Reentry Body Research Articles

Airspace closures due to reentering space objects

Uncontrolled reentries of space objects create a collision risk with aircraft in flight. While the probability of a strike is low, the consequences could be catastrophic. Moreover, the risk is rising due to increases in both reentries and flights. In response, national authorities may choose to preemptively close airspace during reentry events; some have already done so. We determine the probability for a rocket body reentry within airspace over a range of air traffic densities. The highest-density regions, around major airports, have a 0.8% chance per year of being affected by an uncontrolled reentry. This rate rises to 26% for larger but still busy areas of airspace, such as that found in the northeastern United States, northern Europe, or around major cities in the Asia-Pacific region. For a given reentry, the collision risk in the underlying airspace increases with the air traffic density. However, the economic consequences of flight delays also increase should that airspace be closed. This situation puts national authorities in a dilemma—to close airspace or not—with safety and economic implications either way. The collision risk could be mitigated if controlled reentries into the ocean were required for all missions. However, over 2300 rocket bodies are already in orbit and will eventually reenter in an uncontrolled manner. Airspace authorities will face the challenge of uncontrolled reentries for decades to come.

Improving casualty risk estimates for uncontrolled rocket body reentries

Approximately 70 % of launches in 2022 resulted in an uncontrolled rocket body reentry, creating an unnecessary casualty risk to people on the ground, at sea, and in aircraft. Rocket bodies have masses ranging from tens of kilograms to 20 tonnes. Using known rocket body masses and correlations between mass and casualty area, we present revised estimates for the expected risk, finding a 20–29 % probability of one or more casualties over the next decade.Some states use a 1-in-10,000 threshold for accepting an uncontrolled reentry casualty risk when approving a space activity. This threshold, which is not universally agreed upon, represents a risk acceptance by one country, but imposed on the world population. As the use of space expands, with a record 180 successful launches in 2022, states and other launch providers should adopt technologies and mission designs that ensure controlled reentries. Uncontrolled reentries, particularly of large rocket bodies, constitute an unsafe and unnecessary practice.

Effect of Flare Angle and Natural Ventilation on The Aerodynamic Characteristics of a Typical Re-Entry Body At Subsonic and Transonic Mach Numbers

Aerodynamic force and moment measurements were carried out on models of a typical re-entry body, featuring a blunt nose, conical body and flare, to assess the effect of flare angle on the overall aerodynamic characteristics. In one of the configurations, the junction between the cone and the flare was vented out to the base of the model to assess the effect of ventilation on the aerodynamic characteristics. It was expected that the stability characteristics would improve, by virtue of improved contribution from the flare to the normal force of the configuration. However, measurements did not show the expected trends. Instead, there was a remarkable reduction in the axial force with ventilation, by as much as 25% all across the Mach number and angle of attack range. Base pressure measurements indicated that in the low Mach number range pressure rise occured. However, in the high transonic Mach number range, even though the force measurements showed drag reduction, there was no significant rise in base pressure. Ventilation showed delay in transonic drag rise. It is therefore suggested that the overall pressure field is modified by ventilation, which results in drag reduction of the configuration.

High performance computing and inverse problems in acoustics and structural acoustics

Engineering applications in acoustics and structural acoustics commonly require finite element models with large numbers of degrees of freedom. Examples include applications with infinite and semi-infinite domains, as well as problems at high frequency (e.g., ultrasound) where the number of wavelengths in the domain becomes large. The finite element solution of such problems, and their inclusion inside an optimization loop for inverse problems, inevitably involves large numbers of degrees of freedom and systems of equations. Modern high-performance computing is enabling numerical solutions of acoustics applications that were previously intractable. In this talk, we will present an overview of massively parallel acoustic and structural acoustic solution capabilities in Sandia’s Sierra-SD (Structural-Dynamics) software. Sierra-SD is a massively parallel finite element application for structural dynamics and acoustics, having recently demonstrated the implicit solution of models with over 2 × 109 degrees of freedom and running on up to one hundred thousand distributed memory cores. Domain decomposition and MPI parallelism are used to split a large domain into many small domains that can be solved in parallel. Large-scale applications in ship shock loading and vibration of reentry bodies will be shown as demonstrations. [SNL is managed and operated by NTESS under DOE NNSA Contract DE-NA0003525.]

Wind Tunnel Testing of ONERA-M, AGARD-B and HB-2 Standard Models at Off-Design Conditions

Published results for standard wind tunnel models at non-standard test conditions are quite rare and/or may not be available. It has been found that those results are a useful aid in preparations for a number of wind tunnel tests in the Military Technical Institute (VTI) in Belgrade. Test campaigns of standard models at non-standard conditions are performed to serve as an internal database for future wind tunnel tests in such environments. Those tests, that partially overlap the referenced Mach number and/or angle of attack ranges, are conducted in different VTI’s test facilities; different model sizes and support stings were used. The standard models used in static measurements in VTI, ranging from simple missile shapes and re-entry bodies to complicated airplanes, are briefly described and sample non-standard test results are given. The correlation of the test results among models and facilities has been done with references in the available ranges, and, after confirming a good agreement, it is assumed that the results are also valid in the extended ranges of conditions. These results may be useful for researchers in other wind tunnel facilities and for those who handle CFD tools.

Finite-rate chemistry effects in turbulent hypersonic boundary layers: A direct numerical simulation study

The accurate prediction of hypersonic flows is a key challenge for the design of reentry bodies or hypersonic aircraft. Knowledge concerning the wall-bounded turbulence is especially needed. The present work is a fundamental study of a turbulent spatially developing flat-plate boundary layer subjected to high-enthalpy effects. The influence of air chemical reactions, typical of high-speed regimes, is investigated by means of direct numerical simulations. First- and second-order statistics are accurately examined, as well as spectral content and classical correlations.

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.

Aerothermodynamic design and performance analysis of modified nose cones for space reentry vehicles

ABSTRACT Reentry vehicles are blunt-nosed bodies designed primarily to protect them from high heating loads experienced while returning from space. The main intention of this present work is to alleviate the aerodynamic heating of the reentry vehicles by suggesting new geometrical considerations. This proposal implements the surface augmentation of the various conventional nose cones by creating some spherical protrusions over the nose region. This project presents the role of spherical protrusions over the nose part in order to reduce the aerodynamic heating of space reentry vehicles. A comparative numerical study has been made on the existing and proposed reentry bodies to find the degree of reduction in aerodynamic heating. From the numerical simulations, it has been observed that there is a significant alleviation of aerodynamic heating in the proposed nose cone model than in the conventional blunt body. From this simulation analysis, a reduction in aerodynamic heating of about 11% and 35% was observed in the chosen modified spherical and parabolic winged reentry models during hypersonic conditions. This numerical investigation perspicuously explains the importance of placing spherical protrusions over the conventional blunt-nosed reentry vehicles in order to alleviate the maximum degree of aerodynamic heating.

Effects of flap on the reentry aerodynamics of a blunt cone in the supersonic flow

Flap over blunt asymmetric reentry vehicles improves the aerodynamic stability and control. The present study has focused on the reentry aerodynamics of blunt-nosed conical body with flap configurations. Three dimensional, steady, viscous and compressible flow over the reentry body configurations were numerically analyzed by solving Reynolds averaged Navier-Stokes equations and SST K-ω turbulence model. The fundamental governing equations were discretized from the partial differential form to numerical analogue using the finite volume approach. Numerical simulations were carried out to investigate the flow characteristics of the three different reentry body configurations at different pitch angles, flap angles, the Mach numbers, and altitudes. For increment in the pitch angle from 0∘ to 6∘, the axial force coefficient is invariant, while the normal force coefficient linearly increases. It is found that the axial force coefficient is directly proportional to the flap angle and inversely proportional to the Mach number. Presence of flap introduces streamwise vortices and increases the flow complexity after the base to a large extent.

Hot Structure Flight Data of a Faceted Atmospheric Reentry Thermal Protection System

The second sharp-edged flight experiment is a faceted suborbital reentry body that enables low-cost in-flight reentry research. Its faceted thermal protection system consisting of only flat radiation-cooled thermal protection panels is cost-efficient since it saves dies, manpower, and storage. The ceramic sharp leading edge has a 1 mm nose radius in order to achieve good aerodynamic behaviour of the vehicle. The maximum temperature measured during flight was 867°C just before transmission ended and was predicted with an accuracy of the order of 10%. The acreage thermal protection system is set up by 3 mm fiber-reinforced ceramic panels isolated by a 27 mm alumina felt from the substructure. The panel gaps are sealed by a ceramic seal. Part of the thermal protection system is an additional transpiration-cooling experiment in which nitrogen is exhausted through a permeable ceramic matrix composite to form a coolant film on the panel. The efficiencies at the maximum heat flux are 58% on the porous sample and 42% and 30% downstream of the sample in the wake. The transient load at each panel location is derived from the trajectory by oblique shock equations and subsequent use of a heat balance for both cooled and uncooled structures. The comparison to the heat balance HEATS reveals heat sinks in the attachment system while the concurrence with the measurement is good with only 8% deviation for the acreage thermal protection system. Aerodynamic control surfaces, i.e., canards, have been designed and made from a hybrid titanium and ceramic matrix composite structure.

Large scale structural acoustics in Sierra-SD

In this talk, we will present an overview of structural acoustics and model reduction capabilities in Sierra-SD (Structural-Dynamics). Sierra-SD is a massively parallel finite element application for structural dynamics and acoustics, having recently demonstrated the implicit solution of models with over 2 billion degrees of freedom and running on up to one hundred thousand distributed memory cores. Domain decomposition and MPI parallelism are used to split a large domain into many small domains that can be solved in parallel. Sierra-SD offers a wide range of capabilities for model reduction. For acoustic models, infinite elements and perfectly matched layers are available to reduce domain size. For structural models, Craig-Bampton style superelements are available to reduce specific components in the structural portions of the model. Various coupling and handoff methods between linear structural acoustics codes and nonlinear solid and fluid mechanics codes are used to reduce model size. Large-scale, realistic applications will be presented on models such as ship shock loading and vibration of reentry bodies. [Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-NA-0003525.]

Model predictive tether-deployment control for precise landing of tethered reentry body

This paper proposes a model predictive control method for tether deployment for the precise landing of a tethered reentry body. A set of state variables for a tethered reentry system, in which the reentry body precisely lands at the target point, is numerically obtained and expressed in the form of an approximation function. The tether state is controlled by taking into consideration its deviation from the function. The effectiveness of the proposed controller for the precise landing of the reentry body is validated through numerical simulations.

Observed Rotational Motion and Roughness of Reentry Body

Observed Rotational Motion and Roughness of Reentry Body

Bayesian filtering based on solving the Fokker-Planck equation

PurposeThis paper aims to propose Bayesian filtering based on solving the Fokker–Planck equation, to improve the accuracy of filtering in non-Gauss case. Nonlinear filtering plays an important role in many science and engineering fields for estimating the state of dynamic system, but the existing filtering algorithms are mainly used for solving the problem of Gauss system.Design/methodology/approachUnder the Bayesian framework, the time update of this filtering is based on solving Fokker–Planck equation, while the measurement update uses the Bayes formula directly. Therefore, this novel algorithm can be applied to nonlinear, non-Gaussian estimation. To reduce the computational complexity due to standard meshing, an adaptive meshing algorithm proposed which includes the coarse meshing, significant domain determination that is generated using extended Kalman filtering and Chebyshev’s inequality theorem, and value assignment for significant domain. Simulations are conducted on a reentry body tracking problem to demonstrate the effectiveness of this novel algorithm.FindingsIn this way, finer grid points can be placed in the regions with high conditional probability density, while the grid points with low conditional probability density can be neglected. The simulation results indicate that the novel algorithm can reduce the computational burden significantly compared to the standard meshing, while achieving similar accuracy.Practical implicationsA novel Bayesian filtering based on solving the Fokker–Planck equation using adaptive meshing is proposed, and the simulations show that algorithm can reduce the computational burden significantly compared to the standard meshing, while achieving similar accuracy.Originality/valueA novel nonlinear filtering based on solving the Fokker–Planck equation is proposed. The novel algorithm is suitable for non-Gauss system, and can achieve similar accuracy compared to the standard meshing with the significant reduction of computational burden.

Massively parallel structural acoustics in Sierra-SD

Sierra-SD is a massively parallel finite element application for structural dynamics and acoustics. Problems on the order of 2 billion degrees of freedom and running on as up to one hundred thousand distributed memory cores have been solved. Sierra-SD offers a wide range of modern acoustic capabilities. Unbounded problems can be solved with either an absorbing boundary condition, infinite elements, or perfectly matched layers. Problems can be solved in the time domain, frequency domain, or as a linear or quadratic eigenvalue problem. Structural acoustics problems can be solved with monolithic strong coupling, or a Multiple Program Multiple Data (MPMD) coupling with the linear and nonlinear structural Sierra applications. One way handoff is available from other applications in the Sandia National Laboratories’ Sierra Mechanics suite, enabling loading through the Lighthill tensor from incompressible fluid codes to calculate far field noise. Real world applications include ship shock loading and vibration of reentry bodies. [Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.]

Optimization of projectile state and trajectory of reentry body considering attainment of carrying aircraft

As an improvement of traditional maximum range trajectory optimization, both the projectile state and control sequence of reentry body are optimized to achieve the maximum range. To ensure the optimal projectile state is in the reachable domain of the carrying aircraft, the climb of the carrying aircraft and the flight of reentry body are optimized as a whole based on the hp-adaptive pseudospectral method. Meanwhile, the path constraints, control constraints and initial/terminal states constraints are considered in the optimization as well. In face of the fact that the range of the optimal control solution resulted from the pseudospectral method may be unsmooth, virtual control variables (second derivatives of the angle of attack and bank angle) are proposed in the optimization, while the angle of attack and bank angle are treated as the virtual state variables to guarantee the smoothness of the optimal control solution. The validity of the virtual control variables in smoothing the optimal control solution is verified by simulation, and the optimality of the resulting projectile state and control sequence for reaching the maximum range is confirmed using the indirect approach.

Numerical Study of Magnetohydrodynamic Flow Control Along Superorbital Reentry Trajectories

Effects of magnetohydrodynamic flow control on the aerodynamic heating of a superorbital reentry body are examined by magnetohydrodynamic numerical simulation coupled with flight trajectory analysis. The initial flight altitude and velocity are set to 75 km and , respectively. Convective wall heat flux is directly calculated in the magnetohydrodynamic numerical simulation, whereas radiative wall heat flux is calculated by a structured package for the radiation analysis using the output data from the magnetohydrodynamic numerical simulation in an uncoupled manner of flowfield and radiation. Numerical results demonstrate that magnetohydrodynamic flow control significantly mitigates a peak value of total wall heat flux during the flight duration due to a drag-enhancement effect of magnetohydrodynamic flow control, although the total wall heat flux at high altitudes is elevated by magnetohydrodynamic flow control because of a considerable increase in radiative wall heat flux.

The First Mission of Iranian Spacecraft: Heat Shield Design

In the present paper, the Iranian spacecraft is considered, and is studied from an aero thermo dynamic viewpoint to design the proper thermal protection system, for its first mission: the suborbital flight. The design procedure is based on the decoupling of the aerodynamic heating phenomena and the solid phase heating process. Due to the sub-orbital mission of this spacecraft as a first flight, an elastomeric material is used as an unconventional heat shield to protect the blunt body reentry vehicle. The full Navier-Stokes equations are used for heat-flux estimation during flight, and the one-dimensional equations for an ablative materials are used to design the thermal protection system, according to the structural criteria.

再入体缩比模型湍流等离子体电磁散射特性测量

再入体缩比模型湍流等离子体电磁散射特性测量

Modeling of stagnation-line nonequilibrium flows by means of quantum based collisional models

The stagnation-line flow over re-entry bodies is analyzed by means of a quantum based collisional model which accounts for dissociation and energy transfer in N2-N interactions. The physical model is based on a kinetic database developed at NASA Ames Research Center. The reduction of the kinetic mechanism is achieved by lumping the rovibrational energy levels of the N2 molecule in energy bins. The energy bins are treated as separate species, thus allowing for non-Boltzmann distributions of their populations. The governing equations are discretized in space by means of the Finite Volume method. A fully implicit time-integration is used to obtain steady-state solutions. The results show that the population of the energy bins strongly deviate from a Boltzmann distribution close to the shock wave and across the boundary layer. The sensitivity analysis to the number of energy bins reveals that accurate estimation of flow quantities (such as chemical composition and wall heat flux) can be obtained by using only 10 energy bins. A comparison with the predictions obtained by means of conventional multi-temperature models indicates that the former can lead to an overestimation of the wall heat flux, due to an inaccurate modeling of recombination in the boundary layer.