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Re: starship-design: Re: Solar sail breaking
At 12:48 AM 10/21/96, Kevin \"Tex\" Houston wrote:
>Nick Tosh wrote:
>>
>> Hello everybody.
>>
>> From what I've gathered from reading past mailings, stopping a starship
>> powered by a Sol based particle/EM rad beam is a major problem.
>
>Rex <dotarSojat@aol.com> has analysed this problem and a solution
>has been found. While Rex claims it's not very efficient, he does
>prove that it is theoretically sound, and violates no physical laws.
>
>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.
>
>This has been shown to yeild more momentum from the "engine", than the
>ship would absorb from the sail.
>
>Mass ratios and exhaust velocities, depend heavily upon conversion
>ratios
>(converting recieved microwave energy to kinetic energy in the exhaust)
>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?
>Now the problem here is that current linear accelerators are not
>very efficient, according to Rex. He states that at best, they are
>only about 1% effiecient.
>
>In a letter I sent to Tim, I said that I doubted current lineac
>efficiencies could be used to model practical maximums.
>
<<<snip>>>
>
>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!)
>While it is true that we will need a spinning section while we are in
>the target system, we should not need one during the flight.
>
>So again, I propose the following ship configuration:
>
>Consider the in-flight section to be like a soda can, and the habitat
>section to be like a larger soup can. While accelerating toward TC,
>the crew resides in the soda can, at the turn-around point, the soda
>can is extracted from the soup can, turned around, and put back in.
>Upon reaching TC, the crew moves into the soup can, which is spun up
>to provide the required gravity. All of the exploration equipment
>is stored in the soup can. The soda can is now free to be rehabed,
>and the soup can acts like a dry dock. When the time comes to leave,
>the soda can is what returns. the soup can stays behind as a base,
>and if for some strange reason, we decide to leave a permanent force
>behind, then we have a place for them to live. if not, then everyone
>gets back into soda can and heads for earth. The return Module uses
>a microwave Sail to accelerate away from TC, and uses Earth's Masers
>to decelerate.
>
>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?
>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.
>
>Sincerly,
>
>--
>Kevin "Tex" Houston http://umn.edu/~hous0042/index.html
Hey! You forgot my Explorer class with laser launched fuel canisters for
boost phase! ;)
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.
;)
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.
Kelly
----------------------------------------------------------------------
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
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