Transfer Trajectory Research Articles

An Envelope Algorithm for Single Nanoparticle Collision Electrochemistry†

Main observation and conclusionSingle nanoparticle collision has attracted great attention in the last several years to reveal the electron transfer and motion trajectories of individual particles at the electrode surface. An envelope algorithm is proposed for further reading and demonstrating the corresponding current signals, which integrates baseline correction, peak identification and Savitzky‐Golay filter. It is employed for data analysis of the single AgNPs collision on a wireless nanopore electrode to eliminate the current noise and accurately calculate the integrated charges in each current spike. The practicability and robustness of the algorithm are verified under additive Gaussian white noise with the signal‐to‐noise ratio higher than 5. By comparing with traditional Gaussian peak model, the algorithm here shows comparable performance for the peak identification and integrated charge calculation. These results signify a big step from manual Gaussian fitting to automatically data processing method, which facilitates a fast acquisition of intrinsic features in single entity electrochemistry.

The politics of COVID-19 vaccination in middle-income countries: Lessons from Brazil

As the world struggles to meet the challenges of vaccination against COVID-19, more attention needs to be paid to issues faced by countries at different income levels. Middle-income countries (MICs) typically lack the resources and regulatory capacities to pursue strategies that wealthier countries do, but they also face different sets of challenges and opportunities than low-income countries (LICs). We focus on three dimensions of vaccination: procurement and production; regulation of marketing registration; and distribution and uptake. For each dimension we show the distinct challenges and opportunities faced by MICs. We illustrate these challenges and opportunities with the case of Brazil, showing how each dimension has been affected by intense political conflicts. Brazil's procurement and production strategy, which builds on a long trajectory of local production and technology transfer, has been riddled by conflicts between the national government and state governments. The regulatory approval process, based around one of Latin America's most highly-regarded regulatory authorities, has also been subject to acute inter- and intra-governmental conflicts. And with regard to distribution and uptake, in the face of high uncertainty, even with a solid health infrastructure, Brazil encounters difficulties in promoting vaccine delivery. The research also reveals the importance of coordination among these dimensions, in Brazil and beyond. Pandemic preparedness and response must include sharing knowledge of how to produce vaccines and recognition of the crucial linkages between procurement, regulation, delivery, and uptake that are necessary for ensuring access to these products.

Preliminary Analysis on Launch Opportunities for Sun-Earth Lagrange Points Mission from NARO Space Center

In this work, preliminary launch opportunities from NARO Space Center to the Sun-Earth Lagrange point are analyzed. Among five different Sun-Earth Lagrange points, L1 and L2 points are selected as suitable candidates for, respectively, solar and astrophysics missions. With high fidelity dynamics models, the L1 and L2 point targeting problem is formulated regarding the location of NARO Space Center and relevant Target Interface Point (TIP) for each different launch date is derived including launch injection energy per unit mass (C3), Right ascension of the injection orbit Apoapsis Vector (RAV) and Declination of the injection orbit Apoapsis Vector (DAV). Potential launch periods to achieve L1 and L2 transfer trajectory are also investigated regarding coasting characteristics from NARO Space Center. The magnitude of the Lagrange Orbit Insertion (LOI) burn, as well as the Orbit Maintenance (OM) maneuver to maintain more than one year of mission orbit around the Lagrange points, is also derived as an example. Even the current work has been made under many assumptions as there are no specific mission goals currently defined yet, so results from the current work could be a good starting point to extend diversities of future Korean deep-space missions.

Design of Contact-Aided Compliant Flexure Hinge Mechanism Using Superelastic Nitinol

Abstract This paper presents a novel miniature contact-aided compliant mechanism (CCM) that includes flexure hinges and contact-aided structures. This continuum mechanism comprises a nickel–titanium alloy (Nitinol) tube with CCM cut via laser micromachining and actuated using wires bending from −80 deg to +80 deg in four directions. The proposed CCM has the following merits: perfect capacity for deflection around the centroid, a self-backbone, and improved torsional as well as tensile strengths. Further, it is pre-assembled. First, kinematic and static models are used to predict the bending behavior of the mechanism. Thereafter, the maximum strain is evaluated using finite element analysis (FEA) then compared with the static models. Finally, the performances of the mechanism are characterized by experiments. The results validate the proposed models and demonstrate that the torsional and tensile strengths of the proposed CCM increased by more than 100% and 30%, respectively, compared with those of conventional non-CCMs with a similar fatigue life. Moreover, with the integrated forceps and probe, the proposed mechanism can achieve object transfer and square trajectory scanning of the targeted location. These experimental results demonstrate the potential clinical value of the proposed mechanism and provide important insights into the design of long and flexible instruments for endoscopic surgery.

PROGRESS OF THREE-BODY ORBITAL DYNAMICS STUDY

The orbital dynamics in the three-body system is a classical problem in the field of astrodynamics. It has rich theoretical and engineering significance, and have played an important role in the process of space activities extending from near-earth space to deep space. This paper reviews and summarizes the progress of the study of orbital dynamics in the three-body system. Combined with the development trend of deep space exploration in the future, the hotspots and challenges in the research of three-body orbital dynamics are prospected. First, the research background and significance of the three-body problem are surveyed, and the development of the dynamics model of the three-body system is briefly reviewed. Secondly, characteristics of the local motion near the equilibrium point in the three-body problem are systematically summarized. The analytical and numerical methods for periodic orbits are introduced. The latest development of quasi-periodic motion is discussed. Meanwhile, the characteristics and research progress of global periodic motions in the three-body system including resonance orbits, cycler trajectories, and free return orbits are summarized. Next, the research progress of the low-energy transfer and capture trajectory design in the three-body system is analyzed from two aspects of invariant manifold theory and weak stability boundary theory. Finally, the applications of orbital dynamics in the three-body system in formation flight and navigation constellation design are summarized. Several orbital dynamics and control problems in the design of landing trajectories for full lunar-surface coverage, the low thrust orbit optimization of the three-body system, and the utilization of non-linear equilibrium points in the three-body system are addressed for future study.

Low-fuel transfers from Mars to quasi-satellite orbits around Phobos exploiting manifolds of tori

Quasi-satellite orbits (QSOs) are considered by JAXA’s MMX mission, in which CNES is involved, for the scientific observation of the Martian moon Phobos prior to landing and sample return operations. These periodic orbits, originally defined in the Mars-Phobos circular restricted three-body problem, generically lose periodicity once the eccentricity of Phobos’ orbit is taken into account. In this case, QSOs are replaced by quasi-periodic tori. Recent work on MMX project includes, among many others, station-keeping strategies around QSOs exploiting invariant tori in the elliptic Hill problem. In the present paper, a resonant QSO will be first computed in the Mars-Phobos circular restricted three-body problem. Then, by continuation on the eccentricity of the secondary, this QSO will be converted into a periodic resonant QSO in the Mars-Phobos elliptic restricted three-body problem. The latter problem is more precise than the Hill problem at far distance from the secondary and thus more adapted to handle Mars-Phobos transfers. Notice that considering resonant orbits enables to preserve the periodicity of the QSOs when the eccentricity is nonzero. Then, a family of invariant tori surrounding the resonant QSO in the Elliptic Restricted Three-Body Problem will be obtained by continuation on the frequency. In the next step, stable invariant manifolds emanating from the tori will be computed. Finally, two-impulse transfers between a parking orbit around Mars and the tori surrounding the QSO will be presented with the objective to minimize the total velocity increment. Interesting transfer trajectories will be shown allowing for a ballistic approach to Phobos. These trajectories lead to a reduction in the total velocity increment in comparison with classical Mars to QSOs transfers. Here, instead of targeting directly the resonant QSO, the spacecraft will reach first an invariant manifold before coasting along this manifold until encountering a torus surrounding the QSO. Thus, the spacecraft will reach a quasi-periodic QSO inside the torus that is close to the periodic resonant QSO.

Influence of Steering Angle Profiles on the Orbit Transfer Trajectory

This paper considers a planar orbit transfer trajectory design problem using finite thrust modeling. In this problem, the steering angles associated with the thrust direction are calculated from the predetermined profile format, and the unknown parameters in the profile are directly optimized. Three profile formats that were implemented in previous lunar exploration missions are considered. In addition, a steering angle profile defined in the rotating frame and the optimal steering angle profile are newly studied to compare the performances. To this end, the direct parameter optimization problem and the indirect optimization problem are formulated, and the characteristics of the steering angle profile and its influence on the transfer trajectory are analyzed.

Smooth and continuous interplanetary trajectory design of spacecraft using iterative patched-conic method

This paper is concerned with the transfer trajectory design among multiple planets using multiple flybys. The proposed trajectory design method consists of a semi-analytical tuning strategy and iterative patched-conic method. The tuning strategy refers to a method realizing the smooth connection between a hyperbolic trajectory near a planet and a trajectory obtained by Lambert's problem between the planet and another one. The proposed method iteratively solves Lambert's problem and the tuning strategy so that the arrival or departure velocity obtained by Lambert's problem coincides with the velocity at the corresponding point in the sphere of influence (SOI), assigned by the tuning strategy. Consequently, a smooth and continuous trajectory with multiple flybys can be obtained, where the SOI of each flyby planet and the flyby time are explicitly taken into account. Moreover, analytical conditions with respect to the orbital elements of the arrival and departure hyperbolas are provided to minimize velocity mismatch at the periapsis of a flyby planet. Through numerical simulation using the Cassini example, it is shown that the resultant trajectory by the proposed method is close to the optimal trajectory obtained by the n-body problem. Thus, a suitable approximate trajectory can be effectively generated without solving the n-body problem.

Dynamics and control of an electrodynamic tug: Transfer to the graveyard orbit

Space debris transfer to the graveyard orbit is a promising solution for impact mitigation in geosynchronous orbits. This paper is a development on previous work done on the eponymous technique to capture and transfer the debris to graveyard orbit located at 200 km above geostationary orbit. Here, the focus is kept on studying the dynamics and control of the collector-debris system. The debris is assumed to be spherical in shape and composed of a magnetically susceptible material with properties of copper-aluminum alloy. The capture and transfer phase is realized by low-thrust transfer trajectory using electric propulsion engine as main thruster and two control thrusters for continuous actuation of relative position of debris. A feedback control law is developed to ensure that the debris remains at the desired equilibrium position during the transfer maneuver. Stability of the system is investigated using results drawn from numerical simulation. The results show how the choice of control coefficients affects the stability of the system.

Collision-Free Trajectory Design for Long-Distance Hopping Transfer on Asteroid Surface Using Convex Optimization

The irregular shapes and gravitational fields of asteroids challenge the design of collision-free asteroid surface hopping trajectories. A novel collision-free long-distance transfer trajectory design algorithm based on the convex optimization is presented in this article. A combinatorial keepout zone consisting of three spheres is defined to avoid the spacecraft colliding with the asteroid surface during the transfer. The boundary of the keepout zone is close to the surface of the target asteroid. With the Taylor expansion approximation, the nonconvex keepout zone constraint becomes convex. Two convex glide-slope constraints are employed for avoiding colliding during the ascent and descent. Thereafter, a convex optimization problem for solving a collision-free long-distance transfer trajectory between arbitrary two surface points is formulated. Moreover, an ant colony optimization algorithm combined with the proposed method is used to solve the optimal hopping sequence problem for exploring multiple points on the asteroid surface. Finally, several numerical simulation examples for the asteroid 433 Eros validate the feasibility and effectiveness of the algorithm.

A Tale of Community College Transfer Pathway: US-ELs’ Trajectories toward Healthcare Programs

ABSTRACT U.S.-educated English learners (US-ELs) who aspire to obtain a bachelor’s degree are often guided by their high school counselors to attend community colleges first, and are assured that they can always transfer to a university later. However, the literature on US-ELs’ community college transfer is virtually nonexistent. This 13-month multiple-case study documented the transfer trajectories of four US-ELs who intended to enroll in healthcare programs at a community college first and then transfer to a university. Findings showed that all four students fell short of their original transfer aspirations. Five major factors were identified to account for the differences between students’ original plans and actual trajectories, including 1) inadequate high school preparation in science, 2) late enrollment and poor performance in their first program-related courses, 3) linguistic insecurity, 4) underdeveloped knowledge of their intended programs and transfer process, and 5) underuse of advising services. The findings indicate that the community college transfer pathway does not guarantee transfer for US-ELs.

Trajectory Design for Solar Approaching Detection Mission Using Multiple Resonant Gravity Assists of the Venus

To approach close to the Sun, direct launch from the Earth costs a lot of energy, which can be effectively reduced by the gravity assist of the Venus. In this paper, interplanetary transfer trajectories with multiple resonant gravity assists of the Venus are designed for a solar approaching detection mission. And design models for the trajectories with continuous resonant gravity assists, as well as resonant and non-resonant gravity assists combined are built. A mission launched between 2025 and 2028 is studied. The study shows that, compared with trajectory with continuous resonant gravity assists, trajectory with resonant and non-resonant gravity assists combined is useful for reducing transfer time of solar approaching detection mission. And its impact on the energy cost is not universal, which is related to the resonance ratio in the trajectory.

Subsidized Housing Policy Transfer: From Liberal-interventionist Hong Kong to Marketized Socialist Shenzhen

ABSTRACT This paper contributes to the comparative housing and policy transfer scholarship by analysing marketized-socialist Shenzhen’s processes of transferring liberal-interventionist Hong Kong’s subsidized housing policy between 1988 and 2020 and by explaining the transfer trajectory and policy outcomes. Data were collected from in-depth interviews, published policy documents and site visits. Applying policy transfer concepts, the study reveals that the transfer evolved from almost wholesale transplant to self-policy development, then lately signs of re-convergence emerged. Overall, Shenzhen utilises more market resources and regulatory tools in subsidy provision but operates a much smaller public housing sector than Hong Kong. The transfer trajectory and policy outcomes are rooted in incompatibility and changes in policy contextual environment, specifically socio-economic functions of housing policy and the cities’ jurisdictional and spatial scales; and in policy operational environments: differences in planning governance, tenure policy and housing finance model. Temporality is essential for understanding policy transfer and its efficacy.

On levitation by blowing

Anyone who has visited a science museum has seen the demonstration where a beach (or ping-pong) ball is suspended in mid-air at a fixed position by constant blowing from below. After a while, the ball inevitably tumbles to the ground but can easily be rebalanced, by hand, again at the suspension point. Here, we ask a different more delicate question. Can we blow the ball from rest, starting at the nozzle opening (x = 0), moving it up to the suspension point x=x* above the nozzle? We show that it is not possible to do this using constant blowing because the point at which the downward gravitational force balances the upward blowing force is an elliptic fixed point of the governing equations, so there is no transfer trajectory that connects the origin to x*. To overcome this problem, we design time-dependent blowing schedules that achieve the transfer, making use of orbit transfer ideas developed in the orbital mechanics literature. Then, we ask which of these time-dependent schedules are optimal? We show that, generally, it is bang–bang (on–off) blowing schedules that achieve the transfer in minimal time, using minimal energy (action) and minimal air volume. For certain parameter values, however, there are more complicated blowing schedules that are optimal (with respect to energy), which can be designed using the Pontryagin Maximum Principle (PMP) and singular control. We use elementary concepts from mechanics, nonlinear dynamics, and control theory and challenge the inclined experimentalist to try to implement some of these nonconstant blowing schedules in the lab.

Transfers around Phobos via bifurcated retrograde orbits: Applications to Martian Moons eXploration mission

Quasi-satellite or distant retrograde orbits are stable orbits in the restricted three-body problem will be used in remote planetary satellite missions like JAXA’s Martian Moons eXploration (MMX). Due to Phobos’ irregular gravity field, the proximity operations of the MMX mission require sophisticated techniques for transfers and maintenance between different quasi-satellite orbits. This paper focuses on the design of transfer trajectories between Quasi-Satellite Orbits (QSO) around Phobos. We utilize horizontal bifurcated Multi-Revolution Periodic QSOs (MP-QSOs) that are found in the vicinity of an ellipsoidal Phobos under the assumptions of the circular Hill Problem. Transfer strategy via MP-QSOs is explored through transfer maps that illustrate transfer design space between different altitudes QSOs. It is found that transfers via MP-QSOs provide insights on minimum ΔV transfers and the parameters determining the transfer cost. The proposed transfer method is explicitly applied to MMX baseline QSOs. This research has identified that transfers between high(100 × 200 km)-to-mid(50 × 100 km), mid-to-low(30 × 50 km), and lower altitude(<30 km) QSOs via MP-QSOs can be achieved with as low as 11.63 m/s, 3.99 m/s, 1.74 m/s, and 0.97 m/s, respectively.

High-order resonant orbit manifold expansions for mission design in the planar circular restricted 3-body problem

In recent years, stable and unstable manifolds of invariant objects (such as libration points and periodic orbits) have been increasingly recognized as an efficient tool for designing transfer trajectories in space missions. However, most methods currently used in mission design rely on using eigenvectors of the linearized dynamics as local approximations of the manifolds. Since such approximations are not accurate except very close to the base invariant object, this requires large amounts of numerical integration to globalize the manifolds and locate intersections. In this paper, we study hyperbolic resonant periodic orbits in the planar circular restricted 3-body problem, and transfer trajectories between them, by: 1) determining where to search for resonant periodic orbits; 2) developing and implementing a parameterization method for accurate computation of their invariant manifolds as Taylor series; and 3) developing a procedure to compute intersections of the computed stable and unstable manifolds. We develop and implement algorithms that accomplish these three goals, and demonstrate their application to the problem of transferring between resonances in the Jupiter-Europa system.

Computer simulation of single burn transfers between low-Earth and halo orbits in the Sun-Earth system

Halo orbits of Sun-Earth system are utilized in space missions as they allow to maintain the spacecraft in an area that is stationary relative to Sun and Earth. The advantage of halo orbits is their periodicity and their form allowing the spacecraft to avoid the zones of solar interference and the Earth shadow. The transfer between a low-Earth orbit and a halo orbit around a libration point can be realized by a single-burn maneuver, which transfers the spacecraft to an orbit of stable manifold resulting in a halo orbit. An amplitude of halo orbit depends on the altitude of the parking low-Earth orbit at which the transfer maneuver is performed. This work is aimed to explore and systemize the single burn transfer options utilizing single and multiple Earth passing trajectories in the framework of the circular restricted three-body problem. The algorithms providing transfer options for the desired halo orbit and the parking orbit altitude are developed. The transfer trajectories for the Sun-Earth L 1 and L 2 halo orbits in a wide range of out-of-plane amplitudes were constructed and studied. The constructed trajectories were clustered based on the transfer time and the halo orbit amplitude.

Optimal Earth-Moon Transfer Trajectory Design via Differential Dynamic Programming with Input Saturation Constraints

Optimal Earth-Moon Transfer Trajectory Design via Differential Dynamic Programming with Input Saturation Constraints

A New Hyperchaotic Image Encryption Algorithm Based on Stochastic Signals

Image encryption is often used to protect private images during transmission on a public channel. A high dimensional chaotic map has a greater secret key space, better ergodicity and dynamic property than a low-dimensional chaotic system. A seven-dimensional (7D) hyperchaotic map is used to produce chaotic sequences. Given secret keys and SHA-512 function are employed to generate initial values for iteration. Many stochastic signals are injected into one of the variables during iteration to transfer trajectory and increase dynamic behavior of a chaotic system. Three matrices are constructed with generated chaotic sequences. Permutation is performed on the basis of a control matrix. It keeps the pixel far from its neighboring pixels. Cycle shift is executed during bit-level permutation. Characteristic values of scrambling image are calculated and temporary values are achieved successfully. Two dynamic values are also applied during the diffusion process. Experimental results display the effects of the proposed algorithm. Security analysis reveals that the proposed method has some special advantages.

Fast Trajectory Generation and Asteroid Sequence Selection in Multispacecraft for Multiasteroid Exploration.

As an increasing number of asteroids are being discovered, detecting them using limited propulsion resources and time has become an urgent problem in the aerospace field. However, there is no universal fast asteroid sequence selection method that finds the trajectories for multiple low-thrust spacecraft for detecting a large number of asteroids. Furthermore, the calculation efficiency of the traditional trajectory optimization method is low, and it requires a large number of iterations. Therefore, this study combines Monte Carlo tree search (MCTS) with spacecraft trajectory optimization. A fast MCTS pruning algorithm is proposed, which can quickly complete asteroid sequence selection and trajectory generation for multispacecraft exploration of multiple asteroids. By combining the Bezier shape-based (SB) method and MCTS, this study realizes the fast search of the exploration sequence and the efficient optimization of the continuous transfer trajectories. In the simulation example, compared with the traversal algorithm, the MCTS pruning algorithm obtained the global optimal detection sequence of the search tree in a very short time. Under the same conditions, the Bezier SB method obtained the transfer trajectory with a better performance index faster than the finite Fourier series SB method. Performances of the proposed method are illustrated through a complex asteroid multiflyby mission design.