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Re: RE: starship-design: Tugs

In a message dated 8/9/97 11:33:38 AM, lparker@cacaphony.net (L. Parker)

>Kelly and/or Timothy,
>>Kelly wrote:
>>>>>>>That would only work if the sail is anchored to something by cables.
>>>>>>> Otherwise its effectivly a sheet of paper blown in the wind (or a
>>>>>>>shaped peice of paper if you prefer.).
>>>>>>I figured the sail always had to be anchored by cables...
>>>>>Anchored to what?  Unless the anchor weighs enough it can't 'anchor' the
>>>>>sail.  In the case of fuel/sail, the sail is 400 times heavier.
>>>>Anchored to the ship. The ship doesn't need to be heavier, it just should
>>>>want to accelerate less than the sail, which it does as soon as you cut
>The link that Timothy just posted to Landis's paper on sails also has other 
>pages which reminded me of something I had quite forgotten. JPL actually 
>designed several sails for a mission to Halley's comet. NONE of them used 
>the "parachute" arrangement with cables attached to a sail. They were just 
>big square kites with steering vanes and a minimal structure. Even the 
>structure may not be necessary though. 
>Suppose the structure was built-in to the sail itself? If part of your 
>fabric contained hollow channels which could be inflated with gas or foam 
>to stiffen the sail, you wouldn't need any structure at all. Payload 
>fraction could go way up or the sail size down.
>Lee Parker

True, but they were also assuming trivial thrust/acceleration loads and
rates.  We definatly arn't.