Sadly I do understand, I am just not blind to the implied engineering requirements. *40MW/kg !!!!!* The highest power to weight machines (outside of bombs) that humans have ever build were the space shuttle main engines, they did about 3MW/kg utilising a supply of LH2, the best possible coolant, to keep the engine from melting. That is a luxury you do not have with fusion in an ultra-high Isp engine.
At 40MW/kg (and would need to be much higher than that if you wanted any payload) even if your engine miraculously manages to eject 99% of that energy in the exhaust you still have somehow come up with a way of radiating 400kW for every kg of spacecraft from your engine cooling system. And any hot fusion engine requires a driver to initiate the fusion, typically recirculating 0.1-10% of the fusion power output. So being insanely optimistic with a Q of 1000 you are recirculating 40kW/kg of space craft power (4GW for a 100 tonne craft), and somehow cooling that power collection and driver systems as well, all for some small fraction of your total mass budget. Then there are the shielding requirements for the vehicle and occupants who are sitting next to this multiple TW output engine and its incredible gamma ray (at minimum) output. Which are just a couple of simple examples as to why anyone with even cursory knowledge of actual engineering knows that what you suggest is so far beyond the feasible that it is quite simply ridiculous. 100 years from now it might be possible for a spacecraft to achieve 1% of the power and acceleration levels you suggest at an Isp of 7.5e6m/s, but I wouldn't bet on it. On 6 June 2012 21:31, <[email protected]> wrote: > In reply to Robert Lynn's message of Wed, 6 Jun 2012 12:55:31 +0100: > Hi, > [snip] > > You don't understand the nature of technological breakthroughs do you. > > > >I'm sorry, but as an engineer if you imagine that you can build a fusion > >powered spacecraft with an exhaust velocity of 7.5e6m/s and 40MW of engine > >power per kg of spacecraft (from rocket equation with 20% fuel use in 2 > >days at 1g thrust), when nobody can yet build a viable self sustaining > >fusion reactor at any size then you don't deserve a response. > > > >On 6 June 2012 05:16, <[email protected]> wrote: > > > >> In reply to Patrick Ellul's message of Wed, 6 Jun 2012 14:10:21 +1000: > >> Hi, > >> [snip] > >> > >> I wrote to Elon Musk offering to help him build a fusion powered shuttle > >> to get > >> us there in 2 days at 1 g with only 20% fuel mass. > >> > >> No response. > >> > >> > >> >Funded by marketing it as one big reality show... Possible?? And would > you > >> >buy a one way ticket to Mars? > >> > > >> >http://mars-one.com/en/ > >> > > >> >Regards, > >> >Patrick > >> Regards, > >> > >> Robin van Spaandonk > >> > >> http://rvanspaa.freehostia.com/project.html > >> > >> > Regards, > > Robin van Spaandonk > > http://rvanspaa.freehostia.com/project.html > >
