Shujiro Sawai

An autonomous navigation and guidance system for MUSES-C asteroid landing

Abstract ISAS plans to launch an asteroid sample and return spacecraft MUSES-C in 2002 and the spacecraft arrives at near earth asteroid 1989ML in 2003. To approach, rendezvous with, and land on the asteroid safely, the spacecraft has an autonomous navigation, guidance, and control system. That is, it has some functions of station keeping at the distance of about 20 km , landing guidance using optical camera and laser altimeter, hovering at about 20 m above the surface to synchronize the rotation of the asteroid and adjust touchdown attitude, and final descent control including obstacle detection and touch down sensing for reliable and safe collection of asteroid samples. In this paper, at first, the navigation, guidance, and control system onboard MUSES-C is presented, and then, rendezvous and landing scenario are described. Performance and robustness of the system are verified by numerical simulations, GRAphical computer Simulator (GRAS), and hardware simulator called TRAnslational Motion simulator (TRAM). A example of numerical simulation results and brief description of GRAS and TRAM are also shown.

Firing Test of a Hypersonic Turbojet Engine Installed on a Flight Test Vehicle

Hypersonic turbojet engine with pre-cooling system is tested under sea level static condition. The engine is installed on a flight test vehicle, which will fly at Mach 2 speed by a free fall experiment from a stratospheric balloon. Liquid hydrogen fuel and gas hydrogen fuel is supplied to the engine from a tank and cylinders installed in the vehicle. Designated operation of major components of the engine is confirmed. Corrected rotation speed, corrected air flow rate and pressure ratio of the compressor is raised by pre-cooling with liquid hydrogen fuel. Corrected air flow rate and pressure ratio at the pre-cooling operation is reduced comparing from that without pre-cooling on the same corrected rotation speed. There is a deep temperature distortion at the inlet of the compressor and it may cause the performance reduction. Large amount of liquid hydrogen is supplied to the pre-cooler in order to obtain enough pre-cooling performance for Mach 5 flight. Then, fuel rich combustion at the after-burner is adopted. Cowl part of variable geometry nozzle is made with C/C composite material and it has no damage after the combustion test. Operation of the core engine by liquid hydrogen is attained by using a control valve with small effective diameter.

Lunar Holes and Lava Tubes as Resources for Lunar Science and Exploration

The Moon is the nearest celestial body to the Earth. As such, it has long been investigated to understand its formation and evolution, as a paradigm for better understanding the terrestrial planets, as well as all airless bodies in our solar system (e.g., Vesta, Phobos). The Moon’s proximity to the Earth—more than one hundred times closer than any planet — makes it a convenient target for exploration by spacecraft. Since the dawn of the space age in the previous century, we have explored the Moon with several spacecraft and even succeeded in sending astronauts there. One of the lessons of those explorations that hinders any future lunar expeditions is the severe conditions on the lunar surface. The lack of an atmosphere (10-12 torr) means that cosmic/galactic/solar rays, as well as the many micrometeorites directly striking the surface; in addition, surface temperatures vary widely, over a day-night range of more than 300 K.

Superplastic Titanium Tanks for Propulsion System of Satellites

Institute of Space and Astronautical Science (ISAS/JAXA) in collaboration with Mitsubishi Heavy Industries (MHI) has developed fuel and gas tanks for reaction control system and orbital control system of satellites; A tank is fabricated through welding of two thin, hemi-spherical or conical parts, which are fabricated by superplastic blow forming. Mass-productivity is not an important factor but the forming precision and flexibiliry in the process are important for this application. ISAS and MHI, therefore, developed a new blow-forming technique, which has high flexibility in terms of tank size because it requires a furnace but not a hot-press machine. Some typical propulsion tanks fabricated through this process are presented.

Experimental Study on Restart Control of a Supersonic Air-Breathing Engine

To study the dynamic response of a supersonic airbreathing engine and establish control logic for intake unstart, restart control tests were conducted at Mach 3 using a subscale engine model consisting of an axisymmetric intake (inlet) and a turbojet. Assuming that the combustion flame is blown out by intake unstart, restart control follows a sequence. First, after a flow is started the turbojet engine is ignited. Second, the intake is started while the rotational speed and the combustion gas temperature of the core engine are controlled. Third, the intake spike position and the terminal shock position are controlled, and the intake total pressure recovery achieves the design value (60%). The tests were successful, and engine thrust was recovered at approximately 30-40 s after engine start-up. A sudden increase in combustion gas temperature and rotational speed occurred after intake unstart. To reduce the sudden increase in the gas temperature, a new sequence that involved closing a fuel control valve after detection of intake unstart was implemented, and the increase in gas temperature was reduced. To avoid intake buzz, buzz margin control using a bypass door was successfully implemented.

Robotics and autonomous technology for asteroid sample return mission

The MUSES-C mission is the worlds first sample and return attempt to/from the near Earth asteroid. In deep space, it is hard to navigate, guide, and control a spacecraft on a real-time basis remotely from the earth mainly due to the communication delay. So autonomy is required for final approach and landing on an unknown body. It is important to navigate and guide a spacecraft to the landing point without hitting rocks or big stones. In the final descent phase, cancellation of the horizontal speed relative to the surface of the landing site is essential. This paper describes various kinds of robotics technologies applied for MUSES-C mission. A global mapping method, an autonomous descent scheme, and a novel sample-collection method, and asteroid exploration robot are proposed and presented in detail. The validity and the effectiveness of the proposed methods are confirmed and evaluated by numerical simulations and some experiments

AN AUTONOMOUS OPTICAL GUIDANCE AND NAVIGATION AROUND ASTEROIDS

Abstract An impending demand for exploring the small bodies such as the comets and the asteroids envisioned the Japanese MUSES-C mission to the near Earth asteroid Nereus. An autonomous optical guidance and navigation strategy around the asteroid is discussed in this paper. Four major new schemes are dealt with here: They are (1) Aligned intercept guidance, (2) Strategic building of the flight phases, (3) Image processing of line-of-sight shift information instead of characteristic point tracking, and (4) Stability and accuracy analysis associated with the guidance and navigation strategies developed here. Some comprehensive numerical illustrations are also given to support them.

Collision dynamics of a visual target marker for small-body exploration

MUSES-C mission is the world first sample and return attempt to or from a near-Earth asteroid. In deep space, it is hard to navigate, guide and control a spacecraft on a real-time basis remotely from the earth, mainly due to the communication delay. Thus, autonomy and robotics technologies are required for final approach and landing to an unknown body. In the final descent phase, cancellation of the horizontal speed relative to the surface of the landing site is essential. During the touchdown and sampling phase, the spacecraft will be navigated relative to the asteroid surface using an optical target marker (TM) placed on the asteroid surface. By using the TM as a reference point, navigation during the landing phase will be much more reliable and precise. Thus, it is important to design a TM with as small a coefficient of restitution as possible to reduce the settling time. To develop a small coefficient of restitution of less than 0.1 in vertical direction, the authors propose a novel TM, which is constructed out of a shell with beads stored internally. To better predict the performance of such a TM, analytical and numerical investigations are performed. The validity and the effectiveness of the proposed method are confirmed and evaluated by numerical simulations and flight results.

Hypersonic Turbojet Engine Design of a Balloon-Based Flight Testing Vehicle

JAXA is developing Mach 5 hypersonic turbojet engine technology that can be applied in a future hypersonic transport. Now, in Jet Engine Technology Research Center of JAXA, the experimental study, which uses a 1 / 10 scale-model engine, is conducted. In parallel to engine development activities, a new supersonic flight-testing vehicle for the hypersonic turbojet engine is under development since 2004. In this paper, the system configuration of the flight-testing vehicle is outlined and development status is reported.

Aerodynamic design of Balloon-based operation vehicle for precooled turbojet engine demonstration

The Balloon-based Operation Vehicle (BOV) originally developed for the micro-gravity experiments is modified as a supersonic flight demonstrator of a sub-scale precooled turbojet engine developed in Japan Aerospace Exploration Agency. In the supersonic flight demonstration, the vehicle is raised by a high-altitude balloon up to a 40 km altitude and dropped to accelerate the vehicle to a supersonic velocity. To extend the flight time for an engine combustion test in the supersonic environments, the vehicle is redesigned in a wingbody configuration with a main delta wing and movable vertical and horizontal tail wings so that it can be pulled up above an altitude of 5 km. As a result, the vehicle is capable of reaching the maximum flight Mach number of 2 with the dynamic pressure of 25 kPa at an altitude of 17 km, realizing the engine test time longer than 30 sec. The flight demonstration is currently scheduled in 2009. In this article, an overview of the aerodynamic characteristics of the flight demonstrator and the flight trajectory plan is presented.