Flight Results from the SHEFEX2 Hybrid Navigation System Experiment

Abstract

The Hybrid Navigation System was flown on the second SHarp Edge Flight EXperiment sounding rocket mission on June 22, 2012 from Andøya Rocket Range in Norway by the German Aerospace Center (Deutsches-Zentrum für Luft-und Raumfahrt, DLR). The on-board navigation algorithm fuses measurements from an IMU, GPS receiver and star tracker with a delayed extended Kalman filter to estimate a navigation solution over time. The in-flight navigation performance is calculated by comparing the navigation solution returned via telemetry to an accurate reconstruction of the trajectory. Trajectory reconstruction combines all available data sent via telemetry, more accurate state transition and measurement models and additional off-line information using the unscented Kalman filter and unscented Rauch-Tung-Striebel backward smoother. The reconstructed trajectory is computed off-line and is much more accurate than the in-flight navigation solution. Comparing the reconstructed trajectory to the telemetry data shows that the system behaved as expected, although it did not meet its performance requirements. The Hybrid Navigation System software is now at TRL 7.

Computationally Distributed Real-Time Dual Rate Kalman Filter

“…(11) and (14). The main difference is in the dual rate filter's structure and order of equation execution, which brings two key advantages over the measurement extrapolation method and other optimal methods that solve the sensor latency problem.…”

“…Equations (6)(7)(8) represent the time propagation step, and Eqs. (9)(10)(11) are for the measurement update step:…”

“…The new dual rate filter is similar to Larsen's measurement extrapolation method [2] but has some key differences. Variations of the dual rate filter using the extended KF have already been implemented in a number of systems showing some success [8,9], including the hybrid navigation system, which flew on the SHEFEX2 sounding rocket mission [10,11].…”

A Fault-Tolerant On-Board Computing and Data Handling Architecture Incorporating a Concept for Failure Detection, Isolation, and Recovery for the SHEFEX III Navigation System

“…Based on the results and experiences with its navigation experiment 5,6,7,8,9,10,11,12,13,14,15 aboard SHE-FEX II, the Guidance, Navigation and Control (GNC) Department of the DLR Institute of Space Systems is developing a novel, autonomous navigation system for the SHEFEX III guided re-entry vehicle. 16 This system will use innovative approaches such as a hybrid navigation platform, which fuses data from an inertial measurement unit (IMU) combined with GNSS receivers, star trackers, and Sun sensors to provide a highly accurate navigation solution, i. e., the position and attitude of the spacecraft, and time derivatives thereof.…”

Improved Hybrid Navigation for Space Transportation

“…Following the HNS development and SHEFEX2 flight, the Pseudorange-only filter updating was found to yield slow velocity estimation during engine burns [24]. As accuracy is critical during propelled flight phases, both for optimal vehicle steering and for safety monitoring, a GNSS velocity-based measurement should be included.…”