Pitch Maneuver Research Articles

Planning lunar observations for satellite missions in low-Earth orbit

For Earth-observing satellites in low-Earth orbit, radiometric calibration of the sensors on-orbit is critical for maintaining consistent Earth-view (EV) retrievals as the mission progresses. Many of these satellite instruments use on-board calibration targets, EV sites, and observations of celestial targets in order to perform the sensor characterization. Among the celestial targets, the Moon is widely used across a range of Earth-observing instruments in order to perform radiometric calibration, spatial characterization, and sensor intercomparison. Since many of these instruments use satellite maneuvers in order to bring the Moon into view at a desired time, calculating the time and geometric parameters of the observations is vital for mission planning purposes. We develop a simple tool for planning such observations of the Moon and other celestial targets for instruments in low-Earth orbit based on the SPICE toolkit developed by the Navigation and Ancillary Information Facility at NASA. Given a set of satellite orbital data along with a definition of the instrument coordinates, the tool is designed to provide the timing of observations for an arbitrary view-port direction and a maneuver along an arbitrary axis relative to the spacecraft. The tool can be tested versus known lunar observations for the Aqua and Terra moderate resolution imaging spectroradiometer and the Suomi-NPP and NOAA-20 visible infrared imaging radiometer suite instruments for both roll and pitch maneuvers. We also perform simulations of lunar observations for different instrument configurations, orbits, and maneuver types in order to analyze the change in the potential lunar observations. Finally, we show a simple extension of the tool which can be used for identifying planet and star observations.

Influence of Aspect Ratio on Dynamic Stall of a Finite Wing

The influence of aspect ratio () on dynamic stall was studied by comparing experimental performance data and three-component velocity measurements acquired for wings of , 4, and 5, and an airfoil during an unsteady pitch maneuver. A NACA 0012 airfoil was used for all wing models, which were subject to a sinusoidal pitch oscillation between 4 and 22 deg at a reduced frequency of 0.1 and a Reynolds number of . After acquiring the experimental performance data, it was found that decreasing the leads to a decrease in the nonlinear unsteady loading of the wing and postpones the dynamic stall process, which also leads to variations in the pitch damping characteristics. Velocity field measurements revealed that the dynamic stall vortex originates from flow separation at the leading edge across the wing inboard section and convects downstream across the chord, whereas the unsteady separation progresses toward the wing tips with increasing angle of attack. The formation of this vortex was delayed to higher angles of attack with reductions in , and the three-dimensional nature of the unsteady separation process led to a significant spanwise flow component identified in the acquired velocity fields.

Determination of response versus scan angle for the NOAA-20 visible infrared imaging radiometer suite thermal emissive bands from emissive radiation measurements during the pitch maneuver

The visible infrared imaging radiometer suite (VIIRS) is a key sensor onboard the newly launched (November 18, 2017) NOAA-20 satellite and the early launched Suomi National Polar-orbiting Partnership (SNPP) satellite. The two VIIRS sensors are nearly identical in design. Its onboard calibration components include a solar diffuser (SD) and a SD stability monitor for the reflective solar bands, a V-grooved blackbody for the thermal emissive bands (TEBs),and a space view port for background subtraction. These onboard calibrators are located at fixed scan angles. The response versus scan angle (RVS) of the VIIRS scan mirror was characterized prelaunch in lab-ambient conditions and is currently used to calibrate the on-orbit response for all scan angles relative to the calibrator's scan angle. A spacecraft-level pitch maneuver was scheduled during the initial intensive calibration and validation testing for both the NOAA-20 and SNPP. The pitch maneuver provided a rare opportunity for VIIRS to make observations of deep space over the entire range of the scan angle, which can be used to characterize the TEBRVS. We analyze the NOAA-20 pitch maneuver data and assess the derived TEB RVS. A comparison between the RVS determined by the pitch maneuver observations and prelaunch lab measurements is conducted for each band, detector, and mirror side of the half-angle mirror.

Improved algorithm for determining the Visible Infrared Imaging Radiometer Suite Day/Night Band high-gain stage dark offset free from light contamination

Dark offset is one of the key parameters for Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) high-gain stage (HGS) radiometric calibration, whose accuracy strongly impacts applications of DNB low-light detection for Earth observation at nighttime. Currently, DNB observation of the VIIRS onboard calibrator blackbody (OBCBB) view, together with its observation of deep space during the spacecraft pitch maneuver performed early in the mission, has been used to compute the HGS dark offset continuously. However, the relationship between the DNB OBCBB data and the Earth view (EV) data is unclear due to electronic timing differences between these two views. It is questionable whether the DNB OBCBB data can monitor the EV HGS dark offset change. Through comprehensive analysis of the DNB OBCBB data and EV data acquired from the monthly special acquisitions known as the VIIRS recommended operating procedures (VROPs), we have shown that the OBCBB data can only track the dark current component of the DNB HGS EV dark offset, instead of the total dark offset. The DNB observation of deep space during the spacecraft pitch maneuver was also contaminated by starlight. With such background, in this paper we propose an improved algorithm for determining the DNB HGS dark offset. By combined use of the DNB OBCBB data and the DNB VROP data, the generated DNB HGS dark offset is both free from light contamination and capable of tracking continuous drift. The improved algorithm could potentially improve the DNB radiometric performance at low radiance level. Our results provide a solid theoretical basis for dark offset calibration of the VIIRS DNB onboard Suomi National Polar-Orbiting Partnership satellite and the following Joint Polar Satellite System satellites.

A novel technique for hypersonic vehicle control

A novel control technique is investigated for hypersonic aerial vehicles. The technique is based on the use of active shock bumps (SBs) as a form of control device. The SBs deflect to create shockwaves on–demand, at specific locations around the aerial vehicle. As a result, a force is applied on the aerial vehicle, which in turn is used to provide the necessary moment for pitch and roll manoeuvres. In this work, a preliminary aerodynamic analysis of the SB device technique is made by means of CFD. For this purpose, and taking the large corresponding Reynolds numbers of the flow into consideration, the two–dimensional Euler equations are solved. A parametric investigation is carried out, by examining the effect of key parameters, namely the Mach number (M) and device deflection angle (δSB) on the produced force acting on the vehicle, serving as a proof of concept. Using a specific interpolation method, the resultant force is presented as a function of the Mach number and the device deflection angle, on three–dimensional charts, where the effect of each parameter is shown (force–Mach–deflection maps). Furthermore, a preliminary feasibility study is performed, including a kinematic analysis and some key material considerations. Additionally, a kinetic analysis is also conducted to secure the dynamic rigidity of the actuating mechanism and provide an initial estimation concerning weight and basic geometrical parameters of the SB mechanism components.

Avian-inspired energy-harvesting from atmospheric phenomena for small UAVs

Fixed-wing small, unmanned aerial vehicles usually fly in atmospheric boundary layers that are often under the influence of turbulent environments. Inspired by nature’s flyers, an application of an energy-harvesting flight strategy for increasing the energy state of the aircraft is presented. This paper provides basic longitudinal flight dynamic model exposing the physics behind the process. It shows significant power savings in flight with a sinusoidal and stochastic wind profile with active control of energy-harvesting. The active control based on optimized proportional gains was implemented for energy extraction from realistic atmospheric conditions, leading to significant energy savings for a ‘bird-sized’ vehicle. The paper reveals the equipment and necessary preparations for the flight test campaign. Moreover, it describes the design of a custom controller and its calibration in the wind tunnel against roll movements during pitching maneuvers. Finally, it investigates the benefits and potential of the automated process of energy-harvesting with simple proportional control through flight tests in a turbulent environment, validating the concept through the increased energy state of the aircraft.

Feed-Forward Dynamic Stall Control Model

Measurements of the lift coefficient history obtained from a NACA 0018 airfoil undergoing pitching maneuvers with blowing-type active flow control were used to obtain low-dimensional models for control. Disturbance models for the lift response to pitching at different steady-state blowing amplitudes were identified based on a variation of the Goman–Khrabrov model. A plant model for the lift response to sinusoidal blowing amplitude had the form of a time-delay system. The models were used to design a feed-forward controller. The ability of the controller to compensate for lift oscillations during pitching maneuvers was evaluated using a Simulink® model.

Особенности построения системы управления угловой ориентацией подводного аппарата для больших углов наклона

Особенности построения системы управления угловой ориентацией подводного аппарата для больших углов наклона

Computational investigation of vortex structure and breakdown over a delta wing at supersonic pitching maneuver

Unsteady compressible flows over a 60° swept delta wing with a sharp leading edge undergoing pitching maneuvers are computationally studied. Emphasis in this study is on possible supersonic flow structures and vortex breakdown during the pitching motion of a delta wing. Unstructured grid, k–ω SST turbulence model and a dual-time implicit time integration were used. Accurate simulations were performed for various Mach numbers, initial and final angles of attack, and pitch rates to cover different flow structures and phenomena associated with them. The contours obtained by the numerical results which show the flow structures were compared with experimental visualization images. Variations of flow patterns, pressure coefficient on the wing surface, and the lift coefficient during a pitching maneuver are investigated. Vortex breakdown was observed for both subsonic and supersonic flows and its impact on the lift coefficient during the motion was shown.

Postlaunch assessment of the response versus scan angle for the thermal emissive bands of visible infrared imaging radiometer suite on-board the Suomi national polar-orbiting partnership satellite

The visible infrared imaging radiometer suite (VIIRS) is a key sensor carried on the Suomi national polar-orbiting partnership (S-NPP) satellite, which was launched in October 2011. It has several on-board calibration components, including a solar diffuser and a solar diffuser stability monitor for the reflective solar bands, a V-groove blackbody for the thermal emissive bands (TEB), and a space view port for background subtraction. These on-board calibrators are located at fixed scan angles. The VIIRS response versus scan angle (RVS) was characterized prelaunch in lab ambient conditions and is currently used to characterize the on-orbit response for all scan angles relative to the calibrator scan angle. Since the RVS is vitally important to the quality of calibrated radiance products, several independent studies were performed to analyze the prelaunch RVS measurement data. A spacecraft level pitch maneuver was scheduled during the first 3 months of intensive Cal/Val. The S-NPP pitch maneuver provided a rare opportunity for VIIRS to make observations of deep space over the entire range of Earth view scan angles, which can be used to characterize the TEB RVS. This study provides our analysis of the pitch maneuver data and assessment of the derived TEB RVS by comparison with prelaunch results. In addition, the stability of the RVS after the first 5 years of operation is examined using observed brightness temperatures (BT) over a clear ocean at various angles of incidence (AOI). To reduce the impact of variations in the BT measurements, the daily overpasses collected over the ocean are screened for cloud contamination, normalized to the results obtained at the blackbody AOI, and averaged each year.

Analysis and Mitigation of Striping Noise in Two Water Vapor Sounding Channels of Global Precipitation Measurement (GPM) Microwave Imager

AbstractThe Global Precipitation Measurement (GPM) Microwave Imager (GMI) plays an important role in monitoring global precipitation. In this study, an along-track striping noise is found in GMI observations of brightness temperatures for the two highest-frequency channels—12 and 13—with their central frequencies centered at 183.31 GHz. These two channels are designed for sounding the water vapor in the middle and upper troposphere. The pitch maneuver data of deep space confirmed an existence of striping noise in channels 12 and 13. A striping noise mitigation method is used for extracting the striping noise from the earth scene or deep space measurements of brightness temperatures by combining the principle component analysis (PCA) with the ensemble empirical mode decomposition (EEMD) method. A power spectrum density analysis indicated that the frequency of striping noise ranges between 0.06 and 0.533 s−1, where the right bound of 0.533 s−1of frequency is exactly the inverse of the time (i.e., 1.875 s) it takes for the GMI to complete one conical scan line. The magnitude of striping noise in the brightness temperature observations of GMI channels 12 and 13 is about ±0.3 K. It is shown that after striping noise mitigation, the observation minus model simulation (O − B) distributions of both the earth scene and deep space brightness temperatures show no visible striping features.

Robust control of post-stall pitching maneuver based on finite-time observer

This article presents a robust finite-time maneuver control scheme for the longitudinal attitude dynamic of the aircraft with unsteady aerodynamic disturbances and input saturation. To efficiently eliminate the influence of unsteady aerodynamic disturbances, nonlinear finite-time observers are developed. Despite the existence of the nonlinearity and the coupling between aircraft states and unsteady aerodynamic disturbances, the proposed observers can still precisely estimate the unmeasurable unsteady aerodynamic disturbances in finite time. To attenuate the effect caused by input saturation, a finite-time auxiliary system is constructed. With the error between the desired control input and saturation input as the input of the auxiliary system, the additional signals are generated to compensate for the effect of input saturation. Combined with the finite-time observers and the finite-time auxiliary system, a robust finite-time backstepping attitude control design is developed. The finite-time convergence of all closed-loop system signals is rigorously proved via Lyapunov analysis method under the developed robust attitude control schemes. Finally, simulation results are presented to illustrate the effectiveness of the proposed attitude control approaches.

Dynamic Modeling, Analysis, and Testing of a Variable Buoyancy System for Unmanned Multidomain Vehicles

This paper presents the system design and dynamic model of an active variable buoyancy system (VBS) actuator with applications to unmanned multidomain vehicles. Unmanned multidomain vehicles have a unique concept of operations that require nontraditional VBS designs. We present a VBS actuator design that focuses on vehicle design objectives of high endurance, stealth, and loitering while underwater. The design consists of an elastic bladder housed within a rigid ballast tank, hydraulic pump, and proportionally controlled vent valve. Ambient surrounding water is the system working fluid and the elastic bladder serves to separate the gas–water interface, eliminating the risk of the compressed gas escaping when venting the water during extreme pitch maneuvers. A nonlinear analytic model of the VBS is derived and used to examine the parameter design space and the effects on water flow rate, actuation force, and energy efficiency. The VBS actuator design is shown to require a smaller, denser energy storage device than a comparable buoyancy system that uses consumable compressed air. A vehicle model is studied that features forward and aft VBS actuators, which enables vehicle pitch control by shifting the center of gravity along the vehicle's longitudinal axis. The coupling between the VBS actuator dynamics and vehicle dynamics is presented and discussed. A proof-of-concept demonstration is presented and compared to the analytical system model.

Minimum-Time Attitude Control of Deformable Solar Sails with Model Uncertainty

This paper develops a new algorithm for large-angle pitch maneuvers of deformable solar sails in minimum time that avoids overshooting the target angle given a set of model uncertainties. The paper uses a simplified Euler–Bernoulli beam to model the sail’s flexible booms. Model uncertainties include the flexural rigidity of the sail’s booms, the effectiveness of the sail’s reflectivity, and its moment of inertia about the pitch axis. The effect of each of these sources of uncertainty is investigated for a set of three sails of increasing size. The algorithm relies on trajectory-based reachability techniques to obtain a distribution of final states at the end of a large-angle maneuver that depend on the estimated model uncertainties. Using a tunable measure of statistical safety, the algorithm determines the required buffer angle to avoid overshooting the target attitude. Machine learning is used for reducing the parameter uncertainties based on a calibration maneuver. In addition, it is used to obtain a fast-access relationship between the current uncertainty in the model parameters and the required buffer angle.

Active Flow Control of a Low Reynolds Number S809 Wind Turbine Blade Model under Dynamic Pitching Maneuvers

A low Reynolds number wind turbine blade model based on the S809 airfoil was tested in a subsonic wind tunnel to study the structural vibration of the blade under dynamic pitching maneuvers. Piezoelectric-based synthetic jet actuators were embedded inside the blade and activated with a synthetic jet momentum coefficient, Cμ of 2.30 × 10-3. Structural vibration was quantified for a range of unsteady angles undergoing “pitch up and down” and “sinusoidal pitch” maneuvers at a Reynolds number of 5.28 × 104. The blade tip deflection amplitude and frequency were acquired utilizing a pair of strain gauges mounted at the root of the model. Using active flow control vibration reduction was more effective during the pitch up portion of the blade motion cycle compared to the pitch down portion. This effect is due to dynamic stall, where a leading edge vortex is shed during the pitch up motion and contributes to higher lift compared to static angles of attack and lower lift when the blade is pitched down. Dynamic stall was measured with phase-locked stereoscopic particle image velocimetry (SPIV), where global mean flow measurements reveal a shift in location and reduction in the size of a recirculating flow structure near the suction surface of the blade during the pitch up motion compared to the pitch down.

Modeling Lift Hysteresis on Pitching Airfoils with a Modified Goman–Khrabrov Model

Wind-tunnel experiments were conducted on two symmetric airfoils with different thickness ratios as a test of the ability of Goman–Khrabrov-type models to predict the lift coefficient history during pitching maneuvers. The primary difference between the two airfoils was that the thin airfoil had no hysteresis in its lift curve during quasi-steady maneuvers, but static hysteresis was observed with the thick airfoil over a range of . Both airfoils exhibited dynamic hysteresis in the lift coefficient when the wing was pitching. The existence of static hysteresis had a strong effect on the lift response during periodic pitching and must be accounted for in the model. A modified version of the Goman–Khrabrov model was introduced that captured the static hysteresis behavior and the large-scale features of the dynamic hysteresis for the thick airfoil, even when the thick airfoil was in a deep-stall condition. Some deviations between model and experiment were observed at the highest angles of attack, which were attributed to the convection of the dynamic stall vortex and its backwash effect as it leaves the airfoil.

Parameter-Varying Aerodynamics Models for Aggressive Pitching-Response Prediction

Current low-dimensional aerodynamic-modeling capabilities are greatly challenged in the face of aggressive flight maneuvers, such as rapid pitching motions that lead to aerodynamic stall. Nonlinearities associated with leading-edge vortex development and flow separation push existing real-time-capable aerodynamics models beyond their predictive limits, which puts reliable real-time flight simulation and control out of reach. In the present development, a push toward realizing real-time-capable models with enhanced predictive performance for flight operations has been made by considering the simpler problem of modeling an aggressively pitching airfoil in a low-dimensional manner. A parameter-varying model, composed of three coupled quasi-linear sub-models, is proposed to approximate the lift, drag, and pitching-moment response of an airfoil to arbitrarily prescribed aggressive ramp–hold pitching kinematics. An output-error-minimization strategy is used to identify the low-dimensional quasi-linear parameter-varying sub-models from input–output data gathered from low-Reynolds-number () direct numerical fluid dynamics simulations. The resulting models have noteworthy predictive capabilities for arbitrary ramp–hold pitching maneuvers spanning a broad range of operating points, thus making the models especially useful for aerodynamic optimization and real-time control and simulation.

An Integrative Control Method for Bio-Inspired Dolphin Leaping: Design and Experiments

This paper presents the design and implementation of leaping control methods for replicating high-speed dolphin leaping behavior. With full consideration of both mechanical configuration and propulsive principle of a physical robot comprising one neck joint, two propulsive joints, and a pair of two-degrees-of-freedom (2-DOF) mechanical flippers, closed-loop pitch, roll, yaw, and depth control methods are integrated to accomplish precise attitude control. Specifically, two pitch control strategies are proposed to separately satisfy small and large pitch requirements based on the real-time feedback of the pitch angle, while the roll controller is further implemented as a proportional-integral-derivative (PID) loop. A combination of pitch and roll control is utilized to regulate the desired pitch maneuvers. Finally, a parameterized five-phase leaping control algorithm instead of Weihs's three-phase porpoising model is implemented on the self-contained real robot, enabling the examination of biological leaping phenomena which are hard to observe or measure. Latest experimental results reveal that besides high speeds exceeding the minimum exit speeds, the pitch control closely related to pitch angle and submersion depth is another critical factor contributing to effective dolphin leaping.

Validation of ATMS Calibration Accuracy Using Suomi NPP Pitch Maneuver Observations

The Suomi National Polar-orbiting Partnership (SNPP) satellite was launched on 28 October, 2011, and carries the Advanced Technology Microwave Sounder (ATMS) onboard. Currently, ATMS performance in orbit is very stable and the calibration parameters (e.g., noise and accuracy) meet specifications. This study documents an ATMS calibration error budget model and its results for community reference. The calibration accuracy is also verified with the ATMS pitch maneuver observations of cold space. It is shown that the ATMS pitch maneuver cold space observations at center positions are inconsistent with the values predicted by the instrument calibration error budget model. The biases also depend on scan angle. This scan-angle dependence may be caused by the ATMS plane reflector emission. Thus, a physical model is developed to simulate the radiation emitted from the reflector and is recommended as part of ATMS radiance calibration to further improve the sensor data record (SDR) data quality.

Effects of bulbous bow on cross-flow vortex structures around a streamlined submersible body at intermediate pitch maneuver: A numerical investigation

A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found.