The Starseed/Launcher
By Forrest Bishop
Copyright (c) 1996 Forrest Bishop
All Rights Reserved
This system launches phalanxes of Shape-Shifting interstellar nanoprobes
at one third the speed of light. The probes may be capable of inflight
mutual rendezvous, some self-repair, and decelerating to orbit the target
star system. A method of self-replicating at the new star system is proposed.
This is work in progress, so some of the design specifications mentioned
may be changed.
It is customary, in interstellar propulsion studies, to consider the
energy required to send a craft to another star in terms of multiples
of the current world energy consumption. In contrast, the Starseed/Launcher
energies can be phrased in terms of the storage capacity of a car battery.
This represents a decrease of very roughly a million million (10^-12)
in energy usage over the next nearest proposal (Robert Forward's "Starwisp").
Another characteristic of these kinds of machines is the scale of the
various components, usually expressed in kilometers and tons. While the
launcher in this design is about 1000 kilometers long, it is in the form
of a very small diameter "wire", that could be stored on a drum.
The entire mass and volume of the launch system, and its interstellar
probes, might fit into, for example, a single Space Shuttle launch. What
would make this possible, of course, is the ability to fabricate atomically
precise "diamondoid" structures.
The launcher is a type of linear electrostatic accelerator, based in
part on a rotary design of K. Eric Drexler's. Non-contacting electrodes
are embedded in the interior surfaces of the bore with alternating positive
and negative voltages applied to them. Electrons are deposited in the
probe's conductors, and then removed at the next electrode. The motive
force is generated at the gap between two electrodes: a negatively charged
probe conductor is attracted to the "oncoming" positively charged
electrode, and vice versa. An interesting feature of this design is that
no power switching, and the attendant headaches, is required (although
an alternative negative 'electrode' requires a high voltage supply). The
launcher can be pre-charged from a 10 volt supply before the probe is
loosed.
The launch mass of the "individual" interstellar probes is
about a microgram. Each probe is composed of several million "MNT
Active Cells", each about 100 nm in size, and about 2 x 10^-15 grams
in mass. There are also several hundred thousand "Conductor Modules",
basically little wires, that can be rearranged after the launch by the
active cells to make different electrical devices, such as radio antennae.
One result of this is that the individual parts of the probe are reused
several times, in different capacities, during the interstellar passage.
This is one reason the launch mass can be so low.
For launching, the active cell aggregate and the conductor modules are
formed up as a thin, laminated ribbon, with the active cells in the center
layer. This distributes the electrostatic launch forces over a large area,
which is why the acceleration can be on the order of 100 million gravities.
During the boost phase, the clearance between the probe and the tunneling
contacts of the launcher has to be maintained at around a half nanometer,
while the relative velocity climbs to 100 000 km/sec.
Several types of suspension systems are being studied for this, such
as maglev and electrostatics. Jeffrey Soreff has pointed out that the
probe and launcher walls are mutually subjected to hard UV at the c/3
end, if the clearance is on the order of a nanometer. A redesign of the
launcher at this end is required- the clearance has to increase to several
hundred nanometers to avoid "shredding" things.
The launch system could be made up of several (or several billion) individual
launchers ganged together and launching simultaneously or sequentially.
Because the active cells are able to connect together, a number of probes
can rendezvous inflight and join to form larger structures.
[[ One such structure is a diffractive-optic telescope for taking bearings
en route, as well as for imaging the members of the target star. The active
cells may be able to impose active control of the needed tolerances for
this to within a few dozen nanometers.
Small excursions from the desired trajectory, as well as reaction control
in general, can be done by using the active cells as propellant. The efficiency
of this is very poor, but the system has the advantage of being already
built in.]][[edited out]]
Surviving the interstellar trip is very problematical. The probes spend
several (subjective) years being bombarded by cosmic radiation and grains
of dust in the interstellar medium. The dust grains are moving at roughly
one third the speed of light, which is a high enough energy to strip electrons
from the atoms making up the probe. By launching a sequence of probes,
a corridor might be formed by blasting the dust grains with "point
probes", which are also destroyed in the process. The following entourage
would have to be closely in line with, and not too close or too far away
from, these point probes for this to work.
Another possibility is to use superconducting solenoid magnets made from
the conductor modules to ionize and deflect the incoming particles. This
might be done in combination with the sacrificial point probes.
A wilder idea is to launch the probes at a higher speed, perhaps two
thirds the speed of light (The Starseed/Launcher is designed for one third
the speed of light simply as a matter of convenience). It may be possible
for the active cells, which are about 100 nanometers thick, to pass right
through the particles and dust grains without too much interaction [[(an
idea of Forward's)[[edited out]]]]. In other words, it would be like walking
through a wall.
In any case, since the probe phalanx is made up of millions of identical
active cells and conductor modules, all of which are capable of connecting
together and separating, the damaged cells can be either sloughed off
or collected to make new point probes. With the above survival strategies
(and others not mentioned here), it becomes a question of how many probes
need be launched to successfully reach "Star System X".
As the nanoprobe phalanx nears the target star, it may be possible to
decelerate by interacting with the interstellar medium as well as the
stellar wind. The conductor modules are rearranged to form large superconducting
loops, or "Magsails". The supercurrent might be provided by
maser from the launch vicinity, or possibly by interacting with the charged
particle medium. A braking force is generated regardless of the orientation
of the Magsail. Since the stellar wind is blowing radially outward at
around 100 km/sec, the deceleration can be maintained all the way to intersystem
orbit. The Magsail is capable of tacking, somewhat like a Solar Sail,
and so can perform orbital maneuvers such as planetary rendezvous.
The active cell aggregate might also contain "Gantry Cells"
and the other components of the "Overtool" (a Drexler Universal
Assembler). By rendezvousing with native hydrocarbon material, such as
comets, or Saturn-like planetary rings, it may be possible to synthesize
new active cells, machine civilizations, and so forth.
One characteristic this work shares with some other interstellar propulsion
studies is that the further out it goes, the farther out it gets.
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