"Bloody horrible graphite/fibre mix that was a complete pita to machine."
Sounds like some kind of Reinforced Carbon Carbon. Like the nose of the Shuttle (or really high performance brake pads for aircraft).
Might have more in common with ablative heat shields designed for high energy entry, like Jupiter or Venus.
The article said they switched to a Beryllium/tungsten alloy during one of the upgrades.
Which I predict was also a PITA to machine as Be is brittle and highly toxic if airborn.
So, is it "Dr" Cockroach?