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8. Conclusions and future work
The main purpose of the thesis has been the development of a thermal code that could fit the available tools, in particular the Mesher, in order to integrate it in the software architecture of a possible “space-based” version of VIRAF.
Figure 8.1 - VIRAF software architecture (adopted by [8])
Taking into account not only the didactic scope, but also the commercial importance of such activity, about one month has been devoted in selecting which kind of spacecraft architectures could be of interest for these purposes. Despite that, the produced code has assumed a general form, since various models, although simplified, have been analyzed and tested successfully. This was all but taken for granted at the beginning, because the use of skins as the only source for generating GMMs seemed to be quite limiting. In fact, the flexibility is one of the strong points of this work, allowing the user to manage a large variety of spacecraft architectures.
Surely, the main effort has been the building of a thermal model “as volumetric as possible”, starting from 2D surfaces only. From a conceptual standpoint, defining the thickness of a component through its material is not suitable since thickness is a feature of a component and not of its material. Nevertheless, after the adoption of
147 appropriate countermeasures in managing the models (see the modelling criterion in Par. 5.2, pg. 98), the results have been quite satisfactory, putting aside initial skepticism. The errors introduced by this model of materials is irrelevant when speaking of walls, but can become significant for those solid compartments that require more layers of material for a correct representation. In this case, if the layer thickness becomes comparable with the size of the compartment, the error in the computation of conductances can be important and must be evaluated.
Throughout the work, the scheme to satisfy the commissions has been always the same: understand the problem, select an algorithm for solving it, implement the algorithm in a Matlab® script, discuss the results with the team members and, above all, demonstrate the validity of the solution. This “chain” has been successful, because never has been taken for granted during the development of the code. Each chapter of this thesis reproduces the operative rationale followed.
Despite the validity of the work done, the distance that separates the prototype code developed and common software for thermal analysis is large. Putting aside the need of a GUI (Graphic User Interface), the following activities should be considered for a global improvement of the work:
reduction of simulation times: real models are far from those illustrated in this work and their analysis could lead to unacceptable simulation times;
Matlab®, despite its powerful computing tools, is by nature not the best choice and should be substituted with a low-level programming language such as C++;
definition of a different and more detailed model of materials. First, a different way to define materials for walls and compartments should be evaluated in order to make a comparison with the solution proposed. Then, the variation with time of the material features must be considered when simulating the whole mission of a satellite. Moreover, the use of spectral emittances instead of mean values can lead to a more precise estimate of the external heat loads;
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development of an algorithm to account for the shadow projected by parts of a spacecraft to other parts. This is maybe the most important improvement required, since particular attention has been devoted to the correct evaluation of external heat loads; neglecting this aspect could produce relevant errors in particular combination of both geometry and attitude;
testing the code on shapes different from cubes and parallelepipeds in order to enlarge the class of spacecraft that can be analyzed. In doing so, the FDM scheme must be re-discussed, in particular the computation of conductive conductances;
introduction of the Gebhart’s method to compute the radiative conductances;
this could also give an idea of the error committed in using the “effective emittance”, which is sufficient at didactic level only.
On a larger perspective and with reference to VIRAF, an important source for signature assessment is due to the hot plumes coming from the exhaust of combustion products, at least for those spacecraft that require either propulsive or active attitude control subsystems. In this sense, the thermal code developed here would be just a “module” of a larger project that would even involve, for example, a code for computing the temperature field of exhaust plumes. The reference textbook, in this case, would surely be [41].
