Speakers
Description
FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) is the ninth Earth Explorer mission selected by ESA. This mission aims to measure infrared radiation emitted from Earth across the entire far-infrared part of the electromagnetic spectrum, improving the understanding of the greenhouse effect and enhancing the accuracy of climate change assessments.
The FEI instrument consists of two main assemblies: the Optical Head (OH) and the Front-End Electronics (FEE), designed by Leonardo S.p.A. in Campi Bisenzio, Florence. The OH is composed of the Optical Barrel (OB), which houses the optical components and their associated mechanical interfaces, and the Focal Plane Assembly (FPA), which includes the detector, cold-shield aperture, and the electronics required for detector operation. The FEE provides the acquisition signals required by the FPA and performs the main data acquisition and processing functions.
A key innovative feature of the FEI thermo-mechanical architecture is the implementation of a passive thermal coupling between the OH and the FEE, also electrically connected (through a FLEX), using a high-conductivity pyrolytic-graphite thermal strap. The strap provides a conductive thermal path from the OH to the upper panel of the FEE: therefore, the electronic box radiator is the only cold sink for both FEE and OH. In this configuration, the heat dissipated by the FEE is directly rejected to space through its radiator, while the heat generated within the OH – which is located in a separate closure – is transferred via the thermal strap and rejected employing the same radiating surface. This shared-radiator concept enables the thermal control of two physically separated assemblies through a single passive heat-rejection interface (no need for a dedicated radiator on the OH). This innovative architecture seems unusual but allows for a reduction in terms of thermal HW, making the system more compact, while the heat rejection of the inner items is guaranteed even though there is no space available for the allocation of a second radiator.
The proposed thermal architecture has been experimentally verified during the Thermal Vacuum Test (TVAC) campaign performed on the Proto-Flight Model (PFM) in Leonardo S.p.A. facilities. The thermal strap exhibited the expected behaviour throughout the test, enabling the correct thermal control of both the electronic unit and Optical Head and allowing all planned test phases to be successfully completed. The achieved thermal performances ensure compliance with the applicable test requirements and contributed to the successful qualification of the PFM.
This work demonstrates the successful verification of the thermal architecture and its effectiveness as a passive thermal control solution for the FEI instrument, compatible with the stringent accommodation and thermal stability requirements of optical payloads. The versatility of this thermal architecture and the reduced costs (with respect, for example, to the implementation of a heat pipes) paves the way for the application of this approach to other electro-optical payloads.