A water-cooled metal heat shield for future reusable launch vehicles has been developed by the Netherland’s Delft University of Technology.
Although existing metals cannot withstand the temperatures experienced by the Space Shuttle’s ceramic tiles, the new design uses a porous, water-filled layer.
The cooling layer consists of high-porosity aluminium oxide, which can hold up to 70% water by volume. The rest of the shield is made of PM1000, an alloy of nickel, chromium, aluminium, titanium and yttrium oxide.
The water keeps the porous layer cool and evaporation removes a large amount of the thermal energy from re-entry. The Delft researchers claim that it means that relatively little water is needed for the cooling process.
“The idea is mainly suited to small spacecraft and short missions or for small parts of a craft,” says Delft University of Technology researcher and doctoral student Jeroen Buursink. “We must not give the impression that any successor to the Shuttle will be clad entirely in a cooled metal heat shield. At most, it will cover critical points. For 80-90% of the surface an uncooled metal shield will suffice,” he adds.
Buursink proved that it works in principle in laboratory tests by comparing cooled and uncooled shields, which had identical thermal loads applied to them.
The internal structure of the porous aluminium oxide layer ensures that the cooling water is retained in the material, while it moves towards the evaporation surface through a capillary action during re-entry.
Source: Flight International