"DGH" wrote in message .. .
snip

Anyone know why the 2.5 inches of water?
That does not seem enough to provide good radition sheilding but adds a lot
of weight.

One thing that 2.5 inches of water accomplishes is self healing skin
in case of micrometeorites. Another is temperature smoothing. They
wouldn't have to be filled with water immediately, so you could send
them up empty, and gradually fill them with recycled water as it was
available. But I don't know.
Harmon