Path Angle Research Articles

OMOTENASHI trajectory analysis and design: Landing phase

OMOTENASHI is a JAXA 6U cubesat that aims to perform a semi-hard landing on the Moon's surface after being deployed into a lunar fly-by orbit by the American Space Launch System, Exploration Mission-1. OMOTENASHI is a challenging mission – performing a semi-hard landing with a cubesat. One of the main challenges comes from the trajectory, which is characterized by a single deceleration maneuver instead of multiple ones for orbit insertion, descent, hovering and landing. After the deceleration maneuver, there is no time to correct for navigation and execution errors so the robustness of the trajectory is key. This paper presents the analysis and design of the OMOTENASHI landing phase. It studies the performance of the subsystems involved in the landing and proposes a deceleration maneuver to set to zero the vertical velocity at burn-out with a specified height over the Moon's surface, followed by a free-fall. In order to assess the robustness of the trajectory, it considers uncertainties in the state vector and deceleration maneuver execution. The flight path angle at lunar arrival has a great impact on the landing success rate, which imposes a very strong constraint on the design of the transfer phase trajectory. Under the current subsystems design, the most critical factors in the landing success rate are the maneuver orientation and thrust duration. Results suggest accuracy requirements for the landing devices, solid rocket motor and attitude accuracy, as well as for the transfer phase trajectory design. Finally, the navigation and maneuver execution errors may cause OMOTENASHI to prematurely impact against the surface during the solid rocket motor burn. This calls for a trade-off between the targeted final height and the maximum landing velocity.

Dynamic guidance of orbiter gliders: alignment, final approach, and landing

A new algorithm capable of guiding an orbiter glider to a target point with a prescribed alignment and descent path angle is presented. This algorithm can initiate Terminal Area Energy Management (TAEM) before reaching steady state and perform the Final Approach and Landing (FA&L). During TAEM, runway alignment is done through a moving virtual target derived from steady state, while during FA&L, a transient (or flare) is used to reach the extremely shallow descent path angles. All decisions are made dynamically relying solely on local information (position, speed, attitude, and atmospheric parameters), and all structural limits of the glider are respected at all times. As a proof of concept, a Space Shuttle return flight is simulated. For a large multitude of initial conditions and targets, the algorithm is able to consistently deliver distance errors below 19 m (transverse errors below 4 m), alignment errors below $$1^{\circ }$$ , descent path angles at the intended $$-\,2^{\circ }$$ , and vertical descent speeds below 8.5 m/s with control time intervals of 0.1 s.

Experimental advanced RNP to xLS approaches with vertical path coding and automatic landings

ABSTRACTWe report on the flight test results of an Airbus 320 during novel advanced required navigation performance (RNP) procedures which contain a fixed radius turn that delivers the aircraft onto a short instrument landing system (ILS) precision final. Moreover, the advanced RNP part contains altitude constraints and/or a coded vertical path angle. The approaches were flown automatically with guidance and autothrust as computed by the flight management system. We investigated the use of the fixed radius in conjunction with vertical path options onto (a) the performance of the speed profile for arrival time optimisation, (b) the vertical path during the RNP part of the procedure and (c) the performance of the autoland capability after a curved transition onto an ILS.For the trials, we designed five instrument approaches to a runway equipped with ILS. A RF curve terminates at the ILS intercept point at heights of 550, 750, 1000, 1500 and 2000 ft above aerodrome level and each approach had four different initial approach fixes which corresponded to a track angle change of 30°, 60°, 90° and 180° during the constant radius turn-to-final. We constructed the procedure such that the altitude constraints at initial, intermediate and final approach fix describe a continuous vertical path with minus 2° inclination, transitioning to the –3° glide path of the ILS and intercepting the glide path from below. In all cases, the land mode of the flight guidance computer became active between 316 and 381ft radar altitude. The vertical path following error depended on the coding of the procedure in the database. With coded vertical path angle and altitude constraints, the vertical path following error was never greater than +57 m (above desired flight path) during the RNP part when flown by the automatic flight guidance system without any pilot intervention.

First Attempt to Predict User Memory from Gaze Data

Many recommenders compute predictions by inferring the users’ preferences. However, in some cases, such as in e-education, the recommendations of pedagogical resources should rather be based on users’ memory. In order to estimate in real time and with low involvement what has been recalled by users, we designed a user study to highlight the link between gaze features and visual memory. Our protocol consisted in asking different subjects to remember a large set of images. During this memory test, we collected about 19 000 fixation points. Among other results, we show in this paper a strong correlation between the relative path angles and the memorized items. We then applied various classifiers and showed that it is possible to predict the users’ memory status by analyzing their gaze data. This is the first step so as to provide recommendations that fits users’ learning curve.

A controllability perspective of dynamic soaring

Dynamic soaring is an exquisite flying technique to acquire energy from the atmospheric wind shear. In this study, a geometric nonlinear controllability analysis of an unmanned aerial vehicle (UAV) under dynamic soaring conditions is performed. To achieve such an objective, the state-of-the-art mathematical tools of nonlinear controllability are summarized and presented to an aeronautical engineering audience. The dynamic soaring optimal control problem is then formulated and solved numerically. The controllability of the UAV along the optimal soaring trajectory is analyzed. More importantly, the geometric nonlinear controllability characteristics of generic flight dynamics are analyzed in the presence and absence of wind shear to provide a controllability explanation for the role of wind shear in the physics of dynamic soaring flight. It is found that the wind shear is instrumental in ensuring controllability as it allows the UAV attitude controls (pitch and roll) to play the role of thrust in controlling the flight path angle. The presented analysis represents a controllability-based mathematical proof for the energetics of flight physics.

Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA

Abstract. Three-dimensional measurements of gravity waves are required in order to quantify their direction-resolved momentum fluxes and obtain a better understanding of their propagation characteristics. Such 3-D measurements of gravity waves in the lowermost stratosphere have been provided by the airborne Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) using full angle tomography. Closed flight patterns of sufficient size are needed to acquire the full set of angular measurements for full angle tomography. These take about 2 h and are not feasible everywhere due to scientific reasons or air traffic control restrictions. Hence, this paper investigates the usability of limited angle tomography for gravity wave research based on synthetic observations. Limited angle tomography uses only a limited set of angles for tomographic reconstruction and can be applied to linear flight patterns. A synthetic end-to-end simulation has been performed to investigate the sensitivity of limited angle tomography to gravity waves with different wavelengths and orientations with respect to the flight path. For waves with wavefronts roughly perpendicular to the flight path, limited angle tomography and full angle tomography can derive wave parameters like wavelength, amplitude, and wave orientation with similar accuracy. For waves with a horizontal wavelength above 200 km and vertical wavelength above 3 km, the wavelengths can be retrieved with less than 10 % error, the amplitude with less than 20 % error, and the horizontal wave direction with an error below 10∘. This is confirmed by a comparison of results obtained from full angle tomography and limited angle tomography for real measurements taken on 25 January 2016 over Iceland. The reproduction quality of gravity wave parameters with limited angle tomography, however, depends strongly on the orientation of the waves with respect to the flight path. Thus, full angle tomography might be preferable in cases in which the orientation of the wave cannot be predicted or waves with different orientations exist in the same volume and thus the flight path cannot be adjusted accordingly. Also, for low-amplitude waves and short-scale waves full angle tomography has advantages due to its slightly higher resolution and accuracy.

GUIDANCE OF UNMANNED AERIAL VEHICLE ON THE LANDING GEAR OF THE VESSEL USING THE TRAJECTORY OF A GUIDE DOG

The problem of the UAV command on the landing gear of the vessel for a specified time to specified terminal conditions. Problem is solved in two stages: in the first phase as a result of solving the problem of optimal calculation software control when performing the specified terminal conditions is determined by the trajectory of the guide, which is calculated without taking into account the inertia of an aircraft apparatus and control system. When the program determines the optimal pitch angle change, as the sum of the optimum angle of attack changes angle and velocity, as well as the optimum traction motor change programme. In the second phase, the programme received are used to control the inertial aircraft, but by selecting options path angle is provided by pitch stabilization launch on toolpath guide with the specified terminal conditions. Provides a test case.

Simulation of positron and electron elastic mean free path and diffusion angle on DNA nucleobases from 10 eV to 100 keV

Positron and electron interaction collisions in living cells are efficiently simulated by Monte Carlo (MC) codes where huge data tables are needed. Present study provides detailed results of charged particles elastic interactions needed in MC on DNA nucleobases (adenine, thymine, cytosine and guanine, deoxyribose, and phosphoric acid). Indeed, electron and positron elastic cross sections, elastic mean free paths, and elastic angular distributions P(θ) are calculated from 10 eV to 100 keV using a corrected form of the independent atom method taking into account the geometry of the biomolecule. Our calculated results are compared with theoretical data available in the literature in absence of experimental data, in particular for positron. Moreover, our numerical results are presented in analytic format modeled to be used for fast sampling in the MC simulation of elastic collisions; particularly, we provide a useful analytic expression for sampling the elastic diffusion angle. For positron collisions on adenine, the relative error between numerical and analytic elastic diffusion angles is not exceeding 2% in the energy full range 10 eV to 100 keV.

Process-induced residual stress of variable-stiffness composite laminates during cure

One of the most important issues for designing variable-stiffness composite structures reflects on determination of the steered fiber paths. In this paper a linear variation of steered fiber curves and the change rule of the fiber angles were presented to create the mathematical model of variable-stiffness composite laminates. Compared to the straight-fiber laminate, the reference path with linearly changed angles leads to higher mechanical strength and more design freedoms. A novel methodology was developed to predict the distributions of process-induced residual stresses during cure. A three-dimensional (3D) thermochemical model of the curing process was established and the mechanical responses during cure were evaluated coupled with the results of thermochemical analyses. The distributions of the temperature and the degree of cure were obtained. The process-induced residual stresses were calculated using ABAQUS. The resin modulus was determined using the cure hardening instantaneous linear elastic (CHILE) model. The cure kinetic process was simulated using Kamal model for AS4/3501-6 prepregs. The results show that the process-induced residual stresses of variable-stiffness composite panels are reduced with increasing the end angle of the present fiber path during cure.

Modeling water flow on Façade

Abstract This study aims to develop a novel method by which visually to simulate water flow paths on building facades. Rainwater runoff affects the designs of facades in terms of safety and aesthetics because runoff leaves dirt and stains on an aesthetic facade. The first step is to review flow simulation algorithms and identify its limitations in fluid visualization research on flow path simulations. The second step is to review an existing CFD program to identify its limitations, and then establish the goals of the newly proposed method. The third step is to identify the properties and behaviors of water on a surface, including basic fluid mechanics to establish the mechanical relationship between the water and the facade material. The fourth step involves an experiment with water flows to reveal their characteristics based on the literature. The fifth step is to develop an algorithm which visually simulates water flows on a building facade. As a result, “Rainflow01” and “Rainflow02” are developed based on the open-source Grasshopper component “Drainage Polysurface” and Rhino. Rainflow01 and Rainflow02, which work based on the angle variation and critical sliding angle of the water path, present an innovative approach for predictions of water paths over a facade.

Method for estimating tropospheric bias in passive detection system

Electromagnetic wave propagated via troposcatter is a valuable candidate for beyond line-of-sight detection. To improve the location accuracy of passive detection system based on troposcatter, path delay and angle bias caused by tropospheric refraction effect are estimated through the ray tracing method. As well, the Hopfield model is introduced to overcome ray tracing method's dependence on radiosonde data. Finally, consequences indicate that the Hopfield model can describe the tropospheric refraction better than other models. As well, the ray tracing method improved by the Hopfield model can effectively estimate path delay and angle bias.

Downlink compressive channel estimation with support diagnosis in FDD massive MIMO

Downlink channel state information (CSI) is critical in a frequency division duplexing (FDD) massive multiple-input multiple-output (MIMO) system. We exploit the reciprocity between uplink and downlink channels in angular domain and diagnose the supports of downlink channel from the estimated uplink channel. While the basis mismatch effects will damage the sparsity level and the path angle deviations between uplink and downlink transmission paths will induce differences in channel supports, a downlink support diagnosis algorithm based on the DBSCAN (density-based spatial clustering of applications with noise) which is widely used in machine learning is presented. With the diagnosed supports of downlink channel in angular domain, a weighted subspace pursuit (SP) channel estimation algorithm for FDD massive MIMO is proposed. The restricted isometry property (RIP)-based performance analysis for the weighted SP algorithm is given out. Both the analysis and the simulation results show that the proposed downlink channel estimation with diagnosed supports is superior to the standard iteratively reweighted least squares (IRLS) and SP without channel priori or with the assumption of the common supports for uplink and downlink channels in angular domain.

Optimizing a vehicle trans-atmospheric motion using Pontryagin’s maximum principle

The task of optimizing trans-atmospheric motion of a flight vehicle in order to maximize its final velocity with prescribed finite values of the height and flight path angle is considered. The angle of attack acts as control in passive motion of a vehicle. Previously, the sequential linearization method was used to solve this optimization task. It is shown that at great altitudes the control programs are slightly different depending on the chosen initial approximation. Therefore, the aim of this work is to determine the optimum control program on the basis of a strict solution of the optimization task using the Pontryagins maximum principle. Solving the problem of optimizing trans-atmospheric motion of a flight vehicle is illustrated by passive climb of the sub-hypersonic vehicle MPV (the first stage of the aerospace system RASCAL designed in the USA). The coefficient of lift (angle of attack) increases in the greater part of the trajectory to provide the prescribed finite values of height and path inclination and then decreases to provide maximum final velocity. The correctness of the obtained solutions of the optimization task using the maximum principle is confirmed by the zero Hamiltonian value in the optimum trajectory. The results of vehicle motion simulation with optimal control and various initial conditions of motion and the vehicle mass are discussed. The results obtained show that the solutions of the optimization task under consideration using the maximum principle and the sequential linearization principle are in close agreement.

Aeroelasticity of composite plates with curvilinear fibres in supersonic flow

The target of this investigation is to understand the aeroelastic (dynamic or static) instability of variable stiffness composite laminates (VSCLs) in the presence of supersonic airflow. The studied VSCLs have curvilinear fibre paths. Two different types of VSCLs are considered: the first type (already adopted in several previous researches) includes fibre path angles changing linearly from T1 at right and left edges to T0 at the centre, and the second type (not introduced before) includes fibre paths where their angles change linearly from T0 at the left edge to T1 at the right edge. Displacements and rotations in the plate are modelled by a Third-order Shear Deformation Theory (TSDT) and are discretised by a p-version finite element model. Aerodynamic forces due to supersonic airflow, in the steady or unsteady regime, are modelled using linear Piston theory and the equations of motion of the self-excited vibration system are formed using the principle of virtual work. Dynamic (flutter) and static (divergence) instabilities are identified using the eigenvalues of the linear system. Effects of different boundary conditions and various fibre angles as well as the influence of airflow direction on the flutter and divergence occurrence in VSCL plates are studied.

A modular adaptive control design with ISS analysis for nonminimum phase hypersonic vehicle models

SummaryAir‐breathing hypersonic vehicles typically exhibit a nonminimum phase behavior when altitude is controlled via lift generation. This phenomenon prohibits the use of classical inversion‐based control techniques. Dynamic models of these vehicles are also subject to parametric uncertainties and unmodeled dynamics related to flexible effects of the fuselage. In this paper, we present a modular adaptive control method that achieves asymptotic setpoint tracking in both airspeed and altitude using thrust and elevator deflection as the only control inputs for a generic longitudinal model of a hypersonic cruise. The nonminimum phase problem is overcome through output redefinition, with altitude controlled by pitching moment. The internal dynamics, flight path angle, and altitude are then stabilized by saturating the interconnections and exploiting local stability properties. A new technique for the use of saturation functions in error coordinate is presented. The adaptive controller for altitude uses a pitch rate observer combined with projection. This control augmentation decouples the parameter estimation errors from internal dynamics, allowing for the use of small‐gain arguments. Simulation results from a vehicle model with flexible effects and parametric uncertainty are included to demonstrate control effectiveness.

Empirical analysis of the effect of descent flight path angle on primary gaseous emissions of commercial aircraft.

In this study, the effects of descent flight path angle (between 1.25° and 4.25°) on aircraft gaseous emissions (carbon monoxide, total hydrocarbons and nitrogen oxides) are explored using actual flight data from aircraft flight data recording system and emissions indices from the International Civil Aviation Organization. All emissions parameters are corrected to flight conditions using Boeing Fuel Flow Method2, where the ambient air pressure, temperature and humidity data are obtained from long-term radiosonde data measured close to the arrival airport. The main findings highlight that the higher the flight path angle, the higher the emission indices of CO and HC, whereas the lower the emissions index of NOx and fuel consumption. Furthermore, during a descent, a heavier aircraft tends to emit less CO and HC, and more NOx. For a five-tonne aircraft mass increase, the average change in emissions indices are found to be-4.1% and-5.7% (CO),-5.4% and-8.2% (HC), and+1.1% and+1.6% (NOx) for high and low flight path angle groups, respectively. The average emissions indices for CO, HC and NOx during descent are calculated to be 24.5, 1.7 and 5.6 g/kg of fuel, whereas the average emissions for descending from 32,000 ft (9.7 km) and 24,000 ft (7.3 km) are calculated to be 7-8 kg (CO), ∼0.5 kg (HC) and ∼3 kg (NOx).

Neurobehavioral effects of two metabolites of BDE-47 (6-OH-BDE-47 and 6-MeO-BDE-47) on zebrafish larvae

Two metabolites, OH-BDEs and MeO-BDEs, of polybrominated diphenyl ethers (PBDEs) were ubiquitously detected in animal tissues and environmental samples, drawing a widely public concern to their toxicity. The comparison of toxicity between PBDEs and their metabolites has been a focus in recent years, however, comparisons seldom involve neurobehavioral toxicity of PBDEs metabolites in published works. In this study, zebrafish larvae were exposed to 6-OH-BDE-47 and 6-MeO-BDE-47 and their neurobehavioral traits (including locomotion, path angle, and social activity) were recorded using the instrument Zebrabox; meanwhile, light illumination was used as stimuli in the test duration. The results showed larvae were more active in dark periods than light periods, and preferred turning right (+) to left (−). Effects of the two metabolites varied in different behavioral indicators. They induced different effects on path angle but did not reverse the left-right asymmetry. 6-OH-BDE-47 did not induce the effects on larval locomotion and social activity, but mainly decreased average and routine turn numbers; 6-MeO-BDE-47 promoted larvae responsive turns but inhibited social activity. This study offered new experimental means to the neurobehavioral toxicity of various PBDE metabolites. Further studies may focus on the toxic mechanisms of specific neurobehavioral traits.

Unmanned air vehicles for targeting tasks

Unmanned aerial vehicle in surveillance and reconnaissance operations are well known with its flight operations confining to the lateral and longitudinal plane where the altitude is maintained constant. The objective in these operations is to have a wide field of view when camera is mounted underneath the aircraft. However, in obstacle detection algorithms as well as in weapon-target assignments by an unmanned combat air vehicle, the sensors such as cameras and radars are mounted along the X direction of the body fixed frame. The unmanned vehicles with such sensor locations are expected to offer obstacle-camera and weapon-target line-of-sight engagements. These operations by the unmanned vehicles are referred as targeting tasks. In this paper, a procedure to use unmanned vehicles as targeting systems in pitch plane is presented with respect to a fixed order controller at the inner loop. The remote pilot's inputs at the outer loop is disengaged and to mimic these inputs, various flight path angles are scheduled thus depicting autonomous characteristics. Illustrations to depict targeting tasks are provided.

Logarithmic spiral trajectories generated by Solar sails

Analytic solutions to continuous thrust-propelled trajectories are available in a few cases only. An interesting case is offered by the logarithmic spiral, that is, a trajectory characterized by a constant flight path angle and a fixed thrust vector direction in an orbital reference frame. The logarithmic spiral is important from a practical point of view, because it may be passively maintained by a Solar sail-based spacecraft. The aim of this paper is to provide a systematic study concerning the possibility of inserting a Solar sail-based spacecraft into a heliocentric logarithmic spiral trajectory without using any impulsive maneuver. The required conditions to be met by the sail in terms of attitude angle, propulsive performance, parking orbit characteristics, and initial position are thoroughly investigated. The closed-form variations of the osculating orbital parameters are analyzed, and the obtained analytical results are used for investigating the phasing maneuver of a Solar sail along an elliptic heliocentric orbit. In this mission scenario, the phasing orbit is composed of two symmetric logarithmic spiral trajectories connected with a coasting arc.

Optimization of the Mars ionospheric radio occultation retrieval

Electron density is a key parameter to characterize Martian ionospheric structure and dynamics. Based on the ephemeris and auxiliary information derived from the Spacecraft, Planet, Instruments, C-matrix, and Events (SPICE) toolkit, we calculated the bending angle of signal path from the frequency residuals measured by the Mars Express Radio Science Experiment (MaRS) of the Mars Express (MEX) mission under the assumption of a spherically symmetric ionosphere. We stratified the ionosphere into layers and assumed a linear change of bending angle between layers, to derive profiles in radial distance of refractivity with the optimized parameters of upper integral limit of 4890 km and baseline correction boundary of 3690 km. Meanwhile, we also compared the retrieved electron density profiles between the frequency residuals of the single-frequency and differential Doppler of the dual-frequency. In total, ~640 electron density profiles of Martian ionosphere between April 2004 and April 2015 were retrieved successfully. There are 24 profiles identified manually that exhibit an additional sporadic layer occurrence below the normal two-layers. We also found that the peak altitude of this layer increases with the main peak altitude.