Planetary Entry Research Articles

Thermodynamic behavior of high-power inductively coupled plasma quartz tube wall

High-power inductively coupled plasmas are commonly used in planetary entry simulations and are increasingly being used in electric propulsion applications. However, during the operation of the system, the walls of the quartz tube will crack and melt. Its thermodynamic behavior is key to ensuring the safe and reliable operation of the system, which is directly related to the distribution of thermal energy within the discharge volume. In this paper, the temperature and stress distribution of the quartz tube wall of an inductively coupled plasma generator at 27 kW–85 kW are described. A numerical simulation model was established to depict the interaction between the plasma and the quartz tube wall. In the field of experimental research, the temperature of the outer wall of the quartz tube was obtained by using a thermal imager, and a non-uniform B-spline difference method was proposed to fit the outer wall temperature of the quartz tube to eliminate the influence of the induction coil. It is found that the numerical simulation and experimental results show that the temperature is stable region, temperature rise area, temperature drop zone, and the high temperature region of the quartz tube wall is located in the coil area, and the high stress area is also located in this region. On this basis, the outer wall temperature and thermal stress of quartz tubes under different heat fluxes are studied. When the heat flux exceeds 18.6 kW/m2, the stresses in the coil area and downstream of the coil exceed the limit stress. Mechanical failures may occur in areas where the ultimate stresses are exceeded, and these results can provide theoretical data for the optimal design of high-power inductively coupled plasma generators.

A Conceptual Modeling Approach for Performance of Magnetohydrodynamic Drag During Planetary Entry

Future higher-mass Mars missions present numerous engineering challenges and will require significant technological development, particularly of the entry, descent, and landing systems. One such development concept utilizes magnetohydrodynamic interaction with the plasma created during hypersonic planetary entry for energy generation, drag augmentation, and heat-flux mitigation. In this study, a performance estimation methodology for magnetohydrodynamic drag augmentation during Mars entry compatible with conceptual design is developed. A demonstrative investigation utilizing the developed methodology is then conducted, and simulated trajectory results are presented for various entry vehicles and magnetic field strengths. The study results show potential for significant magnetohydrodynamic drag augmentation during hypersonic entry at Mars, with calculated effective ballistic coefficient- reduction factors of up to 4, across entry vehicles ranging in mass from 70 MT to 4 MT. These results show that magnetohydrodynamic drag augmentation can have comparable impact to significant aeroshell diameter increases and also suggest that it could prove an effective form of drag-augmentation control authority by varying the applied magnetic field.

Carbon Monoxide Dissociation at Planetary Entry Conditions Examined by Megahertz-Rate Laser Spectroscopy

A study of carbon monoxide (CO) dissociation was performed in a shock tube at conditions relevant to the high-speed entry of Venus and Mars atmospheres. The CO number density (or mole fraction) and the temperature are probed behind reflected shock waves at 1 MHz using scanned-wavelength laser absorption spectroscopy near 2011 cm−1 (4.97 μm). The wide range of vibrational states (v=1, 4, 8, and 10) probed by this technique enables precise number density and temperature measurements up to and above 9000 K using a Boltzmann population fit of the resolved spectral lines. Mixtures of CO diluted in Ar at 3–60% are shock-heated in a wide range of conditions (T5=4650−11,150 K at p5=0.26–4.07 atm) and compared to state-of-the-art chemical kinetic models. The time-resolved measurements of temperature and number density behind reflected shock waves are utilized to infer the rate coefficients of CO+M→C+O+M for M=CO, Ar. They are found to be kdiss,CO=1.8×1028⋅T−2.7exp(−129,000/T) cm3/(mol⋅s) and kdiss,Ar=1.5×1025⋅T−2.1exp(−129,000/T) cm3/(mol⋅s).

Experimental validation of rotating detonation for rocket propulsion

Space travel requires high-powered, efficient rocket propulsion systems for controllable launch vehicles and safe planetary entry. Interplanetary travel will rely on energy-dense propellants to produce thrust via combustion as the heat generation process to convert chemical to thermal energy. In propulsion devices, combustion can occur through deflagration or detonation, each having vastly different characteristics. Deflagration is subsonic burning at effectively constant pressure and is the main means of thermal energy generation in modern rockets. Alternatively, detonation is a supersonic combustion-driven shock offering several advantages. Detonations entail compact heat release zones at elevated local pressure and temperature. Specifically, rotating detonation rocket engines (RDREs) use detonation as the primary means of energy conversion, producing more useful available work compared to equivalent deflagration-based devices; detonation-based combustion is poised to radically improve rocket performance compared to today’s constant pressure engines, producing up to 10% increased thrust. This new propulsion cycle will also reduce thruster size and/or weight, lower injection pressures, and are less susceptible to engine-damaging acoustic instabilities. Here we present a collective effort to benchmark performance and standardize operability of rotating detonation rocket engines to develop the RDRE technology readiness level towards a flight demonstration. Key detonation physics unique to RDREs, driving consistency and control of chamber dynamics across the engine operating envelope, are identified and addressed to drive down the variability and stochasticity observed in previous studies. This effort demonstrates an RDRE operating consistently across multiple facilities, validating this technology’s performance as the foundation of RDRE architecture for future aerospace applications.

Aero-Thermal Analysis of Rarefied Flow Over Inverse Cone Shaped Objects Using Direct Simulation Monte Carlo Analysis

Abstract When an object undergoes atmospheric entry, it experiences drag and heat load over its surface which determines its trajectory and ability to survive the hostile flow conditions. This work performs numerical analysis using direct simulation Monte Carlo (DSMC) simulations to study key flow features and properties on a cone-shaped body. The cone is created by varying the angle of extrusion (α) of the flat-nosed face of a cylinder in positive and negative directions. Detailed analysis of the key flow features is conducted, and the results of the distribution of surface heat transfer and drag coefficient on each of the negative α are contrasted against the results obtained for zero and positive α for which compressible flow physics are well defined. For α≤45 deg, heat flux increases with an increase in α, while the total drag experienced by the body decreases. Meanwhile, when α is increased in the negative direction, an inverse cone is formed, which creates a cavity inside the body, and the body decelerates more with an increasing magnitude of α. In contrast, the wall heat flux inside the cone remains quite low. These conditions allow the body to maintain a significantly low temperature during high-speed flow, like in the case of planetary entry, in comparison with the high temperature resulting in α≤0 deg cases. The present study also helps to improve the understanding of optimum cone-shaped space objects from the perspective of drag and heat flux.

Numerical Investigation of Film Coefficient Approximation for Chemically Reacting Boundary-Layer Flows

Aerothermal analysis of spacecraft planetary entry is heavily dependent on heritage engineering models. The film coefficient heat transfer model examined in this paper estimates the convective heating to the vehicle for a laminar, dissociated, chemically reacting boundary layer for an Earth atmosphere. This model requires information about the vehicle and flowfield for a given trajectory point and estimates a proportional relationship between enthalpy potential and convective heat flux. In practice it is the aerothermal engineer who must decide which assumptions are appropriate for his/her application. This work looks at numerous CFD simulations for an arbitrary, axisymmetric flight vehicle to analyze the relative importance of both the mass and energy constraints imposed at the wall boundary, as well as the effect of various diffusion models. Within the subset of tested energy boundary conditions, it is found that the most desirable energy boundary condition is the radiative equilibrium boundary condition, which permits conservative estimates of convective heat flux, but also generates flowfield-dependent spatial thermal distributions along the surface. Other key findings are presented in an effort to make the film coefficient engineering model readily available to design engineers across industry.

Multiple-Sliding-Surface Guidance and Control for Terminal Atmospheric Reentry and Precise Landing

The development of an effective guidance and attitude control architecture for terminal descent and landing represents a crucial issue for the design of reusable vehicles capable of performing a safe atmospheric planetary entry. The sliding mode control represents a nonlinear technique able to generate an effective real-time closed-loop guidance law, even in the presence of challenging contingencies. This work proposes a multiple sliding-surface guidance control law that is able to drive a lifting vehicle toward safe landing conditions, associated with a desired downrange, crossrange, runway heading, and final vertical velocity at touchdown, even starting from challenging initial conditions. The time derivatives of the lift coefficient and the bank angle are used as the control inputs, whereas the sliding surfaces are defined so that these two inputs are involved simultaneously in the lateral and the vertical guidance. The commanded attitude is pursued by the attitude control system, which employs a feedback nonlinear control law that enjoys quasi-global stability properties. Effectiveness and accuracy of the guidance and control strategy at hand are proven numerically by means of a Monte Carlo campaign, in the presence of stochastic wind and large dispersions on the initial conditions.

Microstructure of pyrolyzing RTV silicone

This works discusses the high temperature decomposition of Room Temperature Vulcanized (RTV) silicone, an adhesive material used as a gap filler in ablative heatshield for planetary atmospheric entry, and in fire-protection applications. The high temperature behavior of RTV is characterized by intumescence, shrinkage, foaming and formation of a glassy char. In heatshield applications, these phenomena lead to a mismatch between the ablative response of RTV and that of carbon-phenolic tiles, posing numerous design challenges such as tile layout selection, installation of heatshield sensors, prediction of laminar-to-turbulence transition and assessment of heatshield robustness. The ablation response of RTV is not modeled in current design tools because of the lack of data on its high temperature behavior. In this paper, thermogravimetric analysis was conducted to quantify the mass-loss of RTV during pyrolysis, as a function of heating rate. Samples were imaged using environmental scanning electron microscopy at high temperature to observe the microstructural evolution of RTV during charring. Helium pycnometry, mercury intrusion porosimetry and nitrogen adsorption techniques, combined with micro-tomography imaging, were used to quantify the pore size distribution and porosity of charred RTV. Results show that the porosity of charred RTV is about 82% and that the predominant pore sizes are 2, 23, 39 and 98 microns. The net volumetric swelling due to pyrolysis of the material was found to be 10% when heated to 1000 °C. Physical phenomena occurring during high temperature decomposition are discussed based on the experimental observations.

High-speed mid-infrared laser absorption spectroscopy of CO_2 for shock-induced thermal non-equilibrium studies of planetary entry

A high-speed laser absorption technique is employed to resolve spectral transitions of CO_2 in the mid-infrared at MHz rates to infer non-equilibrium populations/temperatures of translation, rotation and vibration in shock-heated CO_2 - Ar mixtures. An interband cascade laser (DFB-ICL) resolves 4 transitions within the CO_2 asymmetric stretch fundamental bands (Delta v_3 = 1) near 4.19 upmu hbox {m}. The sensor probes a wide range of rotational energies as well as two vibrational states (00^00 and 01^10). The sensor is demonstrated on the UCLA high enthalpy shock tube, targeting temperatures between 1250 and 3100 K and sub-atmospheric pressures (up to 0.2 atm). The sensor is sensitive to multiple temperatures over a wide range of conditions relevant to Mars entry radiation. Vibrational relaxation times are resolved and compared to existing models of thermal non-equilibrium. Select conditions highlight the shortcomings of modeling CO_2 non-equilibrium with a single vibrational temperature.

Improving Rule Mining for Entry, Descent, and Landing Simulations Using Knowledge Graphs

Designing planetary entry, descent, and landing (EDL) systems requires analyzing large datasets containing tens of thousands of parameters. These datasets are generally manually analyzed by subject-matter experts trying to find interesting correlations and couplings between parameters that explain the behaviors observed. A popular approach to automate the extraction of explanation rules is association rule mining, in which rules with high statistical strength are mined from the dataset. However, current rule mining algorithms generate too many rules that are redundant, too complex, too obvious, or do not make sense to the user. In this paper, we propose a new approach to improve the comprehensibility, insightfulness, and usefulness of the association rules generated during the analysis of an EDL dataset by leveraging a user-provided knowledge graph. The knowledge graph captures the user knowledge about EDL and the specific problem at hand. We then use a statistical relational learning framework based on probabilistic soft logic to assess the degree of consistency of the rule with the user’s knowledge of the system. The method is validated in a small study with subject-matter experts. The results of the study also show interesting relationships between comprehensibility, usefulness, and insightfulness of the extracted rules.

Magnetohydrodynamic Experiments of Total Heat Flux Mitigation for Superorbital Earth Reentry

A set of experiments was conducted with the aim of evaluating total heat flux mitigation using magnetohydrodynamic flow control over ionized shock layers surrounding planetary entry vehicles. The University of Queensland’s X2 expansion tube was used to generate a flow condition representative of a Mars return trajectory. Spherical permanent magnets were fitted into a scaled test model based on NASA’s Stardust capsule. Thermocouples located at the stagnation point and shoulder of the test model, as well as thin-film heat transfer gauges located in the aft section, measured total heat flux for both magnetic and nonmagnetic experiments. High-speed imaging of the shock layer showed a significant increase in shock standoff when using the magnet, and polynomial fits were derived, describing standoff distance along the model’s forebody. Despite significant noise affecting the heat flux gauges signals for the magnetic experiments, a simple methodology allowed to compare heat flux during the useful test time. It was found that the applied magnetic field significantly reduces total heat flux at the stagnation point and shoulder of the test model, although heat flux to the aft section was found to significantly increase. Reasonable agreement with the numerical predictions was found for the aft section of the test model, but discrepancies were observed at the other locations.

Introduction to the Innovative Methods, Instruments, and Materials for Planetary Entry Virtual Collection

Introduction to the Innovative Methods, Instruments, and Materials for Planetary Entry Virtual Collection

Variable-Fidelity Euler–Lagrange Framework for Simulating Particle-Laden High-Speed Flows

The current work presents a simulation framework for modeling high-speed flows with suspended solid particles using the point-particle discrete element method. The dispersed particle phase is treated in a Lagrangian manner, whereas the dynamics of the surrounding carrier fluid are determined by solving the compressible Navier–Stokes equations in the Eulerian frame. Additionally, a variable fidelity paradigm is adopted with the ability to model one-, two-, and four-way coupling between the dispersed and carrier phases depending on the desired levels of physical realism. Particle mesh-localization is performed using mesh-connectivity information, which also simplifies boundary conditions enforcement, parallelization, and the backcoupling of particle-induced source terms to the carrier fluid. A time-driven hard-sphere approach is employed to accelerate calculations for particle–particle collisions. The particle solution methodology in conjunction with the unstructured, finite-volume US3D flow solver is used to simulate a variety of multiphase flows. These include a series of verification tests and the first-of-its-kind numerical investigation into elevated levels of surface heat flux experienced by the Mars 2020 spacecraft if planetary entry through the Martian atmosphere were to occur during a major dust storm.

Hypervelocity Spherically-Blunted Cone Flows in Mars Entry Ground Testing

Bow-shock standoff distances over sphere and spherically-blunted cone geometries were examined through experiments in two facilities capable of high-stagnation enthalpy hypersonic flows simulating Mars planetary entry conditions. High-speed and high-resolution schlieren images were obtained in the California Institute of Technology T5 reflected shock tunnel and the Hypervelocity Expansion Tube to examine facility independence of the measurements. Accompanying reacting Navier–Stokes simulations were carried out. A recently developed unified model for sphere and sphere–cone behavior was first verified for high-stagnation enthalpy flows through simulations with thermal and chemical nonequilibrium. Shock standoff distance measurements in both facilities were found to be in good agreement with model predictions. The need to account for the divergence of the streamlines in conical nozzles was highlighted and an existing model extended to account for changes in shock curvature between parallel and conical flows. The contributions of vibrational and chemical nonequilibrium to the stagnation-line density profile were quantified using the simulation results comparing three chemical kinetic models.

Expansion Tube Experiments of Magnetohydrodynamic Aerobraking for Superorbital Earth Reentry

A set of magnetohydrodynamic (MHD) aerobraking experiments was conducted with the aim of simulating the Earth reentry environment for Mars return trajectories, and to study the effects of MHD flow control on the ionizing shock layer surrounding a planetary entry vehicle. The X2 expansion tube of the University of Queensland was used, which could provide realistic flowfield boundary conditions, where ionization is spontaneously generated within the shock layer as in true flight and the freestream is nonconducting. Suitable flow conditions providing strong MHD interaction at superorbital Earth reentry velocities were developed. Steel ball and neodymium permanent magnet models were tested, both uncoated and coated with electrically insulating high-temperature epoxy. Shock-layer high-speed imaging showed a significant increase in shock standoff distance for the magnetic models. The experimental shock standoff results generally agreed well with analytical and numerical shock standoff predictions. These experiments demonstrate that a strong MHD interaction can be generated for a Mars return trajectory with moderate magnetic field strengths. Furthermore, they provide a promising framework for future MHD aerobraking experiments to investigate MHD drag force and heat-flux mitigation.

Evolutionary Processes Transpiring in the Stages of Lithopanspermia.

Lithopanspermia is a theory proposing a natural exchange of organisms between solar system bodies as a result of asteroidal or cometary impactors. Research has examined not only the physics of the stages themselves but also the survival probabilities for life in each stage. However, although life is the primary factor of interest in lithopanspermia, this life is mainly treated as a passive cargo. Life, however, does not merely passively receive an onslaught of stress from surroundings; instead, it reacts. Thus, planetary ejection, interplanetary transport, and planetary entry are only the first three factors in the equation. The other factors are the quality, quantity, and evolutionary strategy of the transported organisms. Thus, a reduction in organism quantity in stage 1 might increase organism quality towards a second stress challenge in stage 3. Thus, robustness towards a stressor might in fact be higher in the bacterial population surviving after transport in stage 3 than at the beginning in stage 1. Therefore, the stages of lithopanspermia can themselves facilitate evolutionary processes that enhance the ability of the collected organisms to survive stresses such as pressure and heat shock. Thus, the multiple abiotic pressures that the population encounters through the three stages can potentially lead to very robust bacteria with survival capacities considerably higher than might otherwise be expected. This analysis details an outcome that is possible but probably rare. However, in addition to lithopanspermia, spacecraft mediated panspermia may also exist. The analogous stages in a spacecraft would result in a greater likelihood of increasing the stress tolerance of hitchhiking organisms. Furthermore, missions seeking life elsewhere will frequently be sent to places where the possibility of life as we know it is assumed to exist. Thus, we not only can transport terrestrial organisms to places where they are potentially more likely to survive but also may increase their invasive potential along the way. This analysis highlights further requirements that planetary protection protocols must implement and also provides a framework for analyses of ecological scenarios regarding the transmission of life, natural or artificial, between worlds in a solar system.

Survey of CO2 Radiation Experimental Data in Relation with Planetary Entry

This paper focuses on a survey of experimental data related to radiation into CO2 plasma flows, which are encountered during Mars and Venus entries. The review emphasizes on VUV and IR radiation, since recent experimental efforts has been devoted to these wavelength ranges since they contribute mostly to CO2 plasma radiation. The main objective of the study is to identify the most attractive datasets for future crosscheck comparisons with the results obtained during future test campaigns with ESTHER shock-tube. The survey accounts for the results obtained in shock-tubes, expansion tube and plasma arc-jets for Mars and Venus test campaigns. The experimental results obtained for propulsion related studies have also been considered.

Introduction to the Virtual Collection on Autonomous Guidance, Navigation, and Control for Planetary Entry, Descent, and Landing

Introduction to the Virtual Collection on Autonomous Guidance, Navigation, and Control for Planetary Entry, Descent, and Landing

Semi-analytical and extremal solutions for design and synthesis of powered descent and landing trajectories

Semi-analytical solutions to the optimal control problem for 3-dimensional fuel-efficient planetary landing trajectories with constant exhaust velocity and limited mass-flow rate in a drag-existing central Newtonian field are presented. The first-order optimality conditions reduce the problem to a Hamiltonian canonical system for the design and synthesis of feasible and extremal planetary entry, descent, and landing trajectories. The proposed solutions allow us to describe the state vector and Lagrange multipliers in terms of time and switching function's characteristics to determine the number and sequence of thrust arcs. These solutions can be adjusted for manoeuvres near other celestial bodies for which a central gravitational acceleration can be dominant. The paper describes new extremal trajectories, which are based on the analysis of first- and second-order optimality conditions. The results of this work can be used to support mission design analysis and synthesis of fuel-efficient trajectories.

Pitch damping identification in high speed regimes with a free-to-tumble rig

Many re-entry bodies, even if they are debris or not, have nonlinear dynamic stability characteristics that produce oscillations in flight. The free-to-tumble techniques can be used to extract damping coefficient of specific body for planetary entry. The curve fitting approach is used to predict oscillatory behavior and the damping coefficient for the various test conditions of the wind tunnel obtained after the experimental data. The analysis presented provides an overview of the free-to-tumble test techniques and illustrates the effects of dynamic stability of the inter-stage tronconical system. It is proposed that these test techniques and curve fitting solution be refined in the future to better define the dynamic stability curves for the re-entry bodies.