Re-entry Scenarios Research Articles

Potential Ozone Depletion From Satellite Demise During Atmospheric Reentry in the Era of Mega‐Constellations

AbstractLarge constellations of small satellites will significantly increase the number of objects orbiting the Earth. Satellites burn up at the end of service life during reentry, generating aluminum oxides as the main byproduct. These are known catalysts for chlorine activation that depletes ozone in the stratosphere. We present the first atomic‐scale molecular dynamics simulation study to resolve the oxidation process of the satellite's aluminum structure during mesospheric reentry, and investigate the ozone depletion potential from aluminum oxides. We find that the demise of a typical 250‐kg satellite can generate around 30 kg of aluminum oxide nanoparticles, which may endure for decades in the atmosphere. Aluminum oxide compounds generated by the entire population of satellites reentering the atmosphere in 2022 are estimated at around 17 metric tons. Reentry scenarios involving mega‐constellations point to over 360 metric tons of aluminum oxide compounds per year, which can lead to significant ozone depletion.

Conceptual design for a 5 kWe space nuclear reactor power system

Enhancing the capabilities of unmanned space exploration, such as satellite monitoring and space science missions, requires efficient and reliable nuclear power systems. A viable solution is found in the 1–10 kWe power level of space nuclear reactor power systems, offering advantages such as a manageable research and development process, and relatively low investment requirements. This paper introduces a conceptual design for a 5 kWe space nuclear reactor power system, outlining its components and characteristics. The study includes a thorough analysis of potential challenges, encompassing heat pipe failure accidents, re-entry scenarios, and weight estimation considerations. The results demonstrate that the proposed space nuclear reactor power system effectively meets the safety requirements. The total mass of the power system is estimated at approximately 1.5 tons, with a specific mass of around 300 kg/kWe. This research contributes valuable insights for the design of space nuclear reactor power systems operating within a similar power range.

Unsteady evolution of distributed roughness-induced vortices under re-entry conditions

AbstractThis study investigates a re-entry scenario of an Apollo-like space capsule with Direct Numerical Simulations (DNS). The simulation includes the chemical equilibrium gas model. Cross-flow-like vortices are induced through random distributed roughness patches on the capsule surface. Two different machine learning methods are used to predict the maximum vorticity magnitude downstream of a pseudo-random roughness patch, the wall-normal location of the vortex core and spanwise and wall-normal gradient maxima of u. A large DNS database is formed for training and testing of the neural networks. In order to understand the influence of the vorticity magnitude on the transition process, local one-dimensional inviscid (LODI) relations are used to describe perturbations at the inflow. The disturbance evolution in the streamwise direction is analysed with a two-dimensional Fourier transformation in time and space. We show how the vorticity magnitudes of the cross-flow-like vortices, spanwise and wall-normal derivatives of the streamwise velocity influence the transition location.

Investigation of vortical structures in the wake of pseudo-random roughness surfaces in hypersonic reacting boundary-layer flows

The influence of roughness on the laminar-turbulent transition of hypersonic flows is investigated with Direct Numerical Simulations (DNS) in a re-entry scenario of an Apollo-like space capsule. A Mach 20 flow regime is simulated for conditions at an altitude of 57.5 km. This study uses two different generating shapes (sinusoidal and triangular shaped waves) for random distributed patches. Stronger streamwise vorticity is observed for most configurations with the triangular base functions. The simulation includes the chemical equilibrium gas model. Vortical structures in the wake of both roughness patch types interact with an acoustic perturbation derived from local one-dimensional inviscid (LODI) relations. A breakdown of the cross-flow-like vortex in the wake of the roughness patch is observed for both roughness patches. The growth of modal instabilities is studied with a spatio-temporal Fourier analysis. Both y- and z-type instabilities, which are present in cross-flow vortices at low speeds, are observed for the sinusoidal patch. In the triangular configuration, the y-type instability is the dominating instability which is in line with the stronger wall-normal velocity gradients caused by the increase in spanwise slope of the patch.

Analysis of Propellant Weight under Re-Entry Conditions for a Reusable Launch Vehicle Using Retropropulsion

In this study, a minimum amount of required propellant was calculated by analyzing the sequence with various re-entry conditions. This study aims to obtain data related to variation in trajectory and required propellant weight according to various re-entry scenarios. The drag coefficient at various altitudes, velocities, and thrust was calculated through numerical simulations to raise the reliability of the results. The calculation results were compared to the optimal values extracted from the genetic algorithm. It was observed that the duration of the entry-burn phase is dominant to the total required propellant weight. As a general tendency, high entry-burn starting altitude, high ending Mach number, and low landing-burn starting thrust make the required propellant weight low. However, if the entry-burn ending condition is set to the Mach number, it is necessary to select an appropriate re-entry condition. Additionally, from comparisons with the optimized results, it was confirmed that accurate calculation of the drag coefficient is important to succeed a soft landing of RLV.

Skip Re-Entry Trajectory Detection and Guidance for Maneuvering Vehicles.

The re-entry trajectory of maneuvering vehicles with medium to high hypersonic lift-to-drag ratios is generally planned using quasi-equilibrium flight conditions known from Space Shuttles. They may exhibit an oscillation re-entry phenomenon termed skip re-entry when related components or sensors fail. However, conventional re-entry guidance only considers quasi-equilibrium flights and ignores the possibility of the occurrence of an unexpected skip trajectory; this may lead to the failure of the re-entry mission due to a lack of a corresponding guidance strategy. However, the detection of a skip trajectory is the necessary reference for the decision-making of calling a related guidance algorithm that helps improve the safety of vehicle re-entry. Herein, a skip re-entry detection and trajectory control solution is proposed to play an emergency role in the cases of skip re-entry. Firstly, the oscillation frequency characteristics of the linearized re-entry motion equation of a vehicle are analyzed, and an approximate analytical relationship is constructed for skip altitude estimation. Then, the residual deviation between the altitude feedback data and the estimated skip altitude is calculated and compared with the threshold to determine the occurrence of skip re-entry. In addition, a method for controlling the skip re-entry trajectory with the range extension is developed by controlling the bank angle with a fixed angle of attack profile, satisfying the path constraint requirements. The results indicate that the method effectively performs skip re-entry detection and that it can help extend the range of the vehicles in abnormal re-entry scenarios, keeping the flight within the path constraints and guiding it to the expected location.

“Came for the horses, stayed for the men”: A mixed methods analysis of staff, community, and reentrant perceptions of a prison-equine program (PEP)

Prison-equine programs (PEPs) appear to play a role in rehabilitating incarcerated persons (IPs) by teaching equine and farrier skills, as well as promoting therapeutic effects through the human-animal bond. Using a mixed-methods approach guided by ecological theory, the present study explored the perceptions of PEP staff, graduates, and community members attending a public PEP event. Findings from both thematic qualitative analysis and descriptive quantitative results indicated that community members reported significantly less stigma toward PEP participants than general IPs. Focus group results with PEP staff indicated personal transformation through witnessing PEP participant rehabilitation. Interviews with PEP graduates (i.e., reentrants) identified relationships with staff and peers, as well as the barn environment, in maintaining positive change during reentry. Findings are represented by four themes: Experiencing change, Witnessing change, Mechanisms of change, and Future of the program. These findings are the first to highlight how person-environment interactions create important mesosystem links that may promote development, prime positive reentry scenarios, and enable stakeholder support of PEPs across ecological levels.

Roughness-Induced Boundary-Layer Transition on a Hypersonic Capsule-Like Forebody Including Nonequilibrium

The present work investigates the influence of high-temperature gas effects on the laminar–turbulent transition induced by a patch of distributed roughness on a hemispherical capsule-like geometry. The freestream conditions correspond to a realistic reentry scenario at Mach 20. At these conditions, chemical reactions and nonequilibrium effects are present in the high-enthalpy boundary layer of the hemisphere. Parallel Direct Numerical Simulations are undertaken to analyze the instability mechanisms in the crossflow-type vortex developing in the wake of a skewed protuberance of the roughness patch. Both linear and nonlinear growth of unsteady disturbances forced in the roughness wake, including laminar–turbulent breakdown, are considered in the analysis. The primary focus of the study is how chemical and thermal nonequilibrium affect the location of the laminar–turbulent transition as well as the level of wall heating in the transitional boundary layer for the considered capsule configuration. The results highlight the necessity to include nonequilibrium effects in this problem of roughness-induced transition at high-altitude reentry conditions because the gas modeling turns out to have a notable influence on the development of instabilities, both in the linear and in the nonlinear ranges.

Roughness-Induced Crossflow-Type Instabilities in a Hypersonic Capsule Boundary Layer Including Nonequilibrium

The current study investigates the unsteady disturbance development in a three-dimensional, high-enthalpy boundary layer on a capsule-like hemispherical geometry with pseudo-random distributed roughness. Direct Numerical Simulations are conducted for a typical reentry scenario at where chemical dissociation takes place. Unsteady disturbances at various frequencies are introduced into the flow to analyze the instabilities developing in the wake of the roughness patch. The amplification of small disturbances is shown for various chemical models (i.e., chemical equilibrium, chemical nonequilibrium, and thermochemical nonequilibrium). The largest disturbance amplification is observed for a crossflow-type vortex developing in the wake of the highest skewed protuberance of the roughness patch. The modes of instability of this crossflow-type vortex are analyzed and compared for different frequencies. The influence of the different nonequilibrium effects on the steady base flow as well as on the disturbance development is quantified and compared. The study highlights the necessity to include nonequilibrium effects in transitional scenarios as the unsteady development of the instabilities are affected strongly by the chemical modeling.

Dermal Absorption of Pesticide Residues.

Current guidance for dermal exposure assessment of plant protection products typically uses in vitro skin penetration data for the active ingredient when applied as both the concentrated product and relevant spray dilutions thereof. However, typical re-entry scenarios involve potential skin exposure to a "dried residue" of the spray dilution, from which the absorption of a pesticide may be quite different. The research reported in this paper has shown: (1) The method to assess the transfer of dried pesticide residues from a surface to the skin is reproducible for four active ingredients of diverse physicochemical properties, after their application in commercially relevant formulations. (2) Skin absorption of all four pesticides examined was significantly less from a dried residue than from a spray dilution; the difference, in general, was of the order of a factor of 2. (3) Decontamination experiments with one of the active ingredients tested (trinexapac-ethyl) showed that, post-exposure to a spray dilution, skin surface cleaning must be performed within 1 h to significantly reduce potential systemic exposure (relative to continual contact for 24 h); in contrast, after contact with a dried residue, the sooner decontamination was performed, the greater the decrease in exposure achieved, even when the time of contact was as long as 8 h.

Reentry Trajectory Optimization for a Hypersonic Vehicle Based on an Improved Adaptive Fireworks Algorithm

Generation of optimal reentry trajectory for a hypersonic vehicle (HV) satisfying both boundary conditions and path constraints is a challenging task. As a relatively new swarm intelligent algorithm, an adaptive fireworks algorithm (AFWA) has exhibited promising performance on some optimization problems. However, with respect to the optimal reentry trajectory generation under constraints, the AFWA may fall into local optimum, since the individuals including fireworks and sparks are not well informed by the whole swarm. In this paper, we propose an improved AFWA to generate the optimal reentry trajectory under constraints. First, via the Chebyshev polynomial interpolation, the trajectory optimization problem with infinite dimensions is transformed to a nonlinear programming problem (NLP) with finite dimension, and the scope of angle of attack (AOA) is obtained by path constraints to reduce the difficulty of the optimization. To solve the problem, an improved AFWA with a new mutation strategy is developed, where the fireworks can learn from more individuals by the new mutation operator. This strategy significantly enhances the interactions between the fireworks and sparks and thus increases the diversity of population and improves the global search capability. Besides, a constraint-handling technique based on an adaptive penalty function and distance measure is developed to deal with multiple constraints. The numerical simulations of two reentry scenarios for HV demonstrate the validity and effectiveness of the proposed improved AFWA optimization method, when compared with other optimization methods.

Sensitivity analysis and probabilistic re-entry modeling for debris using high dimensional model representation based uncertainty treatment

Well-known tools developed for satellite and debris re-entry perform break-up and trajectory simulations in a deterministic sense and do not perform any uncertainty treatment. The treatment of uncertainties associated with the re-entry of a space object requires a probabilistic approach. A Monte Carlo campaign is the intuitive approach to performing a probabilistic analysis, however, it is computationally very expensive. In this work, we use a recently developed approach based on a new derivation of the high dimensional model representation method for implementing a computationally efficient probabilistic analysis approach for re-entry. Both aleatoric and epistemic uncertainties that affect aerodynamic trajectory and ground impact location are considered. The method is applicable to both controlled and un-controlled re-entry scenarios. The resulting ground impact distributions are far from the typically used Gaussian or ellipsoid distributions.

On-ground casualty risk reduction by structural design for demise

In recent years, awareness concerning the on-ground risk posed by un-controlled re-entering space systems has increased. On average over the past decade, an object with mass above 800kg re-enters every week from which only a few, e.g. ESA’s GOCE in 2013 and NASA’s UARS in 2011, appeared prominent in international media. Space agencies and nations have discussed requirements to limit the on-ground risk for future missions. To meet the requirements, the amount of debris falling back on Earth has to be limited in number, mass and size. Design for demise (D4D) refers to all measures taken in the design of a space object to increase the potential for demise of the object and its components during re-entry. SCARAB (Spacecraft Atmospheric Re-entry and Break-Up) is ESA’s high-fidelity tool which analyses the thermal and structural effects of atmospheric re-entry on spacecraft with a finite-element approach. For this study, a model of a representative satellite is developed in SCARAB to serve as test-bed for D4D analyses on a structural level. The model is used as starting point for different D4D approaches based on increasing the exposure of the satellite components to the aero-thermal environment, as a way to speed up the demise. Statistical bootstrapping is applied to the resulting on-ground fragment lists in order to compare the different re-entry scenarios and to determine the uncertainties of the results. Moreover, the bootstrap results can be used to analyse the casualty risk estimator from a theoretical point of view. The risk reductions for the analysed D4D techniques are presented with respect to the reference scenario for the modelled representative satellite.

Aerodynamic and aerothermodynamic analysis of high-speed earth re-entry capsule

This paper deals with the computational fluid dynamics analysis of a capsule entering the earth atmosphere at the end of a sample return mission. Several numerical simulations have been carried out to assess the flowfield environment past a sphere-cone capsule, by using non-equilibrium reacting gas approximations. Heat shield ablation and effects of flow plasma radiation on capsule aeroheating are also accounted for in the flowfield analysis. The issue of aerodynamic and aerothermodynamic performance of the entry spacecraft in the framework of a super-orbital re-entry scenario is addressed.

Hypersonic environment assessment of the CIRA FTB-X re-entry vehicle

This paper deals with design activities performed by CIRA in the frame of its flying test bed vehicle development, named FTB-X. The re-entry scenario with the corresponding loading environment for the proposed vehicle, devoted to research activities in re-entry technologies, is reported and analyzed. The hypersonic environment characteristics of FTB-X are investigated on a trajectory-based design approach by means of several engineering and CFD analyses. Being a phase A design, the air is modeled only as a perfect gas and the analyses were based on laminar flow conditions, while only a preliminary analysis of real gas and turbulence effects has been performed in time. The results show that the aerodynamics derived from engineering design approach is sufficiently accurate for preliminary analysis purpose; moreover, surface heat loads were computed on the vehicle configuration for thermal shield design scopes.

Aerodynamic and aerothermodynamic design of Future Launchers Preparatory Program concepts

In the frame of the Future Launchers Preparatory Program, being developed by the European Space Agency, several Reusable Launch Vehicle concepts are under investigation. In this paper the current design activities at phase-A level, carried out by Centro Italiano Ricerche Aerospaziali, are described. The goal has been to define the preliminary hypersonic aerodynamic and aerothermodynamic databases of each vehicle for concept competition. To this end, different design approaches have been addressed as engineering methods and computational fluid dynamics. The re-entry scenario with the corresponding loading environment for each launcher concept is reported and analyzed. The final results, applicable for the prosecution of the launcher design activities, are that, at the condition of descent trajectory peak heating, the vehicle features a stagnation point heat flux ranging form about 500 to 40 kW/m2 whereas the aerodynamic lift-to-drag ratio at 40 deg angle of attach is about 1.0.

Assessment of Dermal Exposure to Pesticide Residues during Re-entry

Currently, the determination of health risks to pesticide applicators from dermal exposure to these chemicals is assessed using either a concentrate of the compound or a relevant aqueous dilution. Neither of these conditions reflects a normal exposure of an individual when re-entering an area after pesticide application, that is, contact with dried residue of the diluted product on foliage. Methodology has therefore been developed to determine a relevant estimate of this potential dermal re-entry exposure from pesticide residues. Potential delivery platforms have been characterized for the transfer of pesticide residue to skin. Spin coating has been used to deposit uniform pesticide layers on to each platform. Five pesticides have been chosen to encompass a wide range of physicochemical properties: atrazine, 2,4-dichlorophenoxyacetic acid (2,4-D), chlorpyrifos, monocrotophos, and acetochlor. In vitro (Franz diffusion cell) experiments have been performed to monitor the transfer of these pesticides from the delivery platforms onto and through excised porcine skin. Parallel experiments were also conducted with aqueous pesticide dilutions for comparison, and a final in vivo measurement using ibuprofen (as a model compound) complemented the in vitro data. The results demonstrate that transfer of chemical residue onto and subsequently through the skin is dependent on the physical attributes of the residue formed. Thus, assessing dermal exposure to pesticides based on skin contact with either the chemical concentrate or a relevant aqueous dilution may incorrectly estimate the risk for re-entry scenarios.

Nonequilibrium Aerothermodynamics for a Capsule Reentry Vehicle

This paper deals with the aerothermodynamic analysis of a capsule Crew Return Vehicle concept for the low Earth orbit support service. The reentry scenario with the corresponding loading environment is described and analyzed. Real gas aerothermodynamics and catalytic effects on the vehicle forebody heat shield have been taken into account. To this end, several Navier-Stokes computational fluid dynamics analyses have been performed in correspondence with the reentry peak heating conditions by considering the air as a nonequilibrium reacting gas mixture. The effects of chemical nonequilibrium on the vehicle forebody heat shield are pointed out, by assuming its surface alternately as a non-catalytic, partially catalytic and fully catalytic wall. This work confirms that the knowledge of the flow chemical environment is crucial for the exact prediction of the vehicle aeroheating. In fact, the possibility of reducing the heat loads by using a low-catalytic heat shield has been highlighted.

Comparative evaluation of absorbed dose estimates derived from passive dosimetry measurements to those derived from biological monitoring: Validation of exposure monitoring methodologies

Passive dosimetry (PD) methods for measuring and estimating exposure to agricultural workers (i.e., persons handling agricultural chemicals and working in treated crops) have been in use since the 1950s. A large number of studies were conducted in the 1950s through 1970s to characterize exposure. Since the 1980s quantitative dermal PD methods are used in conjunction with inhalation PD methods to measure whole-body exposure. These exposure or absorbed dose estimates are then compared to "no effect" exposure levels for hazards identified in toxicology studies, and have become the standard for risk assessment for regulatory agencies. The PD methods used have never been validated. Validation in the context of human exposure monitoring methods means that a method has been shown to measure accurately a delivered dose in humans. The most practical alternative to isolating parts of the body for validating recovery methods is to utilize field exposure studies in which concurrent or consecutive measurements of exposure and absorbed dose have been made with PD and biomonitoring in the same cohorts of individuals. This ensures that a direct comparison can be made between the two estimates of absorbed dose, one derived from PD and the other from biomonitoring. There are several studies available (published and proprietary) employing both of these approaches. Reports involving 14 concurrent or consecutive PD-biomonitoring studies were quantitatively evaluated with 18 different methods of application or reentry scenarios for eight different active ingredients for which measured human kinetics and dermal absorption data existed. This evaluation demonstrated that the total absorbed dose estimated using PD for important handler and reentry scenarios is generally similar to the measurements for those same scenarios made using human urinary biomonitoring methods. The statistical analysis of individual worker PD:biomonitoring ratios showed them to be significantly correlated in these studies. The PD techniques currently employed yield a reproducible, standard methodology that is valid and reliably quantifies exposure.

Risk of nuclear powered space probes

Abstract In recent years, three probes have been sent into outer space: Galileo, Ulysses and Cassini. Each has used for its electricity power source, a radioactive thermoelectric generator (RTG), heated by a source of plutonium 238. Cassini, launched in October 1997, will reach its scientific objective in late June or early July 2004, concurrent with PSAM7. The authors of this paper had the privilege of providing the final review of the Cassini safety assessments for the Office of Science and Technology of the President, before final approval by the President of the United States, as required by law and international treaty, before the launch of any nuclear device into space. In this paper, we will discuss the risk analysis carried out jointly by NASA and DOE and our assessment of their results. Since the United States has established a new initiative for space exploration using a nuclear fission device for exploration of the icy moons of Jupiter (JIMO), we believe the JIMO project can benefit from a critical review of the experience gained by past projects using RTGs, and in particular identification of those aspects which make the risk estimates plausible to the layman. There are several scenarios for possible adverse effects on public health. The probabilities for each scenario must be added to form a number for the overall risk. The probability of each scenario is a product of two basic terms: the probability of release of plutonium and the probability of an individual being hurt by the release. It is evident that the probabilities for the two terms are truly independent. For example, there is reason to believe that the probability of the space probe hitting the earth in a failed ‘swing by’ only has a connection with the stochastic probability of developing lung cancer by the amount of plutonium evaporated and not by the mechanism of cancer induction. Each probability is on the order of one in a million. Then it is easy to understand why the risk to an individual of a ‘swing by’ is less than one in 1011 years, although the more complex NASA-DOE calculations, which allow for a reduction in the plutonium release for many possible reentry scenarios, puts it a factor of 50 smaller. We also comment on the procedures used for calculating the probabilities and consequences of these scenarios, on presenting these calculations to the public, on errors in various public comments on the Cassini Environmental Impact Statement, and on the comparative risks from RTGs and small nuclear reactors.