The ATV Cargo Carrier Visual Video Target Switching Unit Thermal Design and Qualification

摘要

The Visual Video Target Switching Unit (VVTSU) is the control unit dedicated to the Visual Video Target (VVT). The VVTSA, grouping VVTSU and VVT, is a "two-boxes assy," externally located on ATV Front Cone, used to allow ATV monitoring by crewmembers inside the ISS Service Module, during the final approach up to 500 m from the docking port. Alenia Spazio is the responsible of VVTSA and in particular of the design, assembly and qualification of the VVSTU unit: an Engineering Model (for avionic tests), a Qualification Model and two Flight Units (+ 1 Spare) have been designed, assembled and verified in Torino and L'Aquila Laboratories. The VVTSU is powered during the Rendezvous and it presents a high power dissipation, if compared with the reduced dimensions. The thermal control of this unit has been realized using passive means: a high conductive coupling with the fixation bracket, jointed with a radiator on the VVTSU top face. The VTTSU has been subjected to an extensive thermal analysis campaign relating to the examination of the worst hot and cold flight conditions, with the goal to satisfy the equipment specification and in parallel to minimize the impacts at Cargo Carrier interfaces. As a consequence, the temperature levels have been assessed, to be used during the VVTSU Qualification Thermal Vacuum Test (TVT). The TVT was performed adopting a completely passive test setup (without any temperature control via cold plate during the test). A dedicated design was needed, accounting for the relatively high heat dissipation level of the unit. The VVTSU has been fully qualified, considering also the avionic and structural requirements.