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ICAN (Was RE: starship-design: What is safest?)

On Saturday, January 10, 1998 1:11 PM, Timothy van der Linden 
[SMTP:TLG.van.der.Linden@tip.nl] wrote:
> At a site that Lee reported some time ago they talk about 1 Hertz:
> http://antimatter.phys.psu.edu/ICAN-II_Paper/ICAN-
> II_Features.html#thrustAndIsp
> My guess is that the pulsed fusion system you mention are even more
> sophisticated. (If not, (hyper) links are appreaciated.)

The information on that web site is almost a year out of date. I'm not sure 
why they haven't updated it yet. The original concept did indeed specify 1 
Hz. There have since been a few news articles and a TV program report on 
the concept (the producers of the TV program focused more on sails I'm 
afraid, probably because they looked prettier)as well as a paper presented 
somewhere a few months ago. Supposedly the system is undergoing initial 
testing at the moment...

Anyway, somewhere in those reports I read mention of "several" per second, 
which I take to mean 3 or 4 per second. Without another search, I can't 
really give you any supporting references. If I do find them again, I will 
be sure to copy them to the listserv.

Actually, the ICAN concept itself does not provide sufficient ISP for 
interstellar flight, just interplanetary. However, I was approaching this 
as a first generation engine only. The physics support eventually upgrading 
the fusion reaction to Be or Li providing significant increases in thrust. 
The ICAN concept does not include or make use of new magnetic nozzle 
technology that is also emerging at the moment and which would also provide 
additional thrust. 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.

I believe that is a reasonable extrapolation in that it doesn't involve 
anything that we don't already understand the underlying physics of, nor 
does it require FTL or any other exotic technology, just relatively simple 

In order to increase ISP and reliability I had envisioned a cluster of 
engines developed from the ICAN concept. If each one injects its pellet at 
a different time than the others you can probably get an overall frequency 
around 20 to 30 Hz with six engines.

I discussed this somewhat with Kelly. The ICAN concept uses only an initial 
boost phase and then shuts the engines down and coasts the rest of the way 
until it is time to decelerate. This method keeps the engines well within 
current system lifetime capabilities but severely limits velocity. I was 
(am) hoping for a little more than that. 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.