Towards Demisable Fiber Reinforced Plastics

Kurzfassung

For avoiding the Kessler syndrome, satellites in low Earth orbits must be removed in due time after the end of their service life by re-entering into the Earth's atmosphere. Active, controlled re-entry requires availability of thrusters and propellant at the end of the mission. Thus, the active re-entry comes at a high cost and reduces the available payload mass of a mission. It is accordingly desirable to leave the satellite to itself at the end of its life and allow it to re-enter in an uncontrolled way. Unfortunately, parts of such satellites can survive the destructive re-entry flight and may impact on the ground. These debris pose a risk to public safety if they go down over an inhabited area. Rules that limit the acceptable ground risk per mission to a specific threshold are therefore in place in many countries. The typical accepted risk is one incident in ten thousand missions (1:10 000). Fiber reinforced plastics (FRPs) have been considered easily demisable because of their organic matrices and the fact that they would be able to burn at ground conditions. However, wind tunnel tests have revealed that FRPs have a very high demise resistance and can act as an ablative heat shield. This results in FRPs generally being a problematic material in the ground risk assessment. The good news is that there have been material level tests that showed a desirable demise behavior, which resulted in higher demise rates. The goal of the COMP2DEM project is identifying the microscopic and macroscopic parameters that determine the demise process and phenomena and explaining the differences in the observed behavior. Based on this knowledge, new fiber-reinforced plastics with increased demisability shall be formulated. The presentation covers the first phase of the COMP2DEM project: the screening of different FRP variants by thermophysical material characterization and demise simulation in the arc heated wind tunnels of DLR. New FRPs with increased demisability are currently under development and an outlook on the developments in the project is given.