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>From Brian,

>>At 4:57 PM 3/1/96, Brian Mansur wrote:
>>From Brian
>>March 1, 1996
>>MARS HYBRID DESIGN II (Kevin already submitted the first this morning)
>>Total mission time: 50+ years
>>Pathfinder(s) mission flight time: 40+ years
>>Asimov flight time: 24+ years
>>Asimov exploration phase time: Undetermined

Kelly Says:
>If its going to take 50 year to get there.  I think people would put it off
>until they could think up a faster ship.

I'll tell you right now that it will take you at least fifty years to think 
up and build the support systems for another faster ship.  Live with 50 
years or else we don't go at all!

>Or just lose interest in the

Okay, listen up people of America.  Unless we can create anti-matter in 
copius quantities or build a lot more than 1E7 masers plus solar energy 
collectors to power them all so that we can overcome doplar shift on the 
reflector, you're going to have to be patient.  Half a century really isn't 
that long for this kind of a mission.

And remember that twenty-five of the fifty+ years will be an unmanned part 
of the mission where theslow moving deceleration mirror gets into position 
so that we can send a fast moving ship with the exploration crew.  They will 
take 12+ years to get to TC and 12+ years to get back and I figure that they 
will be there for at least 10.  Now if that isn't good enough for you, I 
don't know what is.  Just how fast do want to go?  Warp speed? ;(

>     It is assumed for this mission plan that a high degree of robotic
>automation has already made possible the production of at least 1E18 W
>needed to power 1E7 masers without much human supervision.  It is also
>assumed that this maser array is totally dedicated to the mission and that
>the beam will be left throughout the mission.
>     At least one heavy pathfider vessel will be sent before the Asimov
>using  maser sail to reach a terminal velocity of 1/3c.  Pathfinder carries
>several thousand, heavy duty, heavy weight, individually targetable,
>disassembled mirror arrays that will be deployed roughly 30 years later 
>TC (see reflectors in an upcoming posting).  These arrays (probably making
>an effective 1000 km+ wide reflector) will reflect maser energy back to the
>Asimov for the deceleration phase.  The Pathfinder may or may not have a
>crew depending on the level of automation available at the time of launch.
> Also, it may or may not carry emergency supplies for the Asimov should 
>choose to match speed and dock during the deceleration phase.

Kelly Says:
>Are you assuming the beam would be tight enought to be reflected after 11
>light years.

I'm assuming that we can send a mirror the width of Jupiter if we wanted to. 
 And when I get time to write up the specifics on this idea, you'll see that 
the mirror can actually be thousands of individually targeted mirrors guided 
by the same kinds of gyros that Kevin uses to aim the masers.

>Not to mention assuming a mirror could hit the ships sail
>with the reflected beam, a few light years away?

Remeber the gyros.

>     The  Asimov is maser pushed to a high %c terminal velocity.  It is
>hoped that the maser propulsion system will be efficient enough to push the
>Asimov to a speed at which the effects of time dialation will be useful to
>the crew.  At the very least, a max speed of .75c is assumed here.
>     This ship will consist of an ion drive for in system shuttling around
>TC.  It will also carry the exploration team and their supplies for the
>mission.  Among the supplies already mentioned in other discusions are seed
>robots.  They will be used to start a robot workforce that will help
>construct, among other things, a precision mirror array to reflect the 
>energy from Sol back to the Asimov's maser sail when the exploration phase
>is completed.
>     The exact process has many variations.  If there are several
>Pathfinders, each, the one closest to the Asimov will deploy its reflector
>array and then move to a safe range from the beam path.  The array will
>enter the beam path and redirect the maser energy back to the Asimov.  The
>Asimov, of course, will have turned its sail around (a slow and delicate
>process).  It will also have moved slightly to the side the maser beam
>coming from Sol to prevent blocking of the array.

Kelly says:
>I assume 'array' refers to the reflectors on the pathfinders.

I just realized that you can launch the reflective mirror without sticking 
it on a pathfinder.  The pathfinder was supposed to just be a conviently 
protected package for the mirror.  But if some shielding ideas that I've 
been kicking around are at all worth our time, we can forego the idea of the 
pathfinder completely.

Kelly Says:
>If the Pathfinders are reflecting the beam off to one side.  They will be
>pushed out of the beam in the other direction, and accelerated forward.
>Given that the beam presure is strong enough push the ships in the first
>place, it would be too strong for the ships thrust against.

I'm not sure I understand the last sentence.

Brian Says:
>     Some method of periodic or even continuous course correction on both
>the Asimov's part and the array's will be required to correct for the angle
>at which the maser beam must be reflected.  The Asimov may simply angle its
>sail slightly with the edge furtherest from the Sol to array beam tilted
>back toward Sol.  The array will have to use built in rockets, or else tilt
>from time to time in the proper direction to allow vectorial force to push
>it back into the center of the beam.

Kelly Says:
>This might be complicated given the main sail would be curved like a
>parachute, not flat.

Good point.  Of course the angle of vectorial force will be tiny considering 
the reflector and the Asimov are several AU apart.

Brian Says:
>     Now, assuming that the doplar effect will cause problems with
>reflection of the maser beam, another Pathfinder could deploy it's array 
>continue the decelation process.  Note that I don't know if  the most
>efficient thing that the Asimov can do with the redirected maser beam will
>be to simply bounce it back to space or to power a ion drive.   The exhaust
>from an ion drive would make for nice shielding against large particles.
>     One final note.  As the Asimov and Pathfinder speeds reach equilibrium
>they have the option of docking (assuming the deceleration of the Asimov
>brought it close to the Pathfinder when speed equilibrium was reached.  At
>this point, any crew on the Pathfinder could cross over.  Note that the
>Asimov could dock with only one Pathfinder.

Kelly Writes:
>It could dock with more than one.  But that wold depend on their speeds and
>relative positions.

Have to think about that more, I guess.
Gotta go to class.  I'll finish replies after 5 CT.