To perform the detailed design and analysis of a star tracker based generic safe mode applied to Science Missions

A previous study (TRP Star sensing based safe mode) confirmed the interest of using star tracker as primary sensor in a generic safe mode: versatility, suitability to complex requirements and constraints (e.g. TTC from long distance to Earth such as Mars, Jupiter, Deep Space), cumulative maturity/reliability across missions, reduced development effort (genericity), and operational errors mitigation.The commonality of sensor and reduction of the sensor suite is particularly attractive for cost-effective space missions, since commonality of sensors between several modes relaxes the sensor procurement, integration, verification and testing effort. Additional activities are required in order to implement this attractive solution on a science mission. This activity will perform detailed analysis and design, assess the robustness of star tracker based safe mode to worst case conditions using flight data and simulations. Flight data will consist in star tracker measurements out of normal mode such as sun acquisition, safe mode, star tracker reconfigurations, as retrieved from previous and current mission telemetry.

This activity encompasses the following tasks:-

• Task 1 Science mission (small planetary missions) study cases section and requirements definition considering at least Cost Effectiveness, Operations, Safety, TTC and payload constraints (e.g. TTC pointing requirements, payload attitude constraints, initial conditions).
• Task 2 Assessment of Star tracker acquisition and tracking robustness to worst-case conditions including dynamic conditions and end of life conditions considering proton damage to the detector: Solar Flares, Non-Stellar objects in the field of view (Moon, planets, other satellites, dust), high angular rates, stray light, SEUs
• Task 3 Assessment of the suitability and robustness of state-of-the-art European manufacturers? star tracker products
• Task 4 Safe mode detailed design taking into consideration cost effectiveness: define the AOCS sensors and actuators, the avionics architecture including standard interfaces, and the FDIR strategy.
• Task 5 Safe mode detailed analysis including FMECA (including for example parameters errors such as star tracker matrix error)-
• Task 6 Aquisition and Safe mode Simulator development, Test plan definition, Robustness, FDIR, and performance assessment-
• Task 7 Definition of a test plan, aiming at robustness and performance testing on a representative AOCS (preferably closed loop) testbench including RT aspects, STR model, as well as STR optical stimulation.-
• Task 8 Preliminary assessment of complementary cost-effective attitude determination solution, such as Doppler attitude determination (see Ulysses spacecraft for example)-
• Task 9 Conclusion and way forwardThe expected deliverables are related documentation and study simulator. AOCS testbench and STR physical model and optical stimulation are considered out of scope of the deliverables.