PhD student presentations Seminar

Sairajan Kolasseri Kuttappan "Validation of Spacecraft Finite Element Models"

Finite element modelling is widely used to predict the dynamic behaviour of a complex structure such as a spacecraft before its realization. The method can also be adopted for the modelling of multi-physics systems. The capability of the finite element model to accurately predict the performance of the system is vital for the successful completion of the mission and hence it is assessed by comparing the analytical results with the experimental data. In this presentation, two commonly employed model correlation methods; modal assurance criterion (MAC) and normalized cross orthogonally (NCO) check are examined for their usefulness in the validation of real conventional spacecraft structures. Most practical applications call for a reduction in the number of degrees of freedom of the analytical model to match the experimental sensor locations and it is observed that system equivalent reduction expansion process (SEREP) is well suited for the reduction. As different levels of inaccuracies are inherent in both the experimental and the finite element results, a probabilistic approach is used to assess the robustness of a SEREP based test analysis model by inputting a range of known errors into both the experimental and analytical data. The relationship between the capability of the finite element model to predict the receptance and the quality of the model validation determined using NCO is also investigated using synthetic modes and it is observed that the quantities are not always correlated.  A method to optimally choose the sensor locations in order to increase the probability to pass the NCO is proposed. A new model correlation criterion, termed as Base Force Assurance Criteria (BFAC) is defined and found that BFAC can better correlate the error in the dynamic characteristic of real spacecraft structures than MAC or NCO. The further work (mathematical model validation of multi-physics structures) will also discuss.

Adam White "Adaptive policies for the long-term stability of the LEO Space Debris population"

Our society derives numerous benefits from space-based assets, including Earth observation, navigation, telecommunications, security, economic development and scientific exploration .It is therefore vital that outer space activities remain secure, peaceful and sustainable otherwise these benefits may diminish or disappear. Space debris represents a significant collision risk to operational satellites and is one such threat towards the long-term sustainability of outer space activities.

In order to try to limit the future growth of debris treaties, guidelines, practices, codes of conduct, and standards have been, and are being, developed. However, the space environment is continuously evolving, in ways that are often difficult to predict. Factors such as collisions, explosions, solar and launch traffic variations, anti-satellite tests, and advances in technology or socio-economic drivers all influence the space debris population and add uncertainty to simulation predictions. This uncertainty makes it difficult to identify policies to control the space debris population effectively and efficiently.

One method to tackle dynamic and uncertain conditions is to create debris policies that can anticipate and respond to future events and can navigate towards successful outcomes when surprised by the unforeseen; a process known as adaptive policy management. This presentation documents the current work to develop robust adaptive polices capable of stabilising the long-term LEO space debris population under this uncertainty.