Cold water treatment

Water-cooling could be the key to the safe re-entry of the next generation of reusable spacecraft, according to aerospace engineer Jeroen Buursink of the

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Using the combined properties of a self-repairing alloy and a highly-porous ceramic, Buursink has shown that the water-cooled system can absorb heat loads equivalent to a ceramic heatshield material similar to the Space Shuttle’s — but for a fraction of the cost.

Currently, metal heatshields are only practical on single-use spacecraft, because they work by ablation — as the spacecraft re-enters the atmosphere, the shield begins to burn away. The Shuttle’s ceramic shield absorbs heat and is lighter, but the material is expensive and needs a vast amount of maintenance; checking every individual tile on the craft takes around 40,000 man-hours for each flight.

Buursink’s shield could help solve this problem, by creating a cheaper alternative heatshield for small re-usable craft. The system makes use of water’s almost unsurpassed capacity to absorb heat as it boils, combined with the properties of the metal from which the shield is made. Known as PM1000, this is a nickel-chromium alloy containing small quantities of iron, titanium, aluminium and yttrium oxide. It is made by mixing metal powders under high pressure and temperature in an oxygen atmosphere, which creates a corrosion-resistant chromium oxide layer on its surface.