Jérôme Buffe - Thales Alenia Space, France
As Head of the Mechanical Department of the Platform and Integration Competence Centre in THALES ALENIA SPACE, Jérôme is responsible for management of all the mechanical loads requirements, management of structural design activities and their associated validations either by appropriate tests or analysis, and the management of the final mechanical validation of the behaviour of the satellites at system level. Within this role, Jérôme deals with mechanical expertise actions, including innovations, optimizations and capitalizations of knowledge in space areas.
In addition, Jérôme is responsible for the Global Skill Leadership for the mechanical aspects in the frame of the THALES ALENIA SPACE Competence Network across the company. The aim of this function is to optimize and to harmonize all the activities in all the entities of THALES ALENIA SPACE where the mechanical aspects are effective.
Jérôme is also an active member in the elaboration of the European standardizations for the space community (ECSS), mainly for the mechanical rules and for the associated methodologies.
Optimisation of the validation process by the coherence of the analytical and the test justifications
The objective of the presentation, in the frame of the 2013 NAFEMS conference, is on the topic of the demonstration of the good behavior of a satellite by performing some tests and by adding some pertinent uses of analytical processes or controls, even if the analytical processes are not completely substituting the justifications by tests. That process has to be optimized for sure, but it has to be globally coherent in terms of reliability.
Obviously, first of all, the process has to start with a good analysis of all the events loading the satellite in all its operating phases. And, then, the optimization of the development plan has to be done as soon as possible for the final demonstration, knowing that this plan could be also a driver for the selection of the design.
One of the major points outlined during the presentation will be on the feasibility of the proposed validations, on their reliability and on the impact on the risk analysis associated to the retained development plan. The financial aspects, due to their importance in the current industrial domain, must be introduced in that project analysis.The process used for the elaboration of the validation plan is more and more complex and it has to be the result of a global technico-economical optimization using, from time to time, some mandatory parameters which could be difficult to be handled.
In the current space area and, probably more specially in the satellites domain, some validations can’t be done by tests (gravity on ground, vacuum, combinations of loads, …). Some others can’t be done by analysis (lack of appropriate methodologies, non realistic models, …). In these cases, the construction of the validation plan is essential. But, in all the other cases which seem simple apparently, the interest of the optimization of this plan is relevant and requires attention. The complexity of the validations is amplified by the need to validate in most of the cases the subassemblies at their level, knowing that the validations of the interfaces are always full of importance in the risk analysis as a return of experience. For that, the notion of a pyramidoïdal validation by tests is quite useful as well as a pyramidoïdal validation by analysis is conceivable. It has to be outlined, nowadays, a very important variability on the characteristics for components, for elementary pieces and for interfaces. As a consequence, this point must be included in the validations plan, either through the analytical process by some choices to be taken on the parameters and the methodology, or through the tests to be performed by a pertinent choice of the number and of the types of the specimens to be tested.
The proposed solution for the optimization of the validation plan is the use of what is called a validation matrix with which the control of the justifications is done and with which the best choice of the dispositions can be issued, techico-economically speaking. Obviously, the two different main axes introduced in that matrix involve the analytical process and the testing process, at unit level and at satellite level.Associated to that point, in order to bring the final expected reliability, the application of safety sizing coefficients and the application of qualification factors have to be selected.
We may associate to that philosophy two other well known topics which are full of interest and which are questionable, even if it seems obvious to use them as a reference for the analytical process in the validation exercise. I would include the interest or the need of correlations between analysis and test and also the interest or the need of the optimization or the robustness of the design.
As a conclusion, a relevant overview on the way to optimize the validations of the behavior of the satellites must be used. With the growing complexity of the situations encountered for the designs and their life and with the variability of the characteristics of the products and their performances, the combined validation by analyses and tests is the most appropriate way to find the good approach. The interest of a validation matrix could enable that performance, and the implementation of well appropriate supports as correlations, controls, elementary tests could bring what is often missing for a reliable final demonstration.