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Re: Engineering Newsletter

We were talking about how much drag we might be able to get out of the
interstellar medium.  I dug some old numbers out of my LIT web page and
tinkered with them.  Note that my numbers were for 1.3rd light speed, so I
didn't bother with relativity corrections.

Kelly Starks


Ram Scoop collector
1000 km diameter scoop 200 tons. The speed of light is 300,000 kilometers per
second Assuming your moving at 1/3rd the speed of light (100,000 kilometer
per second, or 1E10 cm/sec) with a scoop area of 1000 km
(pi*R^2=pi(50,000,000cm)^2 = 7.854E15 cm^2). You'd be scooping up the mass in
7.854 E25 cubic centimeters of space.
A big question is the composition of interstellar space. A classic assumption
is that there is nothing but about 1 atom of hydrogen in a cubic centimeter
of space. More recently, people guess it might be less than .054 atoms per
cubic centimeter or as many as 10. Even more recently than that (say the last
few months) it has been proposed that there may be a lot of long-chain carbon
molecules in space. Perhaps 60-200 atoms / molecules.  These small, dark,
heavy molecules might be the missing 90-99% of the mass of the galaxy
(euphemistically called "dark matter").
So far, no one really knows. This is unfortunate, because the composition of
the interstellar medium makes a hell of a difference in the design of a
RAIR-based starship. Since we don't know one way or the other, let's assume
one atom per cubic centimeter at a proton mass of 1.673 E-27 Kg.  At 0.333c,
using the above design figures, our 1000 km in diameter scoop, scoops up a
ram flow of 131.4 grams per second.

473 kilos per hour
4.14 million kilos per year.  (4,140 metric tons per year.)

Given a ship weighing hundreds of times that.  This isn't going to slow us
down much.  But if we want to assume lots of  carbon molecules, the mass
could jump up to the mass of the ship per year.  But thats probably a bad
assumption here near Sol.  Seems this area of the galaxy is in a big bubble
of space blasted nearly clean of debries by a recent supernova.  So we may be
living in one of the worst areas of the galaxy for a ramscoop, or ram
breaked, starship.