Soft Landing Process Research Articles

Braking and attitude control of lunar lander in active descent stage

Abstract China officially launched the lunar exploration project, named “Chang’e Project,” in 2004. Then, in 2013, Chang’e-3 completed the soft landing on the lunar surface, starting a series of studies on the soft landing of spacecraft. This study aims to optimize the dynamic flight guidance and attitude control of the lunar landing module represented by Chang’e-3 in the soft landing stage. After analyzing the attitude control requirements of the soft landing stage of the lunar landing module, this study designs the lunar soft landing process under a variable structure sliding mode (VSSM) control. The study also analyzes the influence of the pulse width modulator (PWM) on the soft landing process. The simulation model of the lunar soft landing guidance and control system is established by MATLAB/Simulink, and the traditional proportional–integral–derivative (PID) control mode is compared with the interference condition. Results show that VSSM + PWM is superior to PID in robustness and accuracy and has a theoretical reference value for future lunar landing exploration and even Mars landing exploration.

Hybrid Position/Force Fully Closed-Loop Control of a Flip-Chip Soft-Landing Bonding System

Flexure-based bonding system driven by piezoelectric actuator is quite appealing for fulfilling the nanoscale-accuracy and high-efficiency interconnection tasks. However, it turns obstreperous to implement it for high-efficiency and nanoscale-accuracy interconnection during the soft-landing operation, largely because of a large amount of noise in force sensor and low efficiency of traditional controller. To this end, this article presents a novel hybrid position/force fully (HPFF) closed-loop control strategy to enable the developed flip-chip bonding system to run in the manner of nanoscale-accuracy and high-efficiency interconnection. The integrator composed of inertial filter (ICIF) method is proposed to improve the operation efficiency and reduce the time used in the soft-landing process. Besides, the stability of HPFF strategy is demonstrated in theory and numerical calculation. Finally, a series of validation experiments including ICIF comparing experiments, closed-loop trajectory tracking experiments, robustness experiments under different loads and HPFF closed-loop control experiments are successfully implemented. All the results uniformly confirm that the developed flip-chip bonding system has achieved satisfactory soft-landing interconnection performance by taking advantage of the proposed HPFF closed-loop control strategy.

Lunar surface soft-landing analysis of a novel six-legged mobile lander with repetitive landing capacity

The autonomous robots consisting of an immovable lander and a rover are widely deployed to explore extraterrestrial planets. Two main drawbacks limit the development of this cooperative work mode: (1) it cannot perform soft-landing missions repeatedly on the planet, owing to the damage of buffer structure during soft-landing. (2) the rover’s detection area is restricted to the vicinity of the immovable lander. To overcome these problems, we have designed an innovative six-legged mobile lander with repetitive landing capacity, called “HexaMRL”, which integrates the functions of a lander and a rover including folding, deploying, repetitive landing, and walking. This novel robot’s legs adopted hybrid mechanism with active and passive compliance. Therefore, it remains to be a great challenge to analyze the robot soft-landing capacity which is determined by the parameters such as spring stiffness coefficient, damper damping coefficient, and initial tiptoe position. In order to solve the problem, the dynamic modeling and assessment criteria were established. The soft-landing process was analyzed through three numerical simulations using three sets of representative parameters based on dynamic model and the set of best effective parameters was chosen to apply in soft-landing experiment on a 5-DOF lunar gravity testing platform (5-DOF LGTP). The experiments were further verified that the selected parameters met the requirement of soft landing on the lunar surface. The HexaMRL provides novel insight for the next generation equipment for lunar exploration, which may be an efficient solution to the extraterrestrial planet exploration.

High‐Precision Carrier Tracking Algorithm for Extremely Weak and High‐Dynamic Signals

AbstractObtaining high‐precision Doppler frequencies for very weak and high‐dynamic signals in deep space exploration is challenging. Such signals are commonly encountered, including in soft landing of lunar probes and the entry, descent, and landing (EDL) phase of Mars probes. Phase‐locked loop (PLL) is a widely used method for measuring high‐precision Doppler frequencies. In this study, two major improvements are applied to PLL. The first is that high precision estimation of initial frequency is achieved by open loop maximum amplitude search algorithm. Second, a novel denoising method is proposed and a new type of phase detector is designed based on this new denoising method. By replacing arctangent phase detector with the novel phase detector, the tracking accuracy and weak‐signal tracking abilities of the PLL are improved. The actual data processing results of soft landing process of lunar probe further verify the excellent performance of the improved PLL.

Impact and stick-slip dynamics in the soft-landing on minor celestial bodies

The soft-landing on the surface of minor celestial bodies has been investigated with considering the impact and stick-slip effect. The polyhedron model is used to analyze the irregular shape and topography and geomorphology of minor celestial bodies. The soft-sphere discrete element method is used to fill the irregular minor celestial body’s polyhedron model and cover the surface of the body; and then the irregular shape, the gravitational environment, as well as the impact and hopping with the surface can be calculated precisely. The dynamical parameters of failed soft-landing and successful soft-landing are calculated and analyzed. In the cases of successful soft-landing, there are two obviously different kinds: firstly, the final position of the lander is near the target position; secondly, the final position of the lander is far from the target position. The difference of these two kinds of results is discussed. This research shows the major dynamical behavior of soft-landing on minor celestial bodies includes impact, hopping, as well as stick-slip effect. If the initial positions of soft-landing are improper chosen, the lander may become orbital motion around minor celestial body after one or more impact and hopping, or turn to quasi-periodic motion around equilibrium points without impact, or perhaps be static far from the initial position after several times of impact and hopping and leads to the failure of the deep space mission. For the successful soft-landing process, after several times of landings on the surface during the soft-landing process, the lander will finally settle on the surface of the minor celestial body. The results show that the soft-landing region should be selected as a flat area or concave region, which is far from the equatorial plane of the minor celestial bodies.

A Computational Comparison of Soft Landing of α-Helical vs Globular Peptides.

The effect of secondary structure on the soft landing process is investigated through direct dynamics simulations of AcA7K and AcKA7 colliding with a fluorinated, organic self-assembled monolayer (FSAM) surface. The α-helical (AcA7K) and globular (AcKA7) peptides each exhibited a similar probability of soft landing with normal incidence at all collision energies considered. Rapid conformational changes were quantified through the calculation of the time dependent, conformational entropy production that took place during the collision events, which is consistent with the prior structural measurements made by Laskin and co-workers on these systems. AcA7K produces more entropy during the collisions than AcKA7.

The Optimization of Satellite Landing Site based on Particle Swarm Optimization

Hazard avoidance is one of the key stages in the satellite's soft landing process, during which the selection of the landing site would have a huge influence on the satellite safe landing. In this paper, a new design method is presented for determining the landing site selection using Particle Swarm Optimization based on the Moon’s grounds image taken by moon satellite. Applying this method, the problem of hazard avoidance can be converted into the optimization of the value of “obstacle function” after processing the image employing the median filter algorithm. In order to discuss and to compare the efficiency of the different optimization methods, three algorithms including Particle Swarm Optimization, Genetic Algorithm and Global Search Algorithm are tested to solve this problem. The results show that Particle Swarm Optimization has the more satisfactory optimization results and the quickest optimization speed in the landing site selection. The detailed comparisons are introduced in the body paragraph.

Statistical Analysis Methodology for STI CES333 Unstable Process Window

STI CMP is a widely used and basic process in current VLSI FEOL manufacturing of both logic and memory chips. Highly selective slurry CES333 is standard for the STI CMP soft-landing process stopping on the barrier layer. However, it has been reported and also observed in mass production that the removal rate of CES333 has a tendency to vary from wafer to wafer, especially at the wafer edge. This is an issue in mass production of smaller technology nodes. More stable performance is, however, difficult to achieve owing to the character of the slurry. A creative method of analyzing a vast database was employed to devise a solution and meet CMP requirements.

Lateral displacement in soft-landing process and electronic properties of size-selected Pt7 clusters on the aluminum oxide film on NiAl(1 1 0)

Adsorption states of size-selected Pt7 clusters soft-landed on an Al2O3/NiAl(110) were investigated using scanning tunneling microscopy and spectroscopy at 300K. Pt7 clusters lay flat on the surface with a planar structure and were preferentially adsorbed on domain boundaries (DBs) of the Al2O3 film. Because the clusters are thermally immobile, adsorption to DBs is controlled by transient mobility on the surface. The mean lateral displacement by transient migration is estimated to be ∼8nm. Distinct conductivity resonances through unoccupied states of the Pt7 clusters were observed near 2V.

An investigation of the internal temperature dependence of Pd–Pt cluster beam deposition: A molecular dynamics study

We investigated the internal temperature dependence of the Pd 1− a Pt a cluster beam deposition in the present study via the molecular dynamics simulations of soft-landing. By analysis of the velocity distribution and diffusion coefficient of the bimetallic cluster, Pd atoms with better mobility improved the diffusibility of Pt atoms. The radial composition distribution showed that a Pt-core/Pd-shell structure of the cluster formed at high internal temperatures through migrations of the Pd atoms from inner to surface shells. In the soft-landing process, the diffusing and epitaxial behaviors of the deposited clusters mainly depended on the internal temperature because the incident energy of the cluster was very small. By depositing clusters at high internal temperatures, we obtained a thin film of good epitaxial growth as the energetic cluster impact. Furthermore, nonepitaxial configurations such as scattered nonepitaxial atoms, misoriented particles, and grain boundaries of (1 1 1) planes were produced in the growth of the cluster-assembled film. As the size of the incident cluster increased, the internal temperature of the cluster needed for better interfacial diffusion and contact epitaxy on the substrate also rose.

Surface morphology and composition of films grown by size-selected Cu nanoclusters

We report the investigation of morphology and composition of copper nanocluster films deposited on Si substrates. The nanoclusters are formed in an aggregation tube at room temperature and magnetron sputtering source is used to get negatively charged Cu-clusters' beam which is subsequently mass-filtered to get size-selected cluster on the substrates as soft-landing process of deposition. For composition of the films, X-ray photoelectron spectroscopy (XPS) technique is used. For morphological changes of the films both scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses are carried out. Additionally, Energy Dispersive X-ray (EDX) spectra support the compositional and structural informations of the film. The analysis of Cu nanoclusters' films reveals that initial nucleation of Cu clusters takes place in the form of isolated islands and the arrival of subsequent Cu clusters onto Si substrates has preferential aggregation around the preceding clusters forming a mound structure.

Development of less expensive process technologies for three-dimensional chip stacking with through-vias

Three-dimensional chip stacking with through-vias is a very promising technology in semiconductor system development. A major problem of this technology is the cost. We analyzed the costs of the fabrication process and identified the three processes of Cu plating, Cu-CMP, and back surface bumps as the high-cost processes. To address these problems, we studied the processes and the stacking structure to improve the productivity. The plating time for Cu plating was reduced by up to 1 hour by optimizing the plating fluid composition and the oxygen bubbling of the plating fluid. In Cu-CMP, 9-µm-thick Cu was polished for 8.7 minutes by using high-speed polishing slurry and the softlanding process. We evaluated a structure where the back surface bumps were removed, and the front surface Cu bumps were directly connected by Cu through-vias and Sn-Ag. We verified the reliability for up to 1000 temperature cycles of this structure which uses a low thermal expansion resin as the adhesive in two-step sealing. From these results, a substantial reduction in the cost of the three-dimensional chip stacking with through-vias has become possible. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(7): 50–60, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20150

Mechanism of neutral cluster beam deposition

Pb cluster based films have been formed by the low energy neutral cluster beam deposition method and characterized by TEM. The deposits are rigid, uniform with the nanometer grain sizes, which are important for nanostructured material applications. The velocities of clusters in the beam obtained by gas aggregation method have been calculated based on the hydromechanic and thermodynamic principles. It is demonstrated that the deposition of the clusters on the substrate surface is a head-on collision and soft landing process, that is, low energy clusters land on the substrate surface without fragment and distortion. Based on these analyses, a physical model has been developed and computer simulations have been performed by assuming the random deposition as well as limited diffusion and coalescence process. The results indicate that the uniform and nearly random stacking properties of the cluster deposits can be described properly by the model.