In a move away from about 50 years convention in materials and aerodynamics, European aerospace firms are looking at faceted sharp edged reentry vehuicles: (paid subscription required)

Advanced thermal protection systems, to be tested in upcoming hypersonic experiments, will enable development of a reusable “sharp-edged” orbital launch vehicle with much greater flexibility than blunt-capsule or shuttle-type designs, say German researchers.

The team at the German Aerospace Center (DLR) in Bremen believes the move to simple, faceted geometries—away from the curved surfaces of conventional reentry vehicles— should also help cut costs while simultaneously offering improvements in aero-thermodynamic performance.

Basically, they are suggesting that the use of flat surfaces will make for more easily constructed heterogeneous materials, kind of like how Chobham armor give tanks angled surfaces, and that this can allow for sharp edged re-entry vehicles that can give more cross range performance and far lower G loads during reentry.

This is not an easy nut to crack. Not only are the temperatures higher with a weak shock wave, on the order of nearly 5,000°F as versus about 2300°F for the shuttle, but the high speed portion of reentry would take something on the order of an hour, as opposed to 10 minutes.

The technologies involved are ceramic matrix composites, basically composites where ceramics replace the conventional resin, advance ablative systems, and effusion cooling, which is basically where very small holes in the surface are used to pass a cooling fluid that carries away heat directly, as well as creating a thin film of relatively cool gas on the surface in question.

Effusion cooling has already been applied to cool combustors, but might prove more problematic in the rather less well controlled environments during reentry.