it moderates the neutrons less so while the U-235 fission decreases, the Pu-239... fission increases. Your shut down reactor comes back to life. Get out the sausages, you've got a nuclear barbecue. All your control rods are already in so you are stuffed (that's the technical term). So they invented boron balls, boron dust and nitrogen injection.

                    Most reactors these days run on enriched uranium. When you have enriched uranium about, or uranium enriched with plutonium, you can get a criticality without a moderator. So if you have pools of melted fuel which keep getting bigger, you get the idea.

                    The radioactive decay lasts a long time by human standards. As I previously mentioned, there are rules (laws) about how much cooling you have to have in service and available, and how much spare emergency water (many swimming pools) you have to have. It's been a long time, but we were allowed to come down to one gas cooling circuit "in air" after many weeks. So that means air at atmospheric pressure in the core with a secondary coolant loop of water.

                    On a spacecraft, the propellant is the coolant (to a first approximation). I dare say you will have other closed cooling loops (primary coolant maybe) connected to very large radiators. In space, the only form of cooling, other than evaporation (the rocket exhaust), is going to be radiation which is extremely inefficient.

                    My hat is off to anyone who can design something like that which is safe, reliable and effective.

                    • (Score: 2, Insightful) by anubi on Tuesday May 14, @08:47AM

                      by anubi (2828) on Tuesday May 14, @08:47AM (#1356912) Journal

                      Thanks for the post!

                      I know something this detailed took a lot of time to write.

                      It's my hope that these forums are archived somewhere. These snippets of knowledge that are posted here are true gems.

                      --
                      "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
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