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RE: starship-design: Tugs

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