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starship-design: Re: ICAN

Hi Lee,

Glad we came to an understanding about the subjects:
- Mining vs. Recycling
- Never ever lasting

About the fusion engines:
The main reason to keep the firing rate low was because waste heat would
otherwise melt the trottle/engine.

You suggested to use multiple engines, but that would increase complexity
and thus lower lifetime. (But I admit also add a certain redundancy which
would increase the time that a certain fraction of the engines keeps working.)

In your first ICAN letter (to me) you wrote:

>In short, I am extrapolating from current technology to 
>technology under development to the next generation of technology which 
>should arise from the generation currently under development; in other 
>words, about fifty years.

This makes my "fears" about complexity even worse. I'm not saying that
fusion engines aren't useful. I'm saying that the ones we need will be just
as or more complex as current rocket engines and thus may shorter lifetimes.
(Which makes Kelly's argument that the engines aren't likely to fail during
the "short" acceleration and deceleration tracks less valid.)
"A pellet injector and a bunch of ion accelerators" do not sound simpler
than a chemical rocket. (Maybe also not more complex, but they feel much
more fragile.)

As a side issue, you wrote:

>If magnetic nozzle technology 
>development proves out, it may be possible to extend the design lifetimes 
>enough to sustain continuous boost. Personally, I think this will take 
>between fifty and one hundred years to perfect, but it will permit cruise 
>velocities approaching c within a few tenths of a percent.

Except of course that cruise velocities over 0.3c still means mass ratios of
more than 100 as long as one uses fusion.