Hayabusa ======== Instrument Host Overview ======================== The HAYABUSA spacecraft is box-shaped with approximate dimensions of 1.5 x 1.2 x 1.2 meters. Two solar panels with a combined area of 12 square meters provide power for the spacecraft including the four ion engines. The spacecraft launch mass was 530 kg including 60 kg of xenon fuel and 70 kg of hydrazine fuel for the attitude control jets. Each of the four ion engines uses microwave ionization of the xenon fuel and electrostatic acceleration of the ionized fuel to generate 5.2 - 23.6 mN of thrust (Isp = 3200 s). Up to 3 of the 4 ion engines operate at one time. The sample return capsule is 40 cm in diameter, has a height of 20 cm and has a mass of 16.5 kg. The surface hopper (MINERVA) is nearly cylindrical (10 x 12 cm) and by itself has a mass of 591 g. The spacecraft was designed to be three axis stabilized with 3 momentum wheels operating in orthogonal directions. Upon its return to Earth in June 2010, the return capsule separated from the mother spacecraft with a velocity of 17 cm/sec. Its spin rate was about 0.2 Hz. At 20 G, a timer was armed to jettison the parachute cover at an altitude of about 10 km. The capsule recovery was near Woomera, Australia, the landing velocity was about 6 m/s and the Landing footprint was estimated to be 169 x 16 km (4 sigma). To assist recovery, the sample capsule had a 242 MHz beacon radio signal. An introduction to the spacecraft description and mission results can be found in [FUJIWARAETAL2006]. Fujiwara, A., J. Kawaguchi, D.K. Yeomans, M. Abe, T. Mukai, and 17 others, The rubble-pile asteroid Itokawa as observed by Hayabusa, Science 312, 1330-1334, 2006. System Description ================== The spacecraft coordinate system has the high gain antenna (HGA) pointing in the +Z direction with the AMICA camera, NIRS, LIDAR, XRS, along with the low gain X and S band antenna pointing in the -Z direction. The ion engines point in the +X direction with the star tracker pointing in the -X direction. The solar panel nearest the star tracker is in the +Y direction (Y = X x Z) with the second solar panel pointing in the -Y direction. Bi-propellant attitude control thrusters are located on each corner of the spacecraft. The power output of the solar panels is 2.6 kw at 1 AU. Along with the solar panels and HGA, the science instruments are hard mounted to the spacecraft. The LIDAR, XRS, AMICA and sample horn are attached to the outside of the -Z deck with the NIRS mounted on the -X deck but pointing in the -Z direction. MINERVA is located on the -Z axis near the sampling horn. The AMICA, NIRS,and LIDAR have co-aligned fields-of-view. The interior of the spacecraft contains the propulsion module. The ionized plasma is accelerated by high-voltage electrodes through four thruster heads which protrude from one side of the spacecraft body to provide ion thrusting of the spacecraft. A nitrogen tetroxide/hydrazine propulsion system with a peak thrust of 22 N was used for maneuvering until late December 2005 when this fuel was exhausted. The spacecraft is powered by gallium-arsenide solar cells and a 15 A-hr rechargeable nickel-metal hydride (Ni-MH) battery. The battery suffered degredation during the close proximity spacecraft activities in late 2005. Because of the sun, Earth and asteroid geometry at encounter and the spacecraft design, most often the spacecraft hovered above the asteroid along the Sun-asteroid line so that radio communications with Earth could be maintained at the same time the solar panels were directed toward the sun. Three optical cameras were carried on board the spacecraft. In addition to the AMICA science camera, two wide angle cameras were used for optical navigation. They were equipped with 500 x 500 CCDs with a resolution of 216 arcsec/px, 13 mm focal lengths and with a f ratio of 9.6. The spacecraft was also equipped with a star tracker (266 x 384 CCD, focal length = 12 mm, f/1.4, resolution = 375 arc seconds). Of the four laser range finders (LRF) on board, three were used to measure the distance to the asteroid's surface when the the spacecraft was close (120 to 7 meters) while the fourth LRF was to be used to detect the deflection of the sampling horn when it touched the surface; this would then trigger the pellet firing to generate surface sample ejecta to capture. The coordinates and some of the larger elements of the spacecraft are shown in the schematic figure below. +Z /\ HGA ------------------- \ / \ / -------------------------- | | | |_ | |_] ion engines | |_] +X _| | NIRS | | | ----| |--------------| |- | | LIDAR XRS | | | | -Z | | | | | | Sample horn / \ Communications Subsystem ======================== The communications subsystem includes the 1.6 meter two axis gimbaled, parabolic high gain antenna (HGA), two medium gain horn antennae (MGA) located on the HGA deck, four micro strip low gain antennae (LGA), an X-band transmitter (XTX), and two X-band receivers (XRX). The uplink frequency is 7156.533 MHz and the downlink frequency is 8408.210 MHz. The signal has right hand circular polarization. The XRX receives and demodulates command signals and receives and filters range signals. The maximum transmitter power is 20 W and the bit rates can be set at 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, or 8192 bps with a maximum of about 5 MB per day. Command and Data Handling Subsystem =================================== The Data Handling Subsystem (DHS) comprises the command and telemetry processors, a solid state Data Recorder (DR), and an interface to a redundant data bus for communicating with other processor-controlled subsystems. The functions provided by the DHS are command management, telemetry management, and autonomous operations. The command function operates on inputs from the two command receivers at one of three rates: 15.625 bps, 125 bps, or 1000 bps. The format of the uplinked commands is Consultative Committee for Space Data Systems (CCSDS) compliant, with only a single virtual channel. Four types of commands are supported: discrete commands are used to turn on or off a function provided by a spacecraft subsystem; serial magnitude commands are used to set values to one or more parameters of a subsystem; user data commands are used to send a block of user data to a subsystem; and memory write commands are used to write a block of data to a portion of a memory installed in a subsystem. The DHS relays these commands as they are to intelligent subsystems (or components) using the data bus, or sends discrete and serial magnitude commands as physical signals to non-intelligent subsystems (or components) on serial interfaces. A series of commands that perform a specific function can be stored as a command macro, which can be executed with a command sent from the ground or by one of the methods described below. The DHS can also store a sequence of time-tagged commands or command macros, which is called a timeline, for later execution at specified spacecraft times. When the DHS detects an anomaly, it can automatically execute a command or command macro. Intelligent subsystems can also request the DHS to issue a command or command macro to another subsystem. During normal operations, most of commands are executed from a timeline, which have been pre-stored from the ground. In this way, most operations are carried out when the spacecraft is out of ground contact. The telemetry function collects engineering status and science data using dedicated serial interfaces from non-intelligent subsystems (or components), or using the data bus from intelligent subsystems (or components). These data are always packetized either by the DHS or by intelligent subsystems (or components), and placed into CCSDS-compliant transfer frames. The transfer frames are directed to the DR, the downlink, or both. Data recorded on the DR are read back, packed into transfer frames and placed into the downlink on command. Recorder playback data can be interleaved with real time data on the downlink. The downlink data rate is selectable among 11 rates ranging from 8192 bps to 8 bps to match the communication link capability throughout the mission. References ========== Fujiwara, A., J. Kawaguchi, D.K. Yeomans, M. Abe, T. Mukai, and 17 others, The rubble-pile asteroid Itokawa as observed by Hayabusa, Science 312, 1330-1334, 2006.