Talk:Fission-fragment rocket

Comments

How could this be possible that it would get an ISP close to that of an antimatter rocket? In antimatter, all of the mass gets converted to energy. In fission, only a very small percentage of the mass in the reactants gets converted to energy. Sounds like someone misread their source.

Hmm, looking some more, I found the problem: There's one extra zero in that ISP  :) Check out http://www.batse.msfc.nasa.gov/colloquia/abstracts_summer05/rsheldon2.html for a reference. 129.255.141.196 (ISP is roughly 1/10th MN/kg) 16:29, 15 Jun 2005 (UTC)

Project 242

Is this someway related to the fission-fragment motor by Carlo Rubbia named "PROGETTO 242" (project 242), from Italian Space Agency? See http://www.crs4.it/Areas/cfd/P242.pdf and http://www.rai.it/Contents/eventi/600/ASIProgetto242.ram.

It does seems similar but I'm not sure if it's the exact same thing as in this article. Whatever it is, this "Project 242" probably deserves its own article.--Hibernian 18:57, 3 August 2006 (UTC)

Clean up

Well written article. Organizing into distinct components and starting reference section. --Rev Prez 14:34, 15 April 2007 (UTC)

A Few Silly (and non-technical) comments

I have a few (obvious) questions concerning the fission-fragment idea :

1) What are the "Numerous technological challenges" referred to within the "design considerations" section?

2) Is the Specific Impulse of the device impeded by the fact that the nuclear reactions which are considered for the fission-fragment design are forced to rely upon the fissioning of HEAVY nuclear materials (I suspect that, if a way were found to utilise nuclear fusion, it might actually be possible to obtain a higher specific impulse than with even the fission-fragment design - my calculations on this point are probably going to be rusty, though they assume that a nuclear fusion reactor would have to rely on a lower mass of reactants in order to release the same amount of energy that a nuclear fission reaction would, with the obvious proviso that a nuclear fusion reactor would be of comparable mass to a nuclear fission reactor at some point in the future).

3) Does anyone with more experience than myself envision that the separation of highly energetic heavy nuclear materials from the fissioning masses used in this engine decision could somehow be used in order to `catalyse'/speed-up or act as a sufficient source of energy to initiate a D-T nuclear fusion reaction (I suspect that, as you are planning to use magnetic confinement techniques anyhow, and it is possible that some nuclear fission reactions will produce the kinds of temperatures needed to initiate and maintain nuclear fusion, then it should be reasonable to assume that a `mixed' fission-fusion nuclear reaction would actually increase the specific impulse to an even higher amount - but, as any good blagger, I haven't actually done the maths, yet).

4) " The axial magnetic field is too weak to affect the motions of the dust particles but strong enough to channel the fragments into a beam which can be decelerated for power, allowed to be emitted for thrust, or a combination of the two. "

Obviously, just use a feedback system to channel the `low-grade' output from the initial nuclear suspension reaction (for those particles which are travelling in the wrong direction and can only be used for power generation via some sort of magnetic deceleration/heating process) in order to yield more energy from the those particles that are travelling in the `right' direction (that way, further `secondary' and tertiary nuclear nuclear reactions could be made to occur at the exhaust possibly increasing the specific impulse a little amount here dependent upon the fission fuel reaction that is being dealt with >).

> I think that the secondary nuclear reactants can be fed in at the exhaust stage for the nanoparticle design (without comprising thrust via, say, reducing the exhaust temperature or inducing reactions which could somehow induce `negative momentum change' due to the fact that the momentum transfer occurs at the `point of fuel fission'. I am uncertain as to whether this is correct).

ConcernedScientist 13:58, 25 August 2007 (UTC)

1) has this been removed?

2) absolutely; a fusion design will outperform the FFR, especially in terms of overall spacecraft performance. However, we actually know how to build a FFR.

3) hmmm. well I can't say for sure, but my guess would be "no" based on poisoning of the fuel load (quenching). The last thing you want is high-z materials entering the fuel anywhere, the effect on radiative cooling is overwhelming.

4) I think a system like this would be used on any such design, not just this "new" one. Neutrons will be unaffected (well, polarized maybe) and continue the reaction within the reactor, but the small chunks of fuel and carbon that break off are highly ionized and suitable for magnetic direction (well, that's basically the whole idea!). Of course they have actually tried this in the "real world", and last time I checked there are still no operational MHD generators in commercial use...

Maury 22:47, 1 December 2007 (UTC)

1) No. Understandably.

2) Your point about how we know how to build a FFR might seem problematic to some (the basic design is on the page, though it is uncertain how many people understand it and to what level of detail).

3) Your comments upon radiative cooling are not eminently clear to me. However, if you are stating that the addition of impurities to a D-T mixture would impede nuclear fusion reactions as the endothermic nature of the fusion of heavy nuclei would have the effect of cooling down the D-T mixture, then I imagine that this may be correct (though the proportion of fast-fissioning nuclei added to a D-T plasma mix and the probability of any resultant endothermic interactions are points for which a detailed analysis would be required).

My imaginings were that, upon the initiation of a nuclear fusion reaction, where the variety of nuclei masses of a fast-fission generated plasma were injected into a D-T plasma stream in an attempt to maintain high plasma temperatures from the fast-fission plasma injection...Rather than IMPEDE a D-T nuclear fusion reaction, the injection of such plasmas (with the impurities associated with a fissioning decay series which is yet to progress to finality), would be beneficial due to the fact that the presence of neutrons over a wide range of energy levels would cause the various fission decay products of the injected FF (fast fission) plasma to fission exothermically - thus increasing the heating effect of the plasma.

If the addition of impurities were a FUNDAMENTAL problem, mixing in cool D-T with the FF plasma and then using a mass spectrometer method to separate heavy and light nuclei would offer a way of generating high temperature D-T plasma which would either self-fusion, or aid in the maintenance of a fusion reaction (especially if one were to consider the use of magnetic confinement techniques for increasing the pressure experienced by such a plasma). Having not done calculations, I would not be able to say whether either of these approaches is correct or useful. Though qualitatively, they may be useful.

In retrospect, does your point about radiative cooling relate to the differing CONDUCTIVITIES of the D-T plasma, and the injected FF plasma, or the effect of the free-electrons within the injected plasma to radiate heat when combined within a mixture? I am uncertain of how well-bound the injective electrons would be within a D-T plasma/FF plasma mix, and what effect this might have on "radiative cooling". My presumption is that the vast majority of FF injected plasma is THERMAL plasma so that its injection can maintain fusion, but even without this, allowing its temperature to normalise with a "low-temp" D-T mix, and then siphoning off the low-z mixture should enable a high temperature plasma which will fusion of its own accord upon an appropriate (EM field induced) pressure increase.

4) I forsee issues with the internal sides of a FF rocket being hit by the Fast-Fission fragments even with magnetic confinement. If you look at the picture for the dusty plasma bed reactor, and assume that we have an electro-magnetic coil for the field (so that the field lines are parallel to the presumed direction of motion of the rocket), then particles headed for the side of the reactor will spiral in such a way that they would travel a greater distance before hitting the internal sides of the FF rocket engine. BUT, they will still hit the internal sides of the engine. These could still be used for energy, but perhaps arranging the density of the nanoparticles in a particular way would help ensure that more of the nanoparticles end up producing thrust parallel to the desired direction.

ConcernedScientist (talk) 19:17, 12 February 2009 (UTC)

Time line question

It is my understanding that many of these types of propulsion research programs regardless of how close they did get to creating these types of engines was abandoned decades ago. If the space race is on again as the media states these days why has no one continued these obviously efficient designs for interplanetary travel? I mean think of the advancement we have made since the 60's when we stopped the last attempts at these designs. 75.170.175.110 (talk) 04:42, 29 October 2008 (UTC)

Well, for one, no one has mentioned how much fuel this would take, and I assume it would be a LOT. Uranium isn't cheap. I can't imagine this costing less than a few hundred billion, maybe a few trillion, maybe more than the GDP of Earth. Also, with exhaust speeds of 5% of the speed of light, using a ridiculously oversimplified notion that the speed at all times = top speed (since I don't know the equation for calculating this otherwise, actual times of transit may be much higher), it would take 150 years to reach the nearest star with a planet (Bernard's Star). We could go to Alpha Centauri in a mere century, but unless it surprises us and has planets, we couldn't do much more than point our cameras at the star and take very boring pictures that look much like pictures of the sun. There are a ridiculous amount of projects with much more scientific validity that we could take on, rather than sending a probe to take pretty pictures and confirm things we already know through other methods. Or did you mean sending humans? In which case, LOL.24.179.56.142 (talk) 01:19, 15 May 2011 (UTC)

24.179.56.142: in the time since you wrote this, a planet has been discovered orbiting the nearby star Proxima Centuari, which is about the same distance as Alpha Centauri, about 4.5 ly away. :) https://wiki.riteme.site/wiki/Proxima_Centauri_b 2600:6C52:6200:381F:6041:AA5D:5681:8198 (talk) 04:42, 13 July 2018 (UTC)

Of course, the AIAA paper cited does mention how much fuel this would take, and your assumption is astoundingly wrong -- only 180kg fuel (perhaps a million dollars fuel cost) to send a 10-ton spacecraft to 550 AU (minimum distance to use the sun as a gravitational lens) in 10 years, and 75.170.175.110 said "interplanetary" implying even shorter distances, so even shorter trip times and/or less fuel. Even a 50 year Alpha Centauri mission with the same 10t spacecraft, while considered "probably not feasible", comes out to only 240t of fuel, or perhaps a billion dollars' worth.

WRT interstellar flight, it seems you're wrongly equating exhaust speed to maximum speed -- rockets don't work by "pushing off" something, but by conservation of momentum, and will continue to accelerate as long as they are firing. Not that it matters -- any such tech would need to be proven and refined on interplanetary missions before we could reasonably talk of scaling it up to interstellar probes. 50.102.164.125 (talk) 09:32, 25 February 2012 (UTC)