Design and Manufacturing of an Inclinometer Sensing Element for Launch Vehicle Applications 2024-26-0419

Design and Manufacturing of an Inclinometer sensing element for launch vehicle applications Tony M Shaju, Nirmal Krishna, G Nagamalleswara Rao, Pradeep K Scientist/Engineer, ISRO Inertial Systems Unit, Vattiyoorkavu, Trivandrum, India - 695013 Indian Space Research Organisation (ISRO) uses indigenously developed launch vehicles like PSLV, GSLV, LVM3 and SSLV for placing remote sensing and communication satellites along with spacecrafts for other important scientific applications into earth bound orbits. Navigation systems present in the launch vehicle play a pivotal role in achieving the intended orbits for these spacecrafts. During the assembly of these navigation packages on the launch vehicle, it is required to measure the initial tilt of the navigation sensors for any misalignment corrections, which is given as input to the navigation software. A high precision inclinometer is required to measure these tilts with a resolution of 1 arc-second. In this regard, an indigenous inclinometer is being designed. The sensing element of this design comprises of a compliant mechanism which is designed to sense the tilt by measuring the displacement of a proof mass occurring due to the respective component of earth’s gravitational acceleration force at a given inclination. This displacement is measured in terms of capacitance change, and is then used to calculate the tilt. The optimum design of this member is arrived upon by choosing the right material and by varying the section and geometry of the sensing elementwhich influences the displacement of the proof mass. It is required to maximise the obtained displacement with high precision in order to achieve robust inclination measurements. A Design of Experiment (DoE) study is conducted to design an optimal geometry of the sensing element to meet the requirement of measuring the inclination with a resolution of 1 arc-second with a range of 1 degree. The results of the DoE and the optimal input parameters selected for the final design are elaborated in this technical paper.The optimum design resulted in a proof mass displacement of more than 20 microns for a tilt of 1 degree (full range). Subsequently, the methods adopted for the precision manufacturing of the microfeatures on the sensing element are also discussed.