David Sooby wrote:

> Perfectly reflective? Yes, it ought to be.  And perhaps it is, or at
> least in some cases perhaps it is.  Consider the following citation
> from _The Cosmic Computer_, in the section concerning exploration of
> the abandoned Port Carpenter starship construction yard on Koshchei.
> In this scene, the explorers have found a partially assembled
> starship:
>
> ~~~~~~~~~~~~~~~~~
> She had all of her collapsium on, except for a hundred-foot circle at
> the top and a number of rectangular openings around the sides. Yves
> Jacquemont said that would be where the airlocks would go.
>
> "They always put them on last. But don't be surprised at anything you
> find or don't find inside. As soon as the skeleton is up they put the
> armor on, and then build the ship out from the middle. It might be
> slower getting material in through the airlock openings, but it holds
> things together while they're working."
>
> They put on the car's lights, lifted to the top, and let down through
> the upper opening. It was like entering a huge globular spider's web,
> globe within globe of interlaced girders and struts and braces,
> extending from the center to the outer shell. Even the spider was
> home—a three-hundred-foot ball of collapsium, looking tiny at the
> very middle.
>
> [...] the shimmering ball in the middle.

Why build a vessel with a core mass that high on the surface of a
planet?