Toshikazu Motoda

Flight control system for the Automatic Landing Flight Experiment

This paper discusses the flight control system developed for the Automatic Landing FLight Experiment, ALFLEX. ALFLEX is an experimental program conducted by the National Aerospace Laboratory and the National Space Development Agency of Japan in order to investigate the automatic landing technology for a future unmanned reentry space vehicle. The ALFLEX vehicle is a dynamically similar sub-scale model of the planned Japanese HII Orbiting Plane, HOPE. Since the HOPE program is in a preliminary conceptual design phase, the ALFLEX vehicle is a scaled model of one of the proposed configurations from 1992 research. The vehicle bare airframe is statically unstable in the pitch axis. In the lateral-directional axes, it has negative weather cock stability and strong dihedral effect, which introduce severe instability. The airframes instability and the landing performance requirement drive the flight control system design to be one of the key technologies in the HOPE program. Since the vehicles maximum L/D is approximately 4, it needs the same landing guidance technique as lifting body research vehicles and the Space Shuttle. This paper discusses the flight control design and the design methods applied to ALFLEX, and discusses lessons learned so far. The results from a preliminary flight test are briefly introduced. The series of automatic landing flights are scheduled for the middle of 1996, at Woomera, Australia, and will verify the guidance, navigation and control design. *Head, Control Qualification Lab., member AIAA Senior research engineer, Flight Research Division *^Research engineer, Control Research Division § Associate senior engineer, Winged Space Vehicle Office ^Engineer, Winged Space Vehicle Office *Asistant manager, Nagoya Aerospace Systems **Asistant manager, Nagoya Aerospace Systems Copyright

Identification of Influential Uncertainties in Monte Carlo Analysis

Monte Carlo simulation is a powerful and a practical tool for evaluating nonlinear systems. Its advantage is that it allows the effects of combinations of uncertainties to be taken into account. When the result of a MonteCarlo simulation is unsatisfactory, further investigations of both the system model and the control system are necessary, and it is important to identify those uncertain parameters that significantly influence the outcome of the simulation. However, the influential parameters are usually difficult to identify because multiple uncertain parameters are incorporated into a simulation simultaneously. A methodology is presented for identifying influential parameters in Monte Carlo analysis. When a Monte Carlo simulation yields an unsatisfactory result, the influential uncertainties are identified by further Monte Carlo simulations incorporating test vectors derived from the original uncertain parameter vector and by a statistical hypothesis test. The method is applied to the simulation results of an unmanned flight system, demonstrating its effectiveness in a practical application.

AUTOMATIC LANDING FLIGHT EXPERIMENT FLIGHT SIMULATION ANALYSIS AND FLIGHT TESTING

Preflight simulation analysis of flight experiment and flight test results are described. The automatic landing flight experiment was conducted in Woomera, Australia, in 1996, to develop the automatic landing technology required for the future Japanese uncrewed spacecraft. To ensure successful landings, computer simulation played an important role in the preflight analysis. Monte Carlo simulation was applied for the analysis. The root sum square method, which is commonly used in Japanese launcher rocket development projects, was also applied. Monte Carlo results were compared with the rss results and the flight test results. All 13 flight tests were successfully completed. Longitudinal guidance in the flare phase was found to be sensitive to some modeling errors. The cause is discussed.

STOCHASTIC GAIN TUNING METHOD APPLIED TO UNMANNED SPACE VEHICLE FLIGHT CONTROL DESIGN

This paper studies the feasibility of applying the stochastic gain tuning method to the flight control system design of space vehicles. Stochastic gain tuning is a form of parameter optimization by which. the probability of the flight control system’s total mission achievement is maximized. This probability is estimated by applying the Monte Carlo method to the results of a large number of simulated flights. The flight simulation model contains various types of uncertain parameter, the stochastic properties of which are defined a priori. The flight control system requirements are defined based on the flight simulation results, and an optimization algorithm called the mean tracking technique is used to tune the feedback/feedforward gains of the flight control laws, which maximizes the probability of mission achievement. Although stochastic gain tuning requires large computational resources, the recent advent of low-cost, high-performance computers means that it has become feasible and practicable if efficient computational algorithms are employed. This paper demonstrates its feasibility by applying it to the designof the flight control system of a re-entry space vehicle, a low-speed sub-scaled model of which was flight tested in 1996.

Numerical analysis for an aerial deployment motion of a folded-wing airplane

An airplane has been planned to be used for Mars exploration. The wing folding technology for such an airplane has been paid attention to because it offers a large wing area to get enough lift force and compactness for transfer to Mars. In addition, aerial deployment allows for using the initial altitude to its advantage. However, aerial deployment motion is complex and has a possibility of failure. This paper presents the result of a numerical analysis for the aerial deployment motion of a folded-wing airplane. The requirements for successful aerial wing deployment were defined. The sensitivity analysis results are evaluated using the requirements. Successful input range, and lower and upper constraints are revealed. The most sensitive requirement is the hinge reaction moment. Successful combinations among a spring, a damper, and aerodynamic force for the safe aerial deployment were quantitatively obtained.

LONGITUDINAL FLIGHT CONTROL FOR SPACE VEHICLE'S AUTOMATIC LANDING

This paper discusses a longitudinal flight path control designed and flight tested for Automatic Landing Flight Experiment, ALFLEX. ALFLEX, the flight test of which was conducted in 1996, demonstrated Japanese potentials for developing a reentry space vehicles automatic landing technology. In the program, however, longitudinal flight path control after the preflare maneuver is one of the critical items needed to satisfy the design requirement for landing on a limited length runway. Robustness against uncertainties and sensor errors is a key issue in longitudinal flight path control. The design was carefully conducted and flight tested. Although the flight test proved that the design result satisfied all the landing requirements, it identified critical parameters affecting the landing performance, such as longitudinal aerodynamics, navigation error and air data sensor error. This paper describes data obtained through the development and flight test, as well as further investigation conducted after the flight test in order to improve landing performance for the future space vehicle development. In the design review, a new approach called stochastic gain tuning is adopted, where the guidance feedback gain is tuned to maximize the probability of mission achievement. The results indicate some possibility of robustness improvement.