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From: m.driussi@genie.com
Subject: (whorl) stardrive
Date: Tue,  3 Nov 98 17:30:00 GMT

Re: questions regarding the stardrive that is pushing the Whorl.

Because the details in the text are so very few, the entire topic is
wildly speculative.

By my reading, at least, it appears that the Whorl had a cruising
velocity of .95 c, or ninety-five percent of light speed.  This
results in a time dilation factor of around 3:1, so that only one
year passes onboard for every three years that pass in the universe
at large.

To current "realistic" stardrive thinking, .95 c is so high that it
is effectively "magic."  Even the most energetic of "realistic"
rockets, a photon drive (thrust produced by the mutual annihilation
of matter and antimatter) with a Mass Ratio of 16 (so a one ton ship
uses 15 tons of reaction mass--in this case, 7.5 tons [!!] of antimatter
and 7.5 tons of matter) can only go .88 c in a voyage where the ship
must come to a stop at the end (i.e., in a forever nonstop flyby this
stardrive and Mass Ratio can maybe hit .9922 c).

An Ion Scoop, like that for the Bussard Ramjet (the great hope of the
60s), while an excellent model for "living off the land" and thereby
avoiding those crushing Mass-Ratio figures, is currently thought to
be incapable of surviving (or attaining) velocities over around .2 c.

So we are left with fringe concept NAFAL (nearly as fast as light)
drives.  The following appropriate the ion scoop's "living off the
land" function: Milton Rothman's wormhole jet ("free" photons
siphoned from nearby stars via wormhole); Clarke's quantum jet from
SONGS OF DISTANT EARTH (perversely limited to .2 c anyway, due to
interstellar friction); the tachyon drive of Haldeman's THE FOREVER
WAR (using tachyons as exhaust for NAFAL travel); and Sheffield's
quantum jet from THE MCANDREW CHRONICLES.  There aren't enough
details to say much about the quantum "spin-ships" of Dan Simmons's
HYPERION, but they would seem to fall into this category; as would
the NAFAL ships of Le Guin's Hainish novels.

(When dealing with these fringe concept drives, it occurs to me that
even discounting Mass-Ratios, another barrier to cross is the fact
that a ship travelling at .95 c has its mass multiplied by 3.2!  So
if your magic jet drive can push an asteroid up to .8 c [at which
point it is really pushing 1.667 times the rest mass of the
asteroid], to attain .95 c will require that the same drive push
twice as much mass.  So even magic drives have consequences.)


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