Tatsuaki Hashimoto

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.

Navigation Shape and Surface Topography Model of Itokawa

[Abstract] This paper describes the process of creating Itokawa shape and surface topography model during the Hayabusas proximity observation. It can be divided into two processes. First half is to estimate camera motion relative to Itokawa and determining its spin axis. Latter half is to estimate 3D shape of Itokawa and to analyze the topography. The authors employed two kinds of methods for shape modeling: a limb profile method and a stereo image analysis method. The combination of the two methods yielded a precise Itokawa model for both rough and smooth surfaces of Itokawa. This paper also describes the process of analyzing surface topography and creating a surface gradient map of Itokawa. The map built by the proposed method was actually used to determine the landing and sampling sites.

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.

Technologies for Lunar Night Survival Powered by Solar Arrays

As a follow-on mission of the lunar orbiter Kaguya (SELENE), a lunar lander SELENE2 is planned by the Japan Aerospace Exploration Agency (JAXA). SELENE-2 will land on the lunar surface and perform in situ scientific observations, environmental investigations, and research for future lunar utilization, including human activity. To realize the SELENE2 mission, the JAXA Space Exploration Center endeavors to develop advanced technologies that will enable lunar surface activities. For example, a lithium-ion battery with energy density of more than 200 Wh/kg is under development. In addition, durability tests of electrical and mechanical parts in low-temperature environments on the lunar surface have been conducted. Following these fundamental studies, a test model of a 10-W class power source using solar arrays and lithium-ion batteries for the operation of mission instruments at night was designed and fabricated. This paper details our technological developments for long-term stay on the Moon.

Preshaping profiler for flexible spacecraft rest-to-rest maneuvers

Abstract A new feedforward algorithm for flexible spacecraft maneuvers is presented. We call this preshaping profiler the nil-mode-exciting (NME) profiler. This algorithm is designed particularly for single-axis rest-to-rest rotational maneuvers (switching maneuvers) with linear actuators. Generally spacecraft with large flexible structure has a lot of large-mass flexible-modes. Therefore, uncertainity of high-order modes needs to be considered for high-accuracy controller design. This paper presents an extra-insensitive maneuvering method which overcomes above-mentioned difficulties. This algorithm includes a preshaping profiler formulated from sampling function (also known as sinc function), consequently feedforward control inputs generated from the preshaping profiler have no frequency response above a certain designed frequency. Therefore residual vibration at the end-point of maneuver can be highly reduced with minimum loss of maneuver agility.

Motion Planning of Intelligent Explorer for Asteroid Exploration Mission

In-situ observations of minor bodies like asteroids or comets are scientifically very important because their sizes are too small to have high internal pressures and temperatures, which means they should hold the early chemistry of the solar system. In recent years, some rendezvous or sample-return missions to small body have received a lot of attention in the world. To date, the missions of NEAR (Farquhar, 2001), Deep Space 1 (Rayman et al., 2000), Deep Impact (Chiu et al., 2000), and Stardust (Atkins, et al., 2000) have been successfully performed, while MUSES-C (Kawaguchi et al., 2000) and Rosetta (Wittmann, et al. 1999) are currently in operation. NEAR spacecraft was successfully put into the orbit of the asteroid 433 Eros in February 2000. After precise remote-sensing observations, NEAR spacecraft succeeded in hard-landing on the surface of EROS in February 2001. In Japan, meanwhile, ISAS (Institute of Space and Astronautical Science) launched an asteroid sample and return spacecraft MUSES-C toward a near Earth asteroid 1998SF36 in 2003 and performed soft landing on the asteroid in 2005. In deep space missions, ground based operation is very limited due to the communication delay and low bit-rate communication. Therefore, autonomy is required for deep space exploration. On the other hand, because little information on the target asteroid is known in advance, robotics technology is used for the spacecraft to approach, rendezvous with, and land on the asteroid safely. Various kinds of advanced and intelligent robotics technologies (Kubota et al. 2001) have been developed and used for navigation and guidance of the explorer to touch down and collect samples. This chapter describes the outline of the sample return mission MUSES-C, descent and touch-down scenario, vision based navigation scheme, sensor based motion planning, autonomous functions, and flight results in detail. This chapter is structured as follows. Section 2 describes the mission purpose and the configuration of MUSES-C spacecraft. In Section 3, navigation sensors are explained. In Section 4 discusses the strategy for autonomous approach and landing. Autonomous descent scheme based on navigation sensors is introduced. In Section 5, a vision based navigation scheme is presented. In Section 6, flight results in MUSES-C mission is presented. Finally, Section 7 is for discussions and conclusions.

Hayabusa's Real-time Landmark Tracking Navigation for Descents and Touching-Downs

In November of 2005, Hayabusa performed descent flights to the Itokawa surface five times. The Itokawa surface is full of boulders against expectation and there are few flat areas where the spacecraft can touch down safely. With the reaction wheels lost prior to the events, it was very difficult to control translation motion accurately, since the guidance accuracy of several millimeters per second was requested. The guidance and navigation before launch assumed the autonomous guidance by identifying the illumination center aboard. However, it was not successful due to the highly irregular shape of the asteroid. On the other hand, the scenario based on the terrain recognition in quasi real time well worked. It was anticipated not useful before launch, since such process was conceived to take a lot of time and not effectively useful in real time operation. The Hayabusa project team devised and built the special tool on the ground and had tuned it before the successful three touch downs and one long landing on the surface

A New Method of Testing Advanced Spacecraft Pointing Control Involving Flexibility

In response to the strong need to demonstrate the validity of newly developed satellite attitude control logics, a new ground test method has been developed. This test method features a scale model called SSDM (Scaled Satellite Dynamic Model). SSDM behaves just like a satellite released in non-gravity field and serves as the satellite attitude dynamics portion in the control loop. This test method enables on-ground dynamic qualification of advanced control laws which so far has been unavailable. As the first application of this method, robust filter control loop for MUSES-B satellite has been tested

Protection against overturning of a lunar-planetary lander using a controlled landing gear

This paper describes an attitude control method to prevent the overturning of lunar and planetary landers. The proposed control method that is based on a variable-damping shock absorber for the landing gear is experimentally validated. Conventionally, the landing gear of lunar and planetary landers has a fixed shock attenuation parameter that is not used proactively for attitude control of the lander during the touchdown sequence. The proposed method suppresses any disturbance to the attitude of the lander by adjusting the damping coefficient of each landing leg independently, based on the angular velocity and displacement velocity of each landing leg. First, the control method for the variable damper is presented. Second, the result of a landing experiment conducted in a two-dimensional plane is shown. These results indicate that the proposed semi-active landing gear system is effective for preventing the overturning of the lander on inclined terrain.