Entry Vehicle Research Articles

Thermochemical Non-Equilibrium in Thermal Plasmas

In this paper, we analyze the departure from equilibrium in two specific types of thermal plasmas. The first type deals with the plasma produced during the atmospheric entry of a spatial vehicle in the upper layers of an atmosphere, specifically the one of Mars. The second type concerns the plasma produced during the laser-matter interaction above the breakdown threshold on a metallic sample. We successively describe the situation and give the way along which modeling tools are elaborated by avoiding any assumption on the thermochemical equilibrium. The key of the approach is to consider the excited states of the different species as independent species. Therefore, they obey to conservation equations involving collisional-radiative contributions related to the other excited states. These contributions are in part due to the influence of electrons and heavy particles having a different translation temperature. This ‘state-to-state’ approach then enables the verification of the excitation equilibrium by analyzing Boltzmann plots. This approach leads finally to a thorough analysis of the progressive coupling until the equilibrium asymptotically observed.

Starchips in solar system planetary exploration: an opportunity for Canada

This paper is intended to provoke a discussion within the space community of how a starchip architecture could benefit the exploration of the solar system and the part that Canada might play in advancing and using this technology. We find that the amount of required development is greatly reduced with a viable pathway to implementing this technology by the mid 2020s. Canada's expertise in optics, spacecraft development and geographical position offers unique advantages over other spacefaring nations in taking advantage of this opportunity. A 1-100 MW facility located above the Arctic Circle would allow for the exploration of much of the solar system through planetary fly-bys. Furthermore, as starchips make excellent entry vehicles and may make effective solar sails, such architecture would enable network science near planets in the inner solar system and on the surfaces of those with substantial atmospheres, such as Mars, Venus, Titan and the Giant Planets.

Computational Fluid Dynamics Simulations of Supersonic Inflatable Aerodynamic Decelerator Ballistic Range Tests

The free-flight behavior of entry vehicles can greatly impact vehicle and mission design. Current methodologies rely heavily on ground and flight experiments, while computational fluid dynamics is largely used as a complement to experiments in the form of static aerodynamic databases. The dynamic stability of entry vehicles is primarily studied through ballistic range experiments and flight tests. In an effort to validate the predictive capabilities of computational fluid dynamics for free-flight aerodynamic behavior, numerical simulations of a ballistic range experiment are performed using the unstructured finite-volume Navier–Stokes solver, US3D. The ballistic range tests used for comparison in this paper were performed on a scaled model of the Supersonic Inflatable Aerodynamic Decelerator geometry. The purpose of these experiments was to provide aerodynamic coefficients of the vehicle as an a priori analysis of dynamic stability coefficients ahead of the Supersonic Flight Demonstration Test. The range data span the moderate Mach number range, 3.8–2.0, with a maximum total angle-of-attack range, 10–20 deg. These conditions are intended to span the Mach/angle-of-attack space for the majority of the flight test. Comparisons to raw vehicle attitude and postprocessed aerodynamic coefficients are made between simulated results and experimental data. The resulting comparisons for both the raw model attitude and derived aerodynamic coefficients show good agreement with experimental results. Additionally, near-body pressure field values for each trajectory simulated are investigated. Extracted surface and wake pressure data give further insight into dynamic/flow coupling, leading to a potential mechanism for dynamic instability.

Mars entry guidance using a semi-analytical method

Future Mars missions may require improved landed accuracy to facilitate the landing site selection and finally access a region of complex terrain with high scientific return. This paper is to develop a novel, robust, and precision entry guidance algorithm for Mars entry vehicles with low lift-to-drag ratios. In the presence of large uncertainties, the entry terminal point controller algorithm can encounter severe performance degradation due to: (1) the small perturbation assumption, and (2) theoretically ignoring deviations in the atmospheric-density model, aerodynamic-force model, etc. Based on numerical technologies and the classical variation method (VM), this work develops a semi-analytical (SA) algorithm, in which combined effects of several dynamic uncertainties now can be addressed. The terminal-downrange error is predicted by a numerical predictor such that the dependence on the reference trajectory can be reduced and then the issue caused by the small perturbation assumption can be addressed. Such a predicted terminal-downrange error is finally corrected by an analytical corrector, which is designed by the VM. It is indicative that there can be no numerical iterations in the SA algorithm. Numerical results demonstrate the effectiveness of the SA algorithm.

Qualitative Assessment of Aerocapture and Applications to Future Missions

We examine the current state of readiness of aerocapture at several destinations of interest, to identify what technologies are needed and to determine if a technology demonstration mission is required, before the first use of aerocapture for a science mission. The study team concluded that the current state of readiness is destination dependent, with aerocaptured missions feasible at Venus, Mars, and Titan with current technologies. The use of aerocapture for orbit insertion at the ice giant planets Uranus and Neptune requires at least additional study to assess the expected performance of new guidance, navigation, and control algorithms and possible development of new hardware, such as a mid-lift-to-drag entry vehicle shape or new thermal protection system materials. A variety of near-term activities could contribute to risk reduction for missions proposing the use of aerocapture, but an end-to-end, system-level technology demonstration mission is not deemed necessary before the use of aerocapture for a NASA science mission.

The High Enthalpy Shock Tunnel Göttingen of the German Aerospace Center (DLR)

The High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR) is one of the major European hypersonic test facilities. It was commissioned for use in 1991 and was utilized since then extensively in a large number of national and international space and hypersonic flight projects. Originally, the facility was designed for the investigation of the influence of high temperature effects such as chemical and thermal relaxation on the aerothermodynamics of entry or re-entry space vehicles. Over the last years its range of operating conditions was subsequently extended. In this framework the main emphasis was to generate test conditions which allow investigating the flow past hypersonic flight configuration from low altitude Mach 6 up to Mach 10 in approximately 33 km altitude. The studies performed in HEG focused on the external as well as internal aerodynamics including combustion of hydrogen in supersonic combustion and the investigation of transition from laminar to turbulent hypersonic flow.

Turbulent Aeroheating Measurements on a 7-Deg Cone in High-Enthalpy CO2 Flow

A database of heating and pressure measurements on a 7 deg half-angle cone in a high-enthalpy expansion tunnel in has been generated to support development and validation of computational models to be employed in the design of future Mars missions. Laminar, transitional, and turbulent simulations were performed at the test conditions for comparisons with the data. Close agreement was obtained for both fully laminar and fully turbulent conditions. For the remaining transitional/turbulent conditions, agreement to within, or slightly more than, the estimated experimental uncertainty was demonstrated. The influence of transition intermittency and transition length models on predicted heating levels was demonstrated, as were differences in turbulent heating predictions generated using various algebraic, one-equation, and two-equation turbulence models. These comparisons provide some measure of confidence in turbulent simulation capabilities; however, because the data were not obtained on a relevant entry vehicle geometry, it is not possible to fully quantify computational uncertainties for the definition of Mars mission aerothermodynamic environments at this time.

Entry trajectory planning with terminal full states constraints and multiple geographic constraints

This paper proposes an online entry trajectory planning algorithm satisfying terminal full states constraints, path constraints and multiple geographic constraints for lifting-body entry vehicles. The vehicle is considered as a 3DOF point mass. The entry trajectory is divided into the initial descent phase, gliding phase and terminal guidance phase. In the gliding phase, a piecewise polynomial in the altitude-versus-velocity plane is used to plan the longitudinal trajectory and a new heading angle corridor based bank angle reversal logic is designed to satisfy all geographic constraints simultaneously. In the terminal guidance phase, an optimal guidance law with terminal angle constraints is adopted to generate the trajectory. Finally, the terminal full states constraints including terminal velocity direction constraints are implemented by iterating over the altitude in the gliding phase. Then the highly constrained entry trajectory planning problem is converted into a one-parameter search problem. The key of this planning algorithm is the use of terminal guidance phase, through which the terminal velocity direction is constrained strictly rather than kept around the line-of-sight angle and the range error caused by great arc assumption is also avoided. Simulation results with the CAV-H model show that this algorithm can generate entry trajectories satisfying complex constraints rapidly and is suitable for various missions.

A Recent Volcanic Eruption Discovered on the Central Mariana Back-Arc Spreading Center

Submarine volcanic eruptions are difficult to detect because they are hidden from view at the bottom of the ocean and far from land-based sensors. However, most of Earth’s volcanic activity is in the oceans along tectonic plate boundaries, and modern tools of oceanography now allow us to find and study recent eruptions in the deep sea. The first known historical eruption on the Mariana back-arc spreading center was discovered in December 2015 during exploration of the southern back-arc for new hydrothermal vent sites. A water-column survey along the axis of the back-arc showed hydrothermal plumes over the site characterized by low particle concentrations and relatively high reduced chemical anomalies. A dive with the autonomous underwater vehicle Sentry collected high-resolution (1 m) multibeam sonar bathymetry over the site, followed by a near-bottom photographic survey of a smaller area. The photo survey revealed the presence of a pristine, dark, glassy lava flow on the seafloor with no sediment cover. Venting of milky hydrothermal fluid indicated that the lava flow was still warm and therefore very young. A comparison of multibeam sonar bathymetry collected by R/V Falkor in December 2015, to the most recent previous survey of the area by R/V Melville in February 2013, revealed large depth changes in the same area, effectively bracketing the timing of the eruption within a window of less than 3 years. The bathymetric comparison shows the eruption produced a string of lava flows with maximum thicknesses of 40–138 m along a distance of 7.3 km (from latitude 15∘22.3′ to 15∘26.3′N) between depths of 4050–4450 m bsl (meters below sea level), making this the deepest known historical submarine volcanic eruption on Earth. The cross-axis width of the lava flows is 200–800 m. The Sentry bathymetry shows that the new lava flows are constructed of steep-sided hummocky pillow mounds and are surrounded by older flows with similar morphology. In April and December 2016, two dives were made on the new lava flows by remotely operated vehicles Deep Discoverer and SuBastian. The pillow lavas have many small glassy buds on the steep flanks of the mounds, locally thick accumulations of hydrothermal sediment near the tops of mounds, and small cones of radiating pillows at their summits. The 2015–2016 observations show a rapidly declining hydrothermal system on the lava flows, suggesting that the eruption had occurred only months before its discovery in December 2015. The morphology of the pillow lavas is similar to other historical eruption sites, so the greater depth and ambient pressure of this site had no apparent effect on the processes of lava extrusion and emplacement. This study reveals that some segments of the Mariana back-arc have active magmatic systems despite the relatively low spreading rate, and that other eruptions are possible in the near future.

Time-optimal memetic whale optimization algorithm for hypersonic vehicle reentry trajectory optimization with no-fly zones

A novel time-optimal memetic whale optimization algorithm (WOA) integrating the Gauss pseudo-spectral methods (GPM), is proposed in this paper for the hypersonic vehicle entry trajectory optimization problem with no-fly zones. The WOA is featured with the strong global search ability and non-sensitive to the initial values, but also shows poor searching convergence speed around the global optimum. Conversely, GPM may be sensitive to the initial solution and easily trapped in a local optimum, but it also possesses more rapid convergence speed around the optimum and higher searching accuracy. Thus, a memetic optimization algorithm which contains a two-stage approach mechanism is proposed for searching the global optimum. The first searching stage, which is driven by an improved WOA (IWOA), works as an initializer of the entire searching due to its strong global search ability and non-sensitive to the initial values. The local optimum reservation and adaptive amplitude factor updating strategy are established to improve the convergent speed and the global search ability of the WOA. Once the changing of fitness value satisfies the predefined criterion, the next searching stage driven by GPM will take the place of the IWOA to expedite the search process around optimum and to obtain a precise global optimal solution. By this hybrid way, the proposed optimization algorithm may find an optimum more quickly and accurately. Simulation results show the proposed algorithm possesses faster convergence speed, higher accuracy, and stronger robustness for the hypersonic vehicle entry trajectory optimization.

Fault tolerant tracking of Mars entry vehicles via fuzzy control approach

In this paper, a fault tolerant attitude tracking control scheme is proposed for Mars entry vehicles (MEVs) with disturbances and actuator failures. The original attitude dynamics of MEVs is divided into two subsystems, named as slow subsystem and fast subsystem, respectively. For slow subsystem, the control-like angular velocity command is generated. For fast subsystem, the Takagi–Sugeno (T-S) fuzzy models are used to describe it at first. Based on these, the partial loss of actuator effectiveness with the generated angular velocity problem is transformed into solving the tracking problem with uncertain parameters. Then, a fault tolerant tracking control scheme is proposed by combining fuzzy line-integral Lyapunov function method with robust H∞ control approach. The proposed controller design is simple and can guarantee the faulty closed-loop system to be stable with acceptable attenuation level. Finally, the effectiveness of the proposed design method is demonstrated in a MEVs attitude control system subject to loss of actuator effectiveness.

Mars entry fault-tolerant control via neural network and structure adaptive model inversion

The capability of autonomous fault detection and reconstruction is essential for future manned Mars exploration missions. Considering actuator failures and atmosphere uncertainties, we present a new active fault-tolerant control algorithm for Mars entry by use of neural network and structure adaptive model inversion. First, the online BP neural network is adopted to conduct the fault detection and isolation. Second, based on the structure adaptive model inversion, an adaptive neural network PID controller is developed for Mars entry fault-tolerant control. The normal PID controller will be automatically switched into neural network PID controller when an actuator fault is detected. Therefore, the error between the reference model and the output of the attitude control system would be adjusted to ensure the dynamic property of the entry vehicle. Finally, the effectiveness of the algorithm developed in this paper is confirmed by computer simulation.

H∞ sampled-data fuzzy control for attitude tracking of mars entry vehicles with control constraints

In this paper, the problem of designing an H∞ sampled-data fuzzy controller is investigated for attitude tracking of Mars entry vehicles with control constraints. Initially, to overcome the difficulty of Takagi–Sugeno (T–S) fuzzy modeling, the original nonlinear error system is divided into a fast subsystem and a slow subsystem on the basis of two time-scale decomposition technique, where the fast subsystem describes the attitude dynamics and the slow subsystem describes the attitude kinematics. Dynamic inversion control method is subsequently employed to obtain the angular velocity command for the slow subsystem. Then, based on the angular velocity command and the T–S fuzzy model of the fast subsystem, a tracking error fuzzy system is derived for the sampled-data fuzzy control design. The existence condition of the constrained H∞ sampled-data fuzzy controllers is provided in terms of linear matrix inequalities (LMIs). The proposed controller can exponentially stabilize the original nonlinear error system with an H∞ tracking performance, provided that the timescale separation between the fast and slow subsystems is valid. Finally, simulation results illustrate the effectiveness of the proposed method.

The Final Stages of Slip and Volcanism on an Oceanic Detachment Fault at 13°48′N, Mid‐Atlantic Ridge

AbstractWhile processes associated with initiation and maintenance of oceanic detachment faults are becoming better constrained, much less is known about the tectonic and magmatic conditions that lead to fault abandonment. Here we present results from near‐bottom investigations using the submersible Alvin and autonomous underwater vehicle Sentry at a recently extinct detachment fault near 13°48′N, Mid‐Atlantic Ridge, that allow documentation of the final stages of fault activity and magmatism. Seafloor imagery, sampling, and near‐bottom magnetic data show that the detachment footwall is intersected by an ~850 m‐wide volcanic outcrop including pillow lavas. Saturation pressures in these vesicular basalts, based on dissolved H2O and CO2, are less than their collection pressures, which could be explained by eruption at a shallower level than their present depth. Sub‐bottom profiles reveal that sediment thickness, a loose proxy for seafloor age, is ~2 m greater on top of the volcanic terrain than on the footwall adjacent to the hanging‐wall cutoff. This difference could be explained by current‐driven erosion in the axial valley or by continued slip after volcanic emplacement, on either a newly formed or pre‐existing fault. Since current speeds near the footwall are unlikely to be sufficient to cause significant erosion, we favor the hypothesis that detachment slip continued after the episode of magmatism, consistent with growing evidence that oceanic detachments can continue to slip despite hosting magmatic intrusions.

Full Three-Dimensional Monte Carlo Radiative Transport for Hypersonic Entry Vehicles

A full three-dimensional photon Monte Carlo radiative transport solver, named StaRad, is developed to calculate thermal radiative heat flux and infrared signatures within equilibrium and nonequilibrium hypersonic flows. The code is developed to investigate arbitrary thermal radiative transport and is line-by-line accurate. The solver makes use of a ray plane tracing scheme. It can be used in combination with different spectral databases, such as NEQAIR, Plasma Radiation Database, or High Resolution Transmission (HITRAN)/HITEMP Radiation Database. Furthermore, it is developed to be coupled with a continuum fluid flow solver code for coupled computations. For this investigation, uncoupled computations will be presented. A validation with a reference method is presented. Because three-dimensional computation of radiative transport is time consuming, differences are investigated between piecewise one-dimensional and full three-dimensional computations. This is especially important for infrared signatures, as well as in the case of a detailed thermal protection design. This computational method can be efficiently used on a general-purpose graphical processing unit; hence, an overview of its benefits and computational speedup is given.

Vision-Based Parking Entry Control System

Vision-based control systems are very promising in the Intelligent Transportation System (ITS). This paper proposes a system that use the vision system to control vehicle entry at the bridge gate at a certain facility. The system detects the presence of the car and captures the front car image to proceed to plate recognition process. Vehicle plate region is extracted using the size filtering, image thresholding and object counting algorithms. Optical character recognition technique is used in the recognition module. The result from the recognition module is then compared to the record in the database for information like the vehicle owner name, type of car, etc. The overall system is implemented and simulated in LabVIEW and the performance of recognition is tested on the real image. The system can successfully detect and recognize the plate number with minimum error.

Re-entry trajectory optimization using pigeon inspired optimization based control profiles

In this paper, the entry trajectory optimization problem of lifting type re-entry vehicle with path constraints is solved using Pigeon Inspired Optimization (PIO). Entry trajectory optimization problem involves finding the control profiles, bank angle, and angle of attack to guide the vehicle safely to the destination. The proposed approach parametrizes the bank angle to be a linear function of energy while the angle of attack is considered to be a monotonic function of Mach number. Thus, the problem of finding control profiles is transformed into three parameter search problem. The PIO algorithm is used to find the values of these parameters that minimizes the objective function. The terminal heading angle offset is minimized using traditional bank reversal logic. A new approach is proposed in which the bank angle is modulated to eliminate the oscillations observed in the altitude profile of an entry vehicle with a high lift to drag ratio (L/D). A methodology to satisfy the given load factor constraint is also proposed, as an alternative to traditional penalty factor approach used for incorporating path constraints in PIO algorithm. The proposed approach is further validated by considering sub-cases with different load factor limits and bank angle as the only control variable. The angle of attack profile obtained from the previous case is considered as the nominal profile. The proposed trajectory optimization strategy using PIO algorithm is simulated for Common Aero Vehicle with high L/D ratio (CAV-H) with different load factor constraint limits. The results show that the obtained angle of attack profile minimizes the peak heat rate experienced by the vehicle and bank angle modulation eliminates the oscillations in the altitude profile as well as makes the entry trajectory satisfy the load factor constraint.

Research on Electric Vehicle Entry Control Strategy Based on Different Scenarios

Environmental pollution is becoming more and more serious. Traditional vehicle exhaust is one of the most important sources of pollution.Compared with traditional cars, electric vehicles have the characteristics of energy saving, emission reduction and pollution free.Large scale electric vehicles will impact the original distribution system to varying degrees.When the valley load is low, the electric vehicle can be charged as a load and connected to the system to recharge.At peak load, electric vehicle can be used as energy storage element to provide power for grid.The orderly access of electric vehicles to the power grid is much less than that of the disorderly access to the grid.For a specific area, the coordination of electric vehicle group with wind power, photo-voltaic power generation or micro grid can provide guarantee for the stability of power system.This paper makes a comparison and analysis of the control strategy of electric vehicles in different scenes, and puts forward the shortcomings in the study of the control strategy, which provides a reference for further research.

Design and Development of Traffic Light and IR Camera Computer Network; a Tool for Infrastructural Planning and Revenue Generation

A traffic light is a device that gives the right of way to any road user. The device is design with three visible colours made up of the Red, Yellow and Green light. It is used to control the movement of vehicles entry or leaving a junction of a town or cities. The red colour light indicates danger or stop movement. The yellow (amber) colour indicates get ready to start or stop movement. The green light indicates crossing the intersection without danger. The infrared camera (IR) is a light emitting diode (LEDs) which can video an image in an extreme low or absence of light condition. The IR camera when installed on a traffic light will capture every vehicle image, colour and the registration number of every vehicle that is given the right of way across an intersection in various locations. The captured data can be stored in a software drive (SD-card) or the hard-disk of the computer. The traffic light and IR camera are interface with a computer network system for visible and data retrieving for further programming processing. This system when installed can be used for infrastructural planning and revenue generation for the Government. It can also be used to prevent road accident and monitor the incessant knapping of the citizen. It serves as a tool for moral discipline for road user when defaulters are persecuted and charge to pay fine. The system will eliminate manual system of controlling traffic and embarrassment caused when there is traffic jam. The system is cheap and easy to install.

Aerothermal Measurements from the ExoMars Schiaparelli Capsule Entry

The instrumentation package was developed to measure aerothermal parameters on the back cover of the ExoMars Schiaparelli lander during Martian entry. The aerothermal sensors called Combined Aerothermal and Radiometer Sensor (COMARS) combine four discrete sensors, measuring static pressure, total heat flux, temperature, and radiative heat flux. After passing all acceptance tests, the Schiaparelli capsule was launched on top of the Proton launcher on March 14, 2016. All sensors operated nominally during the complete entry phase. But the complete data package is not available due to an anomaly that led to the failure of Schiaparelli shortly before landing. Nevertheless, a subset of the flight data was transmitted real-time during the entry and was received by the ExoMars 2016 orbiter, with the exception of the plasma blackout phase. The radiative heat flux on the back cover close to the vehicle shoulder was measured successfully for the first time on a Mars entry vehicle. The measured maximum radiative contribution was 61% of the total heat flux at the first measurement point after the blackout phase and 33% for the next measured trajectory point 10 s later. These measurements confirm recent findings that radiative heating can be a significant portion of total heating on the back cover during Mars entry. The maximum back cover total heat flux rate was measured at approximately 9% of the calculated stagnation point heat flux on the front cover. All measured heat fluxes on the back cover were below the levels that were used to design the thermal protection system.