Speaker
Description
Re-entry studies show that, for most spacecraft, the structure becomes hot before the forces become appreciable, resulting in a thermal model for fragmentation being adequate in many cases. However, for larger spacecraft, the higher mass being decelerated results in significantly higher forces being put through the joints, and this suggests that a thermomechanical model is necessary to capture the fragmentation effects.
A thermomechanical fragmentation model has been designed for use in component-based destructive re-entry tools which is able to capture the forces at joint level. This is based on the construction of a component-joint network, and requires a six-degree-of-freedom simulation tool in order to capture the rotational (centrifugal) effects and the direction of the forces in the joints. This model assumes rigid body motion of the spacecraft and determines the forces required to be passed through the joints in order to maintain the motion as many of the components are not subjected to the decelerative force from the atmosphere. The model has also been applied successfully in panel-based tools.
A matrix of joint-component connections is established, and the unknown joint forces are calculated using the matrix and the known aerodynamic and rotational forces on the components. The model allows for an arbitrary network of joints linking the components, which produces a singular matrix of joint-component connections. This is solved using a Singular Value Decomposition algorithm. A similar approach is used to calculate the moments.
A number of thresholds for fragmentation have been implemented, including tables of force/moment against temperature and a time delay to account for reaction rates. To make full use of the model good threshold values for fragmentation for a range of connection types are required.
