Reentry Research Articles

The Winchcombe fireball—That lucky survivor

AbstractOn February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South‐West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre‐atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s−1). A near‐catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near‐Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.

Numerical investigation of surface catalytic effect on the plasma sheath of a hypersonic re-entry capsule

Radio frequency blackout indicates the communication interruption between signal monitoring sites and re-entry vehicles; it is a serious threat to the safety of astronauts and the space exploration missions. In this study, a surface catalytic model coupled with a thermochemical non-equilibrium computational fluid dynamic model is developed to study the catalytic wall effect on the plasma sheath of a hypersonic re-entry vehicle. The mechanism of the surface catalytic effect on the plasma sheath of a re-entry capsule is revealed by a comparative study. The flow-field characteristics simulated under conditions of the full-catalytic and non-catalytic walls are compared and discussed for the hypersonic atmospheric re-entry capsule at different altitudes. The chemical and physical mechanisms behind the surface catalytic effect of the re-entry capsule are analyzed. The experimental data of Radio Attenuation Measurement-C-II are used to validate the numerical model established in the present study. It is found that the numerical results simulated with the fully catalytic wall are more consistent with the experimental data. Near the capsule wall, the mole fractions of the species N, O, N+, and O+ decrease as the catalytic recombination coefficient increases. Because of the surface catalytic effect, the communication black is mitigated due to the reduction of the electron number density in the wake zone of the capsule.

Polarization Scattering Properties of Inhomogeneous Plasma-Covered Metal Plate

The plasma sheath generated during the reentry of the hypersonic vehicle will significantly influence the amplitude and polarization property of the scattered wave and lead to abnormal scattering characteristics of the hypersonic vehicle. Therefore, an electromagnetic (EM) simulation model of 3-D inhomogeneous plasma-covered metal plate is deployed to study the scattered properties of linear polarization plane wave obliquely incident on the inhomogeneous plasma. Based on the dispersive media’s convolutional perfect matched layer (CPML) and taking the Gaussian pulse linear polarization wave as an example, this article studies the effects of the plasma parameters, including the electron density and the collision frequency, on the scattered properties of plasma covered metal plate. Then, the influences of incident angle and EM wave polarization mode on the polarization properties of the scattered wave are emphatically analyzed. Numerical results indicate that the inhomogeneous plasma presents the cross-polarization isolation effect when the electric field of the plane wave is parallel to the surface of the plasma. On the contrary, the inhomogeneous plasma presents the cross-polarization depolarization effect when the electric field vector intersects with the surface of the plasma. The results provide a theoretical basis for the research on radar cross section (RCS) measurement, polarization matching, and EM stealth of plasma-sheath-covered hypersonic vehicles.

Simulations of Heat and Drag Reduction of Opposing Jet in Hypersonic Flow

To reduce aerodynamic heat and drag, and thus improve the speed of hypersonic vehicles, opposing jet technology has become a research focus because of its excellent heat and drag reduction effect. In this paper, Navier–Stokes equations, the shear stress transport turbulent models, the Gupta chemical kinetics model, and the five-species air model are considered; and a numerical simulation program of hypersonic aerodynamic heat and drag with an opposing jet is developed and verified by existing experimental data. On this basis, the flight conditions of , 14, and 15 at a 30 km flight altitude are simulated numerically; and the complex flowfield structure of the leading edge of a blunt body with or without the opposing jet is analyzed. It is found that the jet can push away the shock wave, playing a good role in reducing heat and drag. The influence of the pressure ratio, Mach number, and jet temperature on reducing heat and drag is investigated. The results indicate that, under the same conditions, increasing the pressure ratio, increasing the jet Mach number, and decreasing the inlet Mach number will be more helpful for reducing heat and drag; whereas increasing the jet temperature is not conducive to heat reduction and has little impact on aerodynamic drag.

Endoscopic removal of a large ingested squeeze ball at the duodenojejunal flexure using multiple devices.

Clinical guidelines recommend endoscopic removal using a basket catheter for blunt and spherical foreign bodies in the small bowel; however, objects with a diameter more than 2.0–2.5 cm cannot typically be passed through the pylorus [1]. This article describes the endoscopic removal of a large ingested squeeze ball at the duodenojejunal flexure using multiple devices.

Revisiting Reentry Roll Resonance

This paper revisits the subject of reentry roll resonance, which occurs when the roll rate and pitch frequency become equal in a spinning reentry vehicle. A first-principles model is developed and analyzed numerically and by using a reduced-order pendulum model for the relative phase of the roll and pitch/yaw axes. The results show good qualitative agreement with recent flight data and provide a natural physical interpretation. Based on the model it is suggested that sustained roll resonance depends primarily on the initial phase relationship between the pitch and roll axes, in addition to the vehicle moments of inertia and the vehicle symmetry. Finally the model is used to propose a mechanism for sustained resonance in vehicles spinning about a major axis, a condition previously thought to be forbidden.

Complex mixture of organic matter in a xenolithic clast from the Zag meteorite revealed by coordinated analyses using AFM-IR, NanoSIMS and STXM/XANES

Primitive carbonaceous xenolithic clasts found in sturdy metamorphosed meteorites often provide opportunities to reach labile volatile-rich materials which are easily destroyed during atmospheric entry and materials which we do not have sampled as individual meteorites. Among them, a xenolithic carbonaceous clast in the Zag H3–6 ordinary chondrite has been providing us with the opportunity to analyze a possible sample from D/P-type asteroids. Here we performed a new suite of coordinated analyses of organic matter in the Zag clast using the atomic force microscope infrared spectroscopy (AFM-IR) combined with nanoscale secondary ion mass spectrometer (NanoSIMS), X-ray absorption near-edge spectroscopy (XANES) coupled with scanning transmission X-ray macroscope (STXM), Raman, and (scanning) transmission electron microscopy [(S)TEM] on adjacent ultramicrotomed thin sections from a single sample grain. We successfully demonstrated the practicality of coordinated analyses using AFM-IR, Raman and NanoSIMS on the same sample area, as well as STXM/XANES on adjacent (and nearly identical) thin sections to those used for AFM-IR. The AFM-IR map and STXM maps provided consistent and complementary results. We found that at least two types of organics were closely mixed in this specimen. One was deuterium-rich, CO rich organics with likely smaller aromatic domains, possibly originating in relatively oxidized environments from D-rich precursors. The other type was less deuterium-rich, but aromatic-rich organics, possibly produced in relatively reduced and higher temperature environments with less deuterium-rich precursors. These characteristics point to complex mixtures of materials with different origins and sampling a wide heliocentric range of the Solar System before accretion in the parent body of the clast.

Multidirectional galloping-based wind energy harvester based on a cylindrical cantilever beam and multi-tooth blunt body

To improve the response-ability of the energy harvester to multi-directional wind, this paper proposes a galloping-based wind energy harvester by fixing a multi-tooth blunt body at the free end of a cylindrical cantilever beam, which consists of a long-straight FeGa thin cylinder and a piezoelectric tube. Combining the structural symmetry advantages of the multi-tooth blunt body and piezoelectric cylinder cantilever, the harvester can respond well to the wind from all directions of the two-dimensional plane. In the simulation and experiment, detailed comparative studies are carried out on the harvesters with square (four-tooth), six-tooth, eight-tooth, ten-tooth, and twelve-tooth blunt bodies. Within the wind speed range of 1.5 ∼ 8 m s−1, the results show that the harvester with a six-tooth blunt body has the best multidirectional wind response performance. When the wind speed is 8 m s−1, the output power of the harvester with a six-tooth blunt body improves by ∼43% more than that of the harvester with a traditional square blunt body. The design idea of the proposed harvester provides a direction for the future in-depth study of multidirectional piezoelectric wind energy harvesting.

Learning-based interfered fluid avoidance guidance for hypersonic reentry vehicles with multiple constraints

To address the problem of no-fly zone avoidance for hypersonic reentry vehicles in the multiple constraints gliding phase, a learning-based avoidance guidance framework is proposed. First, the reference heading angle determination problem is solved efficiently and skillfully by introducing a nature-inspired methodology based on the concept of the interfered fluid dynamic system (IFDS), in which the distance and relative position relationships of all no-fly zones can be comprehensively considered, and additional rules are no longer needed. Then, by incorporating the predictor–corrector method, the heading angle corridor, and bank angle reversal logic, a fundamental interfered fluid avoidance guidance algorithm is proposed to steer the vehicle toward the target zone while avoiding no-fly zones. In addition, a learning-based online optimization mechanism is used to optimize the IFDS parameters in real time to improve the avoidance guidance performance of the proposed algorithm in the entire gliding phase. Finally, the adaptability and robustness of the proposed guidance algorithm are verified via comparative and Monte Carlo simulations.

Aerodynamic performance improvement of a blended wing-body re-entry vehicle using ANSYS CFX

The main objective of this paper is to evaluate the aerodynamic performance of a modified blended wing-bodied re-entry vehicle by computational fluid dynamics. This analysis examines the airflow properties like pressure, density, and temperature under hypersonic flow. The study of a blended wing model at different Mach speeds and angles of attack is also included in the research paper. All the simulations in this paper are performed using the computational fluid dynamics tool of ANSYS CFX. Shear stress transport (SST) turbulence computational fluid dynamics model has been used for numerical analysis. Various inlet conditions are applied to get the aerodynamic parameters. The results revealed that the best Re-entry condition is from 10 to 20 degrees angle of attack at Mach 22, and the vehicle is very stable at a high angle of attack and Mach number. The obtained results have been validated with the public domain literature. The blended wing body has been thoroughly examined in various important locations, particularly the spacecraft nose and flap sections.

Charged Ice Particle Beams with Selected Narrow Mass and Kinetic Energy Distributions.

Small ice particles play an important role in atmospheric and extraterrestrial chemistry. Circumplanetary ice particles that are encountered by space probes at hypervelocities play a critical role in the determination of surface and subsurface properties of their source bodies. Here we present an apparatus for the generation of low-intensity beams of single mass-selected charged ice particles under vacuum. They are produced via electrospray ionization of water at atmospheric pressure and undergo evaporative cooling when transferred to vacuum through an atmospheric vacuum interface. m/z selection is achieved through two subsequent quadrupole mass filters operated in the variable-frequency mode within a range of m/z values between 8 × 104 and 3 × 107. Velocity and charge of the selected particles are measured using a nondestructive single-pass image charge detector. From the known electrostatic acceleration potentials and settings of the quadrupoles the particle masses could be obtained and be accurately controlled. It has been shown that the droplets are frozen within the transit time of the apparatus such that ice particles are present after the quadrupole stages and finally detected. The demonstrated correspondence between particle mass and specific quadrupole potentials in this device allows preparation of beams of single particles with a repetition rate between 0.1 and 1 Hz with various diameter distributions from 50 to 1000 nm at 30-250 eV of kinetic energy per charge. This corresponds to velocities and particle masses quickly available between 600 m/s (80 nm) and 50 m/s (900 nm) and particle charge numbers (positive) between 103 and 104[e], depending upon size.

Two-temperature ablative material response model with application to Stardust and MSL atmospheric entries

Ablative material response codes currently in use consider local thermal equilibrium between the solid phases and the pyrolysis gases. For typical entry conditions, this hypothesis may be justified by the fact that the thermal Peclet number within the pores is small, which is a necessary condition for thermal equilibrium in non-reactive materials. However, the validity of this analysis may fall under some circumstances. The thermal Peclet number may become large due to high pyrolysis gas velocities. Additional physical phenomena not accounted for in the Peclet analysis may become non-negligible, such as the change of enthalpy due to chemical reactions. The objective of this study is two-fold. First, a detailed two temperature material response model for porous reactive materials is presented. This model has been implemented and made available in the Porous material Analysis Toolbox based on OpenFOAM (PATO). Second, the model is applied to the Theoretical Ablative Composite for Open Testing (TACOT) in a wide range of conditions to assess the true range of validity of the thermal equilibrium hypothesis. Simulations are carried out on the Stardust and Mars Science Laboratory (MSL) atmospheric entries. The main design variables have been monitored and compared between the two models: temperature evolution and species concentration within the material, pyrolysis gas blowing rate, extension of the pyrolysis zone, and wall recession due to ablation. Results show that under chemical equilibrium conditions, no significant deviation in the monitored quantities are observed, while under chemical non-equilibrium conditions there is a large impact on the species concentration.

ADP-Based Intelligent Tracking Algorithm for Reentry Vehicles Subjected to Model and State Uncertainties

This article presents an adaptive dynamic programming-based intelligent control algorithm for the attitude tracking issue of reentry vehicles subject to model and state uncertainties simultaneously. The traditional control approaches struggle to achieve satisfactory tracking performance since the model and state are together influenced and deviated by the both uncertainties. Instead, the attitude tracking issue in this article is first transformed into an optimal regulation issue of the tracking error. Then, a novel cost function inspired by the idea of zero-sum game is introduced to eliminate the model uncertainties, and state uncertainties are handled dynamically by updating weights based on the optimality principle of the critic network. Consequently, the intelligent tracking control law is obtained by the optimal regulation. The stability of the system and the convergence of network weights are further analyzed using the Lyapunov stability theory. The effectiveness of the proposed control scheme is verified by simulations.

Molecular ion formation on activated field emitters in atmospheric pressure field desorption mass spectrometry

Atmospheric pressure field desorption (APFD) mass spectrometry (MS) has recently been explored as a new contribution to the field of ambient desorption/ionization (ADI). Depending on the selected polarity applied to the field emitter, ionic and polar analytes were demonstrated to deliver positive as well as negative ions. Whereas this recent study solely reported on the formation of even-electron ions of either polarity, the present work on APFD-MS demonstrates the abundant formation of positive molecular ions, M+•, from polycyclic aromatic compounds. Molecular ions were formed on and desorbed from standard 13-µm activated tungsten wire emitters at atmospheric pressure. The commercial field emitters were positioned at about 2 mm distance in front of the atmospheric pressure interface of a Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometer and the entrance electrode of the interface was set to –4.5 to –5.5 kV with respect to the emitter. Emitter-disrupting electric discharges did normally not occur under these conditions. The electric field strengths achieved at the dendritic microneedles were sufficient to allow for the abundant formation of M+• ions of various polycyclic aromatic compounds such as benzo[a]pyrene, anthracene, fluoranthene, 1,1,4,4-tetraphenyl-butadiene, and 1-aza-[6]helicene. In case of the extremely basic 1-aza-[6]helicene protonation strongly competed with molecular ion formation and tended to suppress the field ionization process. All molecular ion compositions were assured by accurate mass-based formula assignments.Graphical

Analysis of Drag Reduction over Different Types of Blunt Bodies at Different Angle of Attack

Analysis of Drag Reduction over Different Types of Blunt Bodies at Different Angle of Attack

Entry trajectory optimization for hypersonic vehicles based on convex programming and neural network

Trajectory optimization is important in achieving long-range atmospheric entry hypersonic vehicles. However, the trajectory optimization problem for atmospheric entry of hypersonic vehicles is characterized by strong nonlinearity, parameter uncertainties and multiple constraints. This study proposes a novel online trajectory optimization method for hypersonic vehicles based on convex programming and a feedforward neural network. A sequential second-order cone programming (SOCP) method is obtained to describe the trajectory optimization problem after the Gauss pseudo-spectral discretization. Subsequently, multiple optimal trajectories under aerodynamic uncertainties are generated offline and classified as the training and validation datasets. Then, a multilayer feedforward neural network is trained using these datasets and to output the optimal control command online. This method yields approximately 95% shorter computation time compared with the offline SOCP method. Considering the existence of the aerodynamic uncertainties, three terminal states calculated by this method are all smaller than 4.1%. In conclusion, the proposed trajectory optimization method can provide a high-precision, robust entry trajectory for hypersonic vehicles efficiently.

Aerodynamic Thermal Simulation and Heat Flux Distribution Study of Mechanical Expansion Reentry Vehicle

The mechanical expansion reentry vehicle has become the focus of deep space exploration because of its good deceleration effect and high stability. However, due to its special aerodynamic shape, its surface heat flux characteristics are different from traditional reentry vehicles. In this paper, the Two-Temperature model is introduced to simulate heat flux distribution. The influence of different structure parameters and flight parameters on the flow field structure and surface heat flux is also analyzed. The research shows that the Two-Temperature model can improve the prediction accuracy and that the heat flux may peak at the both the head and shoulder of the vehicle. Structural parameters RB, RN, and θ have an obvious negative effect on QO. RB, RN, RR, and LZ have a negative correlation with QR. QR drops first and then rises as θ increases and RS decreases. Flight parameters Ma have a positive effect on QO and QR while H is negative; α makes the heat flux distribution asymmetric.

Thermal design of view port of a sub-orbital flight

The current work deals with a thermal design of a view port for a sub-orbital flight. Geometry of a typical sub-orbital flight was considered for this design. Using a typical suborbital flight trajectory, heat flux was estimated. For atmospheric re-entry, engineering correlations are used to estimate time varying stagnation heat flux from the trajectory data. At a time instant, CFD analysis was carried out to verify the consistency in stagnation heat flux. From CFD analysis, a factor was derived between stagnation heat flux and the heat flux at view port location. This factor was applied over the time varying stagnation heat flux to obtain transient heat flux profile on view port. A grid Independence study was performed and the grid independent results were only used in this study. Different materials were evaluated for the view port and a thermal analysis was carried out to estimate the optimum thickness requirement for each of these material using one dimensional thermal analysis.

Hyperthermal Dynamics and Kinetics of the C(3P) + N2(X1Σg+) → CN(X2Σ+) + N(4S) Reaction

The hyperthermal dynamics and kinetics of the title reaction, which plays an important role in hypersonic chemistry for atmospheric entry vehicles, are investigated using quasi-classical trajectory methods on a recently developed ground electronic state potential energy surface. The dynamics calculations indicated that the reaction follows a complex-forming mechanism, despite its large endoergicity. The calculated differential cross section is forward-backward symmetric, consistent with a long-lived reaction intermediate supported by the NCN potential well. The lifetime of the reaction complex is sufficiently long that the vibrational distribution of the CN product can be predicted by the phase space theory. The calculated vibrational state specific and thermal rate coefficients follow the Arrhenius behavior, and the agreement with existing low-temperature experimental thermal rate coefficients is satisfactory. Extrapolations to high temperatures relevant to hypersonic conditions are provided.

A Machine Learning and Feature Engineering Approach for the Prediction of the Uncontrolled Re-Entry of Space Objects

The continuously growing number of objects orbiting around the Earth is expected to be accompanied by an increasing frequency of objects re-entering the Earth’s atmosphere. Many of these re-entries will be uncontrolled, making their prediction challenging and subject to several uncertainties. Traditionally, re-entry predictions are based on the propagation of the object’s dynamics using state-of-the-art modelling techniques for the forces acting on the object. However, modelling errors, particularly related to the prediction of atmospheric drag, may result in poor prediction accuracies. In this context, we explored the possibility of performing a paradigm shift, from a physics-based approach to a data-driven approach. To this aim, we present the development of a deep learning model for the re-entry prediction of uncontrolled objects in Low Earth Orbit (LEO). The model is based on a modified version of the Sequence-to-Sequence architecture and is trained on the average altitude profile as derived from a set of Two-Line Element (TLE) data of over 400 bodies. The novelty of the work consists in introducing in the deep learning model, alongside the average altitude, and three new input features: a drag-like coefficient (B*), the average solar index, and the area-to-mass ratio of the object. The developed model was tested on a set of objects studied in the Inter-Agency Space Debris Coordination Committee (IADC) campaigns. The results show that the best performances are obtained on bodies characterised by the same drag-like coefficient and eccentricity distribution as the training set.