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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
>(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.
>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

>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

By "them", I assume you mean the sol maser array?

>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.
>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 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