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Session B6: Receiver Design, Signal Processing, and Antenna Technology

Mitigating GNSS Measurement Errors in Suspended Aircraft Tests for Efficient INS/GNSS Integration
Biju VS, Vinoj VS, Anand Shankar OT, Mohammed Basim A, Krishan Kumar, Biju V. Gopal, Rekha AR, Radhakrishna Pillai C, Padmakumar ES, ISRO Inertial Systems Unit
Location: Grand Ballroom GH
Date/Time: Thursday, May. 1, 1:50 p.m.

Global Navigation Satellite System (GNSS) receivers have become a critical component for precise navigation in modern aircraft. This paper investigates the challenges of using GNSS data in a Reusable Launch Vehicle (RLV) during field trials and missions, where the vehicle transitions from a vertical launch configuration to an aircraft-like descent. The RLV is equipped with dual GNSS antennas and an onboard Inertial Navigation System (INS), with navigation outputs generated using a 15- state extended Kalman filter that fuses GNSS and INS data. During autonomous runway landing tests, the RLV was airlifted by a helicopter and released at a predefined point to evaluate navigation accuracy. Performance analysis revealed significant velocity errors exceeding acceptable limits. The study identified three major sources of error: lever arm effects due to rotational motion, helicopter rotor-induced vibrations, and interpolation errors from high-frequency GNSS velocity variations.
To address these challenges, novel techniques were developed, including compensating for lever arm effects by projecting relative antenna velocities to the satellite line-of-sight and applying corrections at the delta range level. A Butterworth band-stop filter was implemented to mitigate rotor-induced vibrations, and the GNSS measurement frequency was increased from 1 Hz to 10 Hz to reduce interpolation errors. Results demonstrate that these techniques reduced velocity errors from 0.24 m/s to below 0.08 m/s. The effectiveness of the proposed methods was validated through multiple helicopter sorties. This work provides a comprehensive framework for mitigating GNSS measurement errors in agile aircraft and offers practical insights for improving navigation performance during field tests and missions.
Index Terms—GNSS, RLV, Aircraft test, Integrated navigation

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