Hypersonic Reentry Vehicle Research Articles

Robust LPV autopilot design for hypersonic reentry vehicle

Purpose – The purpose of this paper is to design a robust angle-of-attack (AOA) tracking control system for the hypersonic reentry vehicle (HRV) based on the linear parameter varying (LPV) theory, as the aerodynamic coefficients of the hypersonic vehicle vary quickly during the reentry phase. Design/methodology/approach – First, longitudinal moment trim is done along the desired flight trajectory. The linearized system at each trim point is built and the dynamic characteristics analysis is made. Then the LPV control law with parameter-dependent quadratic Lyapunov function (PDQLF-LPV) is applied to design the AOA tracking autopilot at each trim point. Frequency performance of the autopilot is assessed and the step response simulation is conducted to validate the effectiveness of the control system. Finally, actual AOA command tracking simulations based on the time-varying nonlinear model are carried out to test the correctness and robustness of the PDQLF-LPV autopilot. Findings – Analysis results demonstra...

Command Tracking Control System Design and Evaluation for Hypersonic Reentry Vehicles Driven by a Reaction Control System

AbstractThis paper addresses the command tracking control system (CTCS) design problem for plants involving input quantization and input saturation. A novel approach is proposed and demonstrated to the angle of attack (AOA) CTCS and bank angle CTCS of hypersonic reentry vehicles (HRV) driven by a reaction control system (RCS). First, the six-degree-of-freedom (6-DOF) nonlinear dynamic model of HRV and the mathematical model of RCS are established, and dynamic analysis is conducted based on the linearized model of HRV. Second, a general CTCS for plants involving input quantization and saturation is designed by solving a convex optimization problem based on linear matrix inequalities (LMIs). Formulations of the domains of attraction and convergence of the closed loop CTCS are derived. Furthermore, input to state stability (ISS) of the closed loop system is analyzed. Finally, the proposed approach is applied to design the longitudinal AOA CTCS and lateral–directional bank angle CTCS of HRV driven by an RCS. ...

Nonlinear estimation with Perron-Frobenius operator and Karhunen-Loève expansion

In this paper, a novel methodology for state estimation of stochastic dynamical systems is proposed. In this formulation, finite-term Karhunen-Loeve (KL) expansion is used to approximate the process noise, resulting in a nonautonomous deterministic approximation (with parametric uncertainty) of the original stochastic nonlinear system. It is proved that the solutions of the approximate dynamical system asymptotically converge to the true solutions in a mean-square sense. The evolution of uncertainty for the KL-approximated system is predicted via the Perron-Frobenius (PF) operator. Furthermore, a nonlinear estimation algorithm, using the proposed uncertainty propagation scheme, is developed. It is found that for finite-dimensional linear and nonlinear filters, the evolving posterior densities obtained from the KLPF-based estimator are closer than those obtained from the particle filter to the true posterior densities. The methodology is then applied to estimate states of a hypersonic reentry vehicle. It is observed that the KLPF-based estimator outperformed the particle filter in terms of capturing localization of uncertainty through posterior densities and reduction of uncertainty.

Air plasma-material interactions at the oxidized surface of the PM1000 nickel-chromium superalloy

Nickel-based superalloys are promising options for the thermal protection systems of hypersonic re-entry vehicles operating under moderate aerothermal heating conditions. We present an experimental study on the interactions between PM1000, an oxide dispersion strengthened nickel-chromium superalloy, and air plasma at surface temperatures between 1000 and 1600K and pressures of 1500, 7500 and 10,000Pa. Pre-oxidized PM1000 specimens are tested in high-enthalpy reactive air plasma flows generated by the Plasmatron wind tunnel at the von Karman Institute for Fluid Dynamics. Microscopic analysis of plasma-exposed specimens shows enhanced damage to the chromia scale at the lowest plasma pressure. Elemental surface analysis reveals the loss of Cr and the enhancement of Ni at the scale surface. A thermodynamic analysis supports the accelerated volatilization of Cr2O3 and the relative stability of NiO in the presence of atomic oxygen. Changes in the reflectance and emissivity of the oxidized surfaces due to plasma-exposure are presented. The catalytic efficiencies for dissociated air species recombination are determined as a function of surface temperature and pressure through a numerical rebuilding procedure and are compared with values presented in the literature for the same material.

Active disturbance rejection based trajectory linearization control for hypersonic reentry vehicle with bounded uncertainties

This paper investigates a novel compound control scheme combined with the advantages of trajectory linearization control (TLC) and alternative active disturbance rejection control (ADRC) for hypersonic reentry vehicle (HRV) attitude tracking system with bounded uncertainties. Firstly, in order to overcome actuator saturation problem, nonlinear tracking differentiator (TD) is applied in the attitude loop to achieve fewer control consumption. Then, linear extended state observers (LESO) are constructed to estimate the uncertainties acting on the LTV system in the attitude and angular rate loop. In addition, feedback linearization (FL) based controllers are designed using estimates of uncertainties generated by LESO in each loop, which enable the tracking error for closed-loop system in the presence of large uncertainties to converge to the residual set of the origin asymptotically. Finally, the compound controllers are derived by integrating with the nominal controller for open-loop nonlinear system and FL based controller. Also, comparisons and simulation results are presented to illustrate the effectiveness of the control strategy.

Range Improvements in Gliding Reentry Vehicles from Thrust Capability

There are diverse applications in which control of a gliding hypersonic reentry vehicle is needed. Recently, it has become feasible to predict the maximum reachable footprint a vehicle can achieve given a span of boundary conditions and constraints. This capability is being newly incorporated into the vehicle design process. The present work demonstrates a method to quickly approximate a footprint area and how such predictions can be informative to design considerations and trajectory planning. The novel design feature investigated is the presence, or absence, of an engine thrusting axially along the vehicle body. Three pairs of notional vehicles, one designed with an engine and one without, are motivated. Reachable footprint dimensions are presented for each and compared over the constraint space and engine design. It is shown that the performance increase, due to the presence of an engine, is most dramatically seen in a situation where a reentry vehicle must divert from a preplanned trajectory. In such a scenario, as time to target decreases, the ratio of reachable footprint area of a vehicle with an engine to that without significantly increases. This insight demonstrates new trade space analysis to inform vehicle design.

Emissivity, catalycity and microstructural characterization of ZrB2–SiCfiber based UHTC at high temperature in a non-equilibrium air plasma flow

ZrB2-based Ultra-High Temperature Ceramics (UHTC) could be used at temperatures above 2000K, a typical limit of most structural ceramics such as SiC-coated C/C composites. In particular, UHTC are candidate materials for thermal protection systems (TPS) for the new sharp-shaped hypersonic re-entry vehicles. Among the open points of research on UHTC materials is the characterization of surface properties like emissivity and catalycity in the high temperature range. High emissivity and low surface catalycity towards the exothermal recombination of oxygen atoms will improve the material performance in re-entry conditions by reducing temperature gradients and thermal stresses.In this paper are presented and discussed the experimental results of emissivity and catalycity of two different UHTC materials based upon the ZrB2–SiCfiber composition with different sintering additives (Si3N4 or ZrSi2). Microstructural characterization by SEM, XRD and XPS have shown oxidation-induced surface modifications with oxide layers composed of silica with trace amounts of boron oxide and zirconia if the maximum reached temperature is lower than about 1800K and only zirconia for higher temperatures. The differences in the oxide layer composition may account for the different thermal radiative properties and catalytic behavior.

3-D numerical calculation of magnetic drag parachute

The concept of using an externally applied magnetic field to add the drag force of a hypersonic reentry vehicle during the blackout was proposed by Bush in 1958. The increased drag force is caused by electromagnetic force that is introduced by interaction between the applied magnetic field and the weakly ionized airflow around the reentry vehicle. We investigated the influences of magnetic field intensities on the drag forces of a reentry vehicle by three dimensional (3-D) magnetohydrodynamics (MHD) simulation. The results showed that the drag fore exerted on the vehicle reached 25 kN when the magnetic field was 0.4 T. The drag force increased with the enhanced intial magnetic field. The bow shock was also pushed far away from the vehicle when the magnetic field was strengthened.

Flight control system design for hypersonic reentry vehicle based on LFT–LPV method

An angle-of-attack tracking control system is designed for the hypersonic reentry vehicle, whose aerodynamic parameters vary dramatically during reentry phase. The linear parameter-varying (LPV) theory based on linear fractional transformation (LFT) model (named as LPV–LFT method) is applied to design the controller for hypersonic reentry vehicle. Longitudinal moment trim of the hypersonic reentry vehicle is made along the desired flight trajectory, and a damping feedback loop is firstly designed to improve the system’s damping and static stability. Then, the linear dynamics model with damping feedback loop is established in LFT structure and treated as the controlled plant, and a parameter-varying reference model is utilized to guarantee the transient performance. The effectiveness of the proposed angle-of-attack tracking control system is validated through the frequency domain analysis and step response simulations. Finally, the actual angle-of-attack command tracking simulations using the nonlinear time-varying mathematical dynamics model are carried out to verify the accuracy and robustness of the hypersonic reentry vehicle control system.

Trajectory Tracking Control of Hypersonic Reentry Vehicle Based on Adaptive Fuzzy System

Considering inaccurate model and simplified calculation problems of the hypersonic reentry vehicle, this paper presents an adaptive fuzzy control system of the trajectory tracking control method. Firstly we introduced the principle of fuzzy system, then used fuzzy control theory to approximate the second-order drag acceleration model and got drag model by fuzzy identification, finally designed the adaptive controller. The simulation results show that the fuzzy adaptive tracking control method don’t depend on the dynamic model, but only rely on drag of the vehicle suffered, it can be measured directly or obtained by the aerodynamic model of the flight, the can generate tracking guidance control law, and the fuzzy adaptive tracking control method enables hypersonic vehicle to track the drag reference trajectory, realizes safe reentry and the terminal states can meet the requirements of the terminal constraints with high precision.

Suboptimal Control Theory for Vehicle Attitude Control System Design

Base on the Lyapunov stability theory, an improved suboptimal control system scheme is advanced in this paper. Aiming at hypersonic reentry vehicle nonlinear properties of the actuator deflection angle rate and the deflection angle were studied. First, the mathematical model of the control system is established according to the flight control system control scheme. Considering the project realize easy, the flight control system is designed based on suboptimal control of Lyapunov stability theory. In order to close to the optimal control, then the suboptimal control design is improved. Finally the controller is applied to the instances, by analyzing the results confirmed the method is correctly.

Computational Study on the Influence of jet on Reduction of Drag Over Cone Flare Bodies in Hypersonic Turbulent Flow

Recently, Nhypersonic research activities around the universe have been in major focus because of the milestone developments in hypersonic reentry vehicles, orbital transfer vehicles, reusable launch vehicles and space recovery experimental modules. One of the major problems in hypersonic flight is drag and with the tremendous progress in computational powers it can be analysed. In this work, the effects of counter flow jet on reduction of drag around two blunt cone flare bodies in the hypersonic turbulent flow are investigated through a numerical study. Flow field around the blunt bodies is calculated numerically for the free stream Mach number of 6.5. Numerical solutions of Navier-Stokes equation and energy equation governing the turbulent flow of compressible fluid are obtained by adopting Finite Volume Method (FVM) through an industry standard CFD code, FLUENT 6.3.26 package. Shear Stress Transport (SST) model was used in the computation of pressure drag, skin friction drag and total drag for both the absence of jet and the presence of jet cases for both the configuration. Contours of Mach number are presented to describe the flow patterns. It is clear that the reduction of drag was greatly influenced by the jet conditions and body shapes.

Human Spaceflight and Hypersonic Re-entry Vehicles: Looking Backward to Step Forward

Human Spaceflight and Hypersonic Re-entry Vehicles: Looking Backward to Step Forward

Multiphysics Coupled Fluid/Thermal/Structural Simulation for Hypersonic Reentry Vehicles

The main goal of the work described in this paper was to set up a procedure for modeling a thermal protection system for a hypersonic reentry vehicle by extending earlier work done by the authors. A multiphysics framework has been setup for the simulation of hypersonic reentry vehicles using commercial codes FLUENT and LS-DYNA with user-defined programming. The computational fluid dynamics code (FLUENT) and the material thermal and structural response code (LS-DYNA) are loosely coupled to achieve the solution. The surface recession resulting from ablation in the reentry vehicle is simulated by implementing a mesh movement algorithm in LS-DYNA. The vehicle considered in the calculation is an axisymmetric vehicle flying at zero degree angle of attack. DOI: 10.1061/(ASCE)AS.1943- 5525.0000113. © 2012 American Society of Civil Engineers. CE Database subject headings: Simulation; Fluid-structure interactions; Vehicles; Thermal factors. Author keywords: Reentry simulation; Multiphysics simulation; Fluid/structure/thermal interaction of reentry vehicle.

Behavior of Carbon-Carbon Composite under Intense Heating

This paper is concerned with modeling of ablation behavior of carbon-carbon composites used in hot spot areas of reentry space and hypersonic vehicles. Of the three modes of ablation (thermal, chemical and mechanical), the chemical (oxidation) is considered to influence the performance of the material. Aerodynamic heat flux need to be computed separately and is the input for this. The thermal field is obtained by 3D finite element method. Nonlinear transient thermal analysis is carried out, as the material properties are dependent on temperatures. Oxidation rates are computed using the analytical relations available in literature. The oxidation is divided into two regimes: reaction rate and diffusion rate controlled. Mainly the surface temperature controls the regime. The oxidation protected materials are considered by using the parameter “activation energy.” The variations of ambient temperature, pressure and oxygen concentration with altitude are taken into consideration. As the recession takes place, newer surfaces are exposed to aerodynamic heating. Numerical examples are presented to show the effects of: heat flux, altitude and oxidation protection on the recession characteristics. Change of regime from reaction to diffusion rate control depends on parameters such as flow velocity and altitude. The latter has significant influence on ablation rate.

Experimental investigation of hypersonic flow induced separation over double wedges

Flow separation occurs over the compression corners generated by deflected control surfaces on hypersonic re-entry vehicles and in the inlet of scram jet engines. Configurations like a double wedge and double cone model are useful for studying the separated flow features. Flow fields around concave corners are relatively complicated and produce several classical viscous flow features depending on the combination of the first and second wedge or cone half apex angles. Particularly characteristic phenomena are mainly shock/boundary layer, shock/shock interaction, unsteady shear layers and non-linear shock oscillations. Although most of these basic gas dynamics characteristics are well known, it is not clear what happens at high enthalpy conditions. This paper reports a result of flow fields over a double wedge at a stagnation enthalpy of 4.8 MJ/kg. The experiment was carried out in a free piston shock tunnel at a nominal Mach number of 6.99. Schlieren and double exposure holographic interferometry were applied to visualize the flow field over the double wedge.

Fluid/thermal/chemical non-equilibrium simulation of hypersonic reentry vehicles

A multi-physics frame work has been setup for the simulation of surface heat flux for nonablating hypersonic reentry vehicles and presented in this paper. The main goal of this work was to set up a simple approach for the heat flux prediction during the reentry of the vehicle. The vehicle considered in the calculation is an axisymmetric vehicle flying at zero degree angle of attack. Chemical nonequilibrium in the flowfield is simulated by implementing a set of finite rate equations in the laminar finite rate model in FLUENT. The frame work set up was validated with the results available in the literature. Good correlation was observed between the results from the commercial code with the implemented equations and the results from the literature.

Planar Fluorescence Imaging and Three-Dimensional Reconstructions of Capsule Reaction-Control-System Jets

Planar laser-induced-fluorescence flowfield visualization has been used to investigate reaction-control-system jet flows in the wake of hypersonic capsule reentry vehicles. Pitch, roll, and yaw reaction-control-system jets were all studied. Planar laser-induced fluorescence was used to obtain offbody flow images at planar slices in these flowfields, which are not easily visualized by other techniques, owing to characteristically low gas density. When viewed individually, these slices are shown to provide spatially and temporally resolved information, including the locations and characteristics of turbulent flow structures and the location of the jet flow relative to the vehicle. In addition, ensembles of slices acquired at multiple locations throughout the flowfield are combined using computer visualization techniques to reconstruct the three-dimensional shape of the flow. Collectively, the offbody flow-visualization data set acquired in these tests represents a valuable complement to surface measurements, especially as a basis for explaining otherwise perplexing discrepancies between such measurements and computational fluid dynamics results. The tests described herein were conducted in the 31-Inch Mach 10 Air Tunnel at NASA Langley Research Center.

Critical Discharge in Actively Cooled Wing Leading Edge of a Reentry Vehicle

The study of an innovative active cooling system of a wing leading edge of a hypersonic reentry vehicle making use of water is addressed. In particular, a steady model is developed to study the critical discharge of the cooling water into a very low-pressure ambient simulating the outlet conditions for both the reentry and wind-tunnel environments. Because of the strongly subcooled operating conditions, the model predicts no flashing within the duct connecting the outlet (hot) manifold to the vacuum ambient. The mass flow rate needed to remove the aerodynamic heat load acting on the external surface is calculated by an iterative procedure. At each iteration, for a fixed value of the mass flow rate, the pressure within the outlet manifold is calculated and the exit section critical pressure is determined as well. Subsequently, a detailed thermo-fluid-dynamic analysis is conducted to evaluate the head losses within the pipes and the peak wet wall temperature. The iteration stops when the mass flow rate guarantees noboiling conditions throughout the system. The findings arising from the steady model are confirmed by unsteady numerical simulations of the system startup.

WORST-CASE ANALYSIS OF FLIGHT CONTROL LAWS FOR RE-ENTRY VEHICLES

This paper reports results of a joint study between ESA, DEIMOS Space S.L. and the University of Leicester on the robustness analysis of flight control laws for future hypersonic re-entry vehicles. We apply a novel hybridised version of the deterministic global optimisation algorithm, DIviding RECTangles (DIRECT), to perform worst-case analysis of a nonlinear-dynamic inversion (NDI) flight control law for a highly-detailed simulation model of a hypersonic re-entry vehicle. Nonlinear clearance criteria widely used in the European aerospace industry for the clearance of flight control laws for highly manoeuvrable aircraft are developed and applied in the context of the re-entry vehicle flight control problem. The proposed approach is shown to have the potential to improve significantly both the reliability and efficiency of the flight clearance process for future re-entry vehicles.