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Re: starship-design: Re: Beam properties, control, etc.

At 2:09 AM 11/3/96, Timothy van der Linden wrote:
>Kelly replied to Rex:
>>>1. Depth of focus
>>>Assume the beam from a 2.31E6-km-diameter microwave antenna is
>>>focused to a sail (beam-spot) diameter of 100 km at a distance of
>>>1 lt-yr.  At the distance from the focus that the beam cross-sec-
>>>tion has grown from the area at the focus by 10 percent (power per
>>>unit area reduced by about 10 percent), say, the radius of the
>>>beam has grown by 100 km * [sqrt(1.1) - 1]/2, or about 2.4 km.
>>>The distance from the focus for that growth is (2.4/2.31E6) *
>>>1 lt-yr, or approximately 1E-6 lt-yr.
>>>So, the sail/ship has to stay within about 1.E-6 lt-yr of the
>>>focus to keep the power from dropping off by more than 10 percent.
>>I read that as about 10,000,000 kilometers, or 32 light secounds.  Not a
>>lot of slack over interstellar distences.  A sligh sail problem could have
>>you well out of that pretty quickly.
>True, it would be a tight schedule: One minute too late at a certain place
>and you have missed the beam for good.
>Sailing on a beam means inherently that every second of the trip is planned,
>slight deviations are allowed, but will be risky. A sail may sound as an
>easy "engine", but you better have a good captain/navigator.

Starting to sound like walking a muti light year tight rope.


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