Mars Atmospheric Entry Research Articles

Path and control-constrained longitudinal guidance for Mars entry

This paper proposes a novel longitudinal reference trajectory tracking guidance framework for Mars atmospheric entry. Unlike traditional methods that require strict adherence to pre-defined safe trajectories, this guidance framework incorporates path constraints into the closed-loop tracking process to ensure safety. The framework comprises a safety module and a guidance law module. The safety module employs an online path constraints management algorithm that converts real-time path constraints into equivalent control constraints and applies them to the guidance module. The guidance law module uses the anti-saturation generalized super-twisting based sliding mode (ASGSTSM) guidance law, which provides sufficient rapidity and robustness to achieve trajectory tracking while accounting for uncertainties and control saturation. Simulation results demonstrate that the proposed guidance framework effectively ensures compliance of the entry vehicle with path constraints. The ASGSTSM guidance law exhibits notable speed and robustness, making it adaptable within the guidance framework. Particularly, in Monte Carlo simulations introducing significant uncertainty, incorporating the ASGSTSM guidance law within the guidance framework resulted in convergence in all trajectory tracking processes, whereas guidance laws in the control group led to numerous failures. Additionally, the paper offers practical principles for designing guidance laws within this universal framework. This facilitates future research to easily replace the guidance law module based on specific mission requirements.

A comparative study of entry guidance for Mars robotic and human landing missions

Human desire to explore Mars has persisted throughout history, and especially, it is required to achieve precise and safe landings on the Martian surface. The atmospheric entry phase plays a crucial role in ensuring mission success, and active research on entry guidance methods continues. This paper presents a comparative study between the two primary types of entry guidance methods: (1) path planning-tracking and (2) predictor–corrector methods by applying them to solve two distinct Mars atmospheric entry guidance problems: (a) robotic entry and (b) human entry missions. Optimization approaches are adopted for the path planning-tracking method. After generating an optimal reference trajectory based on a mission concept-defined cost function, the receding horizon control method is employed to minimize tracking errors. In the predictor–corrector method, two parameterized entry guidance approaches are explored and analyzed. A well-known numerical predictor–corrector method that utilizes a parameterized bank angle profile for entry trajectory generation is tested to demonstrate its robustness against random dispersions. On the other hand, another predictor–corrector type guidance method that assumes a polynomial shape to shape an altitude profile over range-to-go is adopted to show its range control capability. Numerical simulations reveal the pros and cons of each type of entry guidance method, and a suitable guidance method for each Mars entry mission is identified depending on the mission concept and requirements. The analysis results provide future work.

Simulations of Dusty Flows over Full-Scale Capsule During Martian Entry

Suspended dust particles can have adverse effects on heat shields during Mars atmospheric entry. For instance, they can increase both surface heating and surface recession. Current studies on this subject often make many simplifications, focus on a specific physical process, or include flow conditions different from those on Mars. To address this, we perform computational fluid dynamics simulations of hypersonic dusty flows over a full-scale entry capsule based on a realistic flight trajectory. The simulations are performed with an Euler–Lagrange methodology in which the carrier gas solution is obtained with a discontinuous Galerkin method. We employ a recently developed physics-based drag correlation that obtains better agreement with experimental data than popular existing correlations. To improve understanding of the relevant physical processes, which are still not very well understood, the effects of various factors, such as particle size distribution, angle of attack, and two-way coupling, on dust-induced heating augmentation and erosion are assessed.

Mixed uncertainty quantification for terminal flight state of Mars atmospheric entry

China's Tianwen-1 successfully touched down on the surface of the red planet, even though various mixed uncertainties occurred in flight dynamics during Mars atmospheric entry, especially Gaussian mixed uniform uncertainty in the initial state and dynamics parameters. A hybrid algorithm combining sensitivity collocation with nonintrusive polynomial chaos was proposed in this paper. Mixed uncertainty was quantified to reveal the mechanism causing location deviation during parachute deployment from the preplanned point. First, Mars atmospheric entry dynamics containing uncertainty were modeled as stochastic nonlinear dynamics. Second, stochastic variables were approximated using nonintrusive polynomial chaos, and sensitivity collocation was used to characterize state variables under the influence of uncertainty. Finally, the probabilistic distribution of the parachute deployment state was analytically obtained according to the initial and parametric uncertainties at the entry interface. Comparison simulations verified the effectiveness of the proposed technique. Gaussian-uniform mixed uncertainty features from the entry interface to the beginning of parachute deployment were revealed.

Mars Atmospheric Entry Guidance using MPSP with State and Control Constraints

An optimal Mars entry guidance scheme is presented in this paper using the Model Predictive Static Programming (MPSP) technique accounting for the applicable state and control constraints. The guidance scheme is designed to maximize the terminal parachute deployment altitude while applying minimum control effort and satisfying hard constraints on desired terminal conditions such as final velocity and downrange. The proposed guidance computes the optimal bank angle profile to shape the trajectory of the spacecraft. Path constraints on heat rate, dynamic pressure, aerodynamic load, and bounds on bank angle are considered to guide the vehicle safely through the martian atmosphere. Moreover, in order to generate practically realizable bank angle profiles, an additional constraint on the bank angle rate is also applied. Next, using the MPSP technique, the nonlinear constrained optimal control problem is converted into a static quadratic optimization problem with linear equality and inequality constraints to solve it in a computationally efficient manner. The concept of flexible final time MPSP is incorporated to update the final time in an optimal fashion. Numerical simulations illustrate the ability of the proposed method to solve the guidance problem efficiently while satisfying the path and terminal constraints within the desired accuracy.

Nonequilibrium Vibrational, Rotational, and Translational Thermometry via Megahertz Laser Absorption of CO

A mid-infrared laser absorption strategy for simultaneously measuring translational, rotational, and vibrational temperatures of carbon monoxide (CO) at high speeds was developed for application to high-temperature nonequilibrium environments relevant to Mars atmosphere entry. Rapid-tuning scanned wavelength techniques were used to spectrally resolve the R(0,66), P(0,31), P(2,20), and P(3,14) lines of the CO fundamental vibrational bands at a rate of 1 MHz to infer multiple temperatures of CO behind incident and reflected shock waves in a shock tube. A distributed feedback quantum cascade laser was used to probe the P-branch transitions near and an external cavity quantum cascade laser was used to probe the R-branch transition near , both using bias-tee circuitry. The sensing method is shown to resolve each targeted transition with temporal and spectral resolution sufficient for quantitative multi-temperature measurements over a wide range of temperatures and pressures (2100–5500 K, 0.03–1.02 atm), including behind incident shock waves traveling up to 3.3 km/s. Measured temperature results were compared to equilibrium and nonequilibrium simulations.

High-dimensional uncertainty quantification for Mars atmospheric entry using adaptive generalized polynomial chaos

The probabilistic uncertainties in Mars atmospheric entry degrade the entry guidance performance. The propagation law of high-dimensional uncertainty during Mars atmospheric entry is still an open problem that should be investigated. The current work aims to examine the uncertainty propagation during Mars atmospheric entry due to uncertain initial state and model parameters, with introducing the generalized polynomial chaos method into Mars atmospheric entry dynamics simulations. For more efficient and accurate, generalized polynomial chaos is modified through spectral decomposition and random space decomposition. First, stochastic dynamics are modeled and transformed into equivalent deterministic dynamics in a higher-dimensional space and are updated adaptively when the statistic characteristic of the system state changes greatly. Second, the random space is decomposed when the relative error in variance becomes larger than the predefined threshold. In each random sub-domain, the updated generalized polynomial chaos is employed. Finally, the adaptive generalized polynomial chaos is used to quantify the uncertainty propagation in Mars atmospheric entry dynamics. Comparison studies are also performed with traditional generalized polynomial chaos and Monte-Carlo simulations. The influence levels and the evolution profiles of the initial and parametric uncertainties are revealed through numerical simulations.

Barrier Lyapunov function based sliding mode control for Mars atmospheric entry trajectory tracking with input saturation constraint

The nature of the bank angle modulation technique based on the low lift-to-drag aerodynamic configuration of the entry vehicle inevitably introduces the problem of input saturation, which would lead to unexpected tracking performance degradation. To this end, a barrier Lyapunov function (BLF) based sliding mode control is proposed for the Mars atmospheric entry trajectory tracking in this paper. A variable gain super-twisting (VGST) based terminal sliding mode controller is firstly presented. By introducing a novel logarithm-type BLF, the proposed terminal sliding mode controller is proved stable with bounded convergence time in the presence of input saturation and external disturbance. Then, based on the numerical predictor–corrector strategy, the variable gain of terminal sliding mode controller is adjusted onboard to satisfy the constraint of input saturation. The Mars Science Laboratory Mission based atmospheric entry scenario is utilized in the numerical simulation to verify the proposed trajectory tracking method, demonstrating the effectiveness of method of BLF based terminal sliding mode controller design.

A Simple and Accurate Apollo-Trained Neural Network Controller for Mars Atmospheric Entry

We present a new method to design the controller for Mars capsule atmospheric entry using deep neural networks and flight-proven Apollo entry data. The controller is trained to modulate the bank angle with data from the Apollo entry simulations. The neural network controller reproduces the classical Apollo results over a variation of entry state initial conditions. Compared to the Apollo controller as a baseline, the present approach achieves the same level of accuracy for both linear and nonlinear entry dynamics. The Apollo-trained controller is then applied to Mars entry missions. As in Earth environment, the controller achieves the desired level of accuracy for Mars missions using both linear and nonlinear entry dynamics with higher uncertainties in the entry states and the atmospheric density. The deep neural network is only trained with data from Apollo reentry simulation in an Earth model and works in both Earth and Mars environments. It achieves the desired landing accuracy for a Mars capsule. This method works with both linear and nonlinear integration and can generate the bank angle commands in real-time without a prestored trajectory.

CDSDv: A compact database for the modeling of high-temperature [formula omitted] radiation

The Carbon Dioxide Spectral Databank 4000 is tailored for radiative transfer applications relevant for Mars atmospheric entry studies. This is carried out through the refitting of the original database, encompassing individual rovibrational transitions, into a more compact form where rotational transitions for specific vibrational bands are obtained through traditional polynomial expressions, fitted to the levels and transitions of the original database. This originates a certain loss of precision since the fitted expressions do not always reproduce the original data with full accuracy, namely for the perturbed transitions. This is offset by a more compact database suited for wideband radiative transfer simulations. This CDSDv database also provides some minor advantages, such as enabling the thermodynamic use of two-temperature (T, Tv) models and the determination of vibrational Einstein coefficients Av′v″ which may be used in state-to-state kinetic models.

Novel Approach for Mars Entry Blackout Elimination Based on X-Ray Communication

An approach is presented for eliminating communication blackout caused by the plasma sheath encountered during the Mars atmospheric entry phase. On the basis of the high penetration of X-ray beams, the expectation was to avoid communication interruptions by establishing an X-ray communication link between the Mars orbiter and the entry vehicle. In this study, the plasma penetration performance of X-rays is evaluated based on the numerical method. The transmission properties of an X-ray beam in the Martian atmosphere were assessed based on the Monte Carlo simulation. The performance of X-ray communication links in the blackout region is evaluated, and the minimum transmitting power required for low bit-error-rate communication is obtained. The results show that an X-ray beam can not only pass through the plasma sheath generated during the atmospheric entry phase without attenuation but also penetrate the atmosphere and establish a stable communication link between a Mars orbiter and the entry vehicle.

Analysis of the JAXA Nonequilibrium Infrared Emission Spectra for Mars Entry Conditions

Nonequilibrium infrared emission spectra representative of a Mars atmospheric entry mission are modeled using RADIS, a spectral code for CO and based on the HITEMP-2010 and CDSD-4000 databases. The modeled experimental data for the free-flow and the forebody radiation were obtained in the JAXA expansion tube facility. In the expanding flow, good agreement with the experimental data can be obtained using a slightly nonequilibrium distribution and a homogeneous flow. The model suggests that all three vibration modes share a same vibrational temperature slightly higher than the gas temperature. In the shock layer, the forebody radiation includes both and CO emission features. It can be correctly predicted by assuming thermal and chemical equilibrium at .

Mars entry trajectory planning using robust optimization and uncertainty quantification

Due to the existence of obvious uncertainties within Mars atmospheric entry, design and analysis of the optimal trajectory under uncertainties play a significant role in reducing flight risk and maintaining guidance performance and delivery accuracy. In this paper, using robust optimization strategy and uncertainty quantification technique, we developed an innovative approach for planning the Mars entry trajectory under uncertainties. The main contribution of this work is twofold: one is considering both dynamics parameter uncertainty and initial state uncertainty, and the other is simultaneously focusing on the reliability of constraint satisfaction and insensitivity of performance index towards uncertainties. First, Mars entry trajectory planning problem under uncertainties is formulated as a robust optimization problem. Second, the uncertainty propagation with regard to Mars entry dynamics is derived, and the quantification of objective function and constraints under uncertainties is conducted. Third, the robust trajectory optimization problem is transformed into an equivalent optimal control problem in the expanded higher-dimensional state space by polynomial chaos expansion, and the solution is obtained by the hp-adaptive pseudospectral method. Finally, the effectiveness of the proposed method is verified through two Mars entry optimal trajectory cases. And the obtained optimal trajectories are reliable and evidently robust to uncertainties compared to traditional deterministic optimization and reliability-based optimization.

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.

Integrated guidance for Mars entry and powered descent using reinforcement learning and pseudospectral method

Traditional studies on Mars entry, descent, and landing usually take a divide-and-conquer approach where each phase is investigated separately. This paper proposed a new approach to achieve optimal integrated guidance for mid-lift high-mass Mars entry and powered descent. First, optimal Mars atmospheric entry and optimal powered descent are respectively modeled. Second, optimal handover problem is formulated to integrate the optimal Mars entry and powered descent problems in a collaborative optimization manner. Third, hp-adaptive pseudospectral method is employed to capture optimal entry guidance and propellant-optimal powered descent guidance. Reinforcement learning methodology is adopted to obtain the optimal handover, according to a large amount of trial results obtained from solving optimal Mars entry and powered descent problems. Finally, numerical simulations verified the optimality, robustness, and accuracy of the proposed technique through comparing with successive convexification approach under the nominal conditions and uncertainties, and the comparison results demonstrated the significant benefit of the integrated optimal guidance.

Mars atmospheric entry guidance for optimal terminal altitude

Maximizing the terminal altitude for Mars atmospheric entry has long been investigated on trajectory design to allow a sufficient timeline margin for subsequent operations and the scientific requirements of exploring Mars ancient highland. The purpose of this paper is to design an onboard Mars atmospheric entry guidance algorithm, which can achieve the optimal terminal altitude at the predetermined terminal flight range. Two important characters that the optimal bank angle profile are revealed in this paper, offering the gateway to the application of the optimal guidance by onboard parameter searching, which will be accomplished by the numerical predictor-corrector strategy. Moreover, suboptimal situations are also investigated considering the performance restriction of reactive control system (RCS). Effectiveness of the proposed guidance algorithm is demonstrated using scenarios of the Mars Science Laboratory (MSL) mission.

Disturbance observer based model predictive control for accurate atmospheric entry of spacecraft

Facing the complex aerodynamic environment of Mars atmosphere, a composite atmospheric entry trajectory tracking strategy is investigated in this paper. External disturbances, initial states uncertainties and aerodynamic parameters uncertainties are the main problems. The composite strategy is designed to solve these problems and improve the accuracy of Mars atmospheric entry. This strategy includes a model predictive control for optimized trajectory tracking performance, as well as a disturbance observer based feedforward compensation for external disturbances and uncertainties attenuation. 500-run Monte Carlo simulations show that the proposed composite control scheme achieves more precise Mars atmospheric entry (3.8 km parachute deployment point distribution error) than the baseline control scheme (8.4 km) and integral control scheme (5.8 km).

Terminal altitude maximization for Mars entry considering uncertainties

Uncertainties present in the Mars atmospheric entry process may cause state deviations from the nominal designed values, which will lead to unexpected performance degradation if the trajectory is designed merely based on the deterministic dynamic model. In this paper, a linear covariance based entry trajectory optimization method is proposed considering the uncertainties presenting in the initial states and parameters. By extending the elements of the state covariance matrix as augmented states, the statistical behavior of the trajectory is captured to reformulate the performance metrics and path constraints. The optimization problem is solved by the GPOPS-II toolbox in MATLAB environment. Monte Carlo simulations are also conducted to demonstrate the capability of the proposed method. Primary trading performances between the nominal deployment altitude and its dispersion can be observed by modulating the weights on the dispersion penalty, and a compromised result referring to maximizing the 3σ lower bound of the terminal altitude is achieved. The resulting path constraints also show better satisfaction in a disturbed environment compared with the nominal situation.

Multidimensional material response simulations of a full-scale tiled ablative heatshield

The Mars Science Laboratory (MSL) was protected during Mars atmospheric entry by a 4.5 meter diameter heatshield, which was constructed by assembling 113 thermal tiles made of NASA's flagship porous ablative material, Phenolic Impregnated Carbon Ablator (PICA). Analysis and certification of the tiles thickness were based on a one-dimensional model of the PICA response to the entry aerothermal environment. This work provides a detailed three-dimensional heat and mass transfer analysis of the full-scale MSL tiled heatshield. One-dimensional and three-dimensional material response models are compared at different locations of the heatshield. The three-dimensional analysis is made possible by the use of the Porous material Analysis Toolbox based on OpenFOAM (PATO) to simulate the material response. PATO solves the conservation equations of solid mass, gas mass, gas momentum and total energy, using a volume-averaged formulation that includes production of gases from the decomposition of polymeric matrix. Boundary conditions at the heatshield forebody surface were interpolated in time and space from the aerothermal environment computed with the Data Parallel Line Relaxation (DPLR) code at discrete points of the MSL trajectory. A mesh consisting of two million cells was created in Pointwise, and the material response was performed using 840 processors on NASA's Pleiades supercomputer. The present work constitutes the first demonstration of a three-dimensional material response simulation of a full-scale ablative heatshield with tiled interfaces. It is found that three-dimensional effects are pronounced at the heatshield outer flank, where maximum heating and heat loads occur for laminar flows.

Integral design method for simple and small Mars lander system using membrane aeroshell

To execute Mars surface exploration missions, spacecraft need to overcome the difficulties of the Mars entry, descent, and landing (EDL) sequences. Previous landing missions overcame these challenges with complicated systems that could only be executed by organizations with mature technology and abundant financial resources. In this paper, we propose a novel integral design methodology for a small, simple Mars lander that is achievable even by organizations with limited technology and resources such as universities or emerging countries. We aim to design a lander (including its interplanetary cruise stage) whose size and mass are under 1 m3 and 150 kg, respectively. We adopted only two components for Mars EDL process: a “membrane aeroshell” for the Mars atmospheric entry and descent sequence and one additional mechanism for the landing sequence. The landing mechanism was selected from the following three candidates: (1) solid thrusters, (2) aluminum foam, and (3) a vented airbag. We present a reasonable design process, visualize dependencies among parameters, summarize sizing methods for each component, and propose the way to integrate these components into one system. To demonstrate the effectiveness, we applied this methodology to the actual Mars EDL mission led by the National Institute of Information and Communications Technology (NICT) and the University of Tokyo. As a result, an 80 kg class Mars lander with a 1.75 m radius membrane aeroshell and a vented airbag was designed, and the maximum landing shock that the lander will receive was 115 G.