Star Sensing Based Safe Mode
| Programme: | TRP Workplan | Achieved TRL: | 6(SW)/9(HW) |
| Reference: | T705-404EC | Closure: | 2016 |
| Contractor(s): | Airbus DS (FR), Airbus DS (GB), Jena Optronik (DE) | ||
The current approach used for the development of safe modes is to design simple control algorithms using segregated sensors and tailored to each mission requirements. This induces a great diversity of safe modes leading to several limitations such as non-recurring costs and low growth potential (e.g. Earth strobing or de-orbiting). Star trackers (STR) are the most versatile sensors, and change from CCD to CMOS APS-based STR has significantly increased their robustness and reliability.
Objectives:
The objective of this study was then to assess the implications of using STR as primary sensor with or without complementary sensors (avionics, operations, FDIR/RAMS), to investigate the STR performance and robustness, to prototype the design of a versatile architecture, to assess the performances through simulations and to express design requirements at avionics and star tracker level.
Achievements:
Different tests performed on a state-of the art STR demonstrated its performances and robustness to different safe mode conditions (high angular rates and acceleration, radiation, temperature, prolonged sun blinding). Using the same STR SW for safe mode as for normal mode is recommended. Genericity is based on a modular architecture to accommodate differences between missions allowing 95% commonality. Satisfactory behaviour is demonstrated in all simulated scenarios.
Benefits:
Versatility and growth potential for new orbits, de-orbiting and complex pointing requirements (e.g. Earth strobing). Cumulative maturity/reliability across missions. Reduced development effort/time/risk. Similar operations inducing fewer errors.
Further activities:
Test safe mode algorithms with STR flight data. Favour modular safe mode architecture with standard interfaces. Get STR telemetry during safe mode.
