Descent trajectory reconstruction and landing site positioning of Chang’E-4 on the lunar farside

Abstract Chang’E-4 (CE-4) was the first mission to accomplish the goal of a successful soft landing on the lunar farside. The landing trajectory and the location of the landing site can be effectively reconstructed and determined using series of images obtained during descent when there were no Earth-based radio tracking and the telemetry data. Here we reconstructed the powered descent trajectory of CE-4 using photogrammetrically processed images of the CE-4 landing camera, navigation camera, and terrain data of Chang’E-2. We confirmed that the precise location of the landing site is 177.5991°E, 45.4446°S with an elevation of −5935 m. The landing location was accurately identified with lunar imagery and terrain data with spatial resolutions of 7 m/p, 5 m/p, 1 m/p, 10 cm/p and 5 cm/p. These results will provide geodetic data for the study of lunar control points, high-precision lunar mapping, and subsequent lunar exploration, such as by the Yutu-2 rover.

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COMPUTER VISION IN THE TELEOPERATION OF THE YUTU-2 ROVER

ISPRS Annals of Photogrammetry Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-annals-v-3-2020-595-2020 ◽

2020 ◽

Vol V-3-2020 ◽

pp. 595-602

Author(s):

J. Wang ◽

J. Li ◽

S. Wang ◽

T. Yu ◽

Z. Rong ◽

...

Keyword(s):

Computer Vision ◽

Path Planning ◽

Lunar Surface ◽

Control Method ◽

Landing Site ◽

Slope Aspect ◽

Soft Landing ◽

Landing Point ◽

Lunar Farside

Abstract. On January 3, 2019, the Chang'e-4 (CE-4) probe successfully landed in the Von Kármán crater inside the South Pole-Aitken (SPA) basin. With the support of a relay communication satellite "Queqiao" launched in 2018 and located at the Earth-Moon L2 liberation point, the lander and the Yutu-2 rover carried out in-situ exploration and patrol surveys, respectively, and were able to make a series of important scientific discoveries. Owing to the complexity and unpredictability of the lunar surface, teleoperation has become the most important control method for the operation of the rover. Computer vision is an important technology to support the teleoperation of the rover. During the powered descent stage and lunar surface exploration, teleoperation based on computer vision can effectively overcome many technical challenges, such as fast positioning of the landing point, high-resolution seamless mapping of the landing site, localization of the rover in the complex environment on the lunar surface, terrain reconstruction, and path planning. All these processes helped achieve the first soft landing, roving, and in-situ exploration on the lunar farside. This paper presents a high-precision positioning technology and positioning results of the landing point based on multi-source data, including orbital images and CE-4 descent images. The method and its results have been successfully applied in an actual engineering mission for the first time in China, providing important support for the topographical analysis of the landing site and mission planning for subsequent teleoperations. After landing, a 0.03 m resolution DOM was generated using the descent images and was used as one of the base maps for the overall rover path planning. Before each movement, the Yutu-2 rover controlled its hazard avoidance cameras (Hazcam), navigation cameras (Navcam), and panoramic cameras (Pancam) to capture stereo images of the lunar surface at different angles. Local digital elevation models (DEMs) with a 0.02 m resolution were routinely produced at each waypoint using the Navcam and Hazcam images. These DEMs were then used to design an obstacle recognition method and establish a model for calculating the slope, aspect, roughness, and visibility. Finally, in combination with the Yutu-2 rover mobility characteristics, a comprehensive cost map for path search was generated.By the end of the first 12 lunar days, the Yutu-2 rover has been working on the lunar farside for more than 300 days, greatly exceeding the projected service life. The rover was able to overcome the complex terrain on the lunar farside, and travelled a total distance of more than 300 m, achieving the "double three hundred" breakthrough. In future manned lunar landing and exploration of Mars by China, computer vision will play an integral role to support science target selection and scientific investigations, and will become an extremely important core technology for various engineering tasks.

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Waypoint Constrained Multi-Phase Optimal Guidance of Spacecraft for Soft Lunar Landing

Unmanned Systems ◽

10.1142/s230138501950002x ◽

2019 ◽

Vol 07 (02) ◽

pp. 83-104 ◽

Cited By ~ 3

Author(s):

Kapil Sachan ◽

Radhakant Padhi

Keyword(s):

Selection Procedure ◽

Landing Site ◽

Terminal Point ◽

Computationally Efficient ◽

Soft Landing ◽

Hard Constraints ◽

Optimal Guidance ◽

Safety Constraints ◽

Multi Phase ◽

Time Selection

A waypoint constrained multi-phase nonlinear optimal guidance scheme is presented in this paper for the soft landing of a spacecraft on the Lunar surface by using the recently developed computationally efficient Generalized Model Predictive Static Programming (G-MPSP). The proposed guidance ensures that the spacecraft passes through two waypoints, which is a strong requirement to facilitate proper landing site detection by the on-board camera for mission safety. Constraints that are required at the waypoints as well as at the terminal point include position, velocity, and attitude of the spacecraft. In addition to successfully meeting these hard constraints, the G-MPSP guidance also minimizes the fuel consumption, which is a very good advantage. An optimal final time selection procedure is also presented in this paper to facilitate minimization of fuel requirement to the best extent possible. Extensive simulation studies have been carried out with various perturbations to illustrate the effectiveness of the algorithm. Finally, processor-in-loop simulation has been carried out, which demonstrates the feasibility of on-board implementation of the proposed guidance.

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ON IMPROVEMENT OF PARACHUTE-RETROROCKET AIRDROP SYSTEM

Collection of scientific works of the Military Institute of Kyiv National Taras Shevchenko University ◽

10.17721/2519-481x/2019/64-01 ◽

2019 ◽

pp. 5-13

Author(s):

Yu. Adamov ◽

K. Boriak ◽

V. Zavalniuk

Keyword(s):

Horizontal Plane ◽

Slope Angle ◽

Ground Surface ◽

Landing Site ◽

Earth Surface ◽

Jet Engines ◽

The Earth ◽

Descent Trajectory ◽

The Absolute ◽

Absolute Altitude

The paper is devoted to the study of the prospects for improving the parachute-retrorocket airdrop system (PRS) in order to increase its reliability and enable the ability to adjust the orientation of a load in the horizontal plane depending on the slope of the earth's surface at the landing site. The primary task is to improve the accuracy of the altimeter, which determines the triggering moment of the PRS jet engines. The replacement of a mechanical altimeter of an outdated design with a modern electronic radio altimeter based on phased array radar is proposed, which allows to improve the accuracy of determining the absolute altitude(distance to the ground) and to take into account a roll of the load during the descent. The ways of determining the slope of earth's surface at the estimated landing site are also discussed. The results obtained make it possible to increase the accuracy of radio altimeter operation and significantly reduce the probability of an error in determining the absolute altitude due to rocking or static roll of the object. In addition to determining the current values of the height and speed of the descent of the vehicle, the use of a scanning radar makes it possible to estimate the inclination angle of the Earth’s surface at the landing site (in the radar scanning plane). If a certain angle of inclination of the earth surface at the landing site turns out to be too large, the probability of a successful landing can be increased by correcting the object's descent path, taking into account the information received. One of the easiest ways to correct a descent trajectory is to equip an object with small aerodynamic elements (rudders) and electromechanical actuators, ensuring their necessary orientation based on the results of determining the surface relief with radar. As one of the options, the authors propose the use of additional jet engines, which are structurally located on opposite sides of the object of landing in such a way as to form a torque of rotation of the object in a space from 0 ° to 90 ° in the horizontal plane due to the kinetic energy of motion from the actuation of jet engines. The triggering moment of the squibs is calculated based on determining the optimal distance of the object to the ground surface, and the need for triggering the squibs to rotate the object (correcting its position in space) depends on a certain value of the slope angle of the earth surface and comparing it with the admissible critical values of the angle, at which the object loses its stability during landing.

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Determination of Horizontal and Vertical Control Points for Lunar Mapping

Symposium - International Astronomical Union ◽

10.1017/s0074180900178167 ◽

1962 ◽

Vol 14 ◽

pp. 107-111

Author(s):

Marvin Q. Marchant

Keyword(s):

Army Corps ◽

Control Points ◽

Army Corps Of Engineers ◽

The Moon ◽

Entire Surface ◽

Vertical Control ◽

The Earth ◽

Map Service ◽

Lunar Mapping

The determination of horizontal and vertical control points has been undertaken by the Army Map Service, U.S. Army Corps of Engineers, to assure that the entire surface of the Moon which is visible from the Earth may be shown in detail and with greater accuracy than that of any existing map.

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Surface gravimetry on Dimorphos

10.5194/egusphere-egu21-15901 ◽

2021 ◽

Author(s):

Özgür Karatekin ◽

Birgit Ritter ◽

Jose Carrasco ◽

Matthias Noeker ◽

Ertan Umit ◽

...

Keyword(s):

Landing Site ◽

Temporal Variations ◽

The Body ◽

Current Status ◽

Main Body ◽

Gravity Vector ◽

Centrifugal Forces ◽

Soft Landing ◽

Binary Asteroid ◽

Operational Concept

In the frame work of HERA mission, the gravimeter for small solar system objects (GRASS) has been developed to measure the local acceleration vector on the surface of the moonlet of the binary asteroid, Dimorphos. GRASS will be onboard Juventas CubeSat which is one of the two daughtercraft of ESA&#8217;s Hera spacecraft. Launched in 2024 it will arrive in the binary system in 2026. Following the soft-landing of the Juventas CubeSat, GRASS will record the temporal variation of the surface gravity vector.The average gravitational force expected on the Dimorphos surface is around 5 x 10-5 m s-2 (or 5 mGal). Apart from the self-gravitation of the body, centrifugal forces and the acceleration due to the main body of the system contribute to the surface acceleration. The temporal variations of local gravity vector at the landing site will be used to constrain the geological substructure (mass anomalies, local depth and lateral variations of regolith) as well as the surface geophysical environment (tides, dynamic sloped and centrifugal forces).We will present the GRASS science objectives in the Hera mission the operational concept that is foreseen to reach these objectives, its current status of development including first test results and the by simulation estimated performances of the instrument.&#160;

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Topographic and Geomorphological Mapping and Analysis of the Chang'E-4 Landing Site on the Far Side of the Moon

Photogrammetric Engineering & Remote Sensing ◽

10.14358/pers.86.4.247 ◽

2020 ◽

Vol 86 (4) ◽

pp. 247-258 ◽

Cited By ~ 1

Author(s):

Bo Wu ◽

Fei Li ◽

Han Hu ◽

Yang Zhao ◽

Yiran Wang ◽

...

Keyword(s):

Landing Site ◽

Joint Analysis ◽

The Sun ◽

The Moon ◽

Soft Landing ◽

Geomorphological Mapping ◽

Von Karman ◽

Lunar Reconnaissance Orbiter ◽

Integrated Processing ◽

Von Kármán

The Chinese lunar probe Chang'E-4 successfully landed in the Von Kármán crater on the far side of the Moon. This paper presents the topographic and geomorphological mapping and their joint analysis for selecting the Chang'E-4 landing site in the Von Kármán crater. A digital topographic model (DTM) of the Von Kármán crater, with a spatial resolution of 30 m, was generated through the integrated processing of Chang'E-2 images (7 m/pixel) and Lunar Reconnaissance Orbiter (LRO) Laser Altimeter (LOLA) data. Slope maps were derived from the DTM. Terrain occlusions to both the Sun and the relay satellite were studied. Craters with diameters ≥ 70 m were detected to generate a crater density map. Rocks with diameters ≥ 2 m were also extracted to generate a rock abundance map using an LRO narrow angle camera (NAC) image mosaic. The joint topographic and geomorphological analysis identified three subregions for landing. One of them, recommended as the highest-priority landing site, was the one in which Chang'E-4 eventually landed. After the successful landing of Chang'E-4, we immediately determined the precise location of the lander by the integrated processing of orbiter, descent and ground images. We also conducted a detailed analysis around the landing location. The results revealed that the Chang'E-4 lander has excellent visibility to the Sun and relay satellite; the lander is on a slope of about 4.5° towards the southwest, and the rock abundance around the landing location is almost 0. The developed methods and results can benefit future soft-landing missions to the Moon and other celestial bodies.

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Finite-Time Spacecraft’s Soft Landing on Asteroids Using PD and Nonsingular Terminal Sliding Mode Control

Mathematical Problems in Engineering ◽

10.1155/2015/510618 ◽

2015 ◽

Vol 2015 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Keping Liu ◽

Fengxia Liu ◽

Shenquan Wang ◽

Yuanchun Li

Keyword(s):

Sliding Mode ◽

Landing Site ◽

Open Loop ◽

Sliding Mode Controller ◽

Reference Trajectory ◽

Continuous Control ◽

Soft Landing ◽

Terminal Sliding Mode ◽

Nonsingular Terminal Sliding Mode ◽

Motion Characteristics

This paper presents a continuous control law of probe, which consists of PD (proportional-derivative) controller and nonsingular terminal sliding mode controller for probe descending and landing phases, respectively, in the case of the asteroid irregular shape and low gravity. The probe dynamic model is deduced in the landing site coordinate system firstly. Then the reference trajectory based on optimal polynomial in open-loop state is designed, with the suboptimal fuel consumption. Taking into account different characteristics of phases, PD controller and nonsingular terminal sliding mode controller can be employed in the descending phase and the landing phase, respectively, to track the designed reference trajectory. The controller which used the corresponding control methods can meet the motion characteristics and requirements of each stage. Finally simulation experiments are carried out to demonstrate the effectiveness of the proposed method, which can ensure the safe landing of probe and achieve continuous control.

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Dielectric Properties of Lunar Materials at the Chang’e-4 Landing Site

Remote Sensing ◽

10.3390/rs13204056 ◽

2021 ◽

Vol 13 (20) ◽

pp. 4056

Author(s):

Jialong Lai ◽

Feifei Cui ◽

Yi Xu ◽

Chaofei Liu ◽

Ling Zhang

Keyword(s):

Dielectric Properties ◽

Loss Tangent ◽

Estimation Method ◽

Landing Site ◽

Coarse Grained ◽

Fdtd Simulation ◽

Motion Path ◽

Soft Landing ◽

Fine Grained ◽

Exploration Area

On January 3rd 2019, the Chang’e-4 mission successfully landed in the Von Kármán Crater inside the South Pole-Aitken (SPA) basin and achieved the first soft landing on the farside of the Moon. Lunar penetrating radar (LPR) equipped on the rover measured the shallow subsurface structure along the motion path for more than 700 m. LPR data could be used to obtain the dielectric properties of the materials beneath the exploration area, providing important clues as to the composition and source of the materials. Although the properties of the upper fine-grained regolith have been studied using various methods, the underlying coarse-grained materials still lack investigation. Therefore, this paper intends to estimate the loss tangent of the coarse-grained materials at depth ranges of ~12 and ~28 m. Stochastic media models with different rock distributions for the LPR finite-difference time-domain (FDTD) simulation are built to evaluate the feasibility of the estimation method. Our results show that the average loss tangent value of coarse-grained materials is 0.0104±0.0027, and the abundance of FeOT+TiO2 is 20.08 wt.%, which is much higher than the overlying fine-grained regolith, indicating different sources.

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Properties Analysis of Lunar Regolith at Chang’E-4 Landing Site Based on 3D Velocity Spectrum of Lunar Penetrating Radar

Remote Sensing ◽

10.3390/rs12040629 ◽

2020 ◽

Vol 12 (4) ◽

pp. 629 ◽

Cited By ~ 3

Author(s):

Zejun Dong ◽

Xuan Feng ◽

Haoqiu Zhou ◽

Cai Liu ◽

Zhaofa Zeng ◽

...

Keyword(s):

Electromagnetic Waves ◽

Lunar Regolith ◽

Landing Site ◽

Threshold Function ◽

Velocity Spectrum ◽

Maximum Relative Error ◽

Soft Landing ◽

Average Maximum ◽

Effective Instrument ◽

Moon Exploration

The Chinese Chang’E-4 mission for moon exploration has been successfully completed. The Chang’E-4 probe achieved the first-ever soft landing on the floor of Von Kármán crater (177.59°E, 45.46°S) of the South Pole-Aitken (SPA) basin on January 3, 2019. Yutu-2 rover is mounted with several scientific instruments including a lunar penetrating radar (LPR), which is an effective instrument to detect the lunar subsurface structure. During the interpretation of LPR data, subsurface velocity of electromagnetic waves is a vital parameter necessary for stratigraphic division and computing other properties. However, the methods in previous research on Chang’E-3 cannot perform velocity analysis automatically and objectively. In this paper, the 3D velocity spectrum is applied to property analysis of LPR data from Chang’E-4. The result shows that 3D velocity spectrum can automatically search for hyperbolas; the maximum value at velocity axis with a soft threshold function can provide the horizontal position, two-way reflected time and velocity of each hyperbola; the average maximum relative error of velocity is estimated to be 7.99%. Based on the estimated velocities of 30 hyperbolas, the structures of subsurface properties are obtained, including velocity, relative permittivity, density, and content of FeO and TiO2.

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Acupuncture points and cutaneous perforating vessels identified with thermography

Revista Fisioterapia Invasiva ◽

10.1055/s-0039-3401883 ◽

2019 ◽

Vol 02 (02) ◽

pp. 112-112

Author(s):

Soares Parreira F. ◽

Pereira Barbosa M. ◽

Álvarez Prats D. ◽

Carvajal Fernández O.

Keyword(s):

Upper Limb ◽

Odds Ratio ◽

Statistical Difference ◽

Clinical Medicine ◽

Acupuncture Points ◽

Control Points ◽

Precise Location ◽

Cross Sectional ◽

The Real ◽

Thermographic Image

Abstract Aim To confirm the presence of perforating cutaneous vessels (PCV) in different acupuncture points (AP) in the upper limb using thermography. Material and Methods A cross-sectional analytic study in the upper limb of voluntary subjects (n = 7). In total, 91 AP were analyzed, as well as 91 control points (CP), one per each AP. In each subject, first the AP and corresponding CP were marked, and in second place, the real and thermographic images were captured. In the real images, the AP and CP were marked with circles. Thereafter, software was used to fuse the real image with the AP and the CP and the thermographic image with the PCV to observe the presence or lack of the same in the AP and CP. Results When all the AP and CP were analyzed globally, significant differences were observed among these regarding the proportion of points which coincided with PCV (p 0.001). It is possible to verify that in the AP, the percentage of coincidence with PCV is 68.1% and in the control points this is 41.8%. This relationship is demonstrated by the risk ratio and odds ratio values and the confidence intervals (95%CI). Thus, it was verified that in AP the probability (risk) of coincidence with PCV is 1.63 [1.23; 2.16] times greater to the probability in the CP. In the same manner, due to the odds ratio, it is still possible to observe that in the AP the chance (odds) of coincidence with PCV is 2.98 [1.63; 5.47] times greater to the CP. It is also shown that for the AP the likelihood of coinciding with perforating vessels is 7.50 [1.31; 43.03] times greater compared to coinciding with CP. Discussion The presence of PCV in the area of AP must be treated with greater care, both due to the physiology of the same as well as its importance in clinical medicine. Although the precise location of the PCV varies, thermography is a useful tool to evaluate a patient and subsequently apply treatment. Conclusions Overall, a strong statistical difference was found regarding the presence of PCV in the location of AP in the upper limb.

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