>>748

DARPA/Boeing の XS-1/Phantom Express がある．
有翼のサブオービタル機体だが，第2段載せて軌道投入も可能．
複合材極低温タンク利用(液体水素と液体酸素)とある．
http://spaceflight101.com/boeing-darpa-reveal-phantom-express-space-plane-design/

Phantom Express will rely on advanced composite tanks holding
the supercold Liquid Hydrogen fuel and Liquid Oxygen oxidizer
consumed by the AR-22 engine on the plane’s business end.

ちなみに，耐熱システムもかなり充実している．

The hybrid composite-metallic wings and control surfaces for atmospheric flight
will have to withstand temperatures over 1,100°C during the hypersonic flight regime and re-entry,
using third-generation thermal protection systems.