Hypersonic Reentry Vehicle Research Articles

Innovative Thermal Management Concepts and Material Solutions for Future Space Vehicles

When entering a planetary atmosphere, space vehicles are exposed to extreme thermal loads. To protect the vehicle’s interior, a thermal protection system is required. Future aerospace transportation demands solutions that exceed the performance of current systems and up-to-date material limits. Therefore, new and disruptive solutions must be envisaged to meet those extreme conditions. In the search of new solutions for sharp leading edges of future hypersonic reentry or transport vehicles, the THOR project, composed of eight European organizations (industries, research centers, and universities) and one Japanese Agency (Japan Aerospace Exploration Agency), is actively working on definition, design, implementation, and simulation of new passive and active thermal management solutions and their verification in relevant environments (high-enthalpy facilities). This paper provides an overview of the recent developments on the four concepts that are targeted in the project, applying different physical methodologies: 1) passive cooling using highly conductive carbon-based fibers, 2) passive cooling with intensive internal radiative exchange, 3) active cooling based on convection heat transfer using a ceramic sandwich/thermal protection system with ceramic foams/lattices, and 4) active transpiration cooling of external surfaces. Details on these thermal management concepts, requirements from end users, and test configurations, as well as results from experimental and numerical verification, are given.

Adaptive Multistate Markov Channel Modeling Method for Reentry Dynamic Plasma Sheaths

Channel modeling of a plasma sheath for hypersonic reentry vehicles is important in addressing reentry communication blackout issues. Given that the time-varying property of the transmission medium is caused by physical factors such as large-scale flight conditions variation, especially angle of attack, and small-scale fluid turbulence, a new adaptive multistate Markov channel modeling method is proposed to present the dynamic effects of reentry plasma sheaths on wireless channels. First, a quasi-Gaussian function mathematical model for the electron density of a dynamic plasma sheath is established according to the variation frequency of the dynamic physical factors. Then, the time-varying attenuation is calculated by combining the quasi-static Monte Carlo and uniform hierarchical analytical methods for nonuniform electronic density distribution. Finally, a hidden Markov model is employed to model the channel characteristics of the dynamic plasma sheath, and a reversible-jump Markov chain Monte Carlo algorithm is used to adaptively estimate the channel parameters of the multistate Markov channel. Simulation results show that the first-order statistical properties of the proposed channel are in good agreement with the calculated variable attenuation of radio waves, and this method has the adaptive capacity to estimate the number of multiple states and the channel parameters in each state without a need for manual setting.

Protection of pyrolysis gases combustion against charring materials’ surface ablation

Charring ablation materials are widely used for thermal protection systems in a vehicle during hypersonic reentry. The pyrolysis gases from the charring materials can react with oxygen in the boundary layer, which makes the surface ablation rate decrease. The problem of protection of pyrolysis gases combustion against charring materials’ surface ablation is solved by the detached normal shock wave relations and the counterflow diffusion flame model. The central difference format for the diffusion term and the upwind scheme for the convection term are used to discretize the mathematical model of the counterflow diffusion flame. Numerical results indicate that the combustion of pyrolysis gases in the boundary layer can completely protect the materials surface from recession when the velocity of pyrolysis gases injecting to the boundary layer is higher than the critical velocity. There is an allometric relationship between the critical velocity and Mach number, and the combustion heat has little influence on the temperature distribution originating from the aerodynamic heating. This study will be helpful for the design of the thermal protection system in hypersonic reentry vehicles.

Drag and heat reduction mechanism induced by a combinational novel cavity and counterflowing jet concept in hypersonic flows

The drag and heat reduction problem of hypersonic reentry vehicles has always attracted the attention worldwide, and many novel schemes have been proposed recently. In the current study, the research progress of the combinational configuration of the forward-facing cavity and the counterflowing jet has been reviewed, and the conventional cavity configuration has been substituted by an approximate maximum thrust nozzle contour for better heat and surface pressure reduction efficiency. The Reynolds-average of Navier-Stokes (RANS) equations coupled with the SST k–ω turbulence model have been employed to calculate its surrounding flow fields. A validation metric and the grid convergence index (GCI) have been employed to conduct the turbulence model assessment and the grid independence analysis respectively. The axisymmetric assumption has been verified by three-dimensional computational results as well. The obtained results show that the SST k-ω model is more suitable for the novel drag and heat flux reduction scheme proposed in this article, and the axisymmetric assumption is approximately reasonable. After investigating the influence of jet pressure ratio, the novel combinational configuration has been verified to be more effective in heat and surface pressure reduction, and this is because the approximate maximum thrust nozzle contour contributes to better expansion and avoids total pressure loss of the jet.

Back-stepping robust trajectory linearization control for hypersonic reentry vehicle via novel tracking differentiator

This paper proposes a back-stepping robust trajectory linearization control (TLC) design for hypersonic reentry vehicle (HRV) attitude tracking problem from a novel tracking differentiator perspective. First, the attitude kinematics and dynamics for HRV is formulated and rewritten in feedback form with mismatched and matched uncertainties introduced by variations of various aerodynamic coefficients. Second, a sigmoid function based novel tracking differentiator (STD) with global fast convergence property, simple structure and chattering-free in differential estimation is developed to handle the “explosion of term” problem in back-stepping TLC design. In addition, dynamical performance and noise-attenuation ability of STD are analyzed in frequency domain by describing function method. Third, how to convert between sigmoid function based disturbance observer (SDO) and STD is given, and based on the estimates of uncertainties provided by SDO in attitude and angular rate loop, the back-stepping robust TLC is synthesized to track the respective commands in dual-loop. Then, the stability of the composite SDO-enhanced back-stepping TLC approach is established. Finally, extensive simulation results are presented to demonstrate the effectiveness of the proposed control strategy in improving disturbance attenuation ability and performance robustness against multiple uncertainties.

Neural network based semi-empirical models for dynamical systems described by differential-algebraic equations

We analyzed the problem of mathematical modeling and computer simulation of nonlinear controlled dynamical systems usually described by differential-algebraic equations. The problem is proposed to be solved in the framework of the semi-empirical approach combining theoretical knowledge for the plant with training tools of artificial neural network field. The results are presented for a semi-empirical model that simulate the reentry hypersonic vehicle and confirm the efficiency of this approach.

Enhanced trajectory linearization control based advanced guidance and control for hypersonic reentry vehicle with multiple disturbances

In this paper, the guidance and control problem for hypersonic reentry vehicle (HRV) in the presence of control constraints and multiple disturbances is handled based on unified enhanced trajectory linearization control (TLC) framework under reference-tracking methodology. First, based on the nominal trajectory and open-loop command generated by Gauss pseudo-spectral method (GPM), a time-varying feedback guidance law with integral action is synthesized to stabilize the tracking error dynamics along the nominal trajectory under the framework of TLC. Second, to improve the robustness of attitude and angular rate loop, variations of various aerodynamic coefficients and external disturbances are considered as lumped uncertainties, reduced-order linear extended state observers (LESO) with given model information are constructed to estimate the lumped uncertainties in each loop, respectively. In addition, comparisons between the estimation efficiency of LESO and reduced-order LESO are carried out. Then augmented with the disturbance estimates and TLC control law, tracking errors of the rotational dynamics can be actively rejected without sacrificing nominal performances. More importantly, fewer control consumption and smooth transient performances are achieved by using nonlinear tracking differentiator (TD) in attitude loop. The stability of the resulting closed-loop system is well established based on Lyapunov stability theory. Finally, the effectiveness of the proposed advanced guidance and control strategy is verified through extensive simulations on the six-degree-of-freedom reentry flight.

Steady glide trajectory planning method for hypersonic reentry vehicle

The concept of steady glide trajectory with minimum integration of the change rate of longitudinal acceleration was proposed for the equilibrium glide problem with given angle of attack and bank angle profiles,and the planning method of the steady glide trajectory was described. First,the dynamic differential equation in the altitude direction was solved by regular perturbation,and steady glide analytical solutions with high precision,including height,flight path angle and longitudinal acceleration,were obtained. Then the dynamic behaviors of the steady glide trajectory were analyzed,the natural stability and low damping of the trajectory were found,and the expressions of natural frequency and damping were obtained. The results show that the natural frequency is only a function of velocity,while the damping depends on velocity and longitudinal lift-drag ratio. Finally,the pure differential feedback of height deviation is found to be the best scheme for restraining the oscillations of the steady glide trajectory among three feedback schemes,which are pure differential feedback,pure proportional feedback and proportion-differential feedback. The simulation results show that the control of the pure differential feedback scheme is steady,the trajectory oscillation decay fast,and the robustness of the scheme is excellent.

Estimation of surface heat flux for ablation and charring of thermal protection material

Ablation of the thermal protection material of the reentry hypersonic flight vehicle is a complex physical and chemical process. To estimate the surface heat flux from internal temperature measurement is much more complex than the conventional inverse heat conduction problem case. In the paper, by utilizing a two-layer pyrogeneration-plane ablation model to model the ablation and charring of the material, modifying the finite control volume method to suit for the numerical simulation of the heat conduction equation with variable-geometry, the CGM along with the associated adjoint problem is developed to estimate the surface heat flux. This estimation method is verified with a numerical example at first, the results show that the estimation method is feasible and robust. The larger is the measurement noise, the greater is the deviation of the estimated result from the exact value, and the measurement noise of ablated surface position has a significant and more direct influence on the estimated result of surface heat flux. Furthermore, the estimation method is used to analyze the experimental data of ablation of blunt Carbon-phenolic material Narmco4028 in an arc-heater. It is shown that the estimated surface heat flux agrees with the heating power value of the arc-heater, and the estimation method is basically effective and potential to treat the engineering heat conduction problem with ablation.

Disturbance observer-based sliding manifold predictive control for reentry hypersonic vehicles with multi-constraint

The presence of system strong constraints and large uncertainties in reentry hypersonic vehicles deteriorate the system performance. This paper considers disturbance observer-based sliding manifold predictive control design for a reentry hypersonic vehicle. In the outer loop, a new sliding manifold-based predictive control is proposed to realize reference command tracking. In the inner loop, a nonlinear disturbance observer is adopted to estimate lumped disturbances and a sliding manifold-based predictive control is designed to track the expected signal obtained from the outer loop. The use of sliding manifolds and disturbance observer enhance the control system’s robustness to uncertainties. The mode predictive control approach guarantees the satisfaction of the system constraints. The effectiveness of the proposed algorithm is verified by theoretical analysis and simulations.

Separable warhead mathematical model of Supersonic & Hypersonic Re-entry Vehicles

Separating a reentry vehicle into warhead and body is a conventional and efficient means of producing a huge decoy and increasing the kinetic energy of the warhead. This procedure causes the radar to track the body, whose radar cross section is larger, and ignore the warhead which is the most important part of the reentry vehicle. The aerodynamic Coefficients models play an essential part in the simulation and the analysis of the supersonic and hypersonic of the ballistic missiles, especially in the dynamic trajectory planning. This paper builds the aerodynamic coefficients models by the nonlinear least square method based on the separable warhead re-entry vehicle using lebedev aerodynamic calculations. The lift and drag coefficients models can be expressed with the polynomial and the exponential function. So the models fit the aero characteristic well and can be used in practical design and simulation as a reference.

Particle swarm optimization applied to hypersonic reentry trajectories

This paper presents the novel use of the particle swarm optimization (PSO) to generate the end-to-end trajectory for hypersonic reentry vehicles in a quite simple formulation. The velocity-dependent bank angle profile is developed to reduce the search space of unknown parameters based on the constrained PSO algorithm. The path constraints are enforced by setting the fitness function to be infinite on condition that the particles violate the maximum allowable values. The PSO algorithm also provides a much easier means to satisfy the terminal conditions by adding penalty terms to the fitness function. Furthermore, the approximate reentry landing footprint is fast constructed by incorporating an interpolation model into the standardized bank angle profiles. Numerical simulations demonstrate that the PSO method is a feasible and flexible tool to generate the end-to-end trajectory and landing footprint for hypersonic reentry vehicles.

Optimal control problems with stopping constraints

We consider a novel optimal control problem in which the terminal time is governed by a stopping constraint. This stopping constraint is a nonlinear equality constraint depending on the state variables, and the terminal time is defined as the first time at which this constraint is satisfied. Since the stopping constraint causes the terminal time to be an implicit function of the control, the optimal control problem we consider cannot be solved using conventional techniques. We propose a new computational approach that involves approximating the original problem by a standard optimal control problem with fixed terminal time. Our main result shows that this approximation, which depends on two adjustable parameters, can be made to arbitrarily high accuracy. On this basis, the original optimal control problem with stopping constraints can be transformed into a sequence of approximate problems, each of which can be solved readily using conventional optimal control techniques. We conclude the paper by demonstrating this approach with numerical simulations in three application areas: range maximization of a hang glider, range maximization of a hypersonic re-entry vehicle, and time-optimal control of a nuclear reactor.

Modeling Radio Communication Blackout and Blackout Mitigation in Hypersonic Vehicles

A procedure for the modeling and analysis of radio communication blackout of hypersonic vehicles is presented. The weakly ionized plasma generated around the surface of a hypersonic reentry vehicle is simulated using full Navier–Stokes equations in multispecies single fluid form. A seven-species air chemistry model is used to compute the individual species densities in air including ionization: plasma densities are compared with the experiment. The electromagnetic wave’s interaction with the plasma layer is modeled using multifluid equations for fluid transport and full Maxwell’s equations for the electromagnetic fields. The multifluid solver is verified for a whistler wave propagating through a slab. First principles radio communication blackout over a hypersonic vehicle is demonstrated along with a simple blackout mitigation scheme using a magnetic window.

Design, Modeling and Analysis of a Sharp-edge Hypersonic Stealthy Re-entry Vehicle

In 2005 and in 2012, the SHarp Edge Flight EXperiment SHEFEX I and SHEFEX II of DLR have been established. Low lift-to-drag ratio of them limits active control ability. This paper studies on a sharp-edge stealthy re-entry vehicle with high lift-to-drag ratio. The focus will be laid upon designing and modeling of a sharp-edge stealthy re-entry vehicle by analyzing of lift-to-drag ratio and center of gravity, and also upon stealth performance researches. All aerodynamic performance analysis are based on Modified Newtonian Theory, it's proved to be more precise for a sharp-edge hypersonic re-entry vehicle relative to the Piston Theory and Shock-Expansion Method. A procedure based on physical optics and method of equivalent currents for radar cross section calculation. As result, the configuration and the center of gravity are determined, and a good stealth performance is demonstrated.

Six-DOF Modeling and Simulation for Generic Hypersonic Vehicle in Reentry Phase

The purpose of this research is to model a hypersonic vehicle in the pull-up phase and provide an insight into the inherent dynamics. Based on Newtonian mechanics, the theoretical flight dynamic model of the pull-up phase of reentry motion is established; Based on MATLAB/SIMULINK, simulation model for reentry hypersonic vehicle was modeled. Lifting body hypersonic vehicle aerodynamic data is obtained by high-accuracy CFD code which copyright by CAAA. We adopted feedback linearization control theory, pitching angle holding control laws in order to keep maximum lift-drag ratio glider, the six degree of freedom (DOF) simulation validate the control law. The simulation results show some hypersonic flight characteristics, including static unstable, earth radius and rotationeffects and high-coupledcharacteristics. The simulation model and results provide a useful reference for a hypersonic vehicle's dynamics analysis, control law design and overall design.

Sliding mode based trajectory linearization control for hypersonic reentry vehicle via extended disturbance observer

This paper proposes a novel hybrid control framework by combing observer-based sliding mode control (SMC) with trajectory linearization control (TLC) for hypersonic reentry vehicle (HRV) attitude tracking problem. First, fewer control consumption is achieved using nonlinear tracking differentiator (TD) in the attitude loop. Second, a novel SMC that employs extended disturbance observer (EDO) to counteract the effect of uncertainties using a new sliding surface which includes the estimation error is integrated to address the tracking error stabilization issues in the attitude and angular rate loop, respectively. In addition, new results associated with EDO are examined in terms of dynamic response and noise-tolerant performance, as well as estimation accuracy. The key feature of the proposed compound control approach is that chattering free tracking performance with high accuracy can be ensured for HRV in the presence of multiple uncertainties under control constraints. Based on finite time convergence stability theory, the stability of the resulting closed-loop system is well established. Also, comparisons and extensive simulation results are presented to demonstrate the effectiveness of the control strategy.

Control system design for hypersonic reentry vehicle driven by aerosurfaces and reaction control system

The paper addresses the command-tracking-control-system (CTCS) design problem for plants involving continuous and discrete control input simultaneously. A novel approach based on linear matrix inequalities (LMIs) is proposed and demonstrated to the angle-of-attack (AOA) CTCS of hypersonic reentry vehicle (HRV) driven by a hybrid actuator composed of aerosurfaces and reaction control system (RCS). Firstly, the longitudinal nonlinear dynamics model of HRV and the mathematical model of RCS are established, and then the model of the hybrid actuator is described. Secondly, a general command tracking problem is converted to a regulation problem by constructing a deviation system. And the characteristics of the hybrid actuator is considered and modeled definitely based on some modified sector conditions. Then, the CTCS with hybrid actuator is designed by solving a LMIs-based convex optimization problem. Furthermore, the stability performance of the closed-loop CTCS is evaluated and the formulation of the domain of attraction is derived. And the relationship between the size of stability domain and the magnitude of reference command is also discussed. Finally, the proposed approach is applied to the AOA-CTCS of HRV driven by aerosurfaces and RCS, and different sizes and locations of the stability regions are illustrated with different magnitudes of AOA reference command. Validation simulations are carried out by using the longitudinal nonlinear dynamics models of HRV. The research results demonstrate that the proposed LMIs-based approach is well suited for the AOA-CTCS design for HRV driven by aerosurfaces and RCS.

Fluorescence Imaging of Reaction Control Jets and Backshell Aeroheating of Orion Capsule

Planar laser-induced fluorescence of nitric oxide was used to visualize the interaction of reaction control system jet flows on the afterbody of a hypersonic capsule reentry vehicle at the Calspan-University at Buffalo Research Center’s Large Energy National Shock Tunnel I reflected shock tunnel facility. The interaction of pitch and roll jets with the flowfield was investigated. Additionally, thin-film sensors were used to monitor heat transfer on the surface of the model to detect localized heating resulting from the firing of the reaction control system jets. Visualizations of the capsule shear layer using both planar laser-induced fluorescence and schlieren imaging compared favorably. The structure of the roll jet was found to be significantly altered due to interactions with the flowfield. Additionally, the presence of the roll jet appeared to change the nature of the shear layer from steady laminar to unsteady. The pitch jet structure was only disturbed in the far field. Comparison of the planar laser-induced fluorescence jet-fluid visualizations and the surface heat flux distributions indicate that the regions of enhanced aeroheating are not caused by the jet fluid itself impinging on the surface, but rather by the presence of jet-induced horseshoe vortices and shock wave/boundary-layer interactions.

Assessment of Real Gas Effects on Approximate and Boundary Layer Equations for Hypersonic Laminar Flow over Axisymmetric Bodies

Two efficient computational procedures based on the boundary layer equations and approximate relations areassessedin prediction of the laminar hypersonic flowfield for both the perfect gas and equilibrium air around the axisymmetric blunt body configurations. For the boundary layer procedure, the boundary layer equationsutilize the integral matrix solution algorithm for the blunt nose and after body region by using a space marching technique. The integral matrix procedure able us to create accurate and smooth results using the minimum grid in the boundary layer and minimize the computational costs. Applying the approximate method creates a robust and efficient code for heating calculations over the blunt bodies which flies in hypersonic regimes. These algorithms are highly appropriate to design of hypersonic reentry vehicles. The effects of real gas on the flowfield characteristics are also studied in two procedures.