Talk:Fusion rocket

message: I had the experience while in Huntsville AL of meeting a aerospace engineer who is working on a type of plasma/electric engine for spacecraft.  While in a meeting to discuss research, the topic led to fusion engines, of which he briefly discussed an engine he had designed and was contemplating at the time sending to NASA for proposal (this was late in year of 2008).  His design included the plasma engine that they were perfecting at the time, along with a lengthy confinement section which narrowed to the degree where fusion would be accomplished by means of compression of exhaust plasma.  He mentioned it as a "fusion afterburner" though it seemed similar to a ramjet in design.  
The engine, as he mentioned it, would weigh 10 - 15 kilotons, and would fit aboard the Ares cargo launcher, allowing for a test run of the vehicle within the next decade.  There was also mentioned of another two feasible fusion propulsion devices being contemplated elsewhere in the US, one of which would require multiple accelerators aimed at a central target, and both having approximately the same weight.
1stcontact2035 (talk) 17:32, 6 December 2009 (UTC)
thread_title:  Fusion "Afterburner" for Plasma Engine 

message: Unless I'm very much mistaken, practical fusion rockets, as opposed to practical fusion power reactors, don't require a net energy gain. I.e. it is perfectly OK if, for each kWh of electricity (or whatever other energy source) you supply into the engine, you only get e.g. 0.4 kWh of kinetic energy of the exhaust plasma coming out of the nozzle. It's just important that the engine imparts those 0.4 kWh of kinetic energy onto a very tiny amount of plasma, so that the plasma is accelerated to a correspondingly high velocity (which is the efficiency (specific impulse) of the engine). I think this is a very important difference between fusion reactors and fusion rockets, one that's not understood by a lot of interested laymen, and it might make fusion rockets easier to build. After all, achieving hot fusion (outside H bombs) isn't all that hard and has been done for decades, it's the "ignition" (net energy gain) part that's really difficult. Shouldn't we mention this fact briefly? Olaf Klischat (talk) 02:23, 6 April 2013 (UTC)
replies: text: I didn't describe an ion engine: Whether an engine is an ion engine or not depends on the mechanism used to accelerate the plasma, which I didn't specify. An ion engine uses electric fields for that, a fusion engine uses nuclear fusion neutron energy and associated heat and pressure. Why would a fusion engine necessarily have to have a net energy gain? If so, why does the technology for fusion rockets seem to be relatively close to practical application (see e.g. http://www.washington.edu/news/2013/04/04/rocket-powered-by-nuclear-fusion-could-send-humans-to-mars/), when at the same time practical fusion power reactors, which definitely have to have a positive net energy gain to be of practical use, are decades away from it? I would say that even without an energy gain, fusion rockets may offer advances over ion engines in that they may achieve a much higher mass flow rate (and thus, higher thrust) at the same specific impulse. No? Olaf Klischat (talk) 15:10, 14 May 2013 (UTC)
thread_title:  Fusion Rockets don't Require a Net Energy Gain 

message: "This design would thus be considerably smaller and more fuel efficient due to its higher exhaust velocity (Isp=700 km/s)"
While exhaust velocity is measured in km/s, specific impulse is not. I'm removing "Isp=" as it just confuses the article. (For those who are curious, specific impulse is measured in seconds. It's a measure of how long one kg of fuel produces one kg-force (9.8 Newtons) of thrust. So for a fusion rocket with 700km/s exhaust velocity, it's about 71000 seconds.)  -- PaulxSA (talk) 03:40, 13 April 2013 (UTC)
replies: text: A high potential Isp is one of the main benefits, so it would be nice to mention the Isp or exhaust velocities that the sources say might be possible for the different fusion reaction/fuels that might be chosen. Rod57 (talk) 11:23, 16 April 2024 (UTC)
thread_title:  Isp 

message: Most of the confinement schemes use additional propellant (hydrogen or argon) to increase thrust, but the article doesn't say how that would be accelerated and what the thrust to weight ration might be overall (fusion reactor + propellant thruster). Since article mentions journey times, perhaps the sources include the extra detail on mass & thrust. Rod57 (talk) 11:29, 16 April 2024 (UTC)
thread_title:  What thrust to weight ratio predicted, and what sustained acceleration on a long voyage