Masatsugu Otsuki

大気球シンポジウム 平成26年度（2014年11月6-7日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県著者人数: 18名資料番号: SA6000021006レポート番号: isas14-sbs-006

Lunar or planetary exploration is scientifically meaningful because they can give us the hint to throw a light on the origin and evolution of the solar system or the earth, the inner structure of planets, etc. In lunar or planetary exploration missions, it is important to save the weight of spacecraft. Light weight spacecraft leads to low cost and getting more chance to go to the space. Conventionally a lander carries a rover to the surface of the celestial body and the rover traverses the rough terrain to explore in wide region. If the lander and the rover are united, however, the total weight of the spacecraft could be reduced. The authors have already proposed a novel pulley suspension mechanism, which is called Load Equalization Pulley Suspension mechanism: LEPS mechanism, for rovers. The performance of the proposed mechanism as a suspension mechanism of rovers has been evaluated. In this paper, the application of LEPS mechanism to the landing gears of the lander is discussed. By applying the proposed mechanism to the landing gears, the lander can move around the wide region of the surface after landing. The landing dynamics model of the proposed "Movable lander" with LEPS mechanism is introduced. The landing performance is evaluated by 2-dimensional model. The simulation results show that LEPS mechanism has an advantage over normal landing gears.

This paper presents an actively controlled landing gear system and its experimental validations. Active landing gear uses an variable coefficient damper as an shock absorber. We executed landing experiment with the two dimension lander model which introduced an magnetorheological damper as an shock absorber. Damping coefficient is controlled to reduce attitude disturbance during touchdown based on lander attitude and displacement of landing leg. The result of model experiment indicates that the active landing gear can reduce attitude disturbance which causes the lander overturning.

In 2009, the Selenological and Engineering Explorer (SELENE) discovered a vertical hole of 〜60 m diameter and 〜50 m depth in the Marius Hills region on the Moon. After the discovery, two other more gigantic holes were discovered by the SENENE team. The vertical holes were likely formed by volcanic activities or tectonic processes such as skylight formation on lava tubes. The indicative evidence of the existence of underlying caverns associating with the holes was indeed acquired by the US LRO later. Similar vertical holes have been discovered on Mars. Various important knowledge of science on the Moon, the solar system, and extra-terrestrial life will be obtained by direct in-situ explorations into the lunar holes and their associating underlying caverns. However, the exploration of the holes and subsurface caverns require a system which should overcome difficulties, such as the descent into the floors of the holes studded with boulders and the travel into the dark cavern spaces hidden from the lunar surface. We have studied on the exploration system by applying space robotics technology. We report the strategy and system design of the exploration, operational scenario in this paper.

Robotic surface exploration is a key strategy for future lunar or planetary missions. The ability of localization is important for exploration rovers since it will enhance safe and efficient mission operations. The conventional dead-reckoning methods that rely on wheel encoders and inertial measurements are prone to error in uneven terrain of planetary surfaces. This paper proposes an integrated localization system using vision sensors and absolute direction sensors. The performance of the proposed localization system was studied through the field experiments on a four-wheeled test-bed rover operated in a terrestrial analogue.

The performance of an integrated navigation system is studied through the field experiments on a four-wheeled test-bed rover, AKI, operated in a terrestrial analogue. The AKI rover employs novel mobility and navigation systems which enable challenging long-range operations in natural terrain. AKI has a vision-based localization system aided by sun sensors and an inclinometer for absolute attitude estimation. The integration with absolute direction sensors improves accuracy in absolute positioning, as well as obtaining 5x run-time improvement of visual pose estimation. The paper reports the results of field experiment conducted in Izu-Oshima island in 2013, and discusses current challenges of the system.

In this paper, we firstly develop the system which connects an end-effector with wire just before launching the end-effector. We then conduct the experiment and verify the stable connection by six trials. We secondly propose the method to decelerate the flight speed of the end-effector after launching it. The spring is used for smooth deceleration and the ratchet is used for prevent the expanded spring from restoring. We develop the ratchet-reel system and confirm that it decelerates the translational speed of the end-effector as well as its rotational speed through experiments.

This paper presents that the method of position error correction for planetary rovers by using skyline matching azimuth estimation. Skyline matching is the method that estimating position and attitude by comparing two skylines. One skyline is simulated one from a digital elevation model (DEM). The other one is gotten from camera images taking around view. We focus on using azimuth attitude estimated by skyline matching to correct accumulation error of IMU. We modeled IMU angular velocity bias increases linearity. We conducted field experiments in Oshima Island and Chiba. As a result, estimated relative azimuth errors are lower than 1 degree. IMU azimuth errors decreased by 67% (6.25 deg to 2.15 deg ) and IMU position errors decreased by 70% (3.33m to 1.04m).

Next-generation lunar/planetary exploration spacecraft need to solve problems of conventional landing methods and mechanisms such as high rebound, impossibility of reuse and high cost. For this purpose, the authors discuss the landing method by means of Base-Extension Separation landing Mechanism (BESM) which uses energy conversion with springs and separable units. In the authors' conventional studies, its effectiveness was confirmed for a simple case based on single-axis restriction. However, the investigation of tumble prevention cannot be treated in the simple case. The purpose of this preliminary report is the response analysis of a slope landing case of BESM for more practical landing situations.

This paper presents the influence of shadow on the path planning of lunar rovers. To evaluate the influence of shadow, the terrain and shadow on the Moon are first modeled using the DEM derived from Kaguya data. Subsequently, on the basis of a path planning algorithm considering the shadow, numerical simulation is performed for the lunar terrain. In the simulation, a short path crossing shadow is compared with a long path avoiding shadow under various insolation conditions. The simulation results confirmed that although avoiding shadow adds a traveling distance and time, it doses not much affect the average power consumption but contributes to an increase in the average power generated.

This paper presents the control method for vibration due to rotational motion of a casting manipulator . The casting accuracy for bringing an end-effector to a target position, which is attached to the odd end of a wire rotated by the casting manipulator, significantly depends on the attitude at the release time. Further, the attitude of the casting manipulator is horizontally and vertically vibrated by the rotational motion if the rotational axis does not coincide with the position of the gravitational center of the rotated arm; consequently, the considerable casting error occurs. Hence, this paper mentions the vibration problem of the casting manipulator; first, we confirm the stationary and non-stationary vibration experimentally; second, the casting error due to attitude shift is numerically analyzed; finally, the active vibration control method using an actuator is proposed. The vibration reduction due to the shift in yaw angle is particularly verified through the numerical calculation and the effectiveness of the active feedback and feedforward control is shown.

Moon holes were first discovered in the world by JAXA in 2009. It is believed that moon hole is helpful to know the formation of the moon because bedding plane is exposed. In addition, because inner hole is sealed from solar wind, it is also important as a candidate site for base camp in the future. However, exploration of the moon hole is difficult with the conventional robots. A new robot is required for going down and explore moon hole. In this study, a system to throw a small robot into a moon hole with wire is proposed. The author describes modeling and attitude control in a state where the robot is hanging by a wire, and evaluates the effectiveness of the system.

The development of highly accurate landing technology is required for the next generation lunar-planetary exploration lander to touch down on rough but interesting area. For the safe landing, the development of landing leg is required to prevent overturning and reduce landing impact of the lander in the final phase of landing sequence. However, it is difficult to design a landing leg which is applicable to a wide variety of terrain. The active landing leg is proposed as a solution of solving this problem. This paper presents the simulation of the lander with active landing leg and development of experimental system using Magneto-Rheological damper, and examines the landing shock response and penetration of the lander leg to the sand terrain.

This paper presents a technique for driving a wheel to control the sinkage of a planetary rover on loose soil. Dynamic sinkage of the wheels of the rover always occurs when it travels on loose soil in the planetary surface; sinkage is then caused by the soil deformation due to a compressive force generated by the wheel and the soil conveyance due to slippage in the wheel. When the wheel is driven in an acceleration profile with a trapezoidal shape, it is experimentally confirmed that the depth of sinkage changes during both acceleration and deceleration. Further, it is also confirmed that the terminal sinkage is proportional to the magnitude of the maximum rotational acceleration and deceleration of the wheel; consequently, we propose the method of controlling the sinkage by adjusting their magnitude. The proposed control is verified through the experiments using the single wheel test bed and the full body rover with 4 wheels; thus, it is confirmed that twofold increase of sinkage is caused and the terminal sinkage is controlled, especially suppressed.

We propose the method to control landing position and speed of an end-effecter in the air by multidirectional tension of wires. The end-effecter is connected with both dummy weights and reel system via the wires. After launching the end-effecter and dummy weights, its trajectory is changed by each tension of the wires when their motion is geometrically constrained. We develop the motion planner which makes the end-effecter reach the target at a suitable speed, and control algorithm for it. The proposed method is applied to the soft landing of the end-effecter. The effectiveness of the proposed method is verified through the experiment.

In 2009, the Selenological and Engineering Explorer (SELENE, nicknamed Kaguya) discovered a vertical hole of 〜60 m diameter and 〜50 m depth in the Marius Hills region on the Moon. After the discovery of the Marius Hills Hole (MHH), two other more gigantic holes were discovered by a global survey executed by the SENENE team. The vertical holes were likely formed by volcanic activities or tectonic processes such as skylight formation on lava tubes, from the terrestrial analogues. The indicative evidence of the existence of subsurface void spaces associating with the holes was indeed acquired by the US LRO later. Similar vertical holes have been discovered on the Mars. Various important knowledge of science on the Moon, the solar system, and extra-terrestrial life will be obtained by direct in-situ explorations into the lunar holes and their associating subsurface void space. However, the exploration of the holes and underlying subsurface voids require a system with the state of art which can overcome difficulties, such as the descent into the floors of the holes studded with boulders and the travel into the dark void spaces hidden from the lunar surface. We have studied on the exploration system by applying space robotics technology. We report the exploration system design, operational scenario in this paper.

The JAXA lunar orbiter spacecraft "SELENE (Kaguya)" found a vertical cave on the surface of the moon. For underground exploration of the moon, we propose the method to launch the probe vehicle into the cave by casting manipulator system. For the first step, we develop the launcher system which can generate kinetic energy of the end-effecter by rotating the boom and throw it to the target. We then verified that the system can throw the end-effector more than 17 meters and its positioning accuracy is less than 3.4% through experiments.