Masashi Uo

Pole and Global Shape of 25143 Itokawa

The locations of the pole and rotation axis of asteroid 25143 Itokawa were derived from Asteroid Multiband Imaging Camera data on the Hayabusa spacecraft. The retrograde pole orientation had a right ascension of 90.53° and a declination of –66.30° (52000 equinox) or equivalently 128.5° and –89.66° in ecliptic coordinates with a 3.9° margin of error. The surface area is 0.393 square kilometers, the volume is 0.018378 cubic kilometers with a 5% margin of error, and the three axis lengths are 535 meters by 294 meters by 209 meters. The global Itokawa revealed a boomerang-shaped appearance composed of two distinct parts with partly faceted regions and a constricted ring structure.

Guidance and Navigation of Hayabusa Spacecraft for Asteroid Exploration and Sample Return Mission

The Japanese asteroid exploration spacecraft Hayabusa autonomously performed touchdown two times in November 2005. The autonomous guidance and navigation capability is installed aboard the spacecraft. The GNC system collects the laser altimeter, laser range finders and navigation cameras information aboard and is designed to estimate where the spacecraft is and to decide the path correction maneuvers. The programmed function includes the image processing designed to detect an artificial target marker location to approach and cancel the relative velocity. A terrain alignment maneuver is also accomplished by both altitude and attitude control. This paper presents how autonomous guidance and navigation was performed in Hayabusa mission

Optical Hybrid Navigation and Station Keeping around Itokawa

Hayabusa has performed a proximity operation including station keeping and hovering around Itokawa. In order to navigate and to guide the spacecraft to Itokawa, it made highly use of optical hybrid navigation technique combined with the radiometric information obtained on the ground. Hayabusa is also equipped with a sophisticated autonomous navigation and guidance function including onboard image processing and the like. Although one of three reaction wheels failed in late July of 2005, and the second wheel failed in early October, we had succeeded to continue the technology demonstrations and the science observations. This paper presents how those navigation and guidance in proximity phase were carried out, showing flight results.

Nonlinear Six-Degree-of-Freedom Control for Flexible Spacecraft

Abstract A nonlinear six-degree-of-freedom control algorithm for flexible spacecraft has been developed. This algorithm consists of switching curves and control laws based on a sliding-mode control scheme. It can achieve both system stability and minimum fuel consumption simultaneously. The performance of the algorithm is assessed for the final-descent phase of MUSES-C spacecraft, and compared with that of a conventional control algorithm. Simulation results show that the proposed algorithm can improve total fuel consumption and time required for descending from the initial position to the surface of the asteroid.

Vision based navigation by landmark for robotic explorer

The rendezvous and landing missions are very significant for scientific explorations. In such missions, the navigation and guidance based on image data is very important. The spacecraft Hayabusa performed the descent flights to the target asteroid Itokawa in November of 2005. To accurately determine the spacecraft position, a landmark tracking scheme with the help of the ground operation was introduced and developed in the Hayabusa mission. The Hayabusa project team developed new tools that combined human assist with the computer aided terminal display. The proposed landmark tracking scheme contributed to the successful precise navigation to the specified area on the surface. This paper presents a visual navigation method with the landmark tracking used for the Hayabusa mission.

Touchdown Dynamics for Sampling in Hayabusa Mission

Hayabusa spacecraft performed the final descents and touchdowns twice in November 2005. In final descent phase, terrain alignment maneuvers were accomplished to control both altitude and attitude with respect to the surface by using four beams Laser Range Finder onboard. Then Hayabusa spacecraft made dynamic touchdowns the surface of the asteroid by the sampler system to collect samples automatically. This paper presents the terrain alignment maneuver and touchdown scheme. This paper also describes the novel sample horn system and touchdown dynamics. Touchdown tests on the ground are presented. Then the flight results on touchdown dynamics are shown and discussed.

Attitude control challenges and solutions for Hayabusa spacecraft

Hayabusa attempted to touch-down two times in November, 2005 after two years of cruising and two months of proximity observation around ITOKAWA. One of three reaction wheels failed in late July of 2005, and the second wheel failed in early October. While the attitude stabilization logic with two wheels was inherent in the onboard system, the stabilization with one wheel required the use of onboard re-programming function and special ground support operations. This paper describes how the attitude control system and operation were adapted to cope with the loss of reaction wheels, along with the introduction of attitude control system that was designed to realize various attitude functions with minimum onboard resources.

Vision-based guidance, navigation, and control of Hayabusa spacecraft - Lessons learned from real operation -

Abstract Hayabusa spacecraft performed approaching to and landing on the asteroid Itokawa from September to November in 2005 with sophisticated vision-based navigation and guidance. The spacecraft had some autonomous functions of station-keeping, descending, touching down and sampling. Since two of three reaction wheels for attitude control had malfunctions and the autonomous guidance did not work as designed, however, a ground-based landmark optical navigation system was developed. This paper presents the navigation, guidance and control system of Hayabusa spacecraft with some flight results.

Attitude Control System of the X-ray Observatory ASTRO-D

Abstract ASTRO-D is a Japan’s fourth X-ray observation satellite to be launched in the begining of 1993. The satellite is equipped with high-throughput X-ray telescope which provides a large effective area over a wide energy range. The attitude determination and control system of the satellite consist of a pair of star trackers, inertial gyroscopes, attitude control electronics based on a microcomputer, and four momentum wheels in a skewed configuration, and magnetic torquers. In this paper, the following unique features of the attitude control system design to satisfy the mission requirements under the resource restrictions imposed by the launch vehicle capability are described 1. A new initial momentum-transfer and attitude-acquisition control-law using skewed wheels. 2. Unique attitude maneuver-strategy and pointing control schemes for the bias momentum system with four skewed wheel configuration. 3. A large angle maneuver strategy for the biased multi-wheel system. 4. A new scheme of momentum management by magnetic torquing, which takes into account not only wheel unloading but also the safe-hold attitude in contingencies.

Model Predictive Control of Hayabusa2 Probe in the Approach Phase to an Asteroid

Abstract A new asteroid exploration spacecraft “Hayabusa2” as a follow on of “Hayabusa” is now in the course of production and experiment in order to launch in 2014. The touchdown of Hayabusa2 can be split into two phases, i.e., the approach phase and the final descent phase. In the approach phase, the spacecraft is guided and controlled by based on the command from the ground station. In contrast, the spacecraft controls its position and attitude by based on the autonomous computation in the final descent phase. This paper presents the application of the Model Predictive Control (MPC) to the approach phase to the asteroid, and verifies the performance and feasibility of this control algorithm through numerical simulations.