The critical moment when returning from space is the entry into the earth's atmosphere. Temperatures of up to 2,000 degrees Celsius put the material and spacecraft under extreme stresses. The Institute of Structures and Design at the German Aerospace Center (DLR) is researching suitable protective tiles and has successfully tested its latest development on board a Russian FOTON-M2 space capsule. The heat protection for future, reusable spacecraft has passed its baptism of fire.
In Kazakhstan in June 2005, scientists and space experts gathered around a Russian FOTON space capsule. Its speed reduced by parachutes and a braking rocket, the round vehicle had just returned from space and landed in the Kazakh steppe. The scientists present from the DLR Institute of Structures and Design in Stuttgart were able to inspect the condition of their experiment and immediately begin the evaluation on site with a camera and an experienced eye.
The fiber ceramic components attached to the outer shell of the capsule were of particular interest. This was the first time within this experiment on re-entry technology that a thermal protection system made entirely of the ceramic composite material C/C-SiC had flown through the atmosphere. The first impression was already clear: The KERAMIK experiment was a complete success. The CMC components were unaffected by the high heat load. Only the previously dark color of the ceramic had changed to a distinguished gray. All sensors functioned perfectly and provided the necessary data for later evaluation. Peak temperatures of 1500 degrees Celsius were measured.
The experiment consisted of two stiffened C/C-SiC half-shells, which were fitted into a C/C-SiC ring and anchored with three screws per component made of the same material. The diameter of the experiment was 340 millimeters, the diameter of the half-shell components 300 millimeters. L-profiles for reinforcement were attached to the back of the individual components using a special joining process. This allows individual components to be manufactured separately from each other. They are then joined by siliconization, which also reduces the manufacturing risk. The load transmission components were also made of C/C-SiC, as were the bolts and nuts. Thanks to this design, the heat resistance of the material can be used for the entire application without having to consider the temperature limitations of metal components. In addition, high-temperature insulation and a hot gas seal were integrated under and between the components to prevent hot gases from penetrating into the interior of the experiment as part of an overall system approach.
In addition, various new coatings based on yttrium and titanium were applied to one of the components to protect against oxidation. This made it possible to directly compare the effectiveness of the coatings compared to the standard coating with silicon carbide during re-entry.
