Asteroid Multi-band Imaging Camera ================================== Instrument Overview =================== The Asteroid Multi-Band Imaging Camera (AMICA) is one of the Optical Navigation Cameras (ONCs) of the Hayabusa mission, a Japanese-led sample-return mission to the asteroid 25143 Itokawa. The three ONCs are AMICA (also known as ONC-T), and two wide angle navigation cameras ONC-W1 and ONC-W2. The AMICA system was used both for science and for optical navigation. Pre-flight information about the instrument is available in Nakamura et al. (2001). Preliminary results of AMICA are reported in Saito et al. (2006). Full information about the specifications, performance, and calibration of AMICA may be found in Ishiguro et al. (2010). The optical axis of AMICA is designed to be boresighted with the NIRS and LIDAR instruments. In-flight measurements of the star Alpha Scorpii determined that the boresight of NIRS is centered on the (493, 510) pixel in the AMICA frame. Co-alignment of NIRS and LIDAR was adjusted as accurately as possible pre-flight and was confirmed after arrival at Itokawa. AMICA is a refracting telescope consisting of five lenses, each of which is cosmic-radiation-resistant and anti-reflection coated. A quartz optical parallel window is placed in front of the first lens for radiation protection. The SITe CCD chip, developed and built by NEC TOSHIBA Space Systems, Ltd., is of the back-illuminated MPP (Multi-Pinned Phase) type. The CCD is kept below -10 degrees C in ordinary in-flight condition. The CCD dimensions are 1024 x 1000 pixels and the camera field of view is 5.83 x 5.69 degrees. The 12 columns on either side of the 1024 x 1000 pixel array are dark due to an obscuring mask. DNs in these areas were found to be dependent on both incident flux and wavelength, suggesting that the masks are not perfectly impermeable to light. Therefore, these pixels cannot be used for dark current correction. The remaining unobscured region has the dimensions 1000 x 1000. Due to cosmic-ray irradiation during flight, hot pixels have developed in the AMICA CCD. The known hot pixels and their dark rates are tabulated here: pixel (x,y) dark rate (DN/sec) (407,300) 540 (599,408) 330 (820,14) 310 (930,624) 305 (897,716) 290 Since the CCD is of the frame-transfer type, AMICA has no mechanical shutter but the exposure is controlled electronically. 30 different exposure times can be specified from 5.44 ms through 178 sec, plus a zero second exposure. The exposure time accuracy (including for the zero second exposure) is 1 microsec. The zero second exposure is necessary to correct readout smear which is inevitable for shutterless and frame-transfer type CCDs. AMICA has an eight position filter wheel, of which seven filters are nearly eqivalent to the ECAS bands (Tedesco et al. 1982). filter: central wavelength (nm): FWHM (nm): ul 381 45 b 429 108 v 553 72 w 700 70 x 861 81 p 960 75 zs 1008 66 The eighth position has a wide-bandpass filter. filter: central wavelength (nm): FWHM (nm): WIDE 650 300 Each filter aperture is sector-shaped and the filters are placed closely side by side at the edges to enable imaging in case the filter wheel stops accidentally at an improper position. AMICA has four position-angle glass polarizers placed immediately in front of the CCD on one side and each covering 200 x 200 pixels. The four polarizers are placed with position angles of 0, 45, 90, and 135 degrees. The characteristics of AMICA are summarized below. Weight of camera: 1.74 kg Weight of electronics: 4.0 kg Power usage for camera: 6.8 W Power usage for electronics: 9.5 W Dimensions: 120mm x 135mm x 180 mm Effective lens diameter: 15 mm (F/8.0) Focal length: 120.80 mm (fixed) Field of view: 5.83 x 5.69 deg CCD dimensions: 1024 x 1000 pixels Pixel size: 12 micron square Pixel resolution: 20.490 arsec/pix Quantum efficiency: 45% at 350nm, 20% at 1000nm, 8% at 1050nm A/D conversion: 12 bits System spectral response: 360nm - 1050nm Stellar V limiting magnitude: 5 - 6 Electronic shutter exposure time: 5.44 ms - 178 s Image memory storage: 16 frames Filters: 7 bands nearly equivalent to ECAS Polarizers: 4 position-angle glass polarizers References ========== Ishiguro, M., R. Nakamura, D.J. Tholen, N. Hirata, H. Demura, E. Nemoto, A.M. Nakamura, Y. Higuchi, A. Sogame, A. Yamamoto, K. Kitazato, Y. Yokota, T. Kubota, T. Hashimoto, and J. Saito, The Hayabusa Spacecraft Asteroid Multi-Band Imaging Camera: AMICA, Icarus (2010), doi: 10.1016/j.icarus.2009.12.035, 2010. Nakamura, T., A.M. Nakamura, J. Saito, S. Sasaki, R. Nakamura, and three others, plus the AMICA team. Multi-band imaging camera and its sciences for the Japanese near-earth asteroid mission MUSES-C. Earth, Planets, Space 53, 1047-1063, 2001. Saito, J., M. Miyamoto, R. Nakamura, M. Ishiguro, T. Michikami, and 29 others. Detailed images of asteroid 25143 Itokawa from Hayabusa. Science 312, 1341-1344, 2006. Tedesco, E.F., D.J. Tholen, and B. Zellner. The eight-color asteroid survey: Standard stars. Astron. J. 87, 1587-1592, 1982. References ========== Nakamura, T., A.M. Nakamura, J. Saito, S. Sasaki, R. Nakamura, and three others, plus the AMICA team. Multi-band imaging camera and its sciences for the Japanese near-earth asteroid mission MUSES-C. Earth, Planets, Space 53, 1047-1063, 2001. Ishiguro, M., R. Nakamura, D.J. Tholen, N. Hirata, H. Demura, E. Nemoto, A.M. Nakamura, Y. Higuchi, A. Sogame, A. Yamamoto, K. Kitazato, Y. Yokota, T. Kubota, T. Hashimoto, and J. Saito, The Hayabusa Spacecraft Asteroid Multi-Band Imaging Camera: AMICA, Icarus (2010), doi: 10.1016/j.icarus.2009.12.035, 2010. Tedesco, E.F., D.J. Tholen, and B. Zellner, The eight-color asteroid survey: Standard stars, The Astronomical Journal, 87, 11:1585-1592, 1982. Saito, J., H. Miyamoto, R. Nakamura, M. Ishiguro, T. Michikami, and 29 others, Detailed images of asteroid 25143 Itokawa from Hayabusa, Science 312, pp. 1341-1344, 2006.