(urth) The Apu-Punchau Eclipse

Jeff Wilson jwilson at io.com
Wed Jun 11 11:29:29 PDT 2008

Dan'l Danehy-Oakes wrote:
> On Tue, Jun 10, 2008 at 6:07 PM, Jeff Wilson <jwilson at io.com> wrote:
>> Dan'l Danehy-Oakes wrote:
>>> Tzadkiel's Ship -- *counting its sails*, is significantly bigger than a
>>> mile
>>> in diameter, at least for purposes of shadow-casting. Solar sails have
>>> to be (a) very very large and (b) quite opaque in order to be effective.
>> LEO velocity is about 5 miles per second, so each second of eclipse is 5
>> miles worth of ship, plus the penumbra penalty (altitude times twice the
>> tangent of the sun's arc width (0.5 degrees)). There would also need to be
>> some means of maneuvering the entire ship within a moment or a massive
>> number of crew available to trim the sails in a like period of time.
> The numbers I've seen for an effective solar sail are in the range of
> tens of thousands of miles.

I don't think we can square that figure with Sev's account of the masts 
and sails early in URTH. Also, regular solar sails of even that scale 
aren't adequate to propel the Ship out of the solar system in the time 
frame given. Ounces of thrust per acre of sail vs a mass large enough to 
have signifigant surface gravity yields excruciatingly tiny acceleration.

Jeff Wilson - jwilson at io.com
< http://www.io.com/~jwilson >

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