Chang-Hun Lee

Polynomial Guidance Laws Considering Terminal Impact Angle and Acceleration Constraints

The work presented here investigates proposed impact angle control guidance laws with terminal acceleration constraints for a stationary or slowly moving target. These laws, called time-to-go polynomial guidance (TPG), assume the guidance command as a polynomial function of time-to-go and determine the coefficients of the guidance command to satisfy the specified terminal constraints. The closed-form trajectory solutions of the guidance command and the target look angle for lag-free systems are derived and their characteristics are investigated. Based on the results we propose a systematic method to find the guidance gains that satisfy practical limits, such as the actuators command limit and the seekers field-of-view (FOV) limit. A time-to-go estimation method is also discussed for implementing TPG. Nonlinear and adjoint simulations are performed to investigate the performance of TPG.

Design of impact angle control guidance laws via high-performance sliding mode control

In this article, a new impact angle control guidance law for a stationary or slowly moving target is developed using the high-performance sliding mode control methodology. The law can produce various missile trajectories by changing the damping ratio of the guidance loop motion during interception in order to achieve not only the satisfaction of the terminal impact angle constraint but also the additional guidance objectives. Since the proposed guidance law is given using the general function term, different forms of guidance laws can be designed by choosing specific functions. It can also lead to zero magnitude of the guidance command at the terminal time. The first-order lag system and acceleration disturbances such as measurement noise are considered in the guidance law design. These properties can provide the advantages for the guidance operation, whereas other impact angle control guidance laws may not easily allow this. Numerical simulations are performed to investigate the characteristics and performance of the proposed guidance law. Some application results of the proposed guidance law are also shown.

Generalized Formulation of Weighted Optimal Guidance Laws with Impact Angle Constraint

The generalized formulation of weighted optimal guidance laws with impact angle constraint is investigated here. From the generalized formulation, we explicitly find the feasible set of weighting functions that lead to analytical forms of weighted optimal guidance laws. This result has potential significance because it can provide additional degrees of freedom in designing a guidance law that accomplishes the specified guidance objective.

Time-to-go Polynomial Guidance with Trajectory Modulation for Observability Enhancement

A new impact angle control guidance law is introduced for a homing missile system equipped with a passive seeker against a stationary or slowly moving target. The proposed guidance law provides sufficient trajectory modulations, such as oscillatory trajectories, to enhance target observability from angle-only measurements. The derivation of the guidance command is based on the time-to-go polynomial guidance (TPG) law, which is one of the impact angle control laws. Closed-form solutions of the proposed law and their characteristics are investigated. The results inspired the proposed practical time-to-go calculation method and the maximum bounds of guidance gains, which are important for the practical implementation of the guidance law. Linear and nonlinear simulations with a target tracking filter are performed to investigate the performance of the proposed law.

Design of guidance law for passive homing missile using sliding mode control

This paper deals with a new passive homing guidance law for a stationary or a slowly moving target using sliding mode control technique. The proposed guidance law is designed in such a way of increasing the target observability. In addition, it can control a terminal impact angle to maximize warhead effect. The main idea is that we design the nonlinear sliding surface which makes an oscillatory missile motion along the desired impact angle frame so that the proposed guidance law introduces the LOS angle oscillation continuously. And then the enhanced target observability is achieved by comparing with the other conventional guidance laws such as the proportional navigation guidance. On the nonlinear sliding surface, lateral miss distance, velocity and acceleration command are converged to zero at terminal time. In addition, the proposed guidance law is robust with respect to autopilot lag and uncertainty. Finally, the performance of proposed guidance law is evaluated and demonstrated by number of simulations.

Development of a High-Content Screening Method for Chemicals Modulating DNA Damage Response

The cellular response to DNA damage is emerging as a promising target for cancer therapy. In the present study, the authors exploited the relationship between the level of the phosphorylated form of histone H2AX (γH2AX) and the extent of DNA damage and developed a quantitative, cell-based, high-content screening system for measuring the DNA damage response (DDR). In this system, the authors quantified the level of γH2AX by measuring DNA damage–induced γH2AX nuclear foci using an automated cell imager. They found that the total area of γH2AX foci per cell exhibited a good correlation with the concentration of DNA damage–inducing agents, including etoposide. The effects of 2 well-known inhibitors of DNA damage could be quantified using this system, suggesting the suitability of the γH2AX-foci quantification method for large-scale screening applications. This was confirmed by using this method to screen a chemical library; the resulting “hits” included compounds that inhibited early signaling events in DDR, as well those that inhibited subsequent DNA damage repair processes. Overall, this γH2AX foci-measuring system may be an effective screening method for identifying DNA damage response inhibitors that could eventually be used to develop novel anticancer drugs.

Realtime Agile-Turn Guidance and Control for an Air-to-Air Missile

ight path angle, can be chosen at every step time. A backstepping controller is implemented to follow the angle-of-attack command generated from the guidance module. The result obtained from the realtime missile guidance law are compared with the numerically optimized result. The performance of the proposed guidance is comparable to the numerical trajectory optimization, in terms of the attained velocity and ight path angle. Nonlinear simulation results are presented on interception scenarios involving a target located at the rear of the ghter plane.

Time-to-go Polynomial Guidance Laws with Terminal Impact Angle/Acceleration Constraints

Abstract This paper deals with a generalized impact angle control guidance law with terminal acceleration constraint, which is called the Time-to-go Polynomial Guidance (TPG). The guidance command of TPG is initially assumed as a polynomial form of t go , and then the coefficients of this polynomial function are designed to satisfy the terminal impact angle and zero miss-distance constraints. TPG presents a simple form, and it can easily achieve the terminal acceleration and its time-derivative constraints which are predetermined by the specified values. In this study, linear trajectory solutions of TPG are derived and analytically investigated. Numerical and adjoint simulations are performed to investigate the performance of TPG.

High angle of attack missile autopilot design by pole placement approach

This paper presents the missile autopilot design for 180° heading reversal maneuver. For this purpose, angle of attack controller using pole placement approach is designed. The three autopilot gains can be computed from aerodynamic coefficients and three design parameters to satisfy some designer-chosen criteria. Design parameters are closed-loop frequency, damping ratio, and time constant, representing the characteristics of control system. To deal with nonlinear control problems in high angle of attack missile, gain scheduled technique is employed. The simulation results validate performances and capabilities of the control system.

Study of Time-to-go Polynomial Guidance Law with Considering Acceleration Limit

This paper deals with the choice of guidance gain for the time-to-go polynomial (POLY) guidance law when the acceleration limit is existed. POLY is derived based on the assumption that guidance commands are formed by a time-to-go polynomial function. The main characteristic of POLY is that any positive values can be used for its guidance gain. For this reason, it is ambiguous to choose a proper guidance gain. To relieve this difficulty, we firstly derive the closed-form solution of acceleration command and figure out the relationship between the maximum acceleration and guidance gain. From this analysis, we provide a guideline for choosing a guidance gain which satisfies the desired acceleration limit. Finally, the proposed method is demonstrated by simulation study.