Reentry Research Articles

Simulation for the Effects of Aerodynamic Actuation on the Reentry Vehicle Plasma Sheath

Simulation for the Effects of Aerodynamic Actuation on the Reentry Vehicle Plasma Sheath

Meteorite material luminous efficiencies from ground testing of meteoroid entry

The paper reports the determination of luminous efficiency values from ground testing of a comprehensive set of meteorite samples. The ground testing data is translated with commonly used ground to flight extrapolation analogies from atmospheric entry maneuver’s engineering into values of a night observation. This results in a meteor at an altitude of 80km with a flight speed of 11.7km/s of a 34.8 mm diameter spherical meteoroid. A method is developed to determine the total luminous efficiency τ in the bands U, B, V, R, and I from the radiance data and the measured mass loss. For the first time, a measurement of luminous efficiency became possible for known materials. The values itself are in the range of 0.01% to ∼ 1%, which is in the range of previous studies from meteor measurements.

Efficient Method for Heat Flux Calculations within Multidisciplinary Analyses of Hypersonic Vehicles

A large amount of heat flux from aerodynamic heating acts on reusable spacecraft; thus, an accurate heat flux prediction around spacecraft reentry is essential for developing a high-performance reusable spacecraft. Although the approximate convective-heating equations can calculate the heat flux with high efficiency and sufficient fidelity, the heat flux should be evaluated over a thousand times for the entire trajectory in multidisciplinary analyses. For these reasons, it is necessary to develop an efficient method for calculating the heat flux for multidisciplinary analysis. In this paper, an efficient method for heat flux calculation that is adoptable by multidisciplinary analyses for hypersonic vehicles, such as spacecraft, is developed. Approximate convective-heating equations were adopted to relieve the computational cost of estimating the heat flux, and an adaptive time step method for heat flux calculations was developed to reduce the number of heat flux calculations required across the entire flight trajectory. A dynamic factor was introduced that adjusts the time step between each instance of the heat flux calculation. Since the time step using this factor could increase under low heat flux conditions, the number of heat flux calculations decreases by approximately one-tenth with over 90% accuracy. Therefore, the efficiency was improved with high accuracy using the adaptively-determined time step according to this dynamic factor.

Oxidation induced emissivity variations of the Haynes 25 alloy at high temperatures

Haynes 25 alloy is used in the design of propulsion systems for spacecrafts and it can constitute a space debris at the end of life of the mission. All the thruster combustion chambers and nozzles are manufactured with Haynes 25 alloy and the thrusters used storable monopropellant hydrazine. During the atmospheric reentry of thruster pieces at high velocity, the Haynes 25 alloy is submitted to high temperatures in an extreme environment with atomic oxygen. This is why the high temperature oxidation of Haynes 25 was studied, in air plasma conditions in the temperature range 1000–1700 K. Moreover, as emissivity is an important parameter to know for the heat transfer, the spectral directional emissivity was measured on several samples surfaces: pristine, pre-oxidized in air plasma and in situ oxidized in air. The high temperature oxidation of Haynes 25 is moderate up to 1500 K and above an important mass loss occurred up to 1700 K (around 40 mg/cm2), that is the determined melting temperature. The emissivity of pristine Haynes 25 is vey low, around 0.20 at 1350 K and it increases with oxidation up to 0.85–0.90 at 1600 K.

An Asymmetrical Mixed Higher-Order Discontinuous Galerkin Time Domain Method for Electromagnetic Scattering from the Plasma Sheath around a Hypersonic Vehicle

The plasma sheath during reentry of hypersonic vehicle is an unmagnetized and weakly ionized nonuniform plasma flow, which causes radio frequency blackout and strong plasma attenuation of electromagnetic wave. The physical properties of the nonuniform plasma flow were obtained using computational fluid dynamics software with unstructured grids. In this study, a detailed computational model was reconstructed with the high-order Lagrange grids for the nonuniform plasma flow region and the high-order Serendipity grids for the homogeneous medium region. In order to calculate the numerical flux between the two types of grids in the discontinuous Galerkin time domain (DGTD) algorithm, an asymmetric high-order element is constructed as a transition unit. Finally, the simulation results in the plasma sphere show that the above method improves the computational accuracy and decreases calculation. The amplitude and scattering about electromagnetic wave in nonuniform plasma flow are clarified in detail. It is suggested that the presented method could be an effective tool for investigating interaction between electromagnetic waves and plasma flow.

Edge-Based Viscous Method for Mixed-Element Node-Centered Finite-Volume Solvers

A novel, efficient, edge-based viscous (EBV) discretization method has been recently developed and implemented in a practical, unstructured-grid, node-centered, finite-volume flow solver. The EBV method is applied to viscous-kernel computations that include evaluations of mean-flow viscous fluxes, turbulence-model and chemistry-model diffusion terms, and the corresponding Jacobian contributions. Initially, the EBV method had been implemented for tetrahedral grids and demonstrated multifold acceleration of all viscous-kernel computations. This paper presents an extension of the EBV method for mixed-element grids. In addition to the primal edges of a given mixed-element grid, virtual edges are introduced to connect cell nodes that are not connected by a primal edge. The EBV method uses an efficient loop over all (primal and virtual) edges and features a compact discretization stencil based on the nearest neighbors. This study verifies the EBV method and assesses its efficiency on mixed-element grids by comparing the EBV solution accuracy and iterative convergence with those of well-established solutions obtained using a cell-based viscous (CBV) discretization method. The EBV solver’s memory footprint is optimized and often smaller than the memory footprint of the CBV solver. An EBV implementation of a nonlinear extension of the Spalart–Allmaras turbulence model, SA-neg-QCR2000, is also presented and verified. The SA-neg-QCR2000 model is used for simulating turbulent corner flows. Multifold speedup is demonstrated for all viscous-kernel computations, resulting in significant reduction of the time to solutions for several benchmark mixed-element-grid computations, including simulations of subsonic flows around a hemisphere–cylinder configuration and a NASA juncture-flow model, a supersonic flow through a long square duct, and a hypersonic, chemically reacting flow around a blunt body.

A Review of Infrasound and Seismic Observations of Sample Return Capsules since the End of the Apollo Era in Anticipation of the OSIRIS-REx Arrival

Advancements in space exploration and sample return technology present a unique opportunity to leverage sample return capsules (SRCs) towards studying atmospheric entry of meteoroids and asteroids. Specifically engineered for the secure transport of valuable extraterrestrial samples from interplanetary space to Earth, SRCs offer unexpected benefits that reach beyond their intended purpose. As SRCs enter the Earth’s atmosphere at hypervelocity, they are analogous to naturally occurring meteoroids and thus, for all intents and purposes, can be considered artificial meteors. Furthermore, SRCs are capable of generating shockwaves upon reaching the lower transitional flow regime, and thus can be detected by strategically positioned geophysical instrumentation. NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) SRC is one of only a handful of artificial objects to re-enter the Earth’s atmosphere from interplanetary space since the end of the Apollo era and it will provide an unprecedented observational opportunity. This review summarizes past infrasound and seismic observational studies of SRC re-entries since the end of the Apollo era and presents their utility towards the better characterization of meteoroid flight through the atmosphere.

Research on aerodynamic shape optimization of reentry vehicle based on hybrid scale multi-fidelity neural network model

The mechanical expanded reentry vehicle has gained significant attention as a reliable solution for shuttle transportation and deep space exploration missions. However, the aerodynamic characteristics of such a reentry vehicle, including high dimensionality, strong nonlinearity, and parameter coupling, pose a challenge in achieving a balance between precision and efficiency in aerodynamic shape design. In this paper, we propose a hybrid scale multi-fidelity neural network (HS-MFNN) model by integrating low-fidelity and high-fidelity models with neural networks. This model is applied to optimize the aerodynamic shape of the reentry vehicle, addressing the challenge. The feasibility of applying the HS-MFNN model was validated through testing using the MBR function. The advantages of the HS-MFNN model were highlighted through a comparison with other models. Subsequently, the model was utilized in the aerodynamic optimization process of the reentry vehicle. The prediction error for the drag coefficient (Cd) was less than 1%, and for the head stagnation heat flux (QO), it was within 6%. Moreover, the computation time was reduced by three orders of magnitude, ensuring both computational accuracy and efficiency. After optimization, the Cd increased by 5.08%, while the QO decreased by 8.62%. These improvements demonstrate that the use of the HS-MFNN model significantly enhances the aerodynamic performance of the reentry vehicle. Consequently, the HS-MFNN model exhibits great potential for fast and efficient optimization processes.

Aerothermodynamic analysis and rear wake assessment of shock wave interference over blunt leading edge at Mach 6.5

A detailed numerical study of shock-wave interference on a cylindrical blunt leading edge in hypersonic flow is carried out to reveal the effect of shock-shock interaction on peak heating and blunt body aerodynamics. This study is unique in that it examines the effect of interactions on rear wake formation and aerodynamic forces acting on the blunt body. Six different shock wave interference patterns described by Edney are studied for a freestream Mach number of 6.5. Compressible Reynolds-averaged Navier–Stokes equations are solved using finite volume method to obtain accurate prediction of the flowfield and aerodynamic loads. Hugoniot jump conditions are imposed in the inlet boundary to realize oblique shock of desired strength to interact with the detached shock at specific location. Numerical predictions are in good agreement with reported experimental measurements. The results obtained in this study reveals that the type of shock-shock interaction pattern can significantly alter the characteristics of the rear wake. Comparisons to undisturbed flow conditions reveal that Type II to VI interactions lead to an increase in wake size, whereas Type I interaction shows a marginal reduction. These changes in wake size are attributed to modifications in the forebody boundary layer induced by the shock-shock interactions. In the case of Type I interaction, however, the transmitted wave interacting with the rear wake is found to be responsible for the marginal reduction in wake size. This study also shows that changes to the rear wake structure caused by the change in interaction type can affect aerodynamic loads. Type VI interaction recorded a maximum drag coefficient of 2.96, whereas Type IV interaction yielded a maximum lift coefficient of 0.992. These findings demonstrate the potential for dynamically adjusting the control forces of a flying body by manipulating shock interference.

Large-eddy simulation of unsteady flows past a spiked body

Unsteady flows past a spiked body are investigated numerically with wall-resolved large-eddy simulation (LES). The inflow features a Mach number of Ma=2.21 and a Reynolds number of Re=1.2×105. The ratio of the spike length to the blunt body diameter is L/D=1.0. A comparative study of three meshes of different grid resolutions has been conducted by assessing their predictive accuracies and associated subgrid-scale effects. The LES results obtained based on three meshes are compared with the experimental and numerical data found in the literature. A proper orthogonal decomposition (POD) analysis has been conducted based on the pressure and axial velocity fluctuations to investigate turbulence structures. It is observed that the turbulence structures corresponding to the first four POD modes are the most energetic. Furthermore, it is seen that the dominant recirculation zone along the spike in a pulsation cycle can be reconstructed based on the first two POD modes of axial velocity fluctuations. The physical mechanisms of the collapse and inflation processes of the pulsation cycle are investigated based on a detailed transient analysis of fine-resolution LES data. The temporal evolution of vortices and shock waves are investigated. An interesting characteristic Z-shaped trajectory of the instantaneous flow pattern is observed. It is discovered that the pulsation cycle is dominated by the pressure differences between the recirculation zone and two high-pressure regions immediately in front of the cylinder face and near the spike tip.

Geochemical evaluation of cosmic spherules collected from the Central Indian Ocean Basin

Micrometeorites (MMs) significantly contribute to the extraterrestrial material the Earth receives and represent a broader range of precursors than known meteorites. Low sedimentation rates prevalent in the deep-sea regions far away from land provide a unique opportunity for collecting MMs from these least disturbed regions. In the present study, we have studied 305 cosmic spherules recovered from the Central Indian Ocean Basin (CIOB); that have undergone melting during hypervelocity entry into the Earth's atmosphere. During the atmospheric entry, primary signatures of MMs are lost depending upon the extent of heating, complicating the identification of the parent body. Nevertheless, we have tried to relate these cosmic spherules to their respective parent bodies based on elemental ratios present in them, considering atmospheric ablative losses of various elements. The chemical analyses indicate that many deep-sea cosmic spherules are linked to carbonaceous chondrites. Around 239 porphyritic olivines (PO), 42 relict olivines are studied for their textural development and composition during recrystallisation during atmospheric entry. Thirty-zoned olivines are analysed from rim to core to understand various elements behaviour during atmospheric entry. Seawater plays a vital role in eroding these cosmic spherules material, and its effect is also discussed. As most of the recent micrometeorite collections focus on the polar region, these deep-sea spherules will significantly add to the information about the extraterrestrial matter reaching the Earth.

In-situ construction of oxidation resistant porous Mo4.8Si3C0.6/SiC(rGO) composite PDCs served as thermal insulation components of hypersonic vehicles

Actualization of well-balanced high porosity with simultaneous increase in hardness/fracture toughness for thermal insulation composites in hypersonic aerospace vehicle components is always of great challenge. Considering significant toughening effect of unique Mo4.8Si3C0.6-SiC composites microstructure, an agile strategy is proposed to prepare porous Mo4.8Si3C0.6/SiC(rGO) polymer-derived ceramics (PDCs) via re-pyrolysis of ball-milling-induced MoSi2-SiC(rGO)p/polycarbosilane-vinyltriethoxysilane-graphene oxide (PVG) precursors blends with polystyrene (PS) as pore-forming agent. In-situ formed Mo4.8Si3C0.6-β-SiC nanocrystals, possessing eminent mechanical properties and good compatibility with SiOxCy/Cfree, can significantly strengthen interface bonding and increase disorder of ceramic network. Such effective hindrance to crack propagation moderates the inherent brittleness while retaining high hardness of SiC PDCs. Moreover, dense Mo4.8Si3C0.6-β-SiC/SiOxCy/Cfree(rGO) framework, with spontaneous regular pore structure, well balances loading/thermal insulation capacity. Particularly, samples with 10 wt.% PS exhibit outstanding mechanical performances (hardness: 5.10 GPa; fracture toughness: 2.24 MPa·m1/2; compressive strength: 58.15 MPa) and low thermal conductivity (0.8427 W·m-1·K-1). As demonstrated, products remain decent structural integrity after ablation of butane blowtorch flame for 1-20 min. The synergy oxidation with fast response of Mo4.8Si3C0.6 and durability of β-SiC facilitates great anti-oxidation ability, opening up manufacture of SiC-based composites for thermal protection system (TPS) of hypersonic vehicles and re-entry spacecraft with ultra-high speed.

A Brief Review on Hyphenated Techniques

The hyphenated techniques are developed by combining two or three different analytical techniques. Mainly chromatographic techniques are combined with spectroscopic techniques. The separated components obtained from chromatographic techniques are then transmitted to spectroscopic detection technique through an interface. The improvements in hyphenated analytical methods in last two decades have significantly broadened their applications in the analysis of biomolecules especially in natural products. In this review article recent advancement in hyphenated techniques such as GC-MS, LC-MS, LC-NMR, MS-MS, LC-NMR-MS have been highlighted. The term ‘Hyphenated’ refers to separation and identification of the compounds. These techniques also show better analysis of sample compounds with better accuracy, precision and specificity. This review mainly focuses on the instrumental aspects of hyphenated techniques along with their interfaces. The interfaces such as Jet\Orifice separator interface, Electrospray interface, Atmospheric pressure chemical ionization interface have been covered. It has been concluded that these hyphenated techniques have become more advantageous for the analysis of drugs. This technique is useful for quality control, analytical research, impurity profiling and maintenance for human welfare and development.

Numerical study on hydrogen heterogeneous reaction characteristic in a micro catalytic combustor with blunt body

A numerical investigation has been conducted to explore the effect of an inserted blunt body on the heterogeneous reaction (HTR) characteristics in a micro-catalytic combustor operating with premixed hydrogen/air. The two-dimensional numerical model incorporates a comprehensive heterogeneous reaction mechanism of hydrogen employed by experimental verification. The influences of blockage ratio at various inlet velocities have been investigated to obtain optimized design parameters of the combustor. The findings of this research highlight analysis of the positive influence of an inserted blunt body within the combustor, including enhancement of chemical reaction rate and hydrogen conversion ratio. Numerical results shows that the gaseous mixture between the blunt body and catalytic surface noticed a considerable velocity increase, leading to a greater adsorption–desorption of bulk species on the catalytic surface. At the same inlet velocity, the hydrogen conversion ratio gradually increases with higher blockage ratios. When the blockage ratio is less than or equal to 0.6, the average inner wall temperature is positively affected by the increased blockage ratio. However, the effect becomes negative at higher blockage ratios (0.8). The Pr (Prandtl number) number near the gas–solid interface adjacent to the blunt body initially decreases and then increases, while Nu/Nu0 (Nusselt number) and Pe (Peclet number) exhibit an initial increase followed by a decrease. The presence of the blunt body leads to a reduction in the cross-sectional area of the channel, causing an acceleration in fluid velocity near the blunt body and exerting an impact on the boundary layer near the gas–solid interface. This indicates that the addition of the blunt body reduces the boundary layer thickness and enhances the mass and heat transfer characteristics in the region. The study reveal that as the blockage ratio increases, the overall field synergy of the combustor initially increases and then decreases. The peak field synergy is attained at an optimal blocking ratio of 0.6. The findings of this study have important implications for the design of micro-scale combustors.

Martian flow characterization using tunable diode laser absorption spectroscopy, in high enthalpy facilities

This research aims at analyzing thermo-chemical properties of the hypersonic high-enthalpy flow in the L2K wind tunnel, situated in Köln at the German Aerospace Center (DLR). In the L2K wind tunnel, Martian atmosphere can be created, and the facility can simulate heat load conditions encountered during atmospheric entry of Martian missions. The focus of this project is the analysis of the non-intrusive experimental technique “Tunable Diode Laser Absorption Spectroscopy” (TDLAS), based on line of sight absorption spectroscopy, and applied to hypersonic flow. A simplified Martian atmosphere (97% CO2 and 3% N2) was used. A new interpretation for CO-TDLAS experimental technique applied to hypersonic wind tunnel flow analysis was developed. Numerical simulations with the DLR-TAU non-equilibrium flow solver were used as support of this analysis, and match between simulations and experiments was observed. Flow speed and absorption line’s width were measured, and the knowledge of L2K’s flow structure was extended.

Hypersonic Weapons: Vulnerability to Missile Defenses and Comparison to MaRVs

Assessing the utility of hypersonic boost glide vehicles (BGVs) requires comparing their capabilities to alternative systems that could carry out the same missions, particularly given the technical difficulties and additional costs of developing BGVs compared to more established technologies. This paper discusses the primary motivations given for BGVs—most notably countering missile defenses—and summarizes current hypersonic development programs. It finds that evading the most capable current endo-atmospheric defenses requires that BGVs maintain speeds significantly higher than Mach 5 throughout their glide phase, which has implications for their mass and range. The paper then compares BGVs to maneuverable reentry vehicles (MaRVs) carried on ballistic missiles flown on depressed trajectories and shows that MaRVs can offer significant advantages over BGVs in a wide range of cases. Finally, the paper shows that BGV maneuvering during its glide phase can result in substantial costs in range and glide speed.

Turbulent far wake of a body of arbitrary shape

Using a recently proposed closure for the Boussinesq-Reynolds turbulent stress we re-derive Prandtl's result for the turbulent wake width behind blunt bodies. We show that it is valid for a body of arbitrary shape, but only for wakes due to a drag oriented parallel to the incoming flow. If the geometry of the body resisting the flow lacks symmetries forbidding it, the force on the body has also a component orthogonal to the incoming velocity, called lift, that allows, for instance, planes to fly. Using our closure theory we show that this lift generates a wake wider than the drag, with a width growing like the one-half power of the distance to the body, instead of the one-third in the case of drag only. This has important consequences as it leads to a change of structure of the wake that remains turbulent all the way to infinity.

Safety of an express freight train running over a bridge in crosswind

Owing to the blunt car body and high design speed of express freight trains, the running safety is significantly affected by crosswinds when the train runs over a bridge; moreover, severe accidents, such as derailment or overturning may occur. Therefore, adequate measures should be adopted to avoid the occurrence of such accidents. In this study, a finite element model of the train, ballastless track, and parameterized 5-span simply supported girder bridge along with modal superposition method are adopted to establish the train-track-bridge coupling dynamic system. Numerical simulation of stochastic wind speed, wind tunnel tests, and computational fluid dynamics (CFD) simulation of vehicle-bridge scale model were conducted to calculate the wind load acting on the train and bridge. The dynamic responses of the bridge and train were evaluated to present the diagrams of wind and train speed limits for safe operation. The results indicated that the running safety of the vehicle declined with the wind and train speeds, and the wheel unloading rate was the most sensitive to wind speed. For safe operation, the train speed must be restricted if the mean wind speed is greater than 22.7 m/s, and an extreme scenario of derailment may occur for a mean wind speed of 34.0 m/s. In addition, the wind speed limit should be appropriately adjusted and improved according to the pier height of the bridge and terrain category. This research provides a theoretical basis and data support for the assessment of safety of express freight trains in actual operation.

Sliding Mode Controller Based on Genetic Algorithm and Simulated Annealing for Assured Crew Reentry Vehicle

A sliding mode (SM) re-entry control system is proposed for an assured crew re-entry vehicle (ACRV). The vehicle has a low lift/drag ratio (0.3). The trajectory controller drives the ACRV in a predefined track. The reference vectors for the attitude controller are generated by the trajectory controller and navigation system. The feedback SM controller is designed to accommodate the structural parametric uncertainties and environmental disturbances. The SM controller is optimized by both the genetic algorithm (GA) and the simulated annealing (SA) methods. A comparative study is done between both optimization methods and the efficiency of the SA method is proved. The system is subjected to a sensitivity study in terms of various thrust torque profiles. A robustness check is done by changing the system parameters. A pulse width pulse frequency (PWPF) modulator modulates the output torque dictated by the attitude controller. The simulation results demonstrate the proposed method’s effectiveness in achieving the various required parameters.

The propagation of Alfvén wave in magnetized plasma sheath of hypersonic vehicles in near space

Hypersonic plasma sheath could shield communication signals, which results in the so-called “blackout.” Blackout is a major risk to the safety of re-entry vehicles and cruise hypersonic vehicles in near space. In this study, a propagation model of Alfvén waves in plasma sheaths is developed. The impacts of the external magnetic field, the wave frequency, and the boundary conductivity on the Alfvén attenuation were investigated. According to the simulation results, once the conductivity is close to the Alfvénic conductivity near the onboard antenna, the attenuation of Alfvén waves in the plasma sheath could reach its minimum. The total attenuation of the Alfvén wave in the plasma sheath decreases with the carrier frequency. Also, the attenuation decreases with increasing magnetic field strength.