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BOUNCE starship-design: Non-member submission from ["Kevin 'Tex' Houston" <hous0042@tc.umn.edu>]

n.edu by mhub1.tc.umn.edu; Tue, 29 Jul 97 22:49:29 -0500
Message-ID: <33DEB8AD.1A89@tc.umn.edu>
Date: Tue, 29 Jul 1997 22:44:46 -0500
From: "Kevin 'Tex' Houston" <hous0042@tc.umn.edu>
Reply-To: hous0042@tc.umn.edu
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To: Starship design group <starship-design@lists.uoregon.edu>
Subject: Re: starship-design: Deceleration scheme
References: <199707292304.QAA16599@watt> <199707292317.QAA16183@tzadkiel.efn.org>
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Steve VanDevender wrote:

> Has anyone else thought of using a lightsail and beamed power to
> accelerate, and a ramscoop to decelerate?  I think the concept has gone
> by before, but it seems to me to be the best combination.  You don't
> have to carry much fuel, except for maneuvering; you get free braking
> _and_ more fuel from the ramscoop, and maybe you can even afford to
> build another beamer in the target system for a return trip.  This also
> turns the main disadvantage of a ramscoop (drag against the interstellar
> medium) into an advantage.  There's almost no need to fuse the collected
> hydrogen unless you want improved braking efficiency once you get slowed
> down to low speed.

Hey!  That's a great idea.  The "sail" could easily become the "scoop"
(well, not easily, but not impossible).  We'd still have to bring some
fuel/RM with us so we can continue to slow down from less than ramjet
speed.  This could also solve the turning around problem.

Here is a (bad) cross sectional of the scoop/sail system.  Please note
that this is meant to be conceptual and descriptive and not
representative.  Any required support structure has been left out for
clarity.  Drawing does not necessarily reflect the author's true opinion
on the shape of the scoop/sail.  That is because the author does not
have one yet.  Drawing is not to scale.


            /   Scoop / Sail       Beam from earth     
           |   /                <~~WW~~wWw~~ww~w~w~ww~~wWw~~WW
   H+      |            _____________                  
     \      \          /             \                 
      \      \        |  RM TANK      |                
       `-->   \____[X]_\_____________/__                
         _____________________________  |               
 <thrust _____________________________  |               
        ,-->   _________________________|                  
       /      /    [X] /             \                 
      /      /      | |  RM TANK      |                
     H+     /       |  \_____________/                 
           |        |                                  
           |        V                                  
           |    crew sections                          

The beam is a dual frequency UV/MW (Ultraviolet/Microwave)  Most of the
energy is in the MW part, but the low-power UV is at just the right
frequency to ionize hydrogen atoms into H+ (13.6 eV).  Hopefully, this
will also clear away the larger debris.

The sail is a wire mesh made for absorbing microwaves and converting
them to electricity (which has a near 90% conversion factor, Ken).  When
the electrical load on the wires is removed, the mesh should reflect the
microwaves.  During the accel phase, the mesh acts as a sail.  The holes
in the mesh allow the UV portion to pass right through.  During this
phase, the mesh is slightly charged, to encourage Hydrogen ions to pass
through the center of the ship.  I'm not sure if some of the MW should
be converted and used to accelerate the H+, or if there is more momentum
to be gained by reflection. if more momentum can be gained from
accelerating the ions, then that would make the mesh design much
easier.  This looks more and more like the MARS design but designed to
scoop RM instead of bringing it with.

During the decel phase, the mesh and reaction chamber are charged to
extract energy from the on-rushing hydrogen ions, and blast them back
toward the target system.  So there are two sources of power, the
kinetic energy of the craft and the beam from earth.  Adding fusion to
the mix might not be required, nor would the ship have to 'eat' the
scoop/sail as it went along.  once the ship is below a certain speed,
the H+ mass flow will not be very massive, and the ship will have to
switch to on-board RM.

The large RM tanks would protect the crew from microwave radiation
during the trip.  positioning half of the RM tanks ahead would also
protect from incident cosmic rays.  And a set of tanks can be used for
RM as the fuel is used up.

The scoop/sail might be best designed to be in one of two modes
depending on the function of scooping or sailing.  It might also be best
to dispense with reflection of the incoming beam altogether.  a diode
doesn't care which direction the energy comes from, if it's the right
frequency, it gets absorbed and converted to electrical energy.  The
sail might be best described as an antenna.  And since the scoop is
where much of the energy will used, it seems to make sense to co-locate
it with the energy gathering gear.

However we do this, I think we must be resigned to the fact that this is
never going to be a practical method of travel because of the cost
involved.  We should hunt for the lowest cost, of course, but I don't
think we should scrap a workable solution simply because it costs too
much energy or money.  Probably none of our designs will ever be
created, and future generations will smile slightly, just as we do when
viewing Leonardo da Vinci's flying machines.  Every one of his designs
was technically workable, he only lacked a powerful, lightweight motor.
Now that we have internal combustion engines which produce energy many
orders of magnitude above what Leonardo could have possibly dreamed
about; we find that jets and fixed wings are better and faster.  

I think the same will be true of interstellar flight.  I think we _will_
solve the lightspeed and the ZPE barriers, but not anytime soon,
(anything that takes longer than about 50 years is useless to me anyways
;) and not in any way that we are capable of deducing today.  And that's
when the exploration of the universe will begin.  

But I still think it would be fun to see what we can come up with using
current Tech.  

Kevin "Tex" Houston 		http://umn.edu/~hous0042/index.html
Webmaster			http://www.urly-bird.com/index.html
"Whoever undertakes to set himself up as a judge of Truth and
Knowledge is shipwrecked by the laughter of the gods." A. Einstein