Reentry Capsule Research Articles

Passive Fault-Tolerant Control of an Underactuated Re-Entry Capsule

The design of a passive fault-tolerant control for an underactuated re-entry capsule is considered in this paper; however, the control input of the capsule is failed. At first, kinematics and dynamics of the capsule are studied and modeled, and adaptive control law is used to design a passive controller for the control of the capsule. The guidance law for the capsule is designed based on the guidance law which is used in Apollo. A simulation is performed based on Apollo capsule in order to assess the controller. The result shows good control authority of the controller in the presence of failure in roll and yaw control channels. It is also shown that the guidance law is not credible in the presence of yaw channel input failure.

A hybrid numerical scheme for aeroheating computation of hypersonic reentry vehicles

Hypersonic aeroheating simulations were conducted for three-dimensional (3D) reentry capsule for the Mars Science Laboratory (MSL) using the AUSM and the Roe schemes. The study confirms that AUSM family of schemes generate unphysical oscillations in the wall heat flux distributions due to the unstable simulation of the shock wave. And the wall heat flux is underpredicted by the Roe scheme due to excess dissipation, even though captures the shock wave accurately. In order to overcome these limitations, we develop a numerical scheme that can capture the shock wave stably and still maintain an accurate prediction of the heat flux. We propose a novel hybrid scheme that combines both the AUSM+ and Roe schemes. Two different hybrid techniques are proposed for switching between the two schemes, one based on the shock wave detection and other utilizing a criterion based on the distance from the wall. The implementation of the two hybrid schemes for the 3D MSL reentry capsule was studied for prediction accuracy compared to experimental data. It is found that the second hybrid scheme (based on the criterion for switching based on distance from the wall) can eliminate the unphysical oscillations in the wall heat flux distributions and improve the aeroheating prediction accuracy.

Novel Efficient Particle-Based Hybrid Approach for Modeling Hypersonic Rarefied Flows

In the present work, a new two-dimensional parallel particle-based hybrid flow solver has been developed that couples the direct simulation Monte Carlo method and dynamic collision limiter method to simulate multiscale hypersonic rarefied flows. The Kolmogorov–Smirnov statistical test is used as the continuum breakdown parameter in this work. Based on the continuum breakdown parameter, the direct simulation Monte Carlo method is used where nonequilibrium flow regions are encountered, and the dynamic collision limiter method is used where flow regions are found to be in near-equilibrium state. The dynamic collision limiter scheme dynamically assigns a different number of collisions in cells per time step based on the local value of the Kolmogorov–Smirnov parameter such that the number of collisions is limited in near-equilibrium flow regions. Hypersonic flows over a wedge and Soyuz reentry capsule are simulated in the present work at widely different Knudsen numbers, and results are compared with other numerical data and with those obtained from the regular direct simulation Monte Carlo method. The hybrid direct simulation Monte Carlo/dynamic collision limiter particle scheme is shown to be as accurate as direct simulation Monte Carlo for the two flow problems considered in this work, with savings in the computational cost as compared with the direct simulation Monte Carlo method. Thus, the range of applicability of the direct simulation Monte Carlo method can be increased to handle higher density flows by using the direct simulation Monte Carlo/dynamic collision limiter numerical approach developed in this work.

Flight Analysis of Wedge and Blunt Nose Re-entry Capsules

Flight Analysis of Wedge and Blunt Nose Re-entry Capsules

Rarefied aerodynamics of a deployable re-entry capsule

Several research activities have been already carried out in the field of low-ballistic coefficient re-entry capsules based on deployable umbrella-like aero-shield. The flexible aero-shield, made of ceramic fabrics, acts both as an aero-brake and a Thermal Protection System (TPS), making possible to perform a re-entry from orbital or suborbital conditions with relatively low values of the aero-thermo-dynamic loads.Previous studies have already analyzed Aerodynamics of similar systems, identifying self-stabilizing configurations and creating a preliminary database of force and moment coefficients in different flight regimes.This work is intended to provide a systematic overview of the aerodynamic behavior of a deployable capsule in the rarefied regime, where the differences between the re-entry trajectories from Low-Earth-Orbit and suborbital flight conditions are more evident. Particular focus is given to the longitudinal stability analysis, which demonstrates that, as the continuum hypersonic regime approaches, the capsule could show a stable equilibrium condition in the unfavorable reverse attitude. This unwanted equilibrium condition could be counteracted by moving the center of gravity out of the symmetry axis.

Effect of geometrical parameters of reentry capsule over flowfield at high speed flow

The main purpose of the paper is to analyze effect of geometrical parameters of the reentry capsules such as radius of the spherical cap, shoulder radius, back shell inclination angle and overall length on the flow field characteristics. The numerical simulation with viscous flow past ARD (Atmospheric Reentry Demonstrator), Soyuz (Russian) and OREX (Orbital Reentry EXperimental) reentry capsules for freestream Mach numbers range of 2.0-5.0 is carried out by solving time-dependent, axisymmetric, compressible laminar Navier-Stokes equations. These reentry capsules appear as bell, head light and saucer in shape. The flow field features around the reentry capsules such as bow shock wave, sonic line, expansion fan and recirculating flow region are well captured by the present numerical simulations. A low pressure is observed immediately downstream of the base region of the capsule which can be attributed to fill-up in the growing space between the shock wave and the reentry module. The back shell angle and the radius of the shoulder over the capsule are having a significant effect on the wall pressure distribution. The effects of geometrical parameters of the reentry capsules will useful input for the calculation of ballistic coefficient of the reentry module.

Development and on-orbit operation of loop heat pipes on chinese circumlunar return and reentry spacecraft

This paper describes the development and result of ground experiment and analyzes the on-orbit operation of Loop heat pipes (LHP) for the Chinese circumlunar return and reentry spacecraft. A novel LHP was developed to satisfy the thermal control requirements of Inertial measurement units (IMU). The LHP consisted of an integrated evaporator subassembly, a cambered condenser, and an electric explosion valve. Ground experiments were conducted to investigate the startup characteristics, and heat transfer and heat insulation performance of the LHPs. During a flight mission, the LHPs work as a thermal switch and perform both heat transfer and insulation functions. Before returning to the earth’s atmosphere, the valves of the reentry capsule are opened to discharge working fluid and prevent heat transfer from the capsule wall to the devices. In the flight mission, the LHPs performed all the required functions, and the IMU temperatures were maintained within an allowable range.

Identification of the transient temperature and stress distribution in an atmospheric reentry capsule assuming temperature-dependent material properties

The purpose of this work is to develop a method for solving inverse transient-state thermal and strength non-linear problems in complex shapes. Non-linearity is caused both by the material temperature-dependent properties and radiation. The proposed algorithm reconstructs the whole transient temperature and thermal stress distribution based on temperatures measured in the element selected points. Measured transient temperature values are generated during a numerical simulation of aerodynamic heating on the atmospheric reentry capsule. Both constant and temperature-dependent properties of the material are assumed. A comparison is presented between the transient temperature distributions obtained based on the material constant and temperature-dependent properties. Finally, the developed method is used to identify the transient temperature and stress distribution in the atmospheric reentry capsule assuming temperature-dependent properties of the material. The proposed approach is expected to be a good solution for improving spacecraft structures.

Optimum design of ablative thermal protection systems for atmospheric entry vehicles

The Thermal Protection System (TPS) provides spacecrafts entering the atmosphere with the thermal insulation from the aerothermodynamic heating. The design of such a subsystem is very critical, considering that its damage can lead to a catastrophic failure of the whole entry system, in particular if ablative materials are considered. In order to design an ablative TPS, in fact, a reliable numerical procedure, able to compute surface recession rate, pyrolysis and internal temperature histories under severe heating conditions, is necessary. Indeed, the TPS needs to be sized to effectively shield the spacecraft from the high heat fluxes acting during the atmospheric entry phase. At the same time, its weight has to be the minimum value able to guarantee a suitable protection.This article aims to describe an optimization procedure for the design of ablative heat shields. In particular, in the present work, the numerical method is applied to the ablative TPS of the hypersonic reentry capsule Stardust.

Carbon fiber reinforced plastic Composite Structural Analysis on a Reentry Capsule Heat shield

The Reentry capsule exhibits a vast amount of aerodynamic heating and shear stress acting on the structure while entering into the earth atmosphere. Earlier reentry vehicle structures are made up of Metal-matrix composites (MMCs) and ceramic-matrix composites (CMCs) and titanium alloys which are thermally stable and can withstand loads at high temperatures, in this paper we have taken up structural analysis of capsule by replacing Carbon fiber rein forced plastic (CFRP) composite materials. The vehicle enters the earth's atmosphere with a Mach number 15-25 at an altitude of 100km from the sea level where the dense of air present, the capsule penetrate to the earth's atmosphere with a high velocity, the kinetic energy of the vehicles converts into Heat energy, it tends to melting the heat shield of capsule. In this paper we have calculated the Structural and aerodynamic behavior of reentry vehicle at Karman line above sea level and in the dense air. The methodology of this project followed is capsule designed in CATIA and did FEA Analysis.

Investigation of computational flow fields and aeroacoustic characteristics over a re-entry command module

Design and analysis of a wind tunnel model for re-entry vehicle configuration is a prolonged and expensive mission. As the aerothermodynamics loads acting on the vehicle are based on geometry, various wind tunnel models need to be built for aerodynamic characterization by experimental procedure. Alternatively, the intention of this article is to present the influence of aerodynamic and aero acoustic characteristics of a typical re-entry capsule by computational fluid dynamics analysis. A typical re-entry capsule is designed using computational design software and it is imported to a computational fluid dynamics solver and flow simulations are done at various input conditions. Stanford University unstructured computational fluid dynamics solver is used for this purpose to solve complex, multiphysics analysis, and optimization tasks. Computational fluid dynamics results are presented to understand the influence of aerodynamic characteristics of a typical re-entry capsule, by visualizing the flow field around the command module at all the flow regimes like subsonic, supersonic, and hypersonic flows. The flow fields are studied in detail and regions of high flow unsteadiness due to wake separated flow zone are identified. Aeroacoustic loading on the command module at these regions especially at shock wave zone are predicted in the present investigation with high order of accuracy.

Infrared spectroscopic measurements of carbon monoxide within a high temperature ablative boundary layer

Theoretical studies have indicated that the formation of carbon monoxide within a high temperature ablative boundary layer can significantly alter the afterbody radiative heat transfer to the surface of a reentry capsule. This paper represents a first attempt to experimentally measure the concentration of carbon monoxide within the high temperature boundary layer surrounding an ablative material exposed to an atmospheric pressure air plasma. A plasma torch facility was used to produce the high temperature flow and a sample of ASTERM ablative material was inserted into the flow. At the stagnation point, the heat flux to the surface was estimated at 8 MW m−2 and the surface temperature at 2900 ± 100 K. Both emission and absorption spectroscopy techniques were used to measure the distribution of carbon monoxide within the flow. Emission spectroscopy yielded better signal-to-noise measurements, but the absorption spectroscopy measurements were used to validate emission measurements. In the cases examined, both emission and absorption measurements were consistent and in agreement with one another. Estimates of carbon monoxide temperature and mole fraction were deduced from the spectra taken within the boundary layer downstream of the stagnation point. No carbon monoxide was observed at the stagnation point. These measurements provide a test case for numerical simulations of plasma-ablator interactions.

Tether-assisted re-entry capsule deorbiting from an elliptical orbit

The problem of a payload delivery from an elliptical orbit to Earth surface by a space tethered system is considered. This operation includes three stages: tethered motion, orbital flight of the payload to the border of the atmosphere, and its descent into the atmosphere. The third stage is critical for the whole mission, because the payload can be damaged as a result of thermal or dynamic loads. Thus, the first stage should provide the transition of the payload into a trajectory with the permissible loads. The objective of the paper is to determinate the conditions of the payload separation from the tether, which provide minimization of dynamical or thermal loads during the atmospheric motion or minimization of a perigee radius of the payload orbit.The mathematical models for the each stage and equations for loads calculation are presented in the paper. The series of numerical calculation shows that eccentricity of the satellite orbit significantly affects the trajectory of the capsule with the payload in the atmosphere. The location of separation points on elliptical orbits and angles of the tether deflection that provide a transfer of the capsule to the trajectory with minimum perigee radius, dynamical pressure, heat flux, and total heat were found. In contrast to the case of a circular orbit, the separation of the capsule at the local vertical does not provide a transfer into an orbit with a minimum radius of perigee. It was observed that the increase in eccentricity can leads to the decrease of the radius of perigee and the total heat, but at the same time to growth of the dynamic and thermal loads.The radius of perigee of the re-entry capsule cannot be considered as a single indicator of efficiency of the tether deployment control law. The set of thermal and mechanical constraints must be taken into consideration at the stages of the tether control law and the re-entry capsule design developing.

Numerical analysis of Hall effect on the performance of magnetohydrodynamic heat shield system based on nonequilibrium Hall parameter model

Magnetohydrodynamic (MHD) heat shield system, a novel thermal protection technique in the hypersonic field, has been paid much attention in recent years. In the real flight condition, not only the Lorentz force but also the Hall electric field is induced by the interaction between ionized air post shock and magnetic field. In order to analyze the action mechanisms of the Hall effect, numerical methods of coupling thermochemical nonequilibrium flow field with externally applied magnetic field as well as the induced electric field are constructed and validated. Based on the nonequilibrium model of Hall parameter, numerical simulations of the MHD heat shield system is conducted under two different magnetic induction strengths (B0=0.2T, 0.5T) on a reentry capsule forebody. Results show that, the Hall effect is the same under the two magnetic induction strengths when the wall is assumed to be conductive. For this case, with the Hall effect taken into account, the Lorentz force counter stream diminishes a lot and the circumferential component dominates, resulting that the heat flux and shock-off distance approach the case without MHD control. However, for the insulating wall, the Hall effect acts in different ways under these two magnetic induction strengths. For this case, with the Hall effect taken into account, the performance of MHD heat shield system approaches the case neglecting the Hall effect when B0 equals 0.2T. Such performance becomes worse when B0 equals 0.5T and the aerothermal environment on the capsule shoulder is even worse than the case without MHD control.

English

The temperature in the front region of a hypersonic vehicle nose can be extremely high, for example, reaching approximately 11 000 K at a Mach number of 36 (Apollo reentry) due to the bow shock wave. In this case, accurate prediction of temperature behind the shock wave is necessary in order to precisely estimate the wall heat flux. A better prediction of wall heat flux leads to smaller safety coefficient for thermal shield of space reentry vehicle; therefore, the size of thermal shield decreases and the payload could increase. However, the accurate prediction of temperature behind the bow shock wave implies the use of a precise chemical model whose partial differential equations are added to Navier-Stokes equations. This second order partial differential system is very difficult to be numerically integrated. For this reason, the present paper deals with the computational hypersonic aerodynamics with chemical reactions with the aim of supporting Earth reentry capsule design.

Study of droplets distribution on canopy of ringsail parachute in light rain

As a basal part of the entire study of reliability performance of ringsail parachute and re-entry capsule descending in rain environment, droplets distribution characteristics on canopy surface are investigated firstly via two-phase flow approach in the paper. The model of ringsail parachute and capsule is built on the basis of the sizes of Chinese Shenzhou series spacecraft components. The simulation of droplet trajectories is implemented numerically using the Discrete Phase Model. The numerical simulations considering various rainfall rates and velocities of a ringsail parachute and capsule descending in light rain conditions are conducted. The results show that for one specific rainfall rate, there is a homologous critical value of descending speed of parachute and capsule, which is the dividing line between raindrops being trapped and not being trapped by the canopy; if the descending velocity is less than the critical value, no raindrops will be captured; in raindrops-trapped cases the raindrops are distributed on the bottom skirt zones of the canopy surface and not evenly distributed. The work in the paper will be helpful and significant for the further study of the effects of rain environment on the spacecraft recovery.

Numerical simulation of raindrops distribution on canopy surface of hemispherical parachute in heavy rain via two-phase flow approach

The descent of parachute and re-entry capsule in heavy rain has been rarely researched yet. Study of raindrops distribution on canopy surface in heavy rain environment is a key step in the whole research. In this paper, the discrete phase model of two-phase flow approach is applied to simulate the raindrop trajectories in order to research the problem of raindrops distribution on canopy surface when parachute and re-entry capsule are descending in heavy rain. Numerous cases based on different rainfall rates and vertically descending velocities of a simple hemispherical parachute and re-entry capsule are numerically calculated preliminarily. The simulation results are presented, and it is found that the raindrops trapped by the canopy surface are not even-distributed, and raindrops are concentrated near the bottom edges of canopy surface as a result of high-pressure zone enclosed by the parachute; there is a corresponding critical value of descending velocity of parachute and re-entry capsule which determines whether the raindrops will be trapped by the canopy surface for one particular rainfall rate; only above the critical value of descending velocity of parachute and re-entry capsule the raindrops can be trapped by the canopy surface. The conclusions will be of great significance to the further research of the problem of descent of parachute and re-entry capsule in heavy rain.

Dynamic stability analysis and passive control method developing of a reentry capsule

Dynamic stability of a reentry capsule is analyzed numerically and passive control method is developed to reduce the self-excited free-to- pitch oscillation of the reentry capsule. The coupling equations comprising Navier-Stokes equations and Euler rigid body dynamic equation are employed to govern the free-to-pitch motion of the reentry capsule. By solving these equations, the free-to-pitch problem of reentry capsule is simulated numerically. The wake properties, including pressure distribution, vortex core structure and streamlines, were investigated to understand the flow mechanism of the pitching reentry capsule. For better understand the dynamic behavior of the reentry capsule, the unsteady moment of the fore-body and aft-body of the capsule are evaluated respectively. The results showed that the unstable effect is generated by the aft-body of the pitching reentry capsule. Based on the comprehension above, passive control methods are developed. Six modified reentry capsule models with different aft-body shapes are proposed. Theirs free-to-pitch characteristics, including amplitudes and frequencies, are evaluated numerically. The results showed that the dynamic stabilities of reentry capsule could be effectively improved by modifying the aft-body shape.

Aerodynamic-Heating Analysis of Sample-Return Capsule in Future Trojan-Asteroid Exploration

In sample-return missions, the reentry velocity of a sample-return capsule is expected to be approximately ; however, the reentry velocity of the Hayabusa sample-return capsule was . Strong aerodynamic heating caused by a high velocity can damage the capsule during reentry. To overcome this, two designs of high-velocity reentry capsules were proposed. In one design, a rigid flare was attached to decrease the ballistic coefficient by increasing the front projected area. In the other design, the conventional Hayabusa sample-return capsule was used with no modifications. In this study, the aerodynamic heating of the high-velocity reentry capsules and the Hayabusa sample-return capsule was analyzed using numerical simulations. Plasma flow in the shock layer at the front of the capsules and expansion flow in the wake region around the capsules were investigated. The profiles of convective and radiative heat fluxes on the surfaces of these capsules were predicted. The heat fluxes at the stagnation points predicted by the present numerical simulation were in good agreement with that of the empirical models. At the strongest aerodynamic-heating altitude, the total heat fluxes at the rear of the high-velocity reentry capsules and the Hayabusa sample-return capsule were approximately 2% of those in front of the capsules.

Chaotic Motion of a Reentry Capsule During Descent into the Atmosphere

Conical-shaped reentry capsules with a spherical bottom and a displaced center of mass from the axis of symmetry are widely used in astronautics for payload delivery. In the case of control-system breakage, modern reentry capsules allow a successful landing to be carried out in an uncontrolled mode. At the same time, the aerodynamic features of this particular shape create preconditions for chaotic motion. This can lead to an overturn of the capsule, thus creating the risk of an accident. This article explores uncontrolled descent of the reentry capsule, with slight asymmetry, into the atmosphere. The system of differential equations describing uncontrollable descent of an asymmetric capsule in the atmosphere was recorded. Fast and slow variables were introduced. A simplified system of equations was obtained, describing the change of the spatial angle of attack. It was shown that chaotic motion can occur during the uncontrolled descent in the atmosphere. The algorithm of damping coefficient selection was developed on the basis of Melnikov’s method. Its application allows for the elimination of chaos in the whole descent trajectory, thus increasing the system reliability.