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*To*: "'LIT Starship Design Group'" <starship-design@lists.uoregon.edu>*Subject*: RE: starship-design: Timothy's beamed power paper*From*: "L. Parker" <lparker@cacaphony.net>*Date*: Wed, 23 Jul 1997 19:31:02 -0500*Reply-To*: "L. Parker" <lparker@cacaphony.net>*Sender*: owner-starship-design

Timothy. Well, I will grant that the first trip will be the hardest ;-) but, there are a multitude of deceleration schemes available. It may take longer to slow down than it did to accelerate, but once we can get there we can use beamed power at both ends of the journey. A straight solar sail deceleration at the end is not out of the question, it just means that turn over will be earlier. Or perhaps we can use one of Forward's ideas for a two stage mirror/sail where the larger sail continues to accelerate while a smaller central sail is decelerated by the reflection from the main sail. I'm not sure where you got your calculations on the magnetic braking, but everything presented to NASA seems to work. It is a viable concept, although unproven. I think I would consider the fact that it is unproven before your objections regarding the strength of the field or the mass of the wires. (Of course, sail technology in general is unproven <G>.) If worse comes to worse, let's try this: 1) POWERED gravity assist launch 2) Deploy solar sail while DEEP within sun's solar wind (where it is most effective) 3) Additional boost from beamed power arrays until turnover 4) Deployment of retromirror at turnover 5) Solar braking assist from target star 6) Use sail to "tack" into orbit around target star (This is a wide orbit that gradually spirals inward) 7) Construction of power arrays in target system 8) Repeat from 1) but now use beamed power to brake directly into orbit around target star. As far as terminal velocity goes, I don't know the relevant equations and I suspect their derivation will be messy, but I'm fairly sure that if we want to get much above .9 c it is going to be a factor. Once you start factoring in time dilation, the RELATIVE density is going to go up in DIRECT proportion to the time dilation. Something else to consider, the calculations so far on sail material have simply factored in heating from solar light and beamed power, I didn't see any calculations of heating on BOTH sides of the sail. Forget terminal velocity, at what speed does the sail melt? Tungsten has the highest melting point that I can think of. How much power can we beam at a sail 4 microns thick made out of vacuum deposited tungsten before we reach 3,410 degrees C? What is the impact density at various speed regimes given the interstellar density in our region (thin). How much heat will the sail absorb from impact with the interstellar medium at these velocities? Can we develop a coefficient of heat (similar to a coefficient of friction) that can be input into a relativistic rocket equation to yield an upper limit on velocity? This is applicable to ANY starship, not just sail powered ships unless we are going to start speculating about non-material shielding. Lee Parker (o o) ------------------------------------------------------oOO--(_)--OOo--------- Long experience has taught me not to believe in the limitations indicated by purely theoretical considerations. These - as we well know - are based on insufficient knowledge of all the relevant factors." Guglielmo Marconi

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