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An increasing number of spacecraft missions have very stringent requirements for thermal stability to avoid thermally driven noise from affecting the main observables. For example, it may be necessary to reduce temperature fluctuations in the neighbourhood of the instrument below micro-Kelvin (μK). Consequently, the influence of fluctuations in boundary temperature or internal power dissipation on temperature at the instrument detector must be precisely evaluated. Thermal stability requirements are usually expressed as an upper limit on the linear spectrum density (LSD) of temperature fluctuations. This indicates the strength of the response to a perturbation of a given frequency, and is usually stated in units of K/√Hz. The LSD can be estimated by running a succession of transient simulations and applying Fast Fourier Transforms techniques, but this method is time-consuming and has numerical limitations.

FHTS is the thermohydraulic extension to ESATAN, the European space industry standard thermal analyser. Capable of simulating both single- and two-phase flow, FHTS is now being provided with features to facilitate the system-level modelling of capillary-pumped loops. Component models such as the capillary evaporator, capillary filter and two-phase reservoir are under development, as well as generic modelling facilities which will be utilised by these components. The current status of this development is discussed and results from prototyping are presented.

The second major upgrade to the Fluid Heat Transport System extension of the ESATAN thermal analyser culminated in significant improvements and extensions to its two-phase capabilities. The third upgrade is nearing conclusion, the emphasis of this work centring around the improvement of the Graphical User Interface and the validation of the numerical algorithms employed. An interactive environment for the creation of ESATAN thermal models has been developed, easing both creation and visualisation of the model hierarchy. To consolidate this facility the current FHTS Graphical User Interface has now been incorporated within the framework of this tool. Many new capabilities have also been added, most notably the ability to configure, manage and control all files required by an ESATAN model.