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starship-design: Various things

kyle writes:
 > Some stars, mostly the K-class stars, are too young to have much in
 > their systems.

Actually, most K stars are quite old.  Main-sequence stars that live
long enough to have planets that could sustain life typically start out
as F or G stars, becoming K, then M stars late in their lives.  Many
smaller stars are M stars for nearly all of their lives.

In order of decreasing temperature, spectral classes go: O, B, A, F, G,
K, M.  O, B, and A stars are considered too hot to form planets, because
their radiation would dissapate a protoplanetary disk, and are also
short-lived, so any planets that might form will get toasted by the
star's usually violent death.