Luis F. Peñín

Gain-Scheduled FDI for a Re-entry Vehicle

This paper presents the design of a gain scheduled fault detection and isolation (FDI) filter for the Hopper reusable launch vehicle (RLV). The fault scenario is that of faults in the vehicles rudder actuator and sideslip sensor during a focused 90 second period of the re- entry. Both of the considered faults strongly affect the lateral response of the vehicle, making simultaneous FDI difficult. A dynamically stable model of the Hopper RLV is considered and FDI filter design is performed on linearised models of the vehicle trimmed about the re- entry trajectory. H-infinity theory is employed for the FDI filter synthesis, with a set of LTI FDI filters designed at the trim points and then scheduled to form the gain scheduled FDI filter. The effectiveness of the LTI point-design filters and the gain-scheduled filter are determined by simulation using a tightly gain-scheduled model of the linearised vehicles open-loop response that captures the strongly parameter varying vehicle behaviour as it tracks the re-entry trajectory. The advantages of using gain-scheduled FDI filters for FDI on RLVs are highlighted via the simulations.

Application of LPV/LFT Modeling and Data-based Validation to a re-entry vehicle

*† ‡ § ** †† ‡‡ In this article an application of LFT/LPV modeling and data-based validation techniques to a re-entry vehicle is shown. This work is part of a European Space Agency project tasked with examining the use of LPV technologies for the control design process of space systems. The application presented serves as an assessment on the technological readiness level of LPV/LFT modeling approaches and data-based validation algorithms, as well as a review of their features, shortcomings and needs. The selected vehicle is the longitudinal nonlinear motion of NASA HL-20 during an approach trajectory from Mach 4.5 down to 1.5.

Piloted assessment of a fault diagnosis algorithm on the ATTAS aircraft

This paper describes the application of a fault diagnosis algorithm in a simulation campaign conducted with the Advanced Technologies Testing Aircraft (ATTAS). To provide a realistic fault scenario suitable for in-flight testing, the effects of actuator rate saturation were considered to be the result of faults acting on the ATTAS. Fault diagnosis algorithms were designed for these faults using H-infinity fault detection and isolation (FDI) filter synthesis tools and online thresholding algorithms. These fault diagnosis algorithms were assessed in an incremental validation campaign by first using the ATTAS high-fidelity nonlinear model, and then the German Aerospace Center (DLR) ATTAS flight simulator. In-flight data from previous flight campaigns investigating methods to alleviate rate saturation effects was used to assess the performance and robustness of the algorithms under real flight conditions.

Robust Skip Entry Guidance and Control for a Capsule Returning from Lunar Orbit

Next generation space exploration missions will require extremely versatile vehicles that should be able to safely carry both cargo and crew to LEO and beyond LEO destinations and back to Earth. The re-entry phase is very important for the success of such missions and becomes critical in the case of high speed (high energy) entries, which arise in Lunar and Mars missions. Moreover, modern requirements call for flexibility for long ranges, and in case of a low L/D vehicle a controlled skip would be necessary to obtain such requirements. This article presents the development of a fully integrated guidance and control (G&C) system as part of a complete robust GNC system for high-speed entry. An Apollo derived guidance method and a QFT designed attitude control system have been implemented to guide a conical capsule in the context of a long range skip entry from a Lunar return mission. The system has been extensively tested, with 6 degrees-of-freedom simulations performed on re-entry scenarios developed using a high-fidelity functional engineering simulator. The vehicle is steered to the desired landing site and successfully controlled during the most critical phases of the trajectory, being pull out, exit of the atmosphere to perform the commanded skip, and the final entry with reduced velocity. The G&C scheme has proved robust against realistic modeling of dispersions and uncertainties throughout the re-entry.

Hazard Detection and Avoidance in ESA Lunar Lander: Concept and Performance

The ESA Lunar Lander mission is a step in the preparation for future exploration missions, being tasked with demonstrating autonomous soft, safe precision landing on the Moon. The last segment of the mission’s descent and landing phase is the approach phase, during which the GNC subsystem steers the spacecraft to the targeted landing site (LS). The Hazard Detection and Avoidance (HDA) subsystem is active during this phase and uses the measurements provided by a camera and a LIDAR to assess the safety of the terrain. The HDA subsystem also determines which are the ground locations that can be reached by the spacecraft. Based on the safety and reachability assessments, the HDA subsystem then decides autonomously if a retargeting should be commanded to a new LS. In that case, the GNC subsystem is notified and tasked with driving the vehicle to perform a soft landing at the designated LS. This paper describes the concept and performances of the HDA subsystem proposed for the Lunar Lander mission. Sensitivity tests are performed in order to evaluate the robustness of the system. The performance of the HDA subsystem is demonstrated through Monte Carlo simulation campaigns on a functional engineering simulator.

Simulation-Based Fault Analysis Methodology for Aerospace Vehicles

This article presents a fault analysis methodology and toolbox developed to address the two main questions for any fault analysis methodology: i) what is the impact on the closed loop of a specific fault; ii) which fault is more critical. The methodology is based on the idea of computation-based data acquisition and quantitative-based data analysis. The software fault analysis toolbox developed in support of the process uses XML (Extensible Markup Language) and Matlab/Simulink files to provide a structured functionality that facilitates its use and adaptation to different types of missions, vehicles and simulation tools. Its two main functionalities are the generation of fault-data analysis sets (in a form reminiscent of Monte Carlo campaigns) and the automated evaluation of the results (determination of the fault criticality classification). Special emphasis is given to the manner the results are presented so as to facilitate their interpretation by fault analysts due to the explosion of data arising from the many possible faults, at many possible instances and at many possible components. The validity of the process and toolbox are exemplified using the results from a fault analysis study of an atmospheric reusable launch vehicle during the ascent and re-entry phases.

ESA Lunar Lander: Approach Phase Concept and G&C Performance

The ESA Lunar Lander mission is tasked with landing safely on the lunar surface near the lunar South Pole. The mission aims to demonstrate the capability of performing soft precision landings and autonomous hazard detection and avoidance (HDA) during the descent and landing phase. The final portion of the descent and landing phase is the approach phase, during which time the spacecraft is steered to the final landing site via the GNC, while providing a vehicle attitude for sensor observations of the landing site and surrounding terrain. An HDA subsystem is active during this phase and uses data from a camera and a Lidar to assess the safeness of the terrain around the landing site and select a safe landing site for GNC targeting. The GNC drives autonomously the vehicle to perform a soft landing at the landing site, performing trajectory diverts when new landing sites are selected by HDA. This paper describes the GNC concept and architecture for the approach phase of the descent and landing portion of the Lunar Lander mission, with emphasis on the details on the guidance and control (G&C) algorithms and the achieved G&C performances. The performance of the G&C subsystem is demonstrated through Monte Carlo simulation campaigns on a functional engineering simulator, with both the GNC and HDA algorithms active.

IXV Re-entry Guidance, Control & DRS Triggering: Algorithm Design and Assessment

The Intermediate eXperimental Vehicle (IXV) re-entry GNC is tasked with stabilising and manoeuvring the IXV from the Entry Interface Point (EIP, 120 km altitude) suborbital trajectory conditions to the deployment of a 3 stage (supersonic drogue, subsonic drogue and a main parachute) parachute system. The re-entry GNC is comprised of the Guidance, Navigation and Control functions, which are scheduled via a Flight Management function that interfaces the GNC with the vehicle’s mode vehicle management (MVM). Within reentry GNC responsibilities there is also the design and validation of the Descent and Recovery System (DRS) triggering algorithm, which autonomously triggers the extraction of the supersonic parachute. The IXV is a lifting body with a lift-to-drag ratio of 0.7 in the hypersonic regime and, distinct from other re-entry vehicles such as ARD and Orion, is actuated through the combination of two body flaps mounted at the aft windward side of the vehicle and RCS thrusters. The challenges for the IXV re-entry GNC system design are common to those for re-entry vehicles performing a first flight, with the re-entry GNC required to be robust to high levels of uncertainty in the vehicle dynamics. This paper describes the IXV re-entry G&C and DRS triggering algorithms at the current IXV programme status of Phase D, including the assessment of the re-entry GNC performance using the IXV functional engineering simulation developed for the IXV programme.

Flying Qualities Analysis for Re-entry Vehicles: Methodology and Application

In the frame of on-going and future European projects related to atmospheric entry of a space vehicle, it has been identified the need for implementation of a framework for Flying Quality Analysis (FQA), including the definition of a “canvas” for a future FQA standard. This paper presents the development of a detailed FQA methodology and the demonstration of its suitability by the application to different types of vehicles (capsules, lifting bodies, winged vehicles) in various stages of their development process. It includes detailed test campaigns for the identified Flying Quality criteria as well as the validation against closed loop Guidance, Navigation and Control (GNC) simulations for ARD, IXV and HL-20 vehicles. This methodology has been successfully applied in an advanced design phase for the Intermediate eXperimental Vehicle (IXV), superseding former methods and approaches and showing the advantages of such standardized framework for Flying Qualities analyses.

Formation Flying Control in Highly Elliptical Orbits

In this paper a satellite formation flying control design based on nonlinear dynamic inversion is presented. The formation consists of three satellites using a relative leader-follower control scheme flying a highly elliptical orbit around Earth. The resulting controller is subject to environment effects (J2), uncertainty, strong navigation errors and noise using a state-of-the-art formation flying engineering simulator. The results show that the resulting closed-loop can cope successfully with all the considered perturbations while satisfying performance & robustness design requirements throughout the experimental phase of orbit and that during perigee passages it performs reasonably well.