Terminal Flight Research Articles

A Neural-Metaheuristic Kalman Filter for Moving Microburst Wind Shear Identification

Microburst wind shears (MB) are powerful localized three dimensional (3D) columns of wind that occur when cooled air drops from the base of thunderstorms at high speeds. They eventually hit the ground and spread out in all directions. As such MBs are considered a major atmospheric hazard for aircrafts (ACs), especially in terminal flight phases. Though pilots train regularly to survive it, yet the most recommended practice within the aviation community is to avoid its encounter upon detection. Some modern aircrafts have predictive wind shear warning systems, but they have limited short range capability and do not provide quantitative data for engineering application. In this sense, accurate onboard detection and identification of MBs and its characteristics is of importance for flight safety, whose success can lead to design of automatic flight control systems (FCSs) that reduce the risk of aircraft crash landings and accidents. Even though there are some studies on FCS designs for MB encounter, research on MB identification is rare but ongoing. To this aim, the present study is among the firsts that focuses on online identification of multiple and moving MB parameters using onboard aircraft air data and inertial sensors. The identification task is initially performed using the aircraft six degrees of freedom (6DoF) equations of motion (EOM) integrated with a 3D MB model via the utility of nonlinear Kalman filtering (KF) algorithms. Subsequently, an enhanced neural metaheuristic Kalman filter (NMKF) is proposed that improves the estimation accuracy of the MB model parameters. The results demonstrate the efficacy of the proposed NMKF in comparison with previous studies.

Risk-Aware Markov Decision Process Contingency Management Autonomy for Uncrewed Aircraft Systems

Uncrewed aircraft systems (UASs) are being increasingly adopted for a variety of applications. The risk UAS poses to people and property must be kept to acceptable levels. This paper proposes risk-aware contingency management autonomy to prevent an accident in the event of component malfunction, specifically propulsion unit failure and/or battery degradation. The proposed autonomy is modeled as a Markov decision process (MDP), whose solution is a contingency management policy that appropriately executes emergency landing, flight termination, or continuation of planned flight actions. Motivated by the potential for errors in fault/failure indicators, the partial observability of the MDP state space is investigated. The performance of optimal policies is analyzed over varying observability conditions in a high-fidelity simulator. Results indicate that both partially observable MDP and maximum a posteriori MDP policies had similar performance over different state observability criteria, given the nearly deterministic state transition model.

Autonomous flight termination system: The need for an international regulatory frame

Among the unmanned launch service providers, the autonomous flight termination concept is no longer an unknown actor around the table. The goal of these systems is to limit the consequences of the potential feared events caused by a launch vehicle malfunction by automatically terminating the flight of the vehicle in a safe manner, replacing the human component on the traditional flight termination decision in case of failure.Although some public and private players have already designed (and even flown) an autonomous flight termination system, the problem arises when looking into the safety standards that need to be to be applied to launch from different locations, which are highly dependent on the respective safety authorities.This paper aims at analysing the gap in the current launch safety policies and proposing the guidelines to be followed to widen the range of spaceports capable of hosting a launch vehicle with such a feature.

Hypersonic vehicle terminal velocity improvement considering ramjet safety boundary constraint

The air-breathing ramjet is an essential power plant to improve the terminal velocity of hypersonic vehicles. The high-performance requirement of ramjet makes it operate close to the safety boundary, and the optimization of the terminal velocity of vehicle is faced with challenges. An integrated flight/ propulsion model considering thrust and safety performance is constructed, and the trajectory optimization method for the whole flight phase operating process of hypersonic vehicles with multiple performance optimization indicators and complex safety constraints is studied. Moreover, the trajectory optimization results of the whole flight phase for CAV-H and X-43A (powered/unpowered) plans are compared and analyzed, and the dive-acceleration-climb strategy can improve the maneuverability of the vehicle in the ramjet operating phase. Furthermore, the terminal flight velocity of the vehicle in the powered plan is increased from 363.60 m/s to 943.57 m/s under the effect of ramjet. In addition, the trajectory optimization results of vehicle with different geometrical configurations of the ramjet are compared under safety constraints. The results show that the variable geometry ramjet enables the vehicle to increase its terminal velocity by up to 9.73 % with respect to the fixed geometry engine. Hypersonic vehicle terminal velocity is effectively improved by considering ramjet variable geometry adjustment.

Validation results on future flight safety methods to be instituted at the Guiana Space Center -New Generation

In the very short term, the European Spaceport in French Guiana (CSG) will welcome new kinds of missions and launchers, such as Ariane 6, micro-launchers or reusable vehicles, and must prepare to operate them. At the same time, the launch safety process must be improved in order to maintain flight safety standards and to respect the requirements of the French Space Operation Act (FSOA [1]) regarding the new risks induced. The Flight Safety Department at CSG has been working on the development of new methods to fit these upcoming challenges while enabling the best possible protection to people, the environment and infrastructures. These concepts will be implemented with the arrival of the new Operations Centre (CDO).Although the flight termination decision remains on a human authority, the process to evaluate the dangerousness of a mission is optimized in order to gain reactivity and effectiveness. As presented at the 73rd IAC [2], this optimization of methods relies on both decreasing the number of operators within the flight safety team during launch operations and on implementing decision-aiding algorithms to better characterize the launcher condition status at any time. This implies a new distribution of the responsibilities between the safety operators and a redesign of the systems in the future organization at CSG.A large test campaign has already been conducted with the participation of all flight safety officers in order to collect data covering different fields [2]: personal and collective impressions, level of comfort, trust in the new concepts and comparison to the current process, amongst others. In follow-up of this study, to consolidate and validate the operability of the presented concepts and methods, the impacts of this new organization on the flight safety officers have been evaluated in order to apprehend the main changes compared to the current organization. In addition, a specific evaluation was performed in order to study the operator behaviour during various simulations of dangerous-case scenarios in which the launcher trajectory or on-board parameters deteriorated. The most critical cases were analysed in order to measure the reaction times before terminating the flight, with respect to different configurations of launcher abnormality. When comparing the behaviour and the reaction time of operators between the current and the future organization, we obtained conclusive results that are presented in this paper. These results will help to determine and demonstrate the efficiency of the new suggested method for the future flight safety organization at the CSG New Generation. The test campaign presented in this paper was possible following significant ergonomics choices regarding both the flight safety room configuration and the operator HMI layout. Indeed, the enhancement of flight safety operations has been enabled by a careful selection of decision-aiding algorithms and logical equations, however the study determining the most adequate position of HMI elements has also played a major role in the safety officers’ ability to operate the new concepts.This paper will present the results of the test campaign based on initial ergonomic studies enabling this major change in the organization of the flight safety team within the future CSG.

Spin Aerodynamic Modeling for a Fixed-Wing Aircraft Using Flight Data

Novel techniques are used to identify a nonlinear, quasi-steady, coupled, spin aerodynamic model for a fixed-wing aircraft from flight-test data. Orthogonal phase-optimized multisine inputs are used as excitation signals while collecting spinning flight data. A novel vector decomposition of explanatory variables leads to an elegant model structure for spin flight data analysis. Results show good agreement between model predictions and validation flight data. This effort is motivated by interest in developing a flight termination system for a fixed-wing unmanned aircraft that controls a descending spiral trajectory flight path toward a designated impact area. While investigating the feasibility of a robust control method to guide the spinning trajectory, it was helpful to compare a level flight dynamic model with one of the aircraft dynamics and control authority in the neighborhood of a stable, oscillatory spin. In this paper, a nominal flight aerodynamic model is developed and compared to the stall spin model and the spin model outperforms the nominal model for spinning flight.

Ballistic Missile Trajectory Design Considering Impact Angle Constraint

The current paper investigates the problem of guiding ballistic re-entry vehicles to the terminal point under the additional terminal constraint of final flight path angle. In this regard, the classical Lambert’s Problem is reformulated to include the final flight path angle constraint. The proposed solution of the modified Lambert’s problem consists of a minimum of two different trajectories starting from the same initial location and intersecting each other at a location, which is determined by applying the desired time of flight and terminal flight path angle constraints. The modified Lambert strategy strategy is shown to satisfy terminal flight path angle constraint along with the time of flight, initial and final location constraints. This scheme requires the ballistic vehicle to perform an additional stage burn during descent in-order to switch from an initial trajectory, using Lambert strategy, to a final trajectory which satisfies the final flight path angle constraint. An additional stage burn is provided such that the position and velocity of the vehicle traveling in the initial trajectory is matched with that required for it to be on the final trajectory. It is also found that the amount of propellant required for the trajectory transfer, is dependent on the total time of flight and the altitude at which the additional stage burn occurs. The optimal values of these two parameters are found using interior-point optimization technique.

An observation methodology for non-measurable rotorcraft states

In an attempt to reduce acoustic pollution due to terminal flight phases (lift-offs and landings) in the surroundings of heliport, project MANOEUVRES developed a device capable of estimating the acoustic footprint of helicopters on the ground. This device requires knowledge of certain quantities that cannot be directly measured through physical sensors: the tip-path plane angle of attack and the main rotor thrust coefficient. Previous research has demonstrated that these quantities can be accurately estimated using observers that are properly fed with directly measurable flight mechanics and rotor state variables. However, these observers, which are based on linear mathematical models identified offline and employed through interpolation with respect to nominal airspeed, have shown poor robustness when the number of identification input cases is reduced, as required for a realistic design of observers in the field. This issue has particularly emerged when non-trimmed manoeuvres were considered during observation testing. To address this issue, this paper introduces a new baseline for the observation model, which includes dynamic pressure as an additional input. Moreover, a different model structure is considered depending on the observed variable. Specifically, for the tip-path plane angle of attack, a single model covers the entire airspeed range, while observation models for the rotor thrust coefficient are interpolated based on flight altitude. This new approach demonstrates results of comparable or superior quality to previous observation models. Furthermore, it exhibits increased robustness when the pool of identification cases used for observer synthesis is significantly reduced. Such improved performance and ease of synthesis pave the way for the setup and adoption of the proposed observers in the field.

Neural Network-Based Controller for Terminal Guidance Applied in Short-Range Rockets

Precision during the guided terminal flight in short-range rockets is a key factor that must be improved using several methodologies. Traditionally, inertial navigation systems allowed to unbind the accuracy concerning the range. Unfortunately, in short-range rockets, the response of the inertial-based controller has to be fast enough to correct the trajectory in a short time. This fact implies that to achieve high precision, either the use of systems too large to be implemented in portable rockets is required, or systems that are too expensive concerning the total cost of the rocket. For these systems, artificial intelligence-based guidance tactics could improve the precision, since once the network is trained, it is not necessary to know the dynamics of the vehicle, and the network itself can react quickly, simplifying the system and reducing economic costs using relatively simple electronics. The neural networks are trained using a nonlinear-dynamics model based on a simulated flight dynamics and verified with real flight data. The simulation results show that the proposed method works effectively in a six-degree-of-freedom simulation environment, with excellent accuracy and robustness to parameter uncertainty. The appropriateness of the closed-loop performance is validated using Monte Carlo analysis across a wide range of uncertainty scenarios.

Climate, landscape, and life history jointly predict multidecadal community mosquito phenology

Phenology of adult host-seeking female mosquitoes is a critical component for understanding potential for vector-borne pathogen maintenance and amplification in the natural environment. Despite this importance, long-term multi-species investigations of mosquito phenologies across environments and differing species’ life history traits are rare. Here we leverage long-term mosquito control district monitoring data to characterize annual phenologies of 7 host-seeking female mosquito species over a 20-year time period in suburban Illinois, USA. We also assembled data on landscape context, categorized into low and medium development, climate variables including precipitation, temperature and humidity, and key life history traits, i.e. overwintering stage and Spring–Summer versus Summer–mid-Fallseason fliers. We then fit linear mixed models separately for adult onset, peak abundances, and flight termination with landscape, climate and trait variables as predictors with species as a random effect. Model results supported some expectations, including warmer spring temperatures leading to earlier onset, warmer temperatures and lower humidity leading to earlier peak abundances, and warmer and wetter fall conditions leading to later termination. However, we also found sometimes complex interactions and responses contrary to our predictions. For example, temperature had generally weak support on its own, impacting onset and peak abundance timing; rather temperature has interacting effects with humidity or precipitation. We also found higher spring precipitation, especially in low development contexts, generally delayed adult onset, counter to expectations. These results emphasize the need to consider how traits, landscape and climatic factors all interact to determine mosquito phenology, when planning management strategies for vector control and public health protection.

High carbohydrate consumption increases lipid storage and promotes migratory flight in locusts.

Migration allows animals to track favorable environments and avoid harmful conditions. However, migration is energetically costly, so migrating animals must prepare themselves by increasing their energy stores. Despite the importance of locust migratory swarms, we still understand little about the physiology of locust migration. During long-distance flight, locusts rely on lipid oxidation, despite the fact that lipids are relatively rare in their leaf-based diets. Therefore, locusts and other insect herbivores synthesize and store lipid from ingested carbohydrates, which are also important for initial flight. These data suggest that diets high in carbohydrate should increase lipid stores and the capacity for migratory flight in locusts. As predicted, locust lipid stores and flight performance increased with an increase in the relative carbohydrate content in their food. However, locust flight termination was not associated with complete lipid depletion. We propose potential testable mechanisms that might explain how macronutrient consumption can affect flight endurance.

Integrating orientation mechanisms, adrenocortical activity, and endurance flight in vagrancy behaviour

Avian migratory processes are typically precisely oriented, yet vagrants are frequently recorded outside their normal range. Wind displaced vagrants often show corrective behaviour, and as an appropriate response is likely adaptive. We investigated the physiological response to vagrancy in passerines. Activation of the emergency life-history stage (ELHS), assessed by high baseline plasma corticosterone, is a potential mechanism to elicit compensatory behaviour in response to challenges resulting from navigational error, coupled with response to fuel load and flight. We compared circulating plasma corticosterone concentrations and body condition between three migratory groups in autumn: (1) wind displaced southwest (SW) vagrants and (2) long range southeast (SE) vagrants on the remote Faroe Islands, and (3) birds within the expected SW migratory route (controls) on the Falsterbo peninsula, Sweden. Vagrants were further grouped by those sampled immediately upon termination of over-water migratory flight and those already on the island. In all groups there was no indication of the activation of the ELHS in response to vagrancy. We found limited support for an increased rate of corticosterone elevation within our 3 min sample interval in a single species, but this was driven by an individual ELHS outlier. Fat scores were negatively correlated with circulating corticosterone; this relationship may suggest that ELHS activation depends upon an individual’s energetic states. Interestingly, in individuals caught at the completion of an obligate long-distance flight, we found some evidence of corticosterone suppression. Although limited, data did support the induction of negative feedback mechanisms that suppress corticosterone during endurance exercise, even when fuel loads are low.

Examining autonomous flight safety systems from a cognitive systems engineering perspective: Challenges, themes, and outlying risks

Flight safety systems (FSS) act as a method to terminate off-nominal rocket launches which threaten public safety. Traditional FSS delegate decision authority to an experienced Missile Flight Control Officer (MFCO) tasked with flight termination decisions, observing multiple points of telemetry data in real time to ensure nominal flight status. This study examines the engineering trade-offs, complexities, and pitfalls introduced by automating flight termination decision-making through autonomous flight safety systems (AFSS). We approach this problem from a cognitive systems engineering perspective, connecting aspects of AFSS to existing literature in human-machine teaming and resilience engineering. Based on information gathered from a series of semi-structured interviews with various subject matter experts (mission controllers, regulators, engineers, amongst others) and existing literature, we outline a list of four assumptions underlying AFSS operations: (1) The system is fully autonomous, (2) An exhaustive flight safety analysis has been performed, (3) The system will be able to respond appropriately to the world, and (4) MFCO expertise can be captured in (or translated to) software. Our findings highlight that, while the benefits of AFSS hold great promise for increasing the viability of commercial space operations, the automation of an irreversible, instantaneous, and complex decision-making task introduces significant challenges and risks. We propose directions for further research to minimize the likelihood of errant, expensive, and dangerous automated flight terminations.

Using cloud radar to investigate the effect of rainfall on migratory insect flight

Abstract The fate of migrating insects that encounter rainfall in flight is a critical consideration when modelling insect movement, but few field observations of this common phenomenon have ever been collected due to the logistical challenges of witnessing these encounters. Operational cloud radars have been deployed around the world by meteorological agencies to study precipitation physics, and as a byproduct, provide a rich database of insect observations that is freely available to researchers. Although considered unwanted ‘clutter’ by the meteorologists who collect the data, the analysis method presented here enables ecologists to delineate co‐occurring signals from insects and raindrops. We present a method that uses image processing techniques on cloud radar velocity spectra to examine the fate of migrating insects when they encounter precipitation. By analysing velocity spectra, we can distinguish flying insects from falling rain and compare the relative density of insects in flight before, during and after the rainfall. We demonstrate the method on a case of insect migration in Oklahoma, USA. Using this method, we show the first reconstructed images of migrating insect layers in flight during rainfall. Our analysis shows that mild to moderate rainfall diminishes the number of insects aloft but does not cause full termination of migratory flight, as has previously been suggested. We hope this technique will spur further investigations of how changing weather conditions impact insect migration, and enable some of the first of such studies in regions of the world that are underrepresented in the literature.

Influence of Ice Accretion on Stratospheric Airship in the Non-Forming Ascending Process

Ice accretion on stratospheric airships, which affects the net buoyancy and reduces the ascent speed, thereby leading to component failure and further necessitating flight termination, has received considerable attention. In this study, the formation of ice occurred when the airship hit supercooled water droplets during the non-forming ascending process. Theoretical descriptions of an ice accretion model, a thermal model, and a dynamic model for airships were established to estimate the flight performance with ice mass. Then, validation of the simulation and the cloud chamber test was carried out, which indicated that the temperature, liquid water content (LWC), and pressure considerably influenced the ice mass. A lower temperature had a positive effect on ice accretion. The mass of ice accretion increased with the increase in LWC. Ice did not form easily under low pressure due to evaporation and sublimation. Finally, the effects of the ambient LWC and initial helium mass were analyzed. It was shown that an LWC of 0.5 g/m3 resulted in severe degradation of the ascent performance. When the initial helium mass was not sufficient, the airship landed due to ice accumulation. However, redundant inflation increased the ice mass and lowered the cruising altitude.

High-Rate, High-Precision Wing Twist Actuation for Drone, Missile, and Munition Flight Control

This paper covers a new actuation and deflection controller configuration for high-aspect-ratio wings used on subsonic drones, missiles, and munitions. Current approaches to the flight control of these aircraft have unearthed challenges with friction, stiction, slop, bandwidth, and thick boundary layer nonlinearities, which degrade flight control accuracy—especially in terminal flight phases. The approach described in this paper uses directionally attached piezoelectric (DAP) actuators to actively twist a high-aspect-ratio wing for flight control. The DAP actuators were modeled analytically and computationally using linear finite element modeling. A 3″ (7.62 cm) chord × 15″ (38.1 cm) semispan rectangular wing with an NACA 0012 profile was built and structurally tested, demonstrating excellent agreement between theory and experiment. New actuation methods were used to overdrive the PZT-5H piezoelectric elements deep into the repoling range. This overdrive actuation rejuvenated the actuator elements and allowed for dramatically improved deflections with respect to configurations in previous years. Static testing demonstrated deflections in excess of ±1.6° in root-to-tip twist. Dynamic testing showed corner frequencies greater than 310 Hz. A series of wind tunnel tests at up to 180 ft/s (55 m/s, 123 mph, 107 kts, 198 kph) demonstrated excellent roll control authority, rapid manipulation of Clδ, and lift manipulation using quasi-static deflections. The paper concludes with a summary of implications for terminal guidance for drone, missile, and munition flight control in real atmospheres.

Mixed uncertainty quantification for terminal flight state of Mars atmospheric entry

China's Tianwen-1 successfully touched down on the surface of the red planet, even though various mixed uncertainties occurred in flight dynamics during Mars atmospheric entry, especially Gaussian mixed uniform uncertainty in the initial state and dynamics parameters. A hybrid algorithm combining sensitivity collocation with nonintrusive polynomial chaos was proposed in this paper. Mixed uncertainty was quantified to reveal the mechanism causing location deviation during parachute deployment from the preplanned point. First, Mars atmospheric entry dynamics containing uncertainty were modeled as stochastic nonlinear dynamics. Second, stochastic variables were approximated using nonintrusive polynomial chaos, and sensitivity collocation was used to characterize state variables under the influence of uncertainty. Finally, the probabilistic distribution of the parachute deployment state was analytically obtained according to the initial and parametric uncertainties at the entry interface. Comparison simulations verified the effectiveness of the proposed technique. Gaussian-uniform mixed uncertainty features from the entry interface to the beginning of parachute deployment were revealed.

Quantifying the Resilience Performance of Airport Flight Operation to Severe Weather

The increased number of severe weather events caused by global warming in recent years is a major turbulence factor for airport operation and results in more irregular flights. Quantifying the system response status towards turbulence is critical, in order for airports to deal with severe weather. For this reason, we propose a resilience framework that is in compliance with resilience theory to evaluate airport flight operations. In this framework, the departure rate (DPR), normal weather baseline (NWB), and nonnegative general resilience (NGR) were defined and used. Meanwhile, the whole process is divided into five phases before and after disturbance, and the system capacities of susceptibility, absorption, adaptation, and recovery are assessed. In order to clarify the performance of the framework towards various severe weather conditions, an analysis was conducted at Beijing Capital Airport in China based on a dataset that includes both the meteorological terminal aviation weather report (METAR) and flight operations from January to July 2021. The results show that the newly proposed resilience framework can commendably reflect airport flight operation performance. The airport flight operation resilience characteristic is different with severe weather. Compared to sandstorms and snow, airport flight operation with stronger robustness was observed during thunderstorm events. The study also confirms that, as the weather warning level increases, the disruption time increases and response time decreases accordingly. The above results could assist researchers and policy makers in clearly understanding the real-world resilience of airport flight operation, in both theory and practice, and responding to emergent disruptive events effectively.

Fault-Tolerant Control of a Dual-Stator PMSM for the Full-Electric Propulsion of a Lightweight Fixed-Wing UAV

The reliability enhancement of electrical machines is one of the key enabling factors for spreading the full-electric propulsion to next-generation long-endurance UAVs. This paper deals with the fault-tolerant control design of a Full-Electric Propulsion System (FEPS) for a lightweight fixed-wing UAV, in which a dual-stator Permanent Magnet Synchronous Machine (PMSM) drives a twin-blade fixed-pitch propeller. The FEPS is designed to operate with both stators delivering power (active/active status) during climb, to maximize performances, while only one stator is used (active/stand-by status) in cruise and landing, to enhance reliability. To assess the fault-tolerant capabilities of the system, as well as to evaluate the impacts of its failure transients on the UAV performances, a detailed model of the FEPS (including three-phase electrical systems, digital regulators, drivetrain compliance and propeller loads) is integrated with the model of the UAV longitudinal dynamics, and the system response is characterized by injecting a phase-to-ground fault in the motor during different flight manoeuvres. The results show that, even after a stator failure, the fault-tolerant control permits the UAV to hold altitude and speed during cruise, to keep on climbing (even with reduced performances), and to safely manage the flight termination (requiring to stop and align the propeller blades with the UAV wing), by avoiding potentially dangerous torque ripples and structural vibrations.

Arizona Space Grant Consortium Participation and Contribution During the 2017 Solar Eclipse

Students from the Arizona/NASA Space Grant Consortium attended the Montana State University (MSU) Solar Eclipse Workshop in July 2016, where the MSU-designed ground station and payloads were assembled. The team returned with the systems, making modifications and conducting tests leading up to the eclipse in the following areas: ground station tracking and payload improvements, including expanded video capability. With the initial aid of Louisiana State University (LSU), the team upgraded the tracking system to use both Automated Packet Reporting System (APRS) beacons and MSU’s Iridium tracking system. This update improved the accuracy of determining the location of the balloon and payloads. The hardware improvements for the ground station included the addition of mobile HughesNet satellite internet service. Payload improvements included using medium-gain antennas, next generation Ubiquiti modems, and Raspberry Pi 3 computers. In addition, a 360 degree video camera payload was developed. The systems were tested over six balloon flights. During the solar eclipse, the team was in Glendo, WY, and flew the following payloads on two balloons: Digital Video Payload (DVP), Digital Image Payload (DIP), 360 Video Payload, Arizona State University (ASU) Scientific Payload, flight termination payload, and tracking payloads. Each of these payloads functioned correctly with the exception of DVP, possibly due to damage at launch, which meant the team was unable to live stream video during the eclipse. Instead, the team streamed an image slideshow to a NASA website during the eclipse with still images downlinked from the DIP. However, videos from both the DVP and 360 Video Payload were recovered after the flight and later processed. Overall the mission was successful in collecting video, images, and data of the eclipse from the high-altitude perspective.