Henry Spencer wrote:
Correct. The high-temperature metals, unfortunately, tend to be really
dense. Things like niobium and molybdenum are nearly as dense as lead;
tantalum and tungsten are substantially *denser* than lead. They have to
be kept thin or the weight just goes out of sight.

Right...but even 1000 square meters of 1mm nickel superalloy plate is
only 9 tons. 0.5mm of tungsten would be about 10 tons, too, and that's
not quite foil gage. (Obviously, the heat shield wouldn't be a simple
plate, that's just a convenient approximation.)

Using the approximation of heat shields being 12.5% of the re-entry
vehicle, that would leave something like 12- to 15 tons, that should
allow a metallic heat shield on the order of 0.5mm to 1mm thickness for
a vehicle like the shuttle (with roughly 500 square meters
underside/leading edge area.) That should also leave tonnage for
insulation (like the X33's saffil), shouldn't it?

Mike Miller