On the development of a cooled metallic thermal protection system for spacecraft

Abstract

To achieve a significant cost reduction for launch of payloads to space, it is essential that the launcher is reused to the largest possible extent, and that the maintenance and operations cost of this launcher are minimised. To achieve this, work is ongoing on metallic thermal protection systems (TPS) that hold the promise of much reduced maintenance cost compared to other types of TPS. Metals however have a lower temperature limit. To allow the use of metals at higher thermal loads, they can be cooled. A method of achieving this has been invented at TU Delft. The system consists of a metallic skin with at a short distance behind a porous layer saturated with water. The metallic skin radiates thermal energy to the porous layer where water is heated and then evaporated. The water ensures that the temperature of the porous layer remains relatively cool, while the evaporation uses a large amount of energy. The water vapour can be vented overboard, removing this energy from the system. This TPS can give an increase in allowable thermal load of 90% for a given temperature that allows use of a metallic TPS on locations where this was not possible without cooling. Tests were performed to check the basic operation of the system and the basic performance parameters were measured. The basic underlying physical phenomena were described and measured, computer models of varying levels of complexity were made and some initial designs of applications were made. A flight experiment was developed for an ESA mission which will fly in the near future.