# An Effective Sensor Architecture for Full-Attitude Determination in the HERMES Nano-Satellites
## 5 Final Remarks  
The proposed sensor architectures guarantees the solution of the attitude determination problem with a maximum attitude knowledge error of \(1\deg\) at \(1\sigma_{a}\) and with a maximum orbital position knowledge error of \(10\,\mathrm{m}\) at \(1\sigma_{\circ}\). These results were achieved with commercial off-the-shelf (COTS) sensors in the class of nano-satellites. Indeed, the proposed sensor architecture has to be compliant with many constraints in terms of the mass, volume, power, computational resources, and cost budget. Specifically, the attitude determination functions were based on the Quaternion ESTimation (QUEST) algorithm processing Sun and geomagnetic field measurements. This function was combined with gyroscope data to guarantee attitude propagation during eclipses and with on-board sensor calibration functions to improve the attitude estimation performance. The orbit determination block was founded on direct GNSS measurements loosely coupled through an extended Kalman filter (EKF), with accelerometers data and with an on-board orbit propagator. This design allows the robustness of the entire navigation block with respect to GNSS failures and outage periods. Moreover, it allows a direct integration of the proposed sensor architecture in missions with orbital control capabilities. The proposed results describe the sensor performance and features of classical nano-satellite components. In particular, hardware-in-the-loop (HIL) test results were made available and discussed with respect to the selection analyses to build up the proposed sensor architecture. The initial assumptions and justifications were motivated by the design process description, which was supported by extensive testing activities summarized in this manuscript. The same test results were used to fully characterize the complete sensor architecture, in order to set up proper model-in-the-loop  
Figure 17: Orbit determination error.  
(MIL) verification activities demonstrating the accuracy of the full-attitude determination process. The combined verification process at the hardware and model levels allowed achieving high-quality standards in the design of nano-satellite missions. Despite this research work being based on the activities carried out for the HERMES nano-satellites, the information contained in this manuscript can be used as a reference for spacecraft with analogous sensor typologies, mission requirements, or system constraints. All of them are quite common in the rising sector of nano-satellite and CubeSat missions.  
Conceptualization, A.C.; methodology, A.C.; software, A.C.; formal analysis, A.C.; writing--original draft preparation, A.C.; writing--review and editing, A.C.; Project administration, M.L. and R.B.; funding acquisition, M.L. All authors have read and agreed to the published version of the manuscript.  
This work was carried out in the framework of the HERMES-TP and HERMES-SP collaborations. We acknowledge support from the Italian Ministry for University and Research (MUR) and the Italian Space Agency (ASI) under the grant agreement Accordo Attuativo ASI-POLIMI Mission HERMES-Technological Pathfinder--Attivita di sistema n. 2018-13-HH.0 and from the European Union's Horizon 2020 Research and Innovation Framework Programme under the grant agreement HERMES-Scientific Pathfinder n. 821896.  
Not applicable.  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors wish to acknowledge the HERMES group of the ASTRA team at Politecnico di Milano, Department of Aerospace Science and Technology, and the entire HERMES project consortium.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of the data; in the writing of the manuscript; nor in the decision to publish the results.