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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The information on that web site is almost a year out of date.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
fusion.
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.
Lee