High Spin Rates Research Articles

Structural stability of China’s asteroid mission target 2016 HO3 and its possible structure

ABSTRACT Asteroid 2016 HO$_3$, a small asteroid (<60 m) in super fast rotation state ($\sim$28 min), and is the target of China’s Tianwen-2 asteroid sample-return mission. In this work, we investigate its structural stability using an advanced soft-sphere-discrete-element-model code, dembody, which is integrated with bonded-aggregate models to simulate highly irregular boulders. The asteroid body is numerically constructed by tens of thousands particles, and then is slowly spun up until structural failure. Rubble piles with different frictions, cohesions, morphologies, grain size distributions, and structures are investigated. We find a 2016 HO$_3$ shaped granular asteroid would undergo tensile failure at higher strengths as opposed to shear failure in lower strengths, regardless of its shape and constituent grain size ratio. In the tensile failure regime, the critical tensile strength is proportional to the square of the spin rate, but surprisingly, is independent of the internal friction angle. Such relations indicate that the Maximum Tensile Stress criterion emerges as superior paradigm for investigating the failure behaviour of fast-rotating asteroids. We predict that the high-spin rate of asteroid 2016 HO$_3$ requires a surface strength over $\sim$3 Pa and a bulk tensile strength over $\sim$10–30 Pa. Through comparing these strength conditions with the latest data from asteroid missions, we suggest a higher likelihood of a monolithic structure over a typical rubble pile structure. However, the possibility of the latter cannot be completely ruled out. In addition, the asteroid’s surface could retain a loose regolith layer globally or only near its poles, which could be the target for sampling of Tianwen-2 mission.

Optimizing the thermoelectric behavior of novel quaternary CoIrMnX (X=Sn, Sb) alloys through chemical potential or carrier concentration doping

Materials exhibiting significant polarisation at high spin rates are considered the most promising candidates for spintronic devices. This study investigates the mechanical, optical, spin-polarised electronic structure, magnetism, and thermoelectric properties of CoIrMnX (where X = Sn, Sb). We performed calculations of quaternary Heusler alloys using first-principles calculations. The CoIrMnSn and CoIrMnSb compounds have the most stable Type III crystal structures, according to the calculations performed on the alloys under investigation. We found that the two alloys, CoIrMnSn and CoIrMnSb, possessed a half-metallic ferromagnetic structure, characterised by indirect band gaps of 1.008 eV and 0.806 eV in the predominant spin channels, respectively. Both alloys demonstrate a significant overall magnetic moment of 5 and 6 μβ, respectively. CoIrMnX (where X = Sn, Sb) are ferromagnetic half-metals with 100 percent spin polarisation, according to the results. The results of the elastic constants demonstrate the alloys' mechanical stability. We also investigated optical characteristics such as dielectric function, absorption, reflectance, and optical conductivity. CoIrMnX (where X = Sn and Sb) acts as an efficient absorber in the ultraviolet region and possesses a high refractive index. Alloys exhibit considerable potential as viable candidates for implementation in spintronic devices. The maximum ZT value for CoIrMnSn (CoIrMnSb) is 0.915 (0.6619). To achieve this value, it is necessary to either reduce the charge carrier concentration to n = 0.0812 x 1020 (0.0952 x 1020) cm-3 or the μ to 0.83843 (0.83806) Ryd. Substantially examined materials demonstrate considerable potential for application in the field of thermoelectrics.

Stress stiffening effects in flexible Earth observation satellites with spinning appendage

Modern satellites often adopt innovative configurations to meet the escalating requirements of space operations. This study specifically focuses on one such configuration, exemplified by an Earth observation spacecraft equipped with a large rotating payload connected to the main bus through a flexible boom. The rotational motion of the payload is designed to extend the scanned area, resulting in a substantial reduction in the time required to complete a set of measurements, thus enhancing the overall performance. However, this configuration introduces greater complexity both in the analysis of the dynamical behavior and in the design of the control architecture. When dealing with flexible structures subject to rotational motion, as in this scenario, the stiffening effect resulting from inertial loads—particularly the centrifugal action—becomes crucial. In this study, we derive the dynamic equations of the multibody flexible spacecraft using Kane's formulation, which provides a streamlined set of ordinary differential equations by simplifying their derivation. Treating the link as an elastic beam, flexibility is incorporated through a modal decomposition approach that considers nonlinear elastic dynamics, ensuring the inclusion of stress stiffening in the dynamical model. Stress stiffening emerges as a fundamental effect in spinning space structures, where the contribution of the centrifugal force is significant. Incorrect predictions and structural instability for high spinning rates are observed when this effect is neglected. Furthermore, the error associated with overlooking this physical phenomenon is found to be dependent on the spinning rate. We identify kinematical conditions that render this effect negligible in relation to the fundamental deformation frequencies of the space system. Several numerical results are presented and discussed.

Optimizing Spin-Coat Speed for Fabrication of P3HT: PCBM Solar Cells

The effect of spin speed on the orientation of the conjugated polymer chains becomes a matter of concern while fabricating bulk heterojunction devices such as solar cells. The stability and performance strongly depend on the intertwining of the two molecules that form the bulk heterojunctions. In the case of P3HT: PCBM, it is the long chains of P3HT that encompasses the PCBM molecules. This work investigates the fabricating conditions of Poly (3-hexylthiophene) (P3HT) on the glass substrates in terms of spin coating speeds to obtain favourable geometry of P3HT. For this purpose, three different samples were prepared, keeping spin rate as 6850, 8150 and 9700 rpm, respectively. It was observed that at high spin rates, a large centrifugal force acts upon polymer chains, unfolding them into highly oriented structures. These P3HT chains are free from twists, kinks and are not intermingled. The results of the present work advocate fabricating P3HT: PCBM films at spin speeds less than 6850 rpm.

Gravity Modes on Rapidly Rotating Accreting White Dwarfs and Their Variation after Dwarf Novae

Accreting white dwarfs (WDs) in cataclysmic variables (CVs) show short-period (tens of minutes) brightness variations that are consistent with nonradial oscillations similar to gravity (g) modes observed in isolated WDs. The dwarf nova GW Librae was the first CV in which nonradial oscillations were observed and continues to be the best-studied accreting WD displaying these pulsations. Unlike isolated WDs, accreting WDs rotate rapidly, with spin periods comparable to or shorter than typical low-order oscillation periods. Accreting WDs also have a different relationship between their interior and surface temperatures. The surface temperature of an accreting WD varies on a months-to-year timescale between dwarf nova accretion events, allowing study of how this temperature change affects g-mode behavior. Here we show results from adiabatic seismological calculations for accreting WDs, focusing on low-order (ℓ = 1) modes. We demonstrate how g-modes vary in response to temperature changes in the subsurface layers due to a dwarf nova accretion event. These calculations include rotation nonperturbatively, required by the high spin rate. We discuss the thermal history of these accreting WDs and compare the seismological properties with and without rotation. Comparison of g-mode frequencies to observed objects may allow inference of features of the structure of the WD such as mass, surface abundance, accretion history, and more. The variation of mode frequencies during cooling after an outburst provides a novel method of identifying modes.

Preliminary design of the Hayabusa2 extended mission to the fast-rotating asteroid 1998 KY26

The near-Earth asteroid 1998 KY26 is a rendezvous target of the Hayabusa2 extended mission, with a diameter as small as 20–40m and a spin period as short as 10.7min. This research aims to develop a plan for Hayabusa2 operations around this particular asteroid constrained by the remaining spacecraft resources. The main part of this paper begins with the characterization of the orbital and surface dynamics about 1998 KY26. The analysis demonstrates that the orbital motion of the spacecraft in the microgravity environment is dominated by solar radiation pressure, while the centrifugal force due to the high spin rate plays a prominent role at the surface. The dynamical environment significantly differs from that of the original target Ryugu, for which Hayabusa2 was specifically designed, posing technical challenges in close-proximity operations. In particular, this article highlights the feasibility of two primary operations: hovering for station-keeping and controlled descent for close-up observations. The discussion is further extended to more advanced operations, such as those using the projectile and target marker aboard the spacecraft. Our research pushes the envelope to explore one of the smallest members of the Solar System.

Mechanism for control of ball spin rate by the upper limb in baseball pitching based on singular value decomposition

This study aims to examine the mechanism by which the ball spin rate during fastball pitching is controlled by synergistic joint torque. The participants were seven baseball players. The kinematics and kinetics of the fingers, wrist, elbow, and shoulder were calculated using the inverse dynamics method. The synergistic relationship between the joint torques was calculated using singular value decomposition. The similarity of the spatial pattern of the joint torque in each participant was evaluated using cosine similarity. The results indicated that there were three types of synergistic torque control: (1) two pitchers had a synergistic torque control that was primarily based on shoulder internal rotation torque, (2) two pitchers had a synergistic torque control that was primarily based on elbow extension torque, and (3) three pitchers had a synergistic torque control that was primarily based on shoulder horizontal adduction torque. In particular, pitchers with a high spin rate relative to the ball velocity (SPV) had a torque control of the shoulder internal rotation type. In contrast, pitchers with a low SPV had a torque control of the shoulder horizontal adduction type. It is considered that pitchers with a high SPV execute shoulder internal rotation torque, which has the same direction as that of ball spin, based on hierarchical control to increase the ball spin rate. These results suggest that pitchers with high and low SPVs exhibit different motor patterns. Pitchers and coach need to focus on the shoulder joint as well as the fingers when they throw fastball.

Lifted particles from the fast spinning primary of the Near-Earth Asteroid (65803) Didymos

An increasing number of Near Earth Asteroids (NEAs) in the range of a few hundred metres to a few kilometres in size have relatively high spin rates, from less than 4 h, down to ∼2.2 h, depending on spectral type. For some of these bodies, local acceleration near the equator may be directed outwards so that lift off of near-equatorial material is possible. In particular, this may be the case for asteroid Didymos, the primary of the (65803) Didymos binary system, which is the target of the DART (NASA) and Hera (ESA) space missions. The study of the dynamics of particles in such an environment has been carried out – in the frame of the Hera mission and the EC-H2020 NEO-MAPP project – according to the available shape model, known physical parameters and orbital information available before the DART impact. The presence of orbiting particles in the system is likely for most of the estimated range of values for mass and volume. The spatial mass density of ejected material is calculated for different particle sizes and at different heliocentric orbit epochs, revealing that large particles dominate the mass density distribution and that small particle abundance depends on observation epoch. Estimates of take off and landing areas on Didymos are also reported. Available estimates of the system mass and primary extents, after the DART mission, confirm that the main conclusions of this study are valid in the context of current knowledge.

Time-averaged flow field behind a transversely spinning sphere: An experimental study

The aerodynamic forces on a sphere with a rough surface were measured in a water tunnel at a Reynolds number of 7930 and for a range of spinning ratios (α) from 0 to 6.0. The time-averaged flow fields were also measured using particle image velocimetry. The effect of the spinning ratio α on the flow was found to show distinct trends in different regimes, including α≤0.25; 0.25<α≤0.75; 0.75<α≤2.0; 2.0<α≤3.0; and 3.0<α≤6.0. The study identified two critical spinning ratios, where the flow underwent significant changes. The first change occurred in regime II, where the boundary layer over one side of the sphere transitioned from laminar to turbulent, leading to a significant modification in the lift force on the sphere. The second significant change took place across regimes II and III, where the boundary flow in the vicinity of the entire sphere became turbulent. Beyond this range, with α≥3.0, the high spinning rate disturbed the incoming flow, resulting in less-efficient downwash production. The lift increased with α at a slower rate compared to other regimes, and the less-efficient downwash production caused a decrease in drag as more momentum was directed downstream in the horizontal direction.

Transmission property of a high spun optical fiber with single stress element

The transmission property of a high spun optical fiber with single stress element is analyzed comprehensively by a rigorous theory based on the real stress distribution characteristics of the optical fiber. Possible coupling between the fundamental mode and the higher order mode is discussed and the related condition to realize a truly single circular polarization optical fiber is shown. The coupling within the fundamental modes and the transmission property of this kind of fiber with high spinning rate are studied thoroughly. It is shown that an approximate circular polarization maintaining optical fiber is possible if some conditions are satisfied, while a strong robust circular polarization maintaining optical fiber may be hard to be realized. The analysis results are compared with the experiment data by a high spun optical fiber with single stress element, and they are agreed well with each other.

Guidance and Control of Spin-Stabilized Projectiles Based on Super Twisting Algorithm

In this paper, a hybrid integrated guidance and control design exploiting the time-scale separation principle for a canard-guided dual-spin projectile (DSP) is proposed. The DSP consists of two parts: i) the aft part, which has a high spin rate for providing gyroscopic and aerodynamic stability, and ii) the forward part, which contains a course correction fuze that houses two pairs of movable canards to ensure precise interception. The guidance and control algorithms operate in a two-loop structure where the outer guidance loop generates required pitch and yaw rate commands, whereas the inner loop tracks these commands by generating canard deflections. The rolling motion of the forward part is controlled using a coaxial motor. The multibody dynamic model of DSP has seven degrees of freedom and is highly coupled and nonlinear. For the guidance, a finite horizon optimal control problem is formulated as an output regulation problem with output vector taken as pitch and yaw components of zero effort miss vector. A coupled pitch–yaw autopilot for pitch and yaw rate command tracking and a roll autopilot for roll stabilization of the forward part are designed based on super twisting algorithm. The efficacy of the control design is shown through numerical simulations.

Rotational remanent magnetization as a magnetic mineral diagnostic tool at low rotation rates

SUMMARY Prior work on rotational remanent magnetization (RRM) and rotational anhysteretic remanent magnetization (ARMROT) has demonstrated promise for magnetic mineral identification in earth materials. One challenge has been to calibrate the measurements to magnetic mineral types and microstructural controls, since previous studies have used differing spin rates, alternating field (AF) intensities and decay times, which hinders a comparison of data sets. Using a RAPID magnetometer we show that the range of usable practical rotation rates is 0.25–3 Hz [rps] which allows a wide range of RRM and ARMROT characteristics to be utilized (at 100 mT AF field, 100 μT bias field). Sets of magnetic mineral extracts from sediments, and well characterized rock samples that contain the key magnetic minerals magnetite, pyrrhotite and greigite are used for a calibration of the RRM-ARMROT behaviour. Detrital pyrrhotite and pyrrhotite-bearing phyllites have largely small positive effective field (Bg) values (up to 6 μT), with differences in Bg and ARMROT ratios at 0.5 and 2.5 Hz [rps] allowing grain size discrimination. The positive Bg values, and changes in RRM and ARMROT with rotation rates allow distinction of pyrrhotite from magnetite and diagenetic greigite. Diagenetic greigite has Bg values of –83 to –109 μT (at 0.5 Hz [rps]) and unusual RRM variation at low rotation rates caused by anisotropy affects. In contrast to previous work, based on crushed and sized natural magnetite at high spin rates, Bg for single domain magnetite from intact bacterial magnetofossils from Upper Cretaceous Chalk has some of the lowest Bg (0–1 μT) and displays a steep decline in ARMROT with increasing rotation rates. A simple tool for particle size characterization of magnetite may be the ratio of ARMROT at spin rates 2.5 and 0.5 Hz [rps]. Stability of RRM is better studied using RRM acquisition with increasing AF field intensity, since static demagnetization imparts a nuisance gyroremanence along the field axis. Mineral microstructure, dislocations and particle interactions are likely additional effects on RRM behaviour that need more investigation.

SiCN Ceramics as Electrode Materials for Sodium/Sodium Ion Cells – Insights from 23Na In‐Situ Solid‐State NMR

AbstractPolymer‐derived silicon carbonitride ceramic (SiCN) is used as an electrode material to prepare cylindrical sodium/sodium ion cells for solid‐state NMR investigations. During galvanostatic cycling structural changes of the environment of sodium/sodium ions are investigated by applying 23Na in‐situ solid‐state NMR. Changes of the signals assigned to sodium metal, intercalated sodium cation and sodium cation originating from the electrolyte are monitored as well as the occurrence of an additional signal in the region of metallic sodium. The intensity of this additional signal changes periodically with the cycling process indicating the reversibility of structures formed and deformed during the galvanostatic cycling. To identify interactions of sodium/sodium ions with the SiCN electrode materials, the cycled SiCN material is studied by 23Na ex‐situ MAS NMR at high spinning rates of 20 and 50 kHz to obtain appropriate spectral resolution.

Single channel digital controller design for a high spinning rate rolling airframe missile

AbstractSpinning/Rolling Airframe Missiles (RAM) mostly use an analog (ON-OFF type) control approach that deflects control surfaces (fins) at minimum and maximum positions continuously, and control is achieved by applying phase shift between the minimum and maximum deflections during a complete roll cycle. Therefore, the control signal shape changes continuously during the roll cycle. In this study, a novel single channel digital controller is designed and tested for a high spinning rate (10–20 Hz) RAM. The digital controller adjusts the amplitude of fin deflections instead of applying a phase shift. In this way, control signal shapes are predetermined in design to completely decouple yaw and pitch dynamics. At the beginning of each roll cycle, the algorithm decides on the control signal shape and amplitude to apply throughout the cycle. Delays on the actuator system and sensor measurements which might lead to instability at high spinning rates are handled effectively thanks to the predetermined control signal shapes that are changing with 90-degree intervals. Detailed geometry of a surface-to-air spinning missile is used to obtain aerodynamic coefficients for the entire flight regime (i.e. from launch to terminal phase) via Missile DATCOM. The 6-DOF flight dynamics model and the controller algorithms are built in MATLAB/Simulink environment. The proposed digital controller is tested systematically for various scenarios and the performance is compared with the conventional analog control approach. The digital controller gives better performance compared to the analog approach under the influence of servo delays and sensor noise.

A Study of Bound Behavior in Table Tennis Ball

In this study, we have developed a four-roller type table tennis machine that can shoot balls such as a top, back, side and gyro rotations with high speed and spin rate, which are difficult to shoot with existing table tennis machines. Using the developed machine, the table tennis ball was bounced on the table tennis table, and it was investigated the dynamic behavior of the ball before and after the collision. In addition, collision and rebound simulations were performed using the finite element models of a table tennis ball and table. From the results of the bound experiment and simulation, it was found that the coefficient of restitution, flight trajectory and spin rate after the bound change depending on the spin types and the value of the coefficient of friction between the ball and table. In addition, these values were significantly different between the side and gyro spins.

Reconfigurable Asymmetric Embedded Magnetorquers for Attitude Control of Nanosatellites

A miniaturized attitude control system (ACS), which is capable of attaining a high spin rate and good pointing accuracy, is an integral part of any small spacecraft. In this regard, embedded magnetorquers are gaining significant attention because they are inserted in printed circuit board (PCB) internal layers with no extra space occupation and result in almost no mass and development cost. In this article, an innovative embedded magnetorquer with asymmetric nonuniform geometric structure is presented. The proposed magnetorquer is optimized for various parameters of interest, i.e., magnetic moment, resultant generated torque, power consumed, and heat dissipation for a CubeSat standard nanosatellite by means of employing diverse nonunity track-width-ratio geometrical arrangements. The magnetorquer driver and reconfigurable circuit is implemented with commercial-off-the-shelf (COTS) components which are low cost and easily available from the market. Embedded coils with variable trace width were simulated in order to predict the accuracy and to achieve the maximum torque versus power dissipation ratio of the developed models. Time-varying rotational analyses are performed to evaluate the angular spin rates driven by the asymmetric coils. Due to embedded coil structure, a detailed thermal analysis is conducted for various coil configurations (i.e., series, parallel, hybrid, etc.) to preserve thermal limits and to ensure the efficacy of the system. The simulation results were validated through a comprehensive set of experimental measurements which also establishes the framework for selecting the optimal coils configuration based on specific mission requirements.

Design of Magnetorquer-Based Attitude Control Subsystem for FORESAIL-1 Satellite

The magnetorquer-based attitude control system capable of attaining high spin rates and precise pointing control is required for a 3U CubeSat satellite FORESAIL-1. The satellite, developed by the Finnish Centre of Excellence, needs to maintain a spin rate of 24°/s and precise pointing of the spin axis toward the Sun for the particle telescope instrument, as well as to reach 130°/s spin rate for the deployment of the plasma brake. Mission requirements analysis and attitude system requirements derivation are presented, followed by actuator tradeoff and selection, with a detailed design of the complete attitude control system, including the air-cored type of magnetorquer actuators and their drivers, made of H-bridge and filtering components. The design is based on several theoretical and practical considerations with emphasis on the high-power efficiency, such as effects of parallel and serial magnetorquer connections, modeling the magnetorquers with equivalent circuit models for finding a suitable driving frequency and extrapolation methods for efficient dipole moment usage. The in-house manufacturing process of magnetorquers, using a custom 3-D-printer setup, is described. Finally, the testing and verification are performed, by measuring the performance of the manufactured hardware, circuit simulations, and attitude control simulations. It is shown that the manufactured attitude control system fulfills all system requirements. Simulations also confirm the capability to satisfy mission requirements.

Simulation of the Schiaparelli Entry and Comparison to Aerosciences Flight Data

The European Space Agency flew an entry, descent, and landing demonstrator module called Schiaparelli that entered the atmosphere of Mars on 19 October 2016. The entry and descent instrumentation suite had sensors on both the heat shield and backshell and included forebody pressure transducers and thermocouples (Atmospheric Mars Entry and Landing Investigations and Analysis, or AMELIA), along with aftbody pressure transducers and heat flux (COMbined Aerothermal and Radiometer Sensors instrument package, or COMARS) and narrowband radiative heatflux sensors (Infrared CO Two Measurement, or ICOTOM). Because of the failed landing attempt, only a subset of the flight data was transmitted before and after plasma blackout. The goal of this paper is to present comparisons of the flight data with calculations using NASA’s aerodynamic and aeroheating simulation tools. Simulations were conducted at various angles of attack to compare against forebody pressure data and to infer the angle of attack used in full three-dimensional simulations to calculate the total heat flux at the sensor locations. Comparisons with the COMARS total heat flux data and backshell pressure data are presented. Furthermore, due to the sparse dataset, results are also compared with the reconstructed heat flux, which was calculated from an inverse analysis of the AMELIA thermocouple data. The simulations agree within 16% for both the total heat flux measured in flight and the heat flux reconstructed from the thermocouple data. A potential link between the Schiaparelli high spin rate observed during entry as documented in the anomaly report and the unexpected stagnation point pressure measurement is also discussed.

Spin–Orbit Resonances of High-eccentricity Asteroids: Regular, Switching, and Jumping

Abstract Few solar system asteroids and comets are found in high-eccentricity orbits (e > 0.9), but in the primordial planetesimal disks and in exoplanet systems around dying stars such objects are believed to be common. For 2006 HY51, the main belt asteroid with the highest known eccentricity 0.9684, we investigate the probable rotational states today using our computer-efficient chaotic process simulation method. Starting with random initial conditions, we find that this asteroid is inevitably captured into stable spin–orbit resonances typically within tens to a hundred megayears. The resonances are confirmed by direct integration of the equation of motion in the vicinity of endpoints. Most resonances are located at high spin values above 960 times the mean motion (such as 964:1 or 4169:4), corresponding to rotation periods of a few days. We discover three types of resonance in the high-eccentricity regime: (1) regular circulation with weakly librating aphelion velocities and integer-number spin–orbit commensurabilities, (2) switching resonances of higher order with orientation alternating between aligned (0 or π) and sidewise (π/2) angles at aphelia and perihelia, (3) jumping resonances with aphelion spin alternating between two quantum states in the absence of spin–orbit commensurability. The islands of equilibrium are numerous at high spin rates but small in parameter space area, so that it takes millions of orbits of chaotic wandering to accidentally entrap in one of them. We discuss the implications of this discovery for the origins and destiny of high-eccentricity objects and the prospects of extending this analysis to the full 3D treatment.

Separation Experiment for OMOTENASHI Moon Lander at Extremely High Spin Rates

This paper describes a separation experiment conducted at extremely high spin rates for OMOTENASHI, being developed as the world's smallest Moon lander. The experiment validated the separation method used in the landing sequence and the tipoff impulse was estimated from the motion of the separated object. The study showed that the tipoff impulse increases superlinearly in the high spin rate region. This information is indispensable in determining the operational spin rate of OMOTENASHI in orbit. The method described in this paper can be applied widely to separation experiments for small spinning satellites and rocket stages.