Mars Entry Vehicles Research Articles

Aerodynamic Study of Successful Mars Entry Vehicles

Aerodynamic Study of Successful Mars Entry Vehicles

Prescribed-time tracking control of Mars entry vehicle with output constraints

This paper studies the prescribed-time output-constrained tracking control problems for Mars entry vehicle systems. By using the properties of the time-varying high-gain function and output-constrained conditions, time-varying barrier Lyapunov functions are constructed. Based on such Lyapunov functions, time-varying adaptive controllers are designed to solve the considered problem. It is proved that the proposed controllers can drive the errors converge to zero in a prescribed time under unknown disturbances, and the control signals are bounded. Both the symmetric and asymmetric cases are considered. Finally, the effectiveness of the proposed methods is illustrated by several numerical simulations.

Composite continuous fast nonsingular terminal sliding mode trajectory tracking control for Mars entry vehicle

SummaryThis paper presents a composite continuous fast nonsingular terminal sliding mode (CCFNTSM) trajectory tracking control method for Mars entry vehicle. Firstly, the trajectory tracking is transferred into the tracking of the pre‐designed drag acceleration. Secondly, the finite‐time disturbance observer (FTDO) is introduced to estimate the matched and mismatched disturbances. And then, the dynamical fast nonsingular terminal sliding mode manifold is designed based on the estimation information. Finally, the CCFNTSM controller is constructed and its continuity is guaranteed by employing the power function of sliding variable to replace the constant switching gain. Numerical simulation results validate the effectiveness of the proposed control method.

A Distributionally Robust Fusion Framework for Autonomous Multisensor Spacecraft Navigation during Entry Phase of Mars Entry, Descent, and Landing

A robust multisensor navigation filter design for the entry phase of next-generation Mars entry, descent, and landing (EDL) is presented. The entry phase is the longest and most uncertain portion of a Mars landing sequence. Navigation performance at this stage determines landing precision at the end of the powered descent phase of EDL. In the present work, measurements from a ground-based radio beacon array, an inertial measurement unit (IMU), as well as an array of atmospheric and aerothermal sensors on the body of a Mars entry vehicle are fused using an M-estimation-based iterated extended Kalman filtering (MIEKF) framework. The multisensor approach enables an increased positioning accuracy as well as the estimation of parameters that are otherwise unobservable. Furthermore, owing to the proposed statistically robust filter formulation, states and parameters can be accurately estimated in the presence of non-Gaussian measurement noise. Deviations from normally distributed observation noise correspond to outlier events such as sensor faults or other sources of spurious sensor data such as interference. The proposed framework provides a significant reduction in estimation error at the parachute phase of EDL, thereby increasing the likelihood of a pinpoint landing at a chosen landing site. Six states and three parameters are estimated. The suggested method is compared to the extended Kalman filter (EKF) and the unscented Kalman filter (UKF). Detailed simulation results show that the presented fusion architecture is able to meet future pinpoint planetary landing requirements in realistic sensor measurement scenarios.

Indirect neural-based finite-time integral sliding mode control for trajectory tracking guidance of Mars entry vehicle

This article presents an indirect neural-based finite-time integral sliding mode control algorithm for the reference trajectory tracking guidance of Mars entry vehicle under uncertainties. The proposed controller is developed as a combination of finite-time integral sliding mode controller and indirect neural identification. The finite-time integral sliding mode controller is designed by constructing a new type of finite-time integral sliding mode surface to prevent the singularity problem. Moreover, the neural network (NN) is combined with the finite-time integral sliding mode controller to identify the lumped uncertainty and attenuate the chattering phenomenon. Particularly, the concept of indirect neural identification is adopted and only a single adaptive parameter is required to be learned online. In this way, the proposed controller is not only strongly robust against aerodynamic and density uncertainties, but also computationally simple for onboard implementations. Stability argument indicates that the proposed controller can ensure the radial distance tracking error and its time differentiation regulate to the small residual sets around zero in finite time. Lastly, the effectiveness and excellent guidance performance of the proposed control algorithm are demonstrated through simulation studies on a Mars Science Laboratory-type (MSL-type) entry vehicle.

Tianwen-1 Mars entry vehicle trajectory and atmosphere reconstruction preliminary analysis

The Tianwen-1 Mars entry vehicle successfully landed on the surface of Mars in southern Utopia Planitia on May 15, 2021, at 7:18 (UTC+8). To acquire valuable Martian flight data, a scientific instrumentation package consisting of a flush air data system and a multilayer temperature-sensing system was installed aboard the entry vehicle. A combined approach was applied in the entry, descent, and landing trajectory reconstruction using all available data obtained by the inertial measurement unit and the flush air data system. An aerodynamic database covering the entire flight regime was generated using computational fluid dynamics methods to assist in the reconstruction process. A preliminary analysis of the trajectory reconstruction result, along with the atmosphere reconstruction and aerodynamic performance, was conducted. The results show that the trajectory agrees closely with the nominal trajectory and the wind-relative attitude. Suspected wind occurred at the end of the trajectory.

Relationship between the Actual Entry of Vehicles into the Martian Atmosphere and Its Simulation in a Wind Tunnel Using Mars Entry Vehicles of Various Geometries

Relationship between the Actual Entry of Vehicles into the Martian Atmosphere and Its Simulation in a Wind Tunnel Using Mars Entry Vehicles of Various Geometries

FADS based aerodynamic parameters estimation for mars entry considering fault detection and tolerance

Flush air data system (FADS) is able to sense pressure distribution on the surface of the vehicle's forebody during Mars entry phase. Existing studies on the FADS-based aerodynamics data estimation for Mars entry have not attached adequate attention to the potential FADS fault, which should not be ignored in practice from a reliability viewpoint. In this paper, a hybrid method is proposed to simultaneously achieve aerodynamic parameters estimation of Mars entry vehicle and FADS fault detection and tolerance. The estimation procedure merges triples algorithm based coarse estimation with least-square based precise estimation. Meanwhile, a fault identifier matrix is embedded in the estimation procedure, which is worked out from chi-square detection algorithm. The estimation with FADS fault tolerance is realized by the fusion of chi-square detection, hybrid estimation, and random sample consensus algorithms. Comparison simulations demonstrate the effectiveness of the proposed technique.

Modulation of Aerodynamic Angles for Optimal Mars Descent Trajectory using Indirect Approach

A formulation, based on indirect approach, that uses both the aerodynamic angles: angle of attack and bank angle as control variables and maximizes the parachute deployment altitude of a Mars entry vehicle is presented. The complexity of handling the control variable ‘angle of attack’ in the indirect approach is overcome by expressing the aerodynamics coefficients as a quadratic polynomial of angle of attack. The problem is formulated as a two point boundary value problem using the Pontryagin’s principle of the optimal control theory. The solution is obtained using differential evolution technique, a heuristic optimization technique. This is an alternative formulation to the commonly used direct approach using non-linear programming. The solution procedure based on indirect approach reduces the number of unknowns drastically compared to the direct approach. The benefit of using angle of attack modulation in addition to bank angle modulation is quantified. The implication of constraints on minimum allowable altitude and maximum deceleration on the optimized trajectory is analyzed using the new formulation and the solution approach.

Adaptive fixed-time trajectory tracking control for Mars entry vehicle

This paper develops a fixed-time trajectory tracking control scheme for Mars entry vehicle under uncertainty. First, a novel fixed-time nonsingular terminal sliding mode (FTNTSM) surface with bounded convergence time independent on the initial conditions is developed, which not only averts the singularity problem but also assures fast convergence. Second, based on the FTNTSM surface and adaptive technique, a continuous adaptive fixed-time nonsingular terminal sliding mode control (AFTNTSMC) method is proposed. Under the control scheme, the fixed-time convergence of tracking error is assured, and the chattering phenomenon is alleviated. Furthermore, by estimating the square of upper bound of the uncertainty, the designed AFTNTSMC method averts the use of boundary layer technique as imposed in most existing literature on adaptive fixed-time control. The effectiveness of the developed control approach is confirmed by numerical simulations.

Stagnation-Point Aeroheating Correlations for Mars Entry

This work details the development of new stagnation-point aeroheating engineering correlations for Mars entry vehicles. Convective and radiative heating relations were formulated over a wide range of entry conditions. These relations were based on computational fluid dynamics simulations informed by recent experimental testing and modeling enhancements. For convective heating, a relation similar to those proposed in previous works was developed that is accurate to within across the domain of relevant Mars entry conditions. For radiative heating, two different functional forms were developed: exponential and polynomial relations. Each of these relations, which represents two different levels of complexity for implementation, were able to predict the radiative heating within about . The correlations were tested by applying them to the Mars Pathfinder entry trajectory to demonstrate their applicability. These new correlations provide significant improvement over existing relations in terms of the accuracy, the domain of applicability, and the captured physics, including infrared radiation and thermochemical nonequilibrium.

Radiative Heating on the After-Body of Martian Entry Vehicles

The radiative heat flux imparted on the after-body of vehicles entering the Martian atmosphere is simulated. The radiation is dominated by bands emitting in the midwave infrared. This mechanism traditionally has not been considered in the design of past Mars entry vehicles. However, with recent analysis showing that radiative heating can exceed convective heating on after-body surfaces, and with several upcoming and proposed missions to Mars potentially affected, an investigation of this radiation is warranted. This paper aims to quantify and improve understanding of the impact of radiation to aerothermal heating predictions for Mars entry. The tangent-slab approximation is shown to be overly conservative, by as much as 58%, for most of the backshell compared with using a full angular integration method. However, due to the complexity of the wake flow, it is also shown that tangent slab does not always represent an upper limit for radiative heating. Furthermore, analysis shows that it is not possible to provide a general correction factor to convert tangent-slab results to those obtained using the more rigorous full integration method. Radiative heating on the after-body often exceeds convective heating and therefore must be included in thermal protection system design for future missions.

New Method for Systems and Cost Analysis of Human Mars Entry Vehicles

Cost is one of the biggest obstacles to sending humans to Mars. However, spacecraft costs are typically not estimated until after the preliminary vehicle and mission concepts have been designed. By automating the cost estimation process, the effect of any change in vehicle or mission design on the mission cost can be determined more efficiently. This paper describes an extension to the systems analysis for planetary entry, descent, and landing tool. This extension integrates the cost modeling software SEER-H (which stands for system estimation and evaluation of resources hardware) with a number of systems analysis tools. This new method is used to analyze several tradespaces of a hypersonic inflatable aerodynamic decelerator entry vehicle for human Mars missions. Key findings include quantifying the impacts of the ballistic coefficient, the main engine specific impulse, and the thrust-to-weight ratio on the overall cost of the vehicle; as well as how the payload per lander and the number of landers affect the cost of a campaign to Mars.

Reliable Distributed Integrated Navigation Based on CI during Mars Entry

A reliable distributed covariance intersection (CI) fusion integrated navigation algorithm with information feedback during the Mars atmospheric entry is proposed to meet robust, reliable, and high-precision Mars atmospheric entry navigation strategy. A distributed integrated navigation scheme includes four independent subsystems consisting of an IMU and one radio beacon, but each subsystem is weakly observable under limited Mars entry measurements. The scalar weights are fast obtained by maximizing the information contribution of the corresponding estimate. The distributed framework based upon the CI fusion algorithm is designed by using dynamic information distribution coefficients and information feedback strategy. This distributed fusion approach could meet the lower computation cost and robust and reliable capacity and especially is beneficial to the weakly observable or unobservable subsystems during the Mars entry navigation scheme. Numerical simulations show that the proposed distributed CI fusion integrated navigation algorithm can provide consistent navigation accuracy for the Mars entry vehicle and improve the entry navigation robustness under the weakly observable navigation subsystems.

Mars entry guidance using a semi-analytical method

Future Mars missions may require improved landed accuracy to facilitate the landing site selection and finally access a region of complex terrain with high scientific return. This paper is to develop a novel, robust, and precision entry guidance algorithm for Mars entry vehicles with low lift-to-drag ratios. In the presence of large uncertainties, the entry terminal point controller algorithm can encounter severe performance degradation due to: (1) the small perturbation assumption, and (2) theoretically ignoring deviations in the atmospheric-density model, aerodynamic-force model, etc. Based on numerical technologies and the classical variation method (VM), this work develops a semi-analytical (SA) algorithm, in which combined effects of several dynamic uncertainties now can be addressed. The terminal-downrange error is predicted by a numerical predictor such that the dependence on the reference trajectory can be reduced and then the issue caused by the small perturbation assumption can be addressed. Such a predicted terminal-downrange error is finally corrected by an analytical corrector, which is designed by the VM. It is indicative that there can be no numerical iterations in the SA algorithm. Numerical results demonstrate the effectiveness of the SA algorithm.

Fault tolerant tracking of Mars entry vehicles via fuzzy control approach

In this paper, a fault tolerant attitude tracking control scheme is proposed for Mars entry vehicles (MEVs) with disturbances and actuator failures. The original attitude dynamics of MEVs is divided into two subsystems, named as slow subsystem and fast subsystem, respectively. For slow subsystem, the control-like angular velocity command is generated. For fast subsystem, the Takagi–Sugeno (T-S) fuzzy models are used to describe it at first. Based on these, the partial loss of actuator effectiveness with the generated angular velocity problem is transformed into solving the tracking problem with uncertain parameters. Then, a fault tolerant tracking control scheme is proposed by combining fuzzy line-integral Lyapunov function method with robust H∞ control approach. The proposed controller design is simple and can guarantee the faulty closed-loop system to be stable with acceptable attenuation level. Finally, the effectiveness of the proposed design method is demonstrated in a MEVs attitude control system subject to loss of actuator effectiveness.

H∞ sampled-data fuzzy control for attitude tracking of mars entry vehicles with control constraints

In this paper, the problem of designing an H∞ sampled-data fuzzy controller is investigated for attitude tracking of Mars entry vehicles with control constraints. Initially, to overcome the difficulty of Takagi–Sugeno (T–S) fuzzy modeling, the original nonlinear error system is divided into a fast subsystem and a slow subsystem on the basis of two time-scale decomposition technique, where the fast subsystem describes the attitude dynamics and the slow subsystem describes the attitude kinematics. Dynamic inversion control method is subsequently employed to obtain the angular velocity command for the slow subsystem. Then, based on the angular velocity command and the T–S fuzzy model of the fast subsystem, a tracking error fuzzy system is derived for the sampled-data fuzzy control design. The existence condition of the constrained H∞ sampled-data fuzzy controllers is provided in terms of linear matrix inequalities (LMIs). The proposed controller can exponentially stabilize the original nonlinear error system with an H∞ tracking performance, provided that the timescale separation between the fast and slow subsystems is valid. Finally, simulation results illustrate the effectiveness of the proposed method.

Aerothermal Measurements from the ExoMars Schiaparelli Capsule Entry

The instrumentation package was developed to measure aerothermal parameters on the back cover of the ExoMars Schiaparelli lander during Martian entry. The aerothermal sensors called Combined Aerothermal and Radiometer Sensor (COMARS) combine four discrete sensors, measuring static pressure, total heat flux, temperature, and radiative heat flux. After passing all acceptance tests, the Schiaparelli capsule was launched on top of the Proton launcher on March 14, 2016. All sensors operated nominally during the complete entry phase. But the complete data package is not available due to an anomaly that led to the failure of Schiaparelli shortly before landing. Nevertheless, a subset of the flight data was transmitted real-time during the entry and was received by the ExoMars 2016 orbiter, with the exception of the plasma blackout phase. The radiative heat flux on the back cover close to the vehicle shoulder was measured successfully for the first time on a Mars entry vehicle. The measured maximum radiative contribution was 61% of the total heat flux at the first measurement point after the blackout phase and 33% for the next measured trajectory point 10 s later. These measurements confirm recent findings that radiative heating can be a significant portion of total heating on the back cover during Mars entry. The maximum back cover total heat flux rate was measured at approximately 9% of the calculated stagnation point heat flux on the front cover. All measured heat fluxes on the back cover were below the levels that were used to design the thermal protection system.

Disturbance observer based reliable H∞ fuzzy attitude tracking control for Mars entry vehicles with actuator failures

This paper introduces a disturbance observer (DO) based reliable H∞ fuzzy attitude tracking control design for Mars entry vehicles with actuator failures. Initially, to reduce the complexity of Takagi–Sugeno (T–S) fuzzy modeling, the two time-scale decomposition technique is used to divide the original nonlinear attitude tracking error model of Mars entry vehicles into a slow subsystem describing the attitude kinematics and a fast subsystem describing the attitude dynamics. The dynamic inversion control (DIC) method is subsequently applied to the slow subsystem to generate the angular velocity command. Then, the T–S fuzzy modeling method is employed to exactly represent the fast subsystem and a disturbance observer (DO) is constructed to estimate the modeled disturbance based on the derived tracking error fuzzy system of angular velocity. By the technique of linear matrix inequalities (LMIs), a DO based reliable H∞ fuzzy controller of attitude tracking is developed to stabilize exponentially the angular velocity tracking error and the modeled-disturbance state estimation error with an H∞ tracking performance both in nominal and actuator failure cases. Furthermore, it is shown that the original nonlinear tracking error system is also exponentially stable and satisfies an H∞ tracking performance both in nominal and actuator failure cases under the proposed fuzzy control law together with the DIC law, provided that the timescale separation between the fast and slow subsystems is valid. Finally, simulation results illustrate the effectiveness of the proposed design method.

Influence of surface catalysis on coupled aerodynamic heating for Mars entries

The integral simulation of aerodynamic heating for Mars entries encounters great challenges due to exceptional and complex high-temperature real-gas effect and gas-solid thermochemistry effect. Coupling computation strategy for hypersonic nonequilibrium aerodynamic heating and in-depth heat transfer was established in order to accurately predict the thermal environment of Mars entry vehicles. Coupling analysis for the heatshield of Mars entry vehicle was then performed to reveal the mechanism how the nonequilibrium thermochemistry affects the coupled aerodynamic heating. Computation results show that both the convection and diffusion heatflux from non-equilibrium flow field have large influences on the total aerodynamic heating rate; the diffusion component contributes the foremost to the overall aerodynamic heating, especially for that originating from CO2; the current thermal protection structure can effectively prevent the severe thermal load from transferring into the cabin, and the aerodynamic heating and the surface radiation can rapidly get close to thermal equilibrium, accounting for the validation of the radiation equilibrium assumption for uncoupled aerodynamic heating prediction; the heatflux decreases for non- and fully catalytic walls while the finite-rate catalytic heating rises and then drops due to the gas-solid interface thermochemistry effect; the linearity between the surface heatflux and temperature will get weak due to the introduction of diffusion heating induced by the gas-solid interface thermochemistry.