The primary scientific objective of the Hayabusa (formerly Muses-C) mission was to collect a surface sample of material from an asteroid (25143 Itokawa/1998 SF36) and return the sample to Earth for analysis. It was also a technology demonstration mission. Other scientific objectives of the mission include detailed studies of the asteroid's shape, spin state, topography, color, composition, density, photometric and polarimetric properties, interior and history.
Following launch, the original name Muses-C was changed to Hayabusa (the Japanese word for falcon) and the spacecraft was put into a transfer orbit to bring it to asteroid 25143 Itokawa (1998 SF36), a 0.3 x 0.7 km near-Earth object. The ion engines were successfully test-fired starting on 27 May to the middle of June. Rendezvous with the asteroid was to occur in June 2005. The spacecraft was not go into orbit around the asteroid, but remain in a station-keeping heliocentric orbit close by.
Hayabusa was to initially survey the asteroid surface for about three months from a distance of about 20 km. Following this the spacecraft was to move close to the surface for a series of soft landings and collection of samples at three sites. On-board optical navigation was to be employed extensively during this period because the long communication delay prohibits ground-based real-time commanding. The samples, with a total mass of approximately one gram, were to be held inside a separate re-entry capsule. (A small NASA rover was cancelled by NASA due to budget constraints.)
After a few months in close proximity to the asteroid, the spacecraft was to fire its engines to begin its cruise back to Earth. The re-entry capsule was to be detached from the main spacecraft at a distance of about 300,000 to 400,000 km from the Earth, and the capsule was to coast on a ballistic trajectory, re-entering the Earth's atmosphere in June 2007. The capsule was to experience peak decelerations of about 25 G and heating rates approximately 30 times those experienced by the Apollo spacecraft. It was to land via parachute near Woomera, Australia. This scenario was a change from the original plan to launch in July 2002 to the asteroid Nereus.
Spacecraft and Subsystems
The Hayabusa spacecraft had a box-shaped main body 1.5 m along each side and 1.05 m high. The launch mass was 530 kg, including 50 kg of chemical propellant and 65 kg of xenon gas. Two solar panel wings with a total array area of 12 square meters protruded from the side and a 1.5 m diameter high-gain parabolic antenna was mounted on top on a two-axis gimbal.
Hayabusa was propelled during cruise phases by two microwave ion thruster engines, which used a microwave discharge to ionize xenon gas. The ionized plasma was accelerated by high-voltage electrodes through four thruster heads which protrude from one side of the spacecraft body to provide a peak thrust of 20 mN using 1 kW power. A nitrogen tetroxide/hydrazine propulsion system with a peak thrust of 22 N was used for maneuvering. The spacecraft was powered by gallium-arsenide solar cells producing 700 kW at 1 AU and a 15 A-hr rechargeable nickel-metal hydride (Ni-MH) battery. Communications was via X- and S-band low gain antennas and the high gain dish antenna (X-band) with a transmitted power of 20 W. The spacecraft was also equipped with a camera, which was to be used for imaging, visible-polarimetry studies, and optical navigation near the asteroid, a laser ranging device (LIDAR), and near-IR and X-ray spectrometers. The insulated and cushioned re-entry capsule, 40 cm in diameter and 25 cm deep with a mass of about 20 kg, was attached to the body of the spacecraft near the sample collection horn. The capsule had a convex nose covered with a 3 cm thick ablative heat shield to protect the samples from the high velocity (~13 km/s) re-entry. Cost of the Hayabusa spacecraft was roughly 12 billion yen ($100 million U.S.)
Surface Sample Collection
The lander was equipped with a universal sample collection device which was to gather roughly one gram of surface samples taken from the landings at 3 different locations. The device consisted of a funnel-shaped collection horn, 40 cm in diameter at the end, which was to be placed over the sampling area. A pyrotechnic device fired a 10 gram metal projectile down the barrel of the horn at 200 - 300 m/sec. The projectile would strike the surface producing a small impact crater in the surface of the asteroid and propelling ejecta fragments back up the horn, where some of it was funneled into a sample collection chamber. Prior to each sampling run, the spacecraft was to drop a small target plate onto the surface from about 30 m altitude to use as a landmark to ensure the relative horizontal velocity between the spacecraft and asteroid surface was zero during the sampling. After sampling the samples was to be stored in the re-entry capsule for return to Earth.
AKA: Muses-C; Falcon.
Gross mass: 415 kg (914 lb).
First Launch: 2003.05.09.
Number: 1 .