RE: tentative hybrid design.

[Brian Mansur <bmansur@oc.edu>]

>From Brain.

>Kevin sees Brian's "pocket change" and rasies one dollar.  ;)

Brian calls

>I don't have much time right now, so this will be short.

Know the feeling

>Here's the idea I'm thinking of.

>the ship starts off as a hybrid structure.  a MARS-like front end, with
>an explorer-like backend.

Sounds like a dream I had last night.  I'll explain in a minute.

>the ship accelerates out of Sol System with a simple maser sail.  The
>large fuel tanks (used by the MArs as RM, but used by explorer like
>fuel)  on the MARS keep us shielded from interstellar speed-induced
>radiation.  As we approach the halfway point, (speed ~ .9905 C)
>the two ships separate.  the MARS begins converting the masers to
>electricity, cutting it's photon derived thrust to ~5 m/s^2 (1/2 G)
>under computer control, the fuel is thrust out the back end so that it's
>speed is just under the MARS's velocity.  The velocity of the and mass of
>the exhaust can be tailored to the needs of the explorer, since there
>will be no humans aboard the MARS

This sounds something like the scheme I just worked out last night.  I 
thought someone might beat me to the punch.  Later I'll send a formal 
description listed as another hybrid design.

The problem I see with this design is the tremendous initial launch weight 
which can be compensated for by accelerating more slowly than 1g as planned. 
 The crew will have to live in a centrifuge with a floor tilted to take into 
acount the vectorial push of the acceleration.  But if we accelerate at say 
..036g, this shouldn't be too much to compensate for.  .

>Meanwhile, the explorer spreads a large ram scoop out *behind* itself.
>This scoop grabs the (already) ionized fuel, (no containers, just gas)
>and fuses it, redirecting the exhaust at the retreating MARS.  The
>redirected exhaust protects the crew sections from erosion by the fuel.

Kgstar (what's his real name?) was wondering how you are going to get the 
ionized fuel from a catch scoop trailing behind you.  Could we use a 
solonoid collector generated by the ion drive.  This would increase the 
scoop size because the magnetic field that flows toward the decelerator 
would tend to push the ions to the side.  On the other hand, since a wire 
mesh collector several kilometers wide can be made to weigh only a matter of 
grams, the extra weight shouldn't be a problem.  By the way, I'm assuming 
that a ram scoop can be made out of the same wire mesh that the starwisp 
design uses.  Since that is several km across and only 15 grams heavy, I'm 
using it as a model.  I hope it is a valid one..

>The MARS continues along toward TC, getting closer and closer to the
>speed of light.  just before it enters Tau Ceti itself, hundreds of small
>probes luanch away (at perpendicular velocities) get some slight bending
>from the star, and streak away to fly-by various other stars.  The big
>tanks (now empty) and the lineac core crash straight into the star, and
>make nary a splash.

>The crew deploys self-replicating robots (under some human direction) to
>construct the return masers, and a simple manufacturing plant handles the
>return sail (much like chicken wire)  the explorer, after ditching it's
>fusion motor, sails off back toward Sol, where the original masers sit
>waiting for our return.  :)

Why not just build a mirror to reflect the maser from Sol back to the 
Asimov.  Just put this mirror in the Kupier, put some rockets on it for 
course corrections if the beam or the mirrors start to drift away from lock. 
 Weight down the mirror with a lot of fuel to keep the maser beam from 
pushing it off to deep space.  If it can be made heavy enough, it could 
perhaps be used to stop a later mission.     This is only a rough 
description of a more detailed design proposal I have for the reflecting 
mirror.  I have to go to physics class (we're studying mirrors of all 
things), but I will try to get it typed up (and illustrated with ASCII art 
if there are no objections) before 5 PM.  At the latest it will take till 
10:30.