Re: Quick question about a STL trip - and another...

On Aug 22, 3:50 pm, Dr J R Stockton <j...@xxxxxxxxxxxxxxxxxx> wrote:
In rec.arts.sf.science message <ab148998-ddf3-4c3d-bd80-904c80db7745@r66
g2000hsg.googlegroups.com>, Fri, 22 Aug 2008 09:27:30, IsaacKuo
<mech...@xxxxxxxxx> posted:

For a starship with spin gravity, the same basic principle will
apply. The starship's spinning axis is along the direction of
travel. Imagine it's a cylinder, with the central axis pointed
at the destination. The only difference is scale. Instead of
accelerating for just a few seconds, you're accelerating for
months or years on end.

The amount of slant depends on the degree of acceleration,
compared to the level of artificial gravity.

ISTM likely that, for almost all of the time, the ship will be running
at constant acceleration; so skew its innards by design.

Even for a short range trip less than ten light years, the
majority of the time will be spent cruising with no acceleration.
This thread involves trip times of centuries, so even with
multi-decade acceleration and braking legs, the cruising leg
is still the majority of the trip time.

Otherwise, note that any such ship must have a perfect frontal
protection against impacts with particles from electrons to grit.
Therefore, there is no absolute need to minimise the cross-section. Put
the normally-inhabited parts in pods in the ends of arms, and adjust the
arms in the manner of a variable-sweepback wing to keep the apparent
gravity more-or-less perpendicular to the floors and parallel with the
walls.

This logic is a bit strange. Plausibly, providing perfect frontal
protection will be easier and less expensive with a smaller
cross section.

Even so, with the starship configuration I favor it's actually
very easy to simply tilt the crew sections to compensate for
acceleration/deceleration. The starship configuration I favor
is a large magloop with modules strung along it like necklace
beads. It's rather trivial to rotate a module to maintain a
vertical orientation of artificial gravity.

This configuration does not minimize frontal cross section;
a relatively long cylinder would do better. However, the large
magloop is good for the operation of the stardrive. For these
really long journeys, it's may be best for the starship to
reconfigure itself into a smaller radius for the cruise leg,
to minimize drag.

The shielding requirements might be small or even practically
zero. All that's needed is a field of plasma around the starship
to ionize any incoming particles. The magnetic field will do the
rest, deflecting even relativistic particles away from the torus
shaped volume immediately around the magloop. This same
magnetic field will tend to keep any ionized particles trapped
around the starship, so the plasma field may be self replenishing.

The only problem is that this field may be too good at stopping
particles, causing drag against the interstellar medium out to
a large radius beyond the starship. Based on Zubrin's estimates
of the effectiveness of such a mag-brake, it seems that the total
drag is not a problem for relatively short journeys. But for a
multi-century journey, it may be worth the bother to reduce the
starship's radius to lower drag.

Isaac Kuo
.

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