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Re: starship-design: Re: Solar sail breaking

At 10:12 AM 10/21/96, Kevin C Houston wrote:
>On Mon, 21 Oct 1996, Kelly Starks x7066 MS 10-39 wrote:
>> At 12:48 AM 10/21/96, Kevin \"Tex\" Houston wrote:
>> >
>> >The idea is my old Microwave Augmented Rocket System (MARS).  A ship
>> >departs earth with tanks full of Reaction Mass (RM), and accelerates
>> >away from earth using a microwave sail.
>> >
>> >At the turn-around point, (not necessarily the halfway point), the
>> >ship converts the energy from the microwaves into electricity, and
>> >uses that to accelerate the RM to a hefty fraction of C.
>> >
>> >Here is what Rex had to say on this subject.
>> >
>> >--------begin included text-------------------------------
>> >The effects of reduced conversion efficiency (eta less
>> >than 1) on required exhaust velocity, final sail furl and, most
>> >importantly, required mass ratio are given in the table below:
>> >
>> >  eta   exhaust velocity   final sail furl   mass ratio
>> >  1.0        0.883             0.160            9.41
>> >  0.9        0.849             0.105           15.44
>> >  0.8        0.809             0.060           29.05
>> >  0.7        0.760             0.029           67.57
>> >
>> >Producing high efficiency of conversion from received power to
>> >exhaust power may be as challenging (and as crucial to the
>> >success of the concept) as constructing the emitter or the sail.
>> >----------end included text-------------------------------
>> >
>> >So even a fairly high efficiency of .7 means a mass ratio of 68.
>> >This is not too bad, considering some of the other mass ratios I've
>> >seen bandied about.  (114 for really good anti matter ship)
>> What are the cruise speeds and flight times that you can get to with this?
>There is no cruise per se.  The ship is a constant thrust mission,
>but the thrust steadily decreases throughout the mission. then builds
>up again.
>top speed is .93 C
>flight time is 8 years for the crew, and 15 years for earth.

Pretty good for a Tau C. flight.

>> Kevin:
>> >Another problem with this design has been pointed out by Kelly.
>> >I've said that an advantage with this system is that while in flight
>> >we done need any spinning sections.  Kelly's point is that this would
>> >have an adverse effect on the crew.
>> >
>> >Because the power beam from earth is constant (to minimize hassle),
>> >and the ship is going to approach light-speed (.9331 of C) then
>> >something has to give.  That something is the precieved acceleration
>> >felt by the crew.  This will fall to ~1/7 earth normal near the
>> >turn-around point.  As the ship begins to decelerate, the "gravity"
>> >will again climb toward earth normal.
>> >
>> >Kelly fears that extended time at less than 1 Gee will have an adverse
>> >effect on the crew.  I disagree with this because the change will be
>> >relatively slow.  Even after Six months at Zero Gee, Shannon Lucid was
>> >able to walk out of the shuttle after it landed (much to the dismay of
>> >NASA doctors to be sure.)  and this was an abrupt change, a slow build
>> >up of "gravity" should be easy to adapt to, especially if a strict
>> >exercise program is instituted.  hell, we always wondered what the crew
>> >would do with their spare time, now we know.  They'll be exercising!
>> Risian studies on MIR have shown exercise doesn't seem to help much as far
>> as G induced heath problems.  (And they had their guys exercise 6 hours a
>> day!)
>Yes, but that is exercise in micro-gravity.  Our crew will have some
>gravity at every stage of the flight.  at the start and end, it will
>be more earth like;  near the middle, it will be just like living on
>the moon.  if we can have permanent colonies on luna, we can do this

Actualy I doubt well be able to colonise the moon unless we include some
artificial G in the bases.

L5 colonies anyone?

>> >I really think this is the best design we've come up with yet.  Aside
>> >from the cost and the political will issues, none of this technology
>> >is beyond our capability.  We know how to make solar collectors, masers,
>> >linear accelerators and closed system ecologies.
>> >
>> >The question remains, can we build them large enough, precise enough,
>> >efficient enough and will they last long enough to make it to TC and
>> >back agin.  But then, these are engineering problems, not physics
>> >problems.
>> By "them", I assume you mean the sol maser array?
>Sort of.  I mean, can we build the solar collectors big enough, the
>maser array precise enough, the lineac efficient enough, and will
>the closed system ecology last long enough.

?!  Oh, is that all.  ;)

>> >In contrast, the only other viable alternatives (from a physics
>> >standpoint)
>> >is a fusion-sail hybrid (Kelly's fuel-sail) an anti-matter rocket, and
>> >the argosy concept.  The fuel sail and the anti-matter rocket both
>> >require technology that we do not yet posses, and may have trouble with
>> >by 2050 or even 2100.  The argosy concept would take centuries to
>> >get to target star.
>> >
>> >The MARS remains the Fastest, lightest, and easiest (relatively
>> >speaking)
>> >ship to build.
>> Hey!  You forgot my Explorer class with laser launched fuel canisters for
>> boost phase!  ;)
>No I didn't, MARS is both faster and lighter.  we won't even talk about

True, but Explorer is a "viable alternatives (from a physics standpoint)".

>> Also you skiped over the technical problem of building and operating the
>> return launcher array.  Also I cringe when physisists come up with ideas
>> that have clean physics, but very dirty engineering, that they don't want
>> to worry about.
>>  ;)
>you mean like the explorer with laser launched fuel canisters?  ;)

Well I'll admit that had certain... complexity issues.  ;)

>> On the other hand if MARS could be made to work, it would have big speed
>> advantages over the others we've come up with.  Thou I wounder about its
>> range limits.
>This is one of the problems that's worried Tim.  Tim fears that the
>beam will spread out too much.  I think that the beam can be focused
>into a nearly paralell stream of photons.  thus there will be no
>spreading and diffusion.  _IF_ this can be achieved, then range won't
>be a problem at all.  The ship will be able to travel to any star
>within a good 100 light years on a 3-4 light year pulse of maser
>energy.  Since most of a 100 light-year trip will be spent at insanly
>high fractions of C, I expect the one-way trip time to be on the order
>of ten years for the crew.  of course a return mission would arrive
>a good 250 years after departure.

As a practical measure it wouldn't make any sence to launch missions that
would approach, much less exceed, a century.  Not to mention the the crew
would have to assume their would be no maser array in operation at sol by
the time the return.  Such long range flights would have to wait until
better (much better) physics.


Kelly Starks                    Phone: (219) 429-7066    Fax: (219) 429-6859
Sr. Systems Engineer                                     Mail Stop: 10-39
Hughes defense Communications
1010 Production Road, Fort Wayne, IN 46808-4106
Email:  kgstar@most.fw.hac.com