Initial Launch Conditions Research Articles

Impact Time Control Guidance Law for Large Initial Lead Angles Based on Sliding Mode Control

In view of the interception scenario where a missile intercepts a stationary target in the longitudinal plane, an impact time control guidance (ITCG) law is proposed by utilizing the sliding mode control (SMC). An amendatory approach of t go (time-to-go) is adopted where there is no need to take the small-angle assumption into consideration. Under the basis of SMC, the error of impact time is selected as a sliding mode variable, which can converge to be zero in finite time by using the fast power reaching law (FPRL). The guidance law performance has been conducted in one-to-one engagement with different desired impact time. Simulation results demonstrate that the proposed guidance scheme can operate effectively even with a large initial lead angle of the missile, which broadens the initial launch conditions of the missile as well as improving the application capability of the guidance law.

Decentralized Control of Nanosatellite Tetrahedral Formation Flying Using Aerodynamic Forces

A decentralized control algorithm for the construction of a tetrahedral configuration using differential lift and drag forces is proposed in this paper. Four 3U CubeSats launched in LEO are considered. Satellite attitude-controlled motion relative to the incoming airflow provides the required differential forces in order to change the relative translational motion. The developed control algorithm allows one to track the relative reference trajectories for the satellites at the vertices of the tetrahedron of the required shape and size. The influence of the initial launch conditions on the controlled tetrahedral motion is studied in this paper.

Passivity‐based control laws for an unmanned powered parachute aircraft

AbstractIn this paper, the development of passivity‐based control (PBC) algorithms to stabilize an unmanned powered parachute aerial vehicle is presented. The equations of motion of the system are presented in both Lagrangian and Hamiltonian formalisms. The proposed controllers are based on the Hamiltonian function of the system and guarantee the parachute aircraft system stabilization. In the first control law a classic PBC strategy is proposed, and in the second, an interconnection and damping assignment‐passivity‐based control (IDA‐PBC) is chosen because of its inherent robustness against parametric uncertainty and unmodeled dynamics. The control objective is to reach a desired final position despite the initial launch conditions. Numerical simulations with variation in the parachute mass weight and in the presence of wind are carried out to validate our proposed schemes.

Predicting golf ball launch characteristics using iron clubhead presentation variables and the influence of mishits

In golf, it is well understood that the interaction between the clubhead and ball determines the initial ball launch conditions. Specific knowledge regarding these relationships for iron clubs, particularly when clubhead and turf interactions are considered, would be both novel and of benefit to practitioners. Linear regression analysis was used to determine relationships between selected clubhead presentation and shot outcome variables for a sample of 1127 ‘5-iron’ shots hit from natural turf by 96 golfers. As expected, clubhead speed was the most significant predictor of ball speed, with obliquity of impact and eccentricity of the impact location making smaller, yet statistically significant contributions. Marginally ‘fat’ strikes, whereby the leading edge of the clubhead was only slightly beneath the ground at impact, appeared to have a lesser effect than expected in terms of ball speed. Effective loft was found to be the strongest predictor of vertical launch angle, whilst clubhead speed and spin loft had the greatest influence in the model for predicting total spin; inclusion of ‘thin’ strikes (i.e. those struck with the leading edge) appeared to create a non-linear element to these models and consequently overestimated the influence of vertical impact location in both cases. These findings suggest that determination of impact location, particularly for instances whereby ball contact is not wholly on the club face, is critical in research concerning irons. Overall, this study makes an original contribution to the understanding of 5-iron shot outcomes based on clubhead presentation characteristics.

The influence of 5-iron clubhead mass distribution on clubhead presentation and initial ball launch conditions – Part II: Player tests

Iron clubheads can be classified as blades or perimeter-weighted, depending on the distribution of their mass. Despite the widely held views that perimeter-weighting can offer performance benefits for lesser skilled players, a direct comparison with players using these two clubhead types has not been thoroughly investigated. The aims of the study were to determine differences in clubhead presentation and ball launch between a blade 5-iron and a cavity-back 5-iron in a mixed cohort of golfers and examine trends in central tendency and variability in relation to skill for males using the blade club. Nine clubhead presentation variables and six ball launch variables were measured for 96 participants hitting shots from natural turf with each of the clubs. Group means for club effect were analysed statistically using an independent samples approach, whilst a rank-based nonparametric test was used to determine significant trends between handicap categories and ball launch conditions for the male cohort. The cavity-back displayed higher effective loft, lower effective lie and a tendency to have ball strikes closer to the centre. Higher values were also noted for the cavity-back for vertical launch angle and total spin. As expected, higher handicap male golfers showed lesser consistency and displayed slower ball speeds and lower efficiency than the more skilled players. Together these results concur with the findings in Part I in support of the theory of ‘forgiveness’ associated with cavity-back clubs, whilst also highlighting the over-riding importance of skill level on performance.

Lunar Exploration as a Probe of Ancient Venus

Abstract An ancient Venusian rock could constrain that planet’s history and reveal the past existence of oceans. Such samples may persist on the Moon, which lacks an atmosphere and significant geological activity. We demonstrate that, if Venus’ atmosphere was at any point thin and similar to Earth’s, then asteroid impacts transferred potentially detectable amounts of Venusian surface material to the lunar regolith. Venus experiences an enhanced flux, relative to Earth, of asteroid collisions that eject lightly shocked (≲40 GPa) surface material. Initial launch conditions plus close encounters and resonances with Venus evolve ejecta trajectories into Earth-crossing orbits. Using analytic models for crater ejecta and N-body simulations, we find that more than 0.07% of the ejecta lands on the Moon. The lunar regolith will contain up to 0.2 ppm Venusian material if Venus lost its water in the last 3.5 Gyr. If water was lost more than 4 Gyr ago, 0.3 ppm of the deep megaregolith is of Venusian origin. About half of collisions between ejecta and the Moon occur at ≲6 km s−1, which hydrodynamical simulations have indicated is sufficient to avoid significant shock alteration. Therefore, recovery and isotopic analyses of Venusian surface samples would determine with high confidence both whether and when Venus harbored liquid oceans and/or a lower-mass atmosphere. Tests on brecciated clasts in existing lunar samples from Apollo missions may provide an immediate resolution. Alternatively, regolith characterization by upcoming lunar missions may provide answers to these fundamental questions surrounding Venus’ evolution.

The influence of 5-iron clubhead mass distribution on clubhead presentation and initial ball launch conditions: Part I: Golf robot tests

It is well accepted that iron clubhead properties affect shot outcomes in golf. However, the mechanisms that contribute to this relationship have not received recent scientific study. The purpose of this study was to determine how the different clubhead mass distributions in a blade 5-iron and a cavity-back 5-iron affect clubhead presentation and ball launch conditions. Nine clubhead presentation variables and four ball launch variables were measured for ten discrete impact locations and five face angles during swings using a golf robot. Group means were analysed statistically using an independent samples approach to identify differences and linear regression was used to indicate relationships between key launch variables. The cavity-back showed higher effective clubhead loft with greater total ball spin than the blade, despite having matched static lofts, whilst also providing more consistent launch outcomes across a range of impact locations. Evidence of the phenomenon known as the ‘gear effect’ was found for the cavity-back, but not the blade, suggesting that the threshold at which the clubhead’s centre of gravity (CG) is deep enough to detect the gear effect lies between the CGs of the two 5-iron types. These novel robot test findings lend support to the perceived performance benefits of perimeter-weighted irons; whether these effects translate to human golfer swings is reported in Part II of this paper.

Study on the oblique water entry impact performance of AUV under different launch conditions based on coupled FEM-ALE method

In this study, the hydrodynamic response of an autonomous underwater vehicle (AUV) subjected to oblique water entry impact is investigated by employing an explicit FEM technique with arbitrary Lagrangian–Eulerian formulation. The predictive ability of the employed numerical model is validated by correlating the cavity evolution of AUV and peak impact accelerations with the experimental outcomes of the previous research work. The influence of advection algorithms on the water entry phenomenon is studied. It is found that the first order donor cell advection scheme is more suitable for low speed impact problems as it is computationally more efficient. However, for high speed water entry simulations, the van Leer advection scheme gives more accurate results. Moreover, using different water entry angles, the effect of the angle of attack (AOA) and length of AUV and its head shape on the impact performances are investigated and discussed. The results show that the radial impact load is more likely to be influenced by AOA and the effect of AOA on the radial impact load is more significant for a small water entry angle, i.e., 30°, as compared to a large entry angle, i.e., 60°. It is also observed that AUV of a smaller length shows the ricochet behavior at a water entry angle of 30°. It is seen that the head shape has a substantial effect on the axial and radial impact loads and velocity attenuation of a vehicle under water. The conclusions drawn in this research work will be beneficial for the selection of appropriate initial launch conditions and for the designing of an AUV structure.

Assessment of Quality and Reliability of Measurements with XBT Sippican T5 and T5/20

AbstractThe T5 expendable bathythermographs reach the greatest depth within the current XBT family. Since the early 1970s, in several areas they have been providing a significant part of available temperature profiles below 1000 m and therefore represent an important resource for ocean climate study. In this paper we present new results from laboratory tests of Sippican T5 and T5/20 probes and analyses of more than 350 XBT–CTD matched pairs from our own field trials and the World Ocean Database (WOD), and we propose an improved fall rate equation (coefficients: A = 6.720 ± 0.025 m s−1, B = 0.001 60 ± 0.000 15 m s−2, Offset = 1.00 ± 0.65 m). Possible influences of probe physical characteristics and initial launch conditions on the probe motion have also been investigated with launching height and probe weight being identified as important factors. Analyses also confirm that fall speed and pure temperature error increase with water temperature, as previously reported for other XBT types. The uncertainties in depth and temperature measurements are then calculated. Finally, a new correction for a global T5 dataset is proposed, with an update of the currently available schemes.

Cooperative Intercept Guidance of Multiple Aircraft with a Lure Role Included

When threatened by a pursuer, an evading aircraft launches two defenders to accomplish a cooperative evasion, constituting a four-aircraft interception engagement. Under the assumption that the pursuing aircraft adopts the augmented proportional guidance law and first-order dynamics, a cooperative intercept mathematical model with an intercept angle constraint is established, allowing for the cooperative maneuvering of the evader. Based on the differential linear matrix inequality (DLMI), a controller design method of input and output finite time stability (IO-FTS) is proposed and applied to the aircraft’s cooperative intercept scenario. A cooperation performance analysis is carried out for two cases: (1) two defenders intercept the pursuer with various intercept angle constraints, and (2) the evader acts in a lure role to cooperate with two defenders. The simulation results indicate that the proposed method of controller design has the ability to guarantee that the two defenders intercept the pursuer at the preassigned intercept angles. The cooperative intercept scenario with a lure role is shown to be a very effective method for reducing the maximum required acceleration for defenders, which confirms the availability and advantage of cooperation. The strong adaptability and robustness of the cooperative guidance law with respect to various initial launch conditions is also verified.

Investigation of toppling ball flight in American football with a mechanical field-goal kicker

A mechanical field-goal kicking machine was used to investigate toppling ball flight in American football place-kicking, eliminating a number of uncontrollable impact variables present with a human kicker. Ball flight trajectories were recorded using a triangulation-based projectile tracking system to account for the football’s 3-dimensional position during flight as well as initial launch conditions. The football flights were described using kinematic equations relating to projectile motion including stagnant air drag and were compared to measured trajectories as well as projectile motion equations that exclude stagnant air drag. Measured football flight range deviations from the non-drag equations of projectile motion corresponded to deficits between 9 and 31%, which is described by a football toppling compound drag coefficient of 0.007 ± 0.003 kg/m. Independent variables including impact location and impact angle orientation resulted in 15 impact conditions. We found that an impact location of 5.5 cm from the bottom of the ball maximized trajectory height and distance. At the 5.5-cm impact location, alterations in impact angle produced minimal change in football trajectory, including launch angle (range = 1.96 deg), launch speed (range = 1.06 m/s), and range (range = 0.94 m).

Optimization of Allocation and Launch Conditions of Multiple Missiles for Three-Dimensional Collaborative Interception of Ballistic Targets

We consider the integrated problem of allocation and control of surface-to-air-missiles for interception of ballistic targets. Previous work shows that using multiple missile and utilizing collaborative estimation and control laws for target interception can significantly decrease the mean miss distance. However, most of these methods are highly sensitive to initial launch conditions, such as the initial pitch and heading angles. In this work we develop a methodology for optimizing selection of multiple missiles to launch among a collection of missiles with prespecified launch coordinates, along with their launch conditions. For the interception we use 3-DoF models for missiles and the ballistic target. The trajectory of the missiles is controlled using three-dimensional extensions of existing algorithms for planar collaborative control and estimation laws. Because the dynamics of the missiles and nature of the allocation problem is highly nonlinear and involves both discrete and continuous variables, the optimization problem is cast as a mixed integer nonlinear programming problem (MINP). The main contribution of this work is the development of a novel probabilistic search algorithm for efficiently solving the missile allocation problem. We verify the algorithm by performing extensive Monte-Carlo simulations on different interception scenarios and show that the developed approach yields significantly less average miss distance and more efficient use of resources compared to alternative methods.

Sparse supercontinuum with low order solitons in higher order electromagnetic modes

By fine control of initial launch conditions and utilizing the dispersion properties of micro-structured optical fibre for the transmission of higher order electro-magnetic modes, very low order solitons have been generated in a spectrally sparse continuum. The few Raman self-frequency shifted solitons in the near IR demonstrably match with the change in wavelength of the blue emission through group refractive index matching. These experimental spectral results agree with recent theory on the wavelength shift of blue supercontinuum light.

Influences of initial launch conditions on flight performance of high altitude balloon ascending process

Influences of initial launch conditions on flight performance are addressed for the high altitude balloon ascending process. A novel dynamic model was established to describe thermodynamic and kinetic characteristics of balloon which consists of atmospheric, thermal and dynamic submodels. Based on the model, ascending processes of a high altitude balloon under different initial launch conditions were simulated. The initial launch conditions were classified into three types: inflating quantity, launch time and launch position. The ascending velocity and the differential pressure were defined and used as evaluation parameters of flight performance. Results showed that the inflating quantity is the most effective factor for ascending process, and the upper and lower limits were also proposed separately from safety and performance perspectives. For both launch time and launch location conditions, different solar radiation is the main effect approach during ascending process. Specifically, the influence mechanism of launch time in one day and launch longitude are completely identical due to the Earth’s rotation. Results also showed that the sunset process is the optimal selection for safety of balloon and efficient utilization of solar energy. Due to the Earth’s revolution, the influence mechanism of launch date and launch latitude are identical and the effects are more seasonal and less effective. Launch time and location should be considered comprehensively in practical operation of ballooning.

Performance Evaluation of a High-altitude Launch Technique to Orbit Using Atmospheric Properties

The purpose of this paper is to perform the feasibility and performance evaluation of the High-altitude launch technique using high altitude atmospheric Properties to near earth orbits. The current propulsion transportation system from Earth to space has been deemed by many to be expensive, unreliable, and an unnecessarily dangerous means of travel to space. It is suggested in this paper to analyze a different type of launch from a high altitude to the LEO orbit. Two altitudes serve as the initial launch conditions, 20 to 40 km that is evaluated according to thrust profile variations with respect to vehicle’s weight and under launch different angles. the trajectory equations used in the simulation code also take into consideration Spectral and Diffusive reflection model for near space conditions. The methodology is based on the previously mentioned model that calculates the forces affecting a flat plate as it gains altitude. To summarize the results and conclude, when comparing all cases, a higher altitude with a high T/W ratio and a low angle of attack is more desirable.

Guidance and Control Design for a Class of Spin-Stabilized Fin-Controlled Projectiles

This article presents a complete design concerning the guidance and autopilot modules for a class of spin-stabilized fin-controlled projectiles. The proposed concept is composed of two sections: the rapidly spinning aft part contains the charge, whereas the front part, which is roll decoupled from the aft, includes all the necessary electronic equipment and actuator devices needed for guidance and control. As far as the front section is concerned, a skid-to-turn control configuration is adopted, employing two pairs of movable trajectory correction aerodynamic surfaces, whereas a coaxial motor is added for nose roll angle positioning. The main advantage of the overall setup is that, on the one hand, it maintains the inherent dynamic stability properties of a rapidly spinning body due to the aft part, while at the same time, the front part, containing the guidance fuse, remains easy to be fit to any unguided projectile, hence transforming it into a guided one. The design of the guidance and control modules for this configuration still remains a challenging task because the rapid spinning of the body creates a heavy coupling between the normal and lateral projectile dynamics, which must be eliminated. Furthermore, the rapidly changing operating conditions, the extended flight envelope, and the limited actuator and sensor bandwidths make this task even more demanding. A thorough yet practical procedure for the treatment of the preceding issues is described in this work involving several steps, such as nonlinear modeling of the projectile dynamics, equilibrium point computation, and linear parameter-varying modeling, autopilot design as well as guidance algorithms. Finally, complete nonlinear simulations based on realistic scenarios are performed to demonstrate the robustness of the proposed solution with respect to uncertain initial launch conditions.

Poster Session I, July 14th 2010 — Abstracts Accounting for ball performance differences in golf club fitting

Golf club fitting is becoming a more and more precise science. In the last 10 years, a number of different devices have become available to club fitters for measuring either the flight of the golf ball (e.g. Trackman™ and Flightscope® radar devices) or just the initial launch conditions (e.g. Vector Pro™ and 3Trak® camera devices, Golf AchieverTM laser device). In 2008, PING released the nFlight® fitting software to tie in with any of these devices, capture data, digitally analyze and scientifically compare every aspect of every shot taken by a golfer to provide the best possible golf club fitting.One challenge arising from this approach was how to account for large differences in golf ball construction and performance, both in the initial launch conditions immediately after impact and the resultant ball flight. In particular, many golf courses use various kinds of range balls in practice and fitting areas. To conduct a golf club fitting using data derived from these balls could be misleading and result in inappropriate club choices. For example, a driver fitting using an exceptionally high spin ball could result in a low loft and stiff shaft being chosen to minimize the spin rate when actually the high spin is due to the nature of the ball used in the fitting rather than aspects of the golfer’s swing.To account for these differences and ensure accurate data from a golf club fitting, the nFlight® fitting software provides a way to convert launch data from one category of golf ball into another. So far over 60 different brands of ball have been subjected to static, robot and player comparison testing including at least 1500 shots hit by Ping Man, PING’s robotic testing machine. A cluster analysis was used to group similar golf balls into various categories and C# code in the nFlight® fitting software was used to manage the data conversion. The poster describes the testing conducted, the methods behind the cluster analysis and the patent-pending nFlight® fitting software application of the data conversion.

골프 공의 충돌 시 스핀 생성 원리 연구

It is important to improve the initial launch conditions of golf ball at impact between golf club and ball to get a long flight distance. The flight distance is greatly influenced by the initial launch conditions such as ball speed, launch angle and back spin rate. It is also important to analyze the mechanism of ball spin to improve the initial conditions of golf ball. Back spin rate is created by the contact time and force. Previous studies showed that the contact force is determined as the resultant force of the reaction forces normal and tangential to the club face at the contact point. The normal force causes the compression and restitution of ball, and the tangential force creates the spin. Especially, the tangential force is known to take either positive or negative values as the ball rolls and slides along the club face during impact. Although the positive and negative tangential forces are known to create and reduce the back spin rate, respectively, the mechanism of ball spin creation has not yet been discussed in detail in the literature. In this paper, the influence of the contact force between golf club and ball is investigated to analyze the mechanism of impact. For this purpose, the contact force and time at impact between golf club head and ball are computed using FEM and compared with previous results. In addition, we investigate the impact phenomenon between golf club head and ball by FEM and clarify the mechanism of ball spin creation accurately, particularly focusing on the effect of negative tangential force on ball spin rate.