Speaker
Description
PLACEHOLDER FOR EDOARDO MARIA BENIVEGNA
The Fluorescence Imaging Spectrometer (FLORIS) is the Instrument of the FLuorescence EXplorer
Mission (FLEX). This is the Earth Explorer 8 (EE8) mission of European Space Agency, whose
objective is to perform quantitative measurements of the solar induced vegetation fluorescence to
monitor vegetation photosynthetic activity.
The FLORIS thermomechanical architecture is based on an optical bench (OB) that provides support
to both the optics and the two focal plane assemblies (FPAs). In order to maintain the required optical
quality and spectral stability, the OB temperature is actively regulated at 22 °C in operational
condition. The cooling of the FPAs is achieved by a passive radiator placed on top of the OB. The
core of the FPAs are three identical CCD detector units, cooled by an interface with the radiator. A
closed loop thermal control maintains the detectors temperature around -35°C with a stability of ±
0.2°C.
The thermal balance test foresaw five phases: one hot non operative, one cold non operative and three cold operative. The
main purpose of the test - and of the consequent correlation activity - was to investigate the modeling
accuracy of both radiative and conductive links of the two FPAs. During the thermal balance of the
STM, in fact, in place of the FPAs there were two dummies, that accounted only for the dissipation
of the active elements inside these assemblies.
Varying the temperature of the instrument radiator was crucial to collect a good set of data for the
correlation of the thermal model. For this reason, a dedicated shroud was placed right on top of the
radiator.
A non-negligible discrepancy between the predicted and the actual temperatures reached by the
various subsystems emerged right from the beginning of the test. To get a better insight of the
problem, two additional thermal balance phases were performed in the same test campaign. The
major differences between test predictions and test measurements concerned the VAU
temperatures and the power dissipated by both the OB and FPA heater lines.
Find the explanation of this discrepancy was part of the correlation activity. Two TVAC phases were
also included in the data set to assess the impact of the changes implemented to both the GMM and
TMM on a broader range of cases.
The several sensitivity analyses performed showed that the overall coupling between the instrument
and the radiative environment was not sufficiently correlated in the thermal model used for the test
predictions. This was mainly due to the MLI efficiency and affects above all the OB, which is the
largest subsystem of the instrument. The OB was cooled more than predicted also conductively,
through the links to the radiator, the nadir baffle and the bottom cover.
The VAUs power dissipations and the linear conductors between them and the OB have been
lowered, while the internal linear conductors have been increased, all these effects led to a drop in
their temperature.
The GMM has been updated too, including new geometries that increase both the view factor
between the FPAs and the OB assembly, and between the OB and the MLI blankets.
As a result of the implemented modifications, the thermal model of FLORIS PFM meets all the
applicable requirements.
