A Magnetically Levitated Precise Pointing Mechanism for Application to Optical Communication Terminals

Increasing data bandwidth requirements from spacecraft systems is beginning to pressure existing microwave communications systems. Free-Space optical communications allows for larger bandwidths for lower relative power consumption, smaller size and weight when compared to the microwave equivalent. However optical communication does have a formidable challenge that needs to be overcome before the advantages of the technology can be fully utilized. In order for the communication to be successful the transmitter and receiver terminals need to be pointed with a high accuracy (generally in the order of ≤10 μradians) for the duration of communication. In this paper we present a new concept for the precise pointing of optical communications terminals (termed the Precise Pointing Mechanism). In this new concept we combine the separate pointing mechanisms of a conventional optical terminal into a single mechanism, reducing the complexity and cost of the optical bench. This is achieved by electromagnetically actuating the whole telescope assembly in 6 degrees-of-freedom with an angular resolution of less than ±3 μradians within a 10 (Az. El.) field of view and linear resolution of ±2 μm. This paper presents the new pointing mechanism and discusses the modelling, simulation and experimental work undertaken using the bespoke engineering model developed.

Covariance analysis of periodic and quasi-periodic orbits around Phobos with applications to the Martian Moons eXploration mission

Understanding the internal composition of a celestial body is fundamental for formulating theories regarding its origin.Deep knowledge of the distribution of mass under the body’s crust can be achieved by analyzing its moments of inertia and gravity field.In this regard,the two moons of the Martian system have not yet been closely studied and continue to pose questions regarding their origin to the space community;thus,they deserve further characterization.The Martian Moons eXploration mission will be the first of its kind to sample and study Phobos over a prolonged period.This study aims to demonstrate that the adoption of periodic and quasi-periodic retrograde trajectories would be beneficial for the scientific value of the mission.Here,a covariance analysis was implemented to compare the estimation of high-order gravitational field coefficients from different orbital geometries and for different sets of processed observables.It was shown that the adoption of low-altitude non-planar quasi-satellite orbits would help to refine the knowledge of the moon’s libration angle and gravitational field.

Comments on “Sidewinding with Minimal Slip: Snake and Robot Ascent of Sandy Slopes”

Marvi et al(Science,2014,vol.346,p.224)concluded a sidewinder rattlesnake increases the body contact length with the sand when granular incline angle increases.They also claimed the same principle should work on robotic snake too.We have evidence to prove that this conclusion is only partial in describing the snake body-sand interaction.There should be three phases that fully represent the snake locomotion behaviors during ascent of sandy slopes,namely lifting,descending,and ceasing.The snake body-sand interaction during the descending and ceasing phases helps with the climbing while such interaction during the lifting phase in fact contributes resistance.

Intelligent Fuzzy Control in Stabilizing Solar Sail with Individually Controllable Elements

Fuzzy logical control is a robust and effective control method in industrial fields,which renders it applicable to the attitude control of a solar sail.However,it is hard to apply in black-box and time-varying problem as real solar sail attitude control.Considering the lack of a priori knowledge and the unacceptable manual workload in the design of the fuzzy logical controller(FLC),an intelligent FLC designer(IFLCD)is developed by introducing neural network modelling and automatic design method.Besides,IFLCD also supports self-adaption for better control accuracy.By applying the proposed IFLCD in the attitude stabilization of a solar sail with individually controllable elements(SSICE),an effective solution of unmanned,time-varying,and complex system control method is offered without any mathematical model,which also overcomes the difficulties in FLC design Considering the performance degradation,accident,and distance problems faced by spacecraft,IFLCD can help with more practical problems that are hard be solved by traditional control theory.

A high-order target phase approach for the station-keeping of periodic orbits

A novel high-order target phase approach(TPhA)for the station-keeping of periodic orbits is proposed in this work.The key elements of the TPhA method,the phase-angle Poincare map and high-order maneuver map,are constructed using differential algebra(DA)techniques to determine station-keeping epochs and calculate correction maneuvers.A stochastic optimization framework tailored for the TPhA-based station-keeping process is leveraged to search for fuel-optimal and error-robust TPhA parameters.Quasi-satellite orbits(QSOs)around Phobos are investigated to demonstrate the efficacy of TPhA in mutli-fidelity dynamical models.Monte Carlo simulations demonstrated that the baseline QSO of JAXA’s Martian Moons eXploration(MMX)mission could be maintained with a monthly maneuver budget of approximately 1 m/s.