RE: starship-design: Re: Re: regarding fuel expenditures

["L. Parker" <lparker@cacaphony.net>]

On Sunday, November 16, 1997 10:31 AM, Isaac Kuo [SMTP:kuo@bit.csc.lsu.edu] 
wrote:
>
>
> That's not the point.  The point is that the potential extra benefit
> is a ridiculously small amount compared to a percent of c in delta-v.

I wouldn't call thirty percent of c without expending ANY onboard fuel 
ridiculous...

>
> In fact, the disadvantages are such that they overwhelm any advantage.

What disadvantages? Unless you are talking about crewed starships, which I 
conceded upfront were impractical for this maneuver, there aren't any 
disadvantages.

>
> Even without the human limitation, strengthening an unmanned probe
> for 400 g's will increase its mass by at least some small fraction.
> This will make it require _more_ fuel, not less.

Solid state electronics are routinely subjected to far higher accelerations 
and continue to function quite well thank you. (Instantaneous g forces of 
over 1,000 g have been successfully withstood.) These were airborne systems 
designed for aircraft with relatively low payloads. I don't think there is 
any problem here. Perhaps you aren't familiar with the design criteria for 
Starwisp, which is the unmanned probe in question here.

> It would not be significantly faster.  And that's the point.

A running head start at 30 percent of c is significant for an unmanned 
payload unless you can show me that you can accelerate the same payload to 
the same speed without exceeding the mass of the sail (you can't, the free 
fuel will get you every time). YOU must include engines AND fuel. Frankly, 
there is no known drive system capable of doing any more than MATCHING this 
velocity. That point made...

I will agree that 0.3 c is trivial as far as starship velocities go. The 
only way we are going to get there is with ships capable of crowding c and 
no sail is ever going to do that with or without humans aboard. There are 
several promising developments, but I wouldn't characterize them as current 
technology, perhaps within 50 years though.

The reason that Starwisp is important is that it is virtually within our 
reach NOW, it can put probe through all of the local systems within the 
next fifty years if we start soon, and they are small and cheap enough that 
we could literally mass produce them. Without some sort of data on the 
interstellar medium, and the potential destinations, we could waste a lot 
of money and lives on useless trips. If we can get a free boost to 0.3 c 
from the sun for a probe, I don't really care what other sort of drives are 
available.

Lee

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