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

On Aug 22, 7:33 pm, raph...@xxxxxxxxx wrote:
On Aug 22, 5:38 pm, IsaacKuo <mech...@xxxxxxxxx> wrote:

The chip impactors would plausibly be more like very small extremely
thin flakes of foil. With an area of perhaps .1mm by .1mm and a
thickness of 1 micron, the mass of a chip may be on the order of
0.01 micrograms.

These chips are supposed to be robot controlled? Isn't that a little
small for robot controlled?

I assume that by the time humankind can seriously contemplate
the fabulous expense of an interstellar probe mission, our
computer chip fabrication technology will be up to the task.
In order to handle high temperatures, the chip needs to have a
tungsten base with a carbon based semiconductor.

The basic acceleration mechanism is simple absorption/scattering.
The X-ray acceleration laser is tuned to the k-edge transition of
Tungsten (this is very short wavelength and allows for an
extremely long ranged laser). About a third of the x-rays get
absorbed by the chip's tungsten while two thirds gets randomly
scattered. The x-rays mostly pass through the carbon parts.
The result of this is acceleration almost perfectly away from the
laser.

The absorbed x-rays heat up the chip, and this waste heat gets
radiated away with blackbody radiation. Without doing anything
special, this radiation is equal in all directions, producing no
overall thrust. However, the chip is not evenly heated. The
tunsten base is heated the most, while the carbon semiconductor
is not heated much. This provides a temperature differential
which can provide thermo-electric power to the chip as well as
provide differential radiative thrust. The hotter tungsten side
will radiate more than the cooler carbon side, so there will be
some thrust away from the tungsten side. The chip just needs
to rotate around via some mechanism (like shifting c.o.g.) in
order to maneuver.

I wonder if you could arrange the laser in some
way so that the chips automatically move towards the centre line.
(perhaps, designed to move towards the most intense part
of the beam.)

I had come up with a complex scheme for doing this which
required no chip electronic logic. However, it seemed very
iffy compared to a digital logic solution.

This complex scheme involved coin or washer shaped laser
sails. The sails were ridged like a Ruffles potato chip or a
tin roof panel, and coated with strips of carbon insulation
so that waste heat radiation would be sideways. Each
laser sail is launched spinning so that they remained
perpendicular to the beam. This rotation is kept perfectly
in phase so all of the sails are rotating exactly the same.

The laser is then wiggled around into a tight helix, so that
the center of the beam revolves around the desired path
in phase with the rotation of the laser sails. The result is
that any laser sails which drift in a particular direction
receive more laser radiation when their direction of waste
heat thrust is in that direction. This provides a self
correction effect to herd the laser sails back to the desired
path.

This scheme is harebrained.

After coming up with one harebrained scheme after
another, I eventually settled on making the chips smart.
Wiggling the laser into a tight helix may still be a useful
technique for giving the chip navigation information,
but some sort of longer wavelength system of GPS-style
navigation beacons is plausibly more practical.

Also, for it to work, the 'puff' (gas right?) has to be hit by the
impactor.

More likely the chip will power through the gas and might only
interact with a small percentage of the it. That gas would
be blown forward relative to the rest of the gas but won't be
slowed down much, so not much of the KE of the incoming
gas is absorbed. Also, the stationary gas that remains is
just wasted and doesn't provide thrust.

This is related to a recent r.a.sf.science thread about
a 1%c impactor into Earth's atmosphere. Basically, the
incredible impact velocities involved mean that the
impactor violently expands almost instantly--interacting with
a large cross section of the atmosphere. This expansion
results in an explosion in the upper atmosphere rather
than any sort of deep penetration effect.

Much depends on the size of the puff and the relative
masses involved. I'm not sure a puff of gas is the ideal
form for the sacrificial propellant, but it does seem like
the simplest to deploy.

I wonder would a solid disc be better for the target. Its
thickness could be set so that the chip can make a hole,
blasting that portion of the disc forward. It might take
a while before the disc was consumed.

When it is, say, 10% consumed, it could be taken back
into the ship and replaced with another one and then
recycled.

This is very similar to my first idea for the sacrificial
propellant. I was thinking of a foil "sail" suspended by
three or more tethers in front of the starship. I
really liked the ironic look of this. It looks like the
spinaker sail of a traditional sailing ship, inflated in
front of the starship. However, the function couldn't
be more opposite! The function isn't to accelerate
the starship forward, it's to decelerate the starship
rearward. And the "sail" isn't curved forward due to
any sort of "wind" pressure, it's hanging forward due
to inertia while the starship is decelerating and yanking
it rearward. Finally, the ultimate irony is that this
spinaker "sail" isn't even the starship's sail at all. The
true sail is the magloop integral to the starship's main
hull.

Unfortunately, this scheme wouldn't work because
the first impact would likely demolish the entire
***. In order for the *** to have any chance
of survival, it needs to be flat.

Some sort of foil based solid propellant may be better
than a gas puff propellant. The logistics seem a bit
fiddly, compared to the simplicity of puffing gas.

I wonder if the disc would melt, if the chip is moving
fast enough, perhaps, there wouldn't be enough
time for conduction of heat, it would just blast
a cylinder/cone of material directly into plasma.

For this scheme to work, the disc needs to be a thin
foil. The problem isn't conduction of heat, but the
impact explosion products directly impacting with
the rest of the ***. The only way for any of the
*** to survive is if it's shielded from the explosion
products. If the *** is flat, then the region of
the *** immediately around the impact point
can shield the rest of the *** from damage. The
amount of damage diminishes exponentially with
radius from the impact point; the rate depends on
the thickness of the ***. The thinner the ***,
the better the rate.

Isaac Kuo
.

Quantcast