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Re: starship-design: Re: Solar sail breaking
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
top speed is .93 C
flight time is 8 years for the crew, and 15 years for earth.
> >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
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
> >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
> 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.
> >In contrast, the only other viable alternatives (from a physics
> >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
> >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
> 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? ;)
> 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.