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We report the facile fabrication of flexible concave microlens arrays (MLAs) with a well-controlled curvature using a leaky dielectric (LD) via the electrowetting-on-dielectrics (EWOD) phenomenon. MLAs with a larger curvature (up to 0.46 μm−1) are fabricated using the LD compared with the perfect dielectric (PD) (∼0.40 μm−1). The improved curvature is attributed to the better electrowettability (i.e., the smaller contact angle) of the LD on the inner-wall of the microhole arrays of the Si-template. Moreover, the curvature of the MLAs can be well controlled by the applied external voltage or the spin rate. Finally, the as-fabricated MLAs show a favorable reflective focusing performance, refractive imaging performance and scattering performance for potential applications in miniaturized and high-performance flexible optical micro-devices.

The photometry of space objects (SO) makes it possible to determine their state of rotation around the center of mass, orientation of the rotation axis and rotation speed in the most cost-effective manner. However, the methods for determining the attitude parameters from photometric data from a single observation site (OS) require long series of high-quality and high-frequency measurements. We propose a method for determining the orientation parameters of slowly rotating SO based on simultaneous multi-site photometry with a high temporal resolution. Preconditions for planning and building a local photometric network that can accomplish such a task have been tested via computer simulation. Synchronous observations of the unoperated spacecraft TOPEX/Poseidon were carried out. They were attended by the observatories of Odessa, Lvov and Uzhgorod universities, as well as the observation station of the State Space Agency of Ukraine in Zalistsi, Khmelnytsky region, took part. Synchronous network-based photometric observations from three OSs enable us to calculate time lags between correlated light- curve segments and promptly determine the direction of rotation, as well as the spatial orientation of a SO’s spin axis and its angular spin rate. A local network of several distributed observation sites for synchronous monitoring of the rotation of various SO in LEO will make it possible to determine the rotation parameters of also slowly rotating objects that do not exhibit glints within their light curves.

TrackMan, a device used to measure the kinematics of a ball in flight, has recently been used for research and coaching purposes in tennis, and the number of studies on this device is expected to increase. This study is focused on verifying the accuracy of TrackMan; three participants performed services with various velocities and angular velocity combinations. TrackMan and a proven method based on computer vision were used to measure the speed, spin rate, and spin axis of the ball. The results obtained using each method were compared using regression analysis, intraclass correlation coefficients, and Bland–Altman analysis. The speed and spin rate of the two methods agreed well; the degree of error would not be problematic in practical applications. However, TrackMan underestimated the speed if it was unable to detect the hitting position. The spin axis measured by TrackMan was unstable under low spin rate conditions (

This paper presents a new view that regards pose estimation of an uncooperative rotating target as a simultaneous localization and mapping problem. This approach allows loop closing and relocalization when tracking lost or rotating a period. Using the real-time trackable and updatable mapping, the pose, orientation and angular spin rate of this uncooperative rotating target were determined. To evaluate this approach, a conventional and a micro experimental satellites were installed on the turntable for rotating images acquiring, where its experimental environment under a complex lighting condition. The experiments demonstrate that the proposed approach has a great potential on orbit to address simultaneous localization and mapping problem of uncooperative rotating targets.

With the aim to improve the quality of tennis topspin, motion characteristics are analyzed in this paper. In view of the function of tennis serve machine, some relevant principles of elastic mechanics and fluid mechanics are applied to analyze the characteristics of tennis topspin during flying. Mathematical modeling method is used to set up the ball flight pathway equation, and the computer simulation method is applied to simulate the flight pathway of topspin. The study has obtained the range of initial velocity, angle and spin rate by software MATLAB. In terms of the simulation result, some basis reference can be provided for the tennis serve machine.

Background: There are limited data on the performance or pitching metrics of Major League Baseball (MLB) pitchers who returned to play after ulnar collateral ligament reconstruction (UCLR). Purpose: To describe MLB pitcher performance after return from primary UCLR, compare the velocity and pitch characteristics against the preoperative season, and determine if performance analytics can predict successful return to pitching after UCLR. Study Design: Case-control study; Level of evidence, 3. Methods: This study included 63 pitchers who underwent primary UCLR between 2015 and 2019. Publicly available advanced analytics and pitch metrics from the first 2 postoperative seasons were compared with the preoperative (index) season as well as with an uninjured control group. Results: Overall, 57% of the pitchers successfully returned to the MLB level. Although they threw significantly fewer pitches ( P = .012) and innings ( P = .022) in postoperative year 1 as compared with the index season, there were no significant differences in pitch velocity, release extension, perceived velocity, or performance as measured by advanced analytics. Also, as compared with the index season, returners demonstrated increased postoperative spin rates on curveballs ( P = .001) and sliders ( P = .010), and curveball horizontal movement was significantly increased ( P = .007); however, horizontal movement was significantly decreased for 4-seam fastballs ( P = .026), changeups ( P = .005), and sinkers ( P = .019). The vertical movement on 4-seam fastballs was greater ( P < .001) in postoperative year 1, and the vertical movement on curveballs ( P = .031) and sinkers ( P = .010) was greater in postoperative year 2 when compared with the index season. Pitchers who failed to return to the MLB level had a lower preoperative strikeout percentage ( P = .047), fewer strikeouts per 9 innings pitched ( P = .046), fewer wins above replacement ([WAR]; P = .026), and lower player value ( P = .030) than the pitchers who returned. Conclusion: Pitchers returning to the MLB level after UCLR demonstrated changes in pitch movement profiles and spin rates postoperatively, but there were no differences in velocity or many advanced analytics upon return. Pitchers with lower strikeout metrics, fewer WAR, and less player value before surgery may have an elevated risk of failing to return to the MLB level.

In football kicking, a player imparts the initial flight characteristics by impacting the ball with his foot. Imparting the correct combination of flight characteristics is the basis of a successful kick. However, examination of the relationship between foot-ball impact and flight characteristics for a non-spherical ball, the ball shape in Australian football and rugby, has been limited to ball velocity. Consequently, little is known of the relationship with other flight characteristics of ball trajectory and spin. The aim of this study was to determine the relationship between impact and initial ball flight characteristics. A mechanical limb, designed to replicate the impact phase of Australian football, performed punt kicks. Four impact characteristics were systematically examined to determine their influence on flight characteristics: foot velocity, medial–lateral impact location, proximal–distal impact location and ball orientation. This study identified each flight characteristic (ball velocity, elevation angle, azimuth angle and spin rate) were influenced by multiple impact characteristics (foot velocity, ball orientation and/or impact location). For example, elevation angle was increased by foot velocity, relative foot-ball orientation and proximal–distal impact location on the foot. Foot velocity had the largest influence on ball velocity (linear slope = 1.43). Medial–lateral impact location had the largest influence on azimuth angle (linear slope = 2.73). Ball orientation had the largest influence on elevation angle and back-spin rate, both measures were sine dependent (elevation angle curve amplitude = 19.4°; back-spin rate curve amplitude = 2754°/s). Players must control all impact characteristics to successfully kick to their desired destination.

Controlling the spin of a ball is important in a variety of sports, especially baseball. For an athlete to properly train, it is necessary to know spin information immediately after throwing or hitting a baseball. This paper presents a fully automatic and marker-free technique to measure both the spin rate and spin axis of a pitched baseball using a consumer-grade high-speed camera. After tracking a ball from the high-speed video, our technique measures spin rate by detecting periods in which similar ball images appear, and then estimates spin axis by performing rigid registration that considers three-dimensional rotation. By separating the spin rate measurement and spin axis estimation processes, we achieve reasonable computational efficiency and robustness for small blurred baseball images extracted from video. We evaluated the accuracy of our presented technique by using synthesized videos. To illustrate the feasibility of our technique, we applied it to a variety of breaking ball pitches captured under normal outdoor lighting conditions.

The purpose of this study was to examine the accuracy of methods to estimate ball spin rate and spin axis direction using multi-camera tracking technology. The method implemented by Hawk-Eye and a theoretical ball trajectory model were assessed for their accuracy against high speed-vision. A theoretical ball trajectory model was found to estimate ball spin rate and the spin axis direction more accurately than the method used by Hawk-Eye. The superior performance of the ball trajectory model was indicated by a lower mean bias and standard deviation (2.92 ± 222.76) than Hawk-Eye (-100.01 ± 542.44), as well as narrower limits of agreement and a 327.63 RPM lower RMSE. Spin rates less than 4500 RPM were estimated with the highest accuracy, but neither method was able to consistently and accurately estimate spin rates4500 RPM. The application of a trajectory model to multi-camera ball tracking data provides a practical and non-invasive method to accurately estimate the spin imparted when hitting, allowing for large-scale collection of spin rates during matches.

Background: Ulnar collateral ligament (UCL) reconstruction is a common surgery among Major League Baseball (MLB) pitchers that results in a significant number of missed games. Little has been reported regarding game-by-game trends that can identify those on the verge of becoming injured. Purpose: To determine if there is a patterned change in MLB pitchers’ pitch selection, velocity, or spin rate in games leading up to Tommy John surgery that may predict subsequent UCL surgery. Study Design: Case series; Level of evidence, 4. Methods: A retrospective review of MLB pitchers who underwent primary UCL reconstruction between 2009 and 2019 was performed. Pitch characteristics were evaluated on a game-by-game basis for the 15 games leading up to surgery. A Mann-Kendall trend test was used to identify trends in pitch selection, velocity, and spin rate for multiple pitch types. A Kendall τb correlation coefficient was identified, with values closer to 1 or –1 signifying a stronger monotonic trend. Results: A total of 223 MLB pitchers underwent UCL reconstruction in the time period. In the 15 games leading up to surgery, decreases in pitch velocity for 4-seam fastballs (τb = –0.657; P < .001), 2-seam fastballs (τb = –0.429; P = .029), and sliders (τb = –0.524; P = .008) were significantly associated with game number closer to injury. There was a significant positive association in the spin rate for cutters (τb = 0.410; P = .038) and a significant negative association in spin rate for 4-seam fastballs over the course of these 15 games (τb = –0.581; P = .003). In addition, there was a significant positive association in the percentage of curveballs thrown (τb = 0.486; P = .013). Conclusion: The study results suggest that there is a patterned change in certain pitch statistics in MLB pitchers in the games leading up to Tommy John surgery. Although the absolute change from game to game may be small, it may be possible for these trends to be monitored before a player becomes injured, thus reducing the significant burden Tommy John surgery places on these athletes.

Aerodynamic effects play an important part in any sport where the ball experiences significant periods of free flight. This article investigates the aerodynamic forces generated when a football is spinning quickly to generate swerve and more slowly to generate more erratic flight. The work reports on the application of an experimental method that measures the aerodynamic loads on a non-spinning, slowly spinning and fast spinning football, using a phase-locked technique so that orientation-dependent and steady ‘Magnus’ forces can both be determined. The results demonstrate that the orientation-dependent aerodynamic loads, widely seen in non-spinning data in the literature, surprisingly persist up to the highest spin rates reported. When predicting ball flight, it is generally assumed that at low spin rates a quasi-static assumption is acceptable, whereby forces measured on a non-spinning ball, as a function of ball orientation, apply for the spinning case. Above an arbitrary spin rate, the quasi-static ass...

The driver is the club which receives the greatest scrutiny by golfers and the most marketing efforts by manufacturers. One characteristic often indicated and believed to effect driver performance is the degree of loft on the clubface. The purpose of the current study was to investigate the effect that the loft of a driver and gender has on golf ball launch variables and distance. The variables that were examined included club head speed, ball speed, launch angle, descent (impact) angle, total spin, carry, and total distance. Fifteen participants (12 male, 3 female) with a handicap of eight or lower were used to test three different degree drivers (9.5°, 10.5°, and 13°) on the variables listed above. Participants performed ten tested swings for each driver and the variables were measured. The data were analyzed with a two (gender) by three (club face loft) repeated-measures ANOVA. There were significant differences (p < .05) in total spin rate, descent angle, and total distance between the clubs. The male...

The purpose of this study was to analyse the effects of clubhead presentation on golf ball launch conditions and the subsequent shot outcome. Clubhead presentation was measured using a three-dimensional motion capture system for both male and female golfers across a range of skill levels. A Doppler radar was used to track the golf ball during its flight, yielding speed, launch angles, spin rate and distance. Importantly, the measurements of clubhead and ball quantities were taken independently so that any inter-relationships could be evaluated without recourse to any preconceived models. This article provides values for the median launch conditions and shot outcome, and the associated variability in these quantities for golfers was grouped by handicap category and gender. It was shown that the variability in certain outcome quantities was more linked to golfing ability than others. Linear regression was used to demonstrate that differences in clubhead presentation resulted in changes to ball launch conditions as one might expect from physical analysis. Furthermore, the link between the variability in clubhead presentation and the variability in shot outcome was demonstrated. In particular, the importance of impact location variability in determining launch angle and total distance variability was shown.

The purpose of this study was to analyse the performance outcomes of spin bowlers by using a motion analysis procedure to measure the linear and angular kinematics of a spinning ball. A three-dimensional (3D) Cortex motion analysis system was used to track three markers strategically placed on the ball spinning in flight. Data were further processed using 3D vector kinematics to calculate the ball's linear speed, spin rate and direction of the angular velocity vector. Thirty-four district-level spin bowlers, including both finger-spinners and wrist-spinners, were recruited to bowl 20 standard deliveries, and 5 deliveries of any variation in their repertoire. The results show that spin bowlers can produce various combinations of spin rate and angular velocity vector orientations to implement substantially different methods of utilising both swerve and turn off the pitch to deceive the batsman. In particular, it was found that wrist-spin bowlers could potentially swerve the ball either towards the left or r...

In asteroid exploration mission, the spacecraft needs to execute a series of proximity operations such as approaching, accompany flying, orbiting and hovering, which are the premise and key points to achieve asteroid sample return. Based on the concept of Chinese future asteroid exploration missions, this paper studies the dynamics and control of the proximity operation. First, considering the path and line-of-sight angle constraint, the sliding guidance law is used to design the multi-impulse approaching trajectory. A reconstruction iterative strategy is proposed for the perturbation effect including the irregular shaped gravity, solar radiation pressure, and three-body perturbations. Second, in order to obtain the preliminary physical characteristics of the asteroid, the accompany orbit and slow hyperbolic flybys are designed. The equation of the relative distance and velocity of the accompany orbit is established and the families of accompany orbits with different offsets and sizes are discussed. The spin rate and preliminary shape model of the asteroid can be established during the accompany phase. Then, by slow-flybys, the mass and coefficients of the gravity field of the asteroid can be obtained. The relation between flyby velocity, flyby distance, and flyby duration are found to achieve the global mapping of the asteroid. Several kinds of slow-flyby trajectory are presented. Finally, a self-adaptive control law is designed and proved to achieve the stable hovering at any point or region near the asteroid against varies perturbations and model uncertainty. Based on the control law, the fixed-point hovering and local region hovering are investigated respectively, which can be utilized to precise local exploration and imaging. The simulation results of asteroid 2016 HO3 verify the feasibility of the proposed method. The study can provide a reference for Chinese future asteroid exploration missions.

In golf, many parameters of the driver can be modified to maximise hitting distance. The main objective of this study was to determine whether drivers fitted with shafts having high and low kick points would alter selected swing parameters and related launch conditions. In total, 12 elite male golfers (handicap score = 1.2 ± 1.8) had three shots analysed for two drivers fitted with ‘stiff’ shafts with differing kick point location. Stiffness profiles of these shafts were also measured. Five swing and related launch parameters were measured using a real-time launch monitor. The locations of the low and high kick points on each shaft during the golf swing (the dynamic kick points) were confirmed via motion analysis. The driver fitted with the shaft containing the high kick point displayed a more negative (steeper) angle of attack ( p < 0.01), a lower launch angle ( p < 0.01) and an increased spin rate ( p < 0.01) when compared to a driver fitted with a low kick point shaft. It is possible that the attack angle differed between drivers due to the greater amount of shaft bending found late in the downswing (80% of the downswing and just before impact). Future work is needed in this under-researched area to determine why these differences occurred.

While some tennis racket strings have more grip than others do, this does not guarantee that they will impart more spin to a tennis ball. Experiments with hand-held rackets are required to determine the longstanding question of how players can discern that different strings behave differently when laboratory tests indicate that they should play the same. In a previous study, we clarified the top-spin mechanism of a tennis racket by using high-speed video analysis on a tennis court for the first time. Furthermore, we improved it by using lubricated notched nylon strings. These experiments revealed that the more the main strings stretch and bend laterally, the more spin is imparted to the ball. This is due to the restoring force being parallel to the string face when the main strings spring back and the ball is released from the strings. Notched strings reduce the spin rate, but this can be effectively counteracted by employing lubricants. Furthermore, we found that imparting more spin reduces shock vibrations on the wrist during impact. The present study revealed that a ball has a 40% lower spin rate when hit with a racket with notched strings than with one with unnotched strings in the case of nylon (it had to be determined whether new strings or lubricated used strings give more spin). The experiments also showed that 30% more spin is imparted to a ball when the string intersections are lubricated by oil than when notched used nylon strings are used. Furthermore, we found that used natural gut notched strings reduced the spin rate by 70% compared to when new natural gut unnotched strings are used. We also investigated different top-spin behaviors obtained when professional and amateur tennis players hit a ball.

Software designed to quickly and easily calculate the 3-dimensional speed and the spin rate of a tennis ball from high speed video footage from a single camera was validated. The software values were compared to speed values from light gates and spin rate values found by manually tracking the ball logo. The respective ranges were 18–31 ms −1 and 65–165 rad⋅s −1 . The speed values had a mean percentage error of 4.47% (1.08 ms −1 ). The spin rate values had a mean percentage error of 4.14% (4.71 rad⋅s −1 ).

© 2016 The Author(s). In this study a skilled soccer player performed throws for maximum distance while manipulating the backspin on the ball. A video analysis was used to obtain measures of the ball projection variables. We found that putting greater backspin on the ball did not reduce the player’s ability to produce a high projection velocity. Throw distance increased at a rate of about 0.6 m per 1 rev/s increase in backspin, and the experimental data was consistent with the predictions of a mathematical model. We recommend players apply the highest possible backspin when performing a long throw-in.

The most common commercial pitching machines for baseball are the “roller” type and the “arm” type. Pitches such as the fastball, curveball and screwball are easily achieved by the pitching machine with three rollers which were developed by the authors. In this study, the moving behavior and contact stress state of the ball pitched with the three rollers type pitching machine is analyzed using dynamic finite element analysis software (ANSYS/LS-DYNA). The effect of a seam of a baseball to the throw accuracy is analyzed numerically. In the analysis, the finite element models of a detailed baseball with a seam and a pitching machine with three rollers are used. Additionally, the initial velocity and the spin rate of the pitched ball are filmed using a high-speed videograph, and those pictures are compared with the finite element analysis. From the analytical results, it is understood that the coefficient of friction between the baseball and the rollers is not affected. Additionally, it is obvious that the ball's velocity and spin rate are relatively unaffected by the seam orientation, while the throw's horizontal and vertical angles are notably affected by the relative angular velocity of the rollers and the orientation of the seam.

While Satellite Laser Ranging (SLR) stations usually measure distances to the satellites with 5 or 10 Hz repetition rate, and with laser pulse widths of 35–100 ps and larger, the SLR station Graz started to range in October 2003 with a repetition rate of 2 kHz, with very short laser pulses of 10 ps. This results in a high density of measurements, which substantially increases the precision of statistical Normal Points, and also allows identification of single retro-reflector prisms from various satellites ( Kirchner et al., 2007 ) within the data. Analysis of these single prism returns now allows determination of satellite spin rate and spin rate changes, as well as spin axis orientation. The advantages of using kHz SLR data, instead of classical photometry methods, are the possibility of measuring very low spin rates, without using any additional equipment, during day and night. In this paper, we analyse Graz kHz SLR data to determine spin parameters of LAGEOS-1.

The influence of the spin rate profiles on the stability of polarization transformations of all-fiber polarization transformers (AFPTs), which behave as a broad-band all-fiber quarter-wave plate, is analyzed by the super-mode theory. Huang firstly proposed and demonstrated these AFPTs, and suggested qualitatively that to perform a stable polarization transformation, the variation of the spin rate from zero to fast of the AFPT should be slow. However a compact fiber structure is desirable for an optical current transformers (OCT) system, and bending or wrapping AFPTs will weaken their abilities to hold the output SOPs. A first-order analytical approximation describing the coupling between the two local eigen-modes in the AFPT is derived, and two more detail suggestions for the spin rate profiles design of AFPTs are proposed. A random orthogonal axial gradient method (ROAGM) is developed to optimize the spin rate profiles. Numerical simulations show that for an AFPT with a shorter length, the stable transformation can also be obtained by a carefully designed spin rate profile according the two suggestions.

A rotationally skew fold membrane for the spinning solar sail is discussed to examine the deployment characteristics. The membrane is characterized by double corrugation fold and is advantageous in the complete folding and compact storage. Spinning experiments with scaled models are performed to investigate the geometrical and deployment characteristics. As the result of the spinning experiments, it is indicated that the rotationally skew fold membrane is completely deployed and there is a minimum spin rate to complately deploy. The fact that the spin-direction wrapped membrane realizes quick deployment is also indicated. To investigate the dynamic characteristics, a non-dimensional similarity parameter derived with the theoretical analysis for one-dimensional Z-fold membrane is expressed by the geometrical parameters as the radius, folding pitch, material properties and spin rate. The theoretical similarity parameter is applied to the results of the spinning experiments and indicates the effect of the folding pitch of the rotationally skew fold membrane. Also the similarity parameter based on the experimental results is introduced.

A formation of distributed sensors has great potential to enhance Earth surveillance. This paper investigates the dynamics of tethering several subsatellites together in a three-dimensional configuration. To keep the system oriented toward Earth, the Likins-Pringle rigid body equilibria are used as a baseline design. A flexible lumped-mass model is used to assess the stability of the tethered system. Three parameters related to the formation size, masses and spin rate are varied in order to find designs that demonstrate desirable dynamic behavior. While none of the designs are Lyapunov stable, formations with a spin axis near the local vertical are well-behaved over time spans of several orbits.

The drag and lift coefficient characteristics of rotating cylinder with arc grooves is investigated. The circular cylinders with grooves have thirty-two arc grooves of different depth on the cylinder surface. Pressure of the cylinder surface is measured with the Reynolds number Re= (0.4-1.8) ×105, and rotation of 0-4500rpm.The drag and lift coefficients are calculated from pressure distribution. At Re=0.4×105, the drag coefficient CD of smooth cylinder is constant until the spin rate ratio α (α=rotating speed/uniform flow) =0.6, and CD decreases afterwards at 0.6 1.0×105.As groove depth becomes deep, CD becomes constant value as α increase. The lift coefficient CL of smooth cylinder increases as a increase.However, CL decreases to the minimum value as α further increase and CL increases again with the increase of α, CL indicated negative lift in Re>1.0×105.CL of cylinder with grooves become monotonous increases tendency in Re>1.0×105.As groove depth becomes deep, the increasing gradient of CL becomes small.

In soccer, the world's most popular ball game, there are no systems currently in use capable of measuring soccer ball speed and spin. This paper describes a novel image recognition system capable of obtaining accurate measurements of ball velocity, elevation, spin rate and spin axis. Two sequential images of a soccer ball, a fixed time interval apart, are obtained and a series of image-processing techniques are employed to identify the spatial position of the ball within the image frame and the specific ball orientation. The soccer ball is marked with a total surface-marking scheme using coloured panels, such that a single 2D view of the ball gives a unique pattern for any orientation. A pattern matching algorithm is used to determine the specific ball orientation, and comparison of the two ball images allows the determination of ball velocity, launch elevation, spin rate and spin axis orientation to a high degree of accuracy.

Flight behavior of a mortar launched, parachute deployed imaging system is examined with particular attention to characterizing the quantity and quality of recorded image data. Coverage area of the imager, blur due to motion of the imager, and view time are evaluated for different system configurations allowing important design parameters to be identified. It is shown that proper tailoring of the dynamic characteristics of the system greatly improves gathered image data quantity and quality. Coning of the canister is an important system characteristic that largely drives total ground coverage. Canister coning is influenced in a complex manner by system geometric parameters. Mounting the parachute riser to the canister in such a way that the connection is off the axis of symmetry of the canister is a powerful technique to increase coning of the canister. Likewise, increasing riser length also yields increased coning. Increasing spin rate of the canister leads to a proportional increase in image blur, which is largest toward the edge of the image. Also, increased canister weight tends to increase the descent rate, which reduces total view time. At the same time, increased descent rate increases the spin rate for cross type parachutes, leading to increased image blur. @DOI: 10.1115/1.1789974#

The design of the satellite for the GG experiment was addressed in phase-A level studies in 1997–2000, based on an equatorial orbit, and more recently re-addressed for sun-synchronous orbit (SSO). The mission consists of an experiment running uninterrupted with few operational modes, small telemetry rates, easily controlled by one ground station. The satellite is small, low-weight, with low power demand. The configuration, resembling a spinning top, is very compact and stiff. The main requirements are for thermal stability, drag-free control and spin rate control. The reconfiguration to SSO makes the mission suitable for a low-cost launch, and improves the thermal performance.  2003 Elsevier B.V. All rights reserved.

We analyzed the spin on a baseball pitched by a professional pitcher, who utilized eight distinct, different types of pitches in official league games. In the experiments he pitched each of the eight pitches twice from an official pitching mound to a catcher. The video image of the pitched baseball from just before until 500 milliseconds after ball release was taken with a high-speed video camera at a rate of 1,000 frames per second. A special apparatus was used to obtain the direction of spin axis and the spin rate. Both values varied considerably depending on the type of pitch. In the four kinds of pitches which were thrown with a grip similar to that of the four-seam fastball, ball spin was altered by changing the direction of spin axis and/or orientation of the seams. The other three kinds of pitches thrown with a grip different from that of the four-seam fastball. These pitches had a slower speed and/or slower spin rate than the four-seam fastball. Moreover, the subject was able to throw these different pitches without changing the throwing motion as viewed by a batter. Mastery of these skills is what made him an elite pitcher with a long career.

When a ball is incident obliquely on a flat surface, the rebound spin, speed, and angle generally differ from the corresponding incident values. Measurements of all three quantities were made using a digital video camera to film the bounce of a tennis ball incident with zero spin at various angles on several different surfaces. The maximum spin rate of a spherical ball is determined by the condition that the ball commences to roll at the end of the impact. Under some conditions, the ball was found to spin faster than this limit. This result can be explained if the ball or the surface stores energy elastically due to deformation in a direction parallel to the surface. The latter effect was investigated by comparing the bounce of a tennis ball with that of a superball. Ideally, the coefficient of restitution (COR) of a superball is 1.0 in both the vertical and horizontal directions. The COR for the superball studied was found to be 0.76 in the horizontal direction, and the corresponding COR for a tennis ball was found to vary from −0.51 to +0.24 depending on the incident angle and the coefficient of sliding friction.

In this paper, a new robust surface pattern matching technique is proposed for estimating the spin rate and spin axis of a spinning ball from a multi-exposed image under varying illumination conditions. In the proposed technique, robust surface pattern extraction based on the OFF cell model of the human visual system is employed to obtain high-contrast surface patterns and a novel rotational surface pattern matching based on the contrast response difference between the patterns is then used to estimate the spin rate and spin axis of the ball with high accuracy. The proposed technique is highly robust and highly accurate when compared to correlation-based techniques. In addition, the processing time for the new technique is less than in the other techniques. The performance of the proposed technique is verified through real experimental results under various illumination conditions.

With the loss of the battery system of ABRIXAS shortly after launch and consequent absence of telemetry, there was urgent need to determine ABRIXAS' spin rate and orientation in order to assess the possibility of re-establishing telemetry during periods of full-Sun orbits. We, therefore, conducted optical and video observations of ABRIXAS passages with a 1-second time resolution, and later simulated the optical appearance of ABRIXAS for several passages based on a three-dimensional model of the reflectivity properties of the 2.5m × 1.8m × 1.2m size-satellite. Here we present the results of the comparison of our grid of light curve models with the observations and show (i) how the spin rate of ABRIXAS slowed down between June and December 1999 and (ii) what information can be deduced on the temporal change of the orientation of the spin axis. We conclude with discussing the benefit of using ground based optical observation as a cost effective way to develop information about the orientation of a satellite when there is no telemetry.

Spectral transmittance of spun hi-bi (highly birefringent) fibres with different spin rates is studied by an experimental method. It is found that, as the spin rate is raised to a certain high value, the transmittance of this kind of fibre drops down in a certain long wavelength band. This phenomenon of the spun type fibres is attributed essentially to microbending produced in the spinning-drawing processes.

We report a new flow control method for centrifugal microfluidic systems; CO2 is released from on-board stored baking powder upon contact with an ancillary liquid. The elevated pressure generated drives the sample into a dead-end pneumatic chamber sealed by a dissolvable film (DF). This liquid incursion wets and dissolves the DF, thus opening the valve. The activation pressure of the DF valve can be tuned by the geometry of the channel upstream of the DF membrane. Through pneumatic coupling with properly dimensioned disc architecture, we established serial cascading of valves, even at a constant spin rate. Similarly, we demonstrate sequential actuation of valves by dividing the disc into a number of distinct pneumatic chambers (separated by DF membranes). Opening these DFs, typically through arrival of a liquid to that location on a disc, permits pressurization of these chambers. This barrier-based scheme provides robust and strictly ordered valve actuation, which is demonstrated by the automation of a multi-step/multi-reagent DNA-based hybridization assay.

A wind tunnel test was conducted to empirically determine the relationship between the Magnus force (M), spin rate (ω), and linear velocity (V) of a spiked volleyball. This relationship was applied in a two-dimensional mathematical model for the trajectory of the spiked volleyball. After being validated mathematically and empirically, the model was used to analyze three facets of play that a coach must address: the importance of topspin, possibility of overblock spiking, and optimum spiking points. It was found that topspin can increase the spiking effectiveness dramatically in many ways. It was also found that a shot spiked from about 2 m behind the net has the least possibility of being blocked.

We describe an OFDR-based procedure to measure the spin of optical fibers with spin rates exceeding OFDR resolution. Fibers are twisted to locally unwind the spin and measurements are afterward reassembled with optimal fitting.

A research effort to characterize the flight characteristics at range of the M855 North Atlantic Treaty Organization (NATO) ball ammunition was conducted by the U.S. Army Research Laboratory, Flight Sciences Branch. This development effort required a soft recovery method. A two phase test approach to recover M855 projectiles with little to no damage was undertaken. Both phases utilized gelatin blocks as the catch medium for the projectile. Bullet catchers currently on the market for forensic science often impart some damage to the projectile. This level of damage was considered too great for the current study. Long range calculations show that the velocity of the bullet slows down faster than the bullet's spin rate decays. The flow angle across the bullet changes accordingly and creates the bullet's characteristic behavior. Recovery of the projectile to verify engraving angles is therefore, necessary. This report discusses catching M855 projectiles at energy equivalent states by varying impact range and velocity.

The equations of motion for a ball moving in a vertical plane are used to calculate flight paths for a typical golf ball subjected to a variety of launch conditions, spin rates, atmospheric parameters, and wind fields. Time histories of the ball's velocity, flight-path angle, height, range, and spin rate between tee and first impact illustrate that lift induced by the ball's spin has a significant effect on driving range, actually causing the flight-path angle to increase during the first few seconds of flight. While light winds have the expected effects, heavy tailwind is shown to spoil the carry of the ball. Linearized sensitivity analysis indicates that wind uncertainty is an important contributor to impact range and time uncertainty.

The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is believed to alter the spin states of small bodies in the solar system. However, evidence for the effect has so far been indirect. We report precise optical photometric observations of a small near-Earth asteroid, (54509) 2000 PH5, acquired over 4 years. We found that the asteroid has been continuously increasing its rotation rate ω over this period by d ω/ dt = 2.0 (±0.2) × 10 –4 degrees per day squared. We simulated the asteroid's close Earth approaches from 2001 to 2005, showing that gravitational torques cannot explain the observed spin rate increase. Dynamical simulations suggest that 2000 PH5 may reach a rotation period of ∼20 seconds toward the end of its expected lifetime.

The increase in sophistication of shoulder and gun launched smart weapon systems have increased the demands placed on the flight motion simulator. The high spin rate and accelerations seen during launch drastically exceed the capability of the roll axes on today’s motion simulators. Improvements are necessary to the bearing and drive system to support these requirements. This paper documents the requirements, design, and testing of a flight motion simulator produced to meet these challenges. This design can be incorporated into a new flight motion simulator, or as this paper describes, can be retrofitted into an existing flight motion simulator to improve its capability.

AIAA Atmospheric Flight Mechanics 2004, August 16 - 19, 2004, Providence, USA, available, unclassified, unlimited

As part of the low cost design, the spinning Genesis spacecraft has no High Accuracy Navigation Systems (HANS) on board, such as gyros or accelerometers. All science requirements are met, although accurate pointing estimation is limited to spin rates less than 2 rpm, due to star tracker characteristics, and less than 28/spl deg/ off Sun, because of the two-axis Sun sensor characteristics. Payload contamination concerns result in thruster locations that produce uncoupled forces, and significant translational delta-V, whenever pointing or spin rate are changed. Nevertheless, with creative systems, mission and subsystems design, planning and operations, Genesis should exceed all science objectives. The Genesis lessons learned will benefit future mission design and operations in the areas of both planned activities and off-nominal situations.

A formation of distributed sensors has great potential to enhance Earth surveillance. This paper investigates the dynamics of tethering several subsatellites together in a three-dimensional configuration. To keep the system oriented toward Earth, the Likins-Pringle rigid body equilibria are used as a baseline design. A flexible lumped-mass model is used to assess the stability of the tethered system. Three parameters related to the formation size, masses and spin rate are varied in order to find designs that demonstrate desirable dynamic behavior. While none of the designs are Lyapunov stable, formations with a spin axis near the local vertical are well-behaved over time spans of several orbits.

Webersat has exhibited strange dynamic behavior as confirmed by telemetry; the spin rate has decreased from 5 to 0.05 rpm over the last year. The elongated shape of Webersat is noted to result in an unstable spin about the Z-axis. It is proposed that, in the future, spin-stabilized satellites should be designed to be short and fat about their spin axis rather than tall and thin. The Webersat space frame can be made to spin about the Z-axis if the masses are redistributed so as to produce an overall increase in the moment of inertia about the spin axis.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We devised a unique array of cube-corner reflectors on a spherical satellite so that laser ranging could be used to detect the spin rate and the optical degradation. On the H2A-LRE satellite, there are reflectors made of synthetic silica and ones made of BK7 glass. We report that the degradation of the BK7 reflectors, as well as the spin rate of the satellite, can be monitored through a spectral analysis of laser-ranging data. The center-of-mass correction of the Laser Ranging Equipment satellite was calculated at 210 +/- 10 mm for all possible systems and throughout the degradation process of the BK7 reflectors.

The paper presents the descriptions of recently developed numerical algorithms that prove to be useful for the solution of the free vibration problem of spinning structures. First, a generalized procedure for the computation of nodal centrifugal forces in a finite element owing to any specified spin rate is derived in detail. This is followed by a description of an improved eigenproblem solution procedure that proves to be economical for the free vibration analysis of spinning structures. Numerical results are also presented which indicate the efficacy of the currently developed procedures.

A space test of a pulsed-plasma engine was carried out on the Engineering Test Satellite-IV. The engine was operated successfully more than 300,000 times in space. The spin rate of the satellite was measured with a high accuracy for the impulse estimation of the engine. The spin rate change was, however, smaller than that given by simple estimation based on the impulse measured by the ground test. It was observed that the variation of the spin rate was the same order of magnitude as the variation due to the natural damping by air drag or the temperature variation of the satellite. The impulse of the engine calculated from the space test data taking account of these effects agreed with the impulse measured by ground tests using a pendulum.