IRIDIUM-NEXT Star Tracker Thermal Design: lessons learned and learning curve in a small series production

IRIDIUM-NEXT is the second generation of a global satellite constellation, composed by 66 cross-linked LEO satellites covering the whole globe. The attitude determination for each satellite is assigned to one MHSTR (MultiHead Star Tracker) consisting of 3 Star Trackers (STR). The prime contractor is Thales Alenia Space and, in this context, Selex ES has the full responsibility of the Star Tracker procurement. The launch of the first satellite is expected in 2015. Given the thermal insulation requirements between the STRs and the S/C (with a conductance lower than 0.1 W/K), the STR design is strongly affected in both the thermal and the structural aspects. The thermal detailed design of the sensor has been focused on:

• Characterization and development of the thermal paths in order to keep the sensor temperature lower than 15°C
• Optimization of the coatings The thermal design has been numerically analyzed and verified through experimental tests to validate the model. The paper describes the development of both the thermal and geometrical detailed mathematical models, the execution of the thermal balance test (TBT) and the following correlation activity for the TMM. The prediction of the expected in-orbit performances are also reported. Reference is made to the optimization of the recurring testing activities, in light of the small series (250 units) production launched.