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Re: starship-design: LINAC efficiency

In a message dated 2/15/01 6:38:56 PM, stevev@efn.org writes:

>KellySt@aol.com writes:
> > And again, our analysis here was that you couldn't scoop up as much
>mass as 
> > the mass of the scoop over any nearby mission.
>You would need a large scoop cross-section, but it's not inconceivable.
>Let's say your scoop can pick up on average 1 hydrogen atom per cubic
>centimeter.  Over a distance of 4.3 light years, you can pick up about
>* 10^-5 kilograms of hydrogen per square meter of scoop area.  So to
>pick up 10^9 kg of hydrogen during that trip, for example, you'd need a
>scoop with an area of 1.5 * 10^13 m^2, or some 2000 km in radius.
>This is all just back-of-the-envelope calculation, of course, but it's
>clearly an indication that you'd need a very large ramscoop to make a
>reasonably-sized ship work.

And do you really expect the mass of the equipment needed to manage a 2000km 
ramscoop, projected far enough ahead to scoop in without excessive drag or 
power loads, and able to hold together at high thrust levels, would weigh 
less then 10^9 kg?    Also this area of the galaxy has significantly less 
then 1 hydrogen atom per cubic centimeter.