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At 10:48 AM 3/5/96, Brian Mansur wrote:
>>From Brian 10:40 AM CT 3/5/96
>[Much discussion deleted]
>>Kelly Says:
>>>Thats a very long time to wait around for first initial survey reports!
> At
>>>61 years (2111) you'ld get you first report back from Tau.  If you were
>>>that patient, you wern't that interested.  You might as well have just
>>>photo recon from orbiting 1000 kilometer telescope arrays.  You'ld get a
>>>lot of the data, 60 years earlier.
>>I see where our differences in opinion are coming from.  You and I have
>>different ideas as to what a kind of human universe this hybrid idea will
>>taking form.  And I admit that it is my fault here because you are sticking
>>to the LIT charter and I'm not qualifying my designs by noting that I am
>>limiting my technology to what would be available to 2050.  Sorry.
>>Thats ok.  Its an old argument in the group.  As I mentioned in those draft
>>web pages I sent around (and got no responce to!).  If you slip the time
>>table to a cetury from now, you have to start guessing what new
>>technologies, and Physcics! will be avalible.  A hundred years ago Fusion,
>>fission, relativity, momentum transfer of momentum, and a bunch more were
>>not enve theories.  Physisists (sp?) are currently mutering about inertian
>>and kinetic energy (i.e. what the hell are they), mater conversion,
>>controled distortion of space and time, alternate dimentions, faster than
>>light travel, and even freakier stuff.  By 2050 a lot of these mutterings
>>will be hardened theories, and our designs will look like a Saturn-V the
>>size of a mountain fueled by burning coal.
>>But, if you don't know what we'll get, you got to plan conservativly.
>I'm hoping that conservative includes future automated industry that makes
>today's automated factories look like how the first English factories do
>compared to today's.

I'm kind of dubious on that one.  You are talking about fully self
replicating machines, constructing power transmitters with billions of
times the power of Earths current electric grid, and and mirrors the size
of planets, all fielded in 50 years.  I'ld kind of think that was a non
conservative assumption.

>[Much more discussion deleted]
>>Brian Says:
>>If the reflector is construction at Kupier Belt distance, it won't be
>>any faster than Pluto.  That is until we put the mirror into the beam path.
>> Then it will slowly accelerate.  With relatively minor course corrections,
>>it will stay in the beam.
>>Pluto moves MUCH faster than Earth.  Your mirror would quickly move out of
>>the beam.  even if the beam was larger than Earths orbit.
>(imitating Homer Simpson's voice) Doh!  Doh!  Doh! Doh!  Doh!  Doh!  Doh!
>Doh!  Doh!  Doh!  Doh! Doh!  Doh!  Doh!  Doh! Doh!  Doh!  Doh!  Doh! Doh!
> Doh!  Doh!  Doh! Doh!  Doh!  Doh!  Doh! Doh!  Doh!  Doh!  Doh! Doh!  Doh!
> Doh!  Doh! Doh!
>David gave me these numbers
>Pluto's mean orbital velocity is 4.74 km/sec.
>Earth's mean orbital velocity is 29.79 km/sec.
>Are these right?  They seem backwards.

I'ld agree.   It seems odthat you'ld accelerate out from the inner system
to a slower velocity.  I suppose you might be losing the dif to potential
energy changes.

But I suppose it isn't critical for our discusion.  Assumeing a beam
diameter 40 times the dimeter of earth.  4.76Km/s will still have you cross
the beam in 31 hours.

>>Then how do you slow down the packaged mirrors without the pathfinder
>>rockets?  Or is this the expendable set?  I'm confused.
>The decel mirrors are expendable.  Again, considering the automation level
>of the civilization necessary just to put together such mirrors and maser
>arrays to launch them, I'm not worried about the cost.

I've noticed the cost isn't discused much by us.  Stark raving fear perhaps?

>>>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.
>>>Brian Says:
>>>I'm not sure I understand the last sentence.
>>>Kelly Says:
>>>The beam holds the projected momentum needed to push our obserdly heavy
>>>ship.  If said ship isn't in the beam, the reflectors in the beam will
>>>to angle relative to the beam.  That will mean that the thrust angles on
>>>the reflectors and the receaving ship, will also be angled.  Since the
>>>thrust isn't paralell to the beam/course.  The ship and reflectors will be
>>>pushed out to the sides.  I.E. off the beam, and off course.
>> ------------\
>>           /
>>          /
>>         \--------
>>Brian Says:
>>Understood as inevitable.  Here are some ideas I put into an e-mail sent to
>>you just a little earlier today which address the problem.
>>Begin Excerpt
>>I'll go ahead and put a few ideas I had for mirror and ship course
>>corrections here.  We could have the Asimov detach its ion drive and cable
>>connect it to an edge of the wire mesh sail and the hab section.  The drive
>>could then gently pull the whole set up back onto the beam path.   We could
>>also, perhaps have the maser array at Sol periodically decrease power to
>>allow this tug to do its job without being microwave fried.  We would have
>>to do something about shielding the tug, of course.
>>Perhaps the tug could be a pair light rockets hanging onto opposite sides
>> 1000km+ wide sail.  They could have their own shielding and would be in
>>excellent positions to do their jobs.
>>End Excerpt
>>Hanging them on the sails doesn't matter.  The weight after all is in the
>>ship, not the sail.
>>Given the power levels of the beam, the lateral thrusters on the ship and
>>mirror assembly would need to be incredable.  Possibly prohibativly so.
>Are you saying that the power level of the beam will keep us from
>manuvering?  If so, we can periodically turn it off like I suggested.

Well my thought was that the main beam would throw the ship and mirror off
to the side very quickly.  Assuming a 1% lateral thrust, thats a .1 m/s
accell.  You'ld drift 373,000 kilometers and get a lateral speed of 8.6
kilometers per secound, after 1 day.  (Well ok you'ld exit the beam after a
couple hours and stop accelerating.)  Rockets that could push back against
that load would rival the stardrive for powe.  But of couse you can't
thrust laterally without twisting the mirrors (no known material can stay
optically flat over that distence under any load.)

So if everything isn't precisely balenced and trimed you'ld get radically
out of alignment.  If that happens not only do you lose power and have a
hell of a time geting back aligned.  Since the ships could be light months
apart, you couldn't correct your aim for where the ship really is.

>What we need is a powerful enough rocket, probably ion drives that can
>periodically tug the Asimov, its sail, and the tugs themselves, perhaps a
>few thousand km back toward the beam every now and then.  Lets assume that
>the tug accelerator weighs 10 tons/m, and the drive needs to be 1000 m long.
> This does not account for fuel because I don't know what that will be:
>hopefully 10ton/m is an overestimate.   Two accelerators will weigh 20,000
>together.  By the way.  At rest, I figured we might put them along an axis
>perpendicular to the direction we want to tugs to tug.
>What we need to do is find exactly how many km we'll have to adust over the
>flight.  Then we can find better weight values.  To find the km
>displacement, lets say that for safety, the Asimov is traveling 100,000 km
>to the side of the beam.  Also assume that the decel reflector (during decel
>phase) and the reaccel mirror (durring reaccel phase) never come closer than
>1 AU from the Asimov.  Can anyone do the trig here?  I'll see if I can find
>the time get the numbers myself, but I don't make promises even when
>relatively simple mathmatics are involved.
>I also have an idea to add to my mirror paper.  I'll probably reprint this
>next paragraph in it later but here it is anyway.  How about putting a
>Fresnel lens in the path to TC to refocus our beam.  The lens could be of
>the thin variety, although I believe we would have some power losses through
>the lens.
>The lens could be launched and stopped at the desired position if we
>attached detachable reflective sail blankets on both sides.  One side would
>reflect maser energy for acceleration.  The other would be the surface
>facing TC to which a decel mirror.  The decel mirror would be like the kind
>envisioned for the Asimov and so would probably be launched separately.  I
>guess this idea would add several more years to our launch time-table
>assuming we only had enough masers and power to launch the weight of 1
>reflective mirror at a time.  By the way, I have little conception as to how
>much this Fresnel lens would weigh and I don't know if it would experience
>acceleration while refocusing.  For aiming I suggest the famous Waveguide
>gyros simply because I don't have any better ideas.
>>>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
>>>>at which the maser beam must be reflected.  The Asimov may simply angle
>>>>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
>>>>from time to time in the proper direction to allow vectorial force to
>>>>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.
>>>Brian Says:
>>>Good point.  Of course the angle of vectorial force will be tiny
>>>the reflector and the Asimov are several AU apart.
>>>Kelly Says:
>>>Oh, I forgot you couldn't do that with the reflectors and get the beam to
>>>the ship.
>>Brian Says:
>>Huh?  I don't understand this.
>>If you angle the mirrors to counter thrust you back into the beam, you'ld
>>be reflecting the beam away from the ship not toward it.  Trying to
>>anticipate where the ship is relative to the mirror array would be a
>>problem too.  The mirrors obviously can't 'aim' in the conventional sence
>>due to the time delay.
>Don't we already have computers that could be programed to reasonably figure
>this aiming problem out?

They could given current accurate info.  But given that the info has to
travel at the spped of light, it would be months out of date by the time
the mirror systems got it.  Given that the actuall rates will varry back
and forth a bit durring the interveaning time (given random flexing of the
sail, and random variations of the beam), and we can't predict what these
variations will be.  The aiming calculations will be precise calculations
bases on very bad information.  I.E. computer generated guesses.  Even
assuming not one unexpected thing ever happens on the ship or mirror.  If
you guess wrong even once.  You're aiming the beam into empty space and the
ship is racing away from where you think it is.

Just to complicate things.  The mirror is moring at a high fraction of the
speed of light.  So relatavistic distortion will distort the beam, mirror,
and apparent space.

>>You might try a secondary set of sails rigged to provide lateral thrust.
>>After all.  Only a tiny fraction of the beam will hit the reflectors (The
>>beam would after all be pretty spread out), and only a fraction of the
>>reflected beam would hit the main sail (since you can't aim accuratly,
>>shotgun the area).
>I'm not sure I follow you here?  I think I need a diagram.

         / /

A little hard to folow I know, but you have a secound set of sails
connected to each mirror and sail, angled to the beam shining on them.
These are angled to provide lateral thrust against the main lateral thrust
of the main mirror/sails
..  They would use parts of the beam that pass to the side of the areas that
the mirror and sail would see (yes that means the beam would need to be
huge, which would waste the vast majority of its power.  Probably 99%-
99.99% of it).

Oh, and you have to make sure the cross thrust dosen't distort the
optically perfect surfaces or the mirrors.

>>>Kelly Says:
>>> Also targeting on a moving ship when you get a few light months
>>>apart is dangerous.
>>Brian Says:
>>See my above question on just how well Kev's gyroes could be adapted to
>>for mechanical reflection.  If this isn't solvable for aiming mirrrors, I
>>guess its back to the drawing board.
>So does anyone know if these gyros will work.  Kev?  Haven't heard from you
>yet bud.

Even if the gyros would work, how flat can you keep hundreds of miles of
unsupported (you are in spec) chicken wire being blown down wind under VERY
high thrust loads?



Kelly Starks                       Internet: kgstar@most.fw.hac.com
Sr. Systems Engineer
Magnavox Electronic Systems Company
(Magnavox URL: http://www.fw.hac.com/external.html)