For a fusion thruster, expansion of fusion products is directly used for thrust. Fusion products don't stick around long enough for a second reaction.
D-D → T + p+ (50%)
D-D → He3 + n° (50%)
D-T → He4 + n°
D-He3 → He4 + p+
The way to deal successfully with it is to split your R&D efforts into two types. One pursues these ideas, trying to cover those light years between feasibility and practicality. The other is to pull only ready-to-apply items together into a vehicle design and check that out; that's how you go fly.
Mix the supporting technology development with the vehicle design/checkout activity on the same contract, and the odds are heavily in favor of you never flying anything. US DOD gave up on ramjet and tried to leapfrog to scramjet, but scramjet wasn't, and still isn't, ready to apply.
GW
I never suggested we should not do the research--it should be done separate from the hardware boys.
]]>I realize that a successful concept demonstration and working propulsion unit are two different animals entirely, but if the basic concept was proven to work as intended years ago, is there any reason to not move forward with it?
Everyone wants high payload mass fraction, high speciic impulse, and high thrust. You're never going to get all three with chemical (ever), nuclear thermal (at least not until you get into exotic liquid or gas core technologies), or ion (unless someone out there has a GW class reactor that produces 1kW/kg that they'd like to sell to us) propulsion. This is the only system I've seen that stays within the realm of conventional physics and provides all three "nice to have's" from the rocket scientist's wish list.
In order to get something better than what we have, you have to try something new. That's all there is to it. If we did have it, there's no reason why we couldn't mount a mission in ten years time.
]]>As I have said before, there's light years of distance to cover between a successful feasibility demonstration test of a new concept, and having something actually ready for general application. Ugly (and very unpopular) little fact of life, but there it is.
The way to deal successfully with it is to split your R&D efforts into two types. One pursues these ideas, trying to cover those light years between feasibility and practicality. The other is to pull only ready-to-apply items together into a vehicle design and check that out; that's how you go fly.
You have to do both types of R&D or you never get any progress. But dare not to mix them!
GW
That seems the be the NASA model, though!
]]>The way to deal successfully with it is to split your R&D efforts into two types. One pursues these ideas, trying to cover those light years between feasibility and practicality. The other is to pull only ready-to-apply items together into a vehicle design and check that out; that's how you go fly.
Mix the supporting technology development with the vehicle design/checkout activity on the same contract, and the odds are heavily in favor of you never flying anything. US DOD gave up on ramjet and tried to leapfrog to scramjet, but scramjet wasn't, and still isn't, ready to apply.
That's why the US is still flying subsonic cruise missiles, while most of its adversaries now have supersonic ramjet cruise missile anti-ship weapons. Stupidity incarnate.
You have to do both types of R&D or you never get any progress. But dare not to mix them!
GW
]]>Dynamo design with regenerative back mmf
So Lockheed Martin Says It's Made a Big Advance in Nuclear Fusion...
]]>As it turns out, replicating what goes on in a star without replicating the conditions inside a star is really difficult. Who knew? Fortunately, FDR isn't trying to achieve any sort of continuous fusion reaction and that's a good thing (in this case). As previously stated, it's just a powerful pulse jet system that uses super-heated plasma to produce thrust. No electrical power generation from fusion whatsoever, just thrust.
Incidentally, some smart kids (actually, they're my age or a little younger) from MIT figured out how to absorb neutrons without killing the containment. REBCO is seriously strong stuff (for dealing with mechanical loads and neutron radiation, that is), as most high grade stainless steels generally are. ITER doesn't use REBCO, so I foresee coil / containment longevity problems, but there's no chance of a redesign at this point.
ITER's design will never be practical for electrical power production, but MIT's device should be since it solves the electromagnet power / longevity, fuel blanket, and magnetic field stability problems (with substantially high electromagnetic pressures with lower input power). It would seem that plasma stability is the most intractable problem that all previous experiments had. The electromagnets are just not powerful / efficient enough, thus the very large minimum size required to get more power out than was put in. Like fission reactors, fusion reactors are subject to process-specific scaling laws and steady state operational issues.
]]>We're nowhere close to having a workable fusion reaction system to produce electrical power, but the FDR does not produce a single kilowatt of electrical power from the fusion reaction and the process is an incredibly brief pulse versus continuous operation. For all intents and purposes, the FDR is a fusion powered pulse jet system.
MSNW LLC has already generated thrust by collapsing an aluminum foil liner around a D-T pellet. The neutron radiation is a problem, but the liner captures most of the neutron radiation produced and the Lithium fuel is a pretty good neutron absorber. The supersonic foil liner compression was proven to produce jet power from D-T fusion back in 2013. I guess we can pretend that the results that Dr. Slough's team obtained through actual experimentation weren't what they were, but NASA has provided funding for this project every year since 2012, IIRC.
The FDR is mostly an engineering problem at this point, meaning integration of the chamber / nozzle / foil extruder, how many kW/kg for the solar arrays, and how many kJ/kg for the super capacitors.
]]>D2 + T2 ------------> 2 He4 + 2 n + delta H (enthalpy).
The resulting neutron flux requires massive shielding for the system.
]]>Controlled fusion has been going on for decades. Our scientists have never managed to get more power out than put into the reaction for purposes of generating electrical power, as a function of thermal losses and containment issues related to the low strength of the magnetic fields that earlier generations of superconductors were capable of producing for a given amount of electrical power consumption. On that front, high-strength REBCO tape is a gamer changer. There were plasma confinement issues in the past, but these have mostly been resolved with better containment methodologies and better superconducting electromagnets that generate higher field strengths that dramatically reduce field instabilities to hold onto the super heated plasma. We've had the process going continuously for 102 seconds in China.
The FDR operates over fractional second time scales in pulses, which is something we've repeatedly demonstrated without issue. That means we squeeze a foil liner out of an extruder, inject a D-T pellet into the chamber, as the D-T pellet passes into the throat of the electromagnetic nozzle, electromagnetic compression of the foil liner at supersonic speeds using a 1MA pulse of current through the electromagnetic coils creates an exponentially increasing B field around the D-T pellet which initiates fusion and turns the compressed foil liner into a plasma to absorb most of the neutrons generated in the process, and finally the exhaust products from the vaporized liner are ejected out the back of the electromagnetic nozzle at tremendous velocity, which is what creates the 5100s Isp. This process repeats every 5 to 10 seconds as the solar arrays recharge the super capacitor banks.
]]>Not that it shouldn't be worked on, mind you! Just don't hold your breath waiting for it to happen.
Von Braun was right, you go with what you have in hand, or else you will never go.
The corollary is that there are a whole slew of things that might keep you from going, but waiting on the emergence of a new technology that is critical to success vs failure is quite certain to keep you from going.
GW
]]>