5:15 PM - 6:45 PM
[PPS03-P09] Development Status of DESTINY+ Onboard Cameras for Flyby Imaging of (3200) Phaethon
Keywords:DESTINY+, (3200) Phaethon, Flyby observation, Camera
DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLy-by and dUst Science) is a mission proposed for JAXA/ISAS Epsilon class small program, scheduled to be launched in 2025. The flyby target of the DESTINY+ mission is the near-Earth asteroid (3200) Phaethon, known as an active asteroid and the parent body of the Geminid meteor shower. The size of (3200) Phaethon is estimated to be 5-6 km. The spacecraft will perform a flyby of (3200) Phaethon at a closest approach distance of 500±50 km and relative speeds of ~36 km/s. In this mission, two onboard cameras, the Telescopic CAmera for Phaethon (TCAP) and the Multiband CAmera for Phaethon (MCAP), will capture spatially resolved images of (3200) Phaethon. These observations will contribute to understanding the nature of a meteor shower's parent body, one of the sources of interplanetary dust particles that is a potential transport medium of organic matter to Earth.
The images of (3200) Phaethon for scientific objectives will be taken around the closest approach during the flyby. In this phase, automatic asteroid tracking using the TCAP images will be conducted by controlling the tracking mirror of TCAP and the spacecraft's rolling motion.
TCAP is a panchromatic camera designed to observe the global shape, semi-global features, and local surface features of (3200) Phaethon. To conduct these observations, TCAP is equipped with a tracking mirror capable of changing the boresight direction and keeping the asteroid in the field of view of TCAP throughout the flyby. The key specifications of TCAP include a focal length of 787.7 mm, aperture of φ114.0 mm, field of view of 0.81 deg × 0.81 deg, and IFOV (FOV per pixel) of 7 μrad/pixel. TCAP also serves as the optical navigation camera for flyby observation, and these specifications are essential for both scientific imaging and the successful execution of the flyby imaging sequence. Given that the angular velocity at the closest approach is around 4.1 deg/s, which exceeds the capacity of spacecraft attitude control alone, the use of a tracking mirror is imperative. Achieving high pointing accuracy and stability is crucial to maintaining the asteroid within the field of view of TCAP and capturing images without motion blur. The apparent diameter of (3200) Phaethon is calculated to be around 0.69 deg at the closest approach, assuming a diameter of 6 km for (3200) Phaethon, whereas the field of view of TCAP is 0.81 deg × 0.81 deg. Therefore, TCAP requires high pointing accuracy to establish tracking while keeping the asteroid in the field of view. Additionally, high pointing stability is essential to capture images of Phaethon without introducing blurring.
An engineering model (EM) of TCAP was manufactured, and basic functional and performance tests confirmed compliance with the requirements. Subsequently, environmental tests were conducted, but during the impact test, a problem was identified with the bend mirror of the tracking mirror module. At the time of this writing, improvements to the mirror adapter are underway, and testing will resume shortly.
MCAP is a multiband camera with wavelengths of 425, 550, 700, and 850 nm. The focal length, aperture, field of view, and IFOV are 99 mm, φ20.8 mm, 6.5 deg × 6.5 deg, and 54 μrad/pixel, respectively, for all bands (Focal length varies slightly with band). MCAP has multiple optical systems and sensors to capture images in all bands simultaneously. MCAP employs branching optical systems that separate incident light into two imaging sensors using a dichroic prism. As a result, four bands can be covered with two branching optical systems. Although the spatial resolution of MCAP is inferior to that of TCAP, comparing images taken by MCAP with the high spatial resolution images from TCAP allows for understanding the correlation between surface materials and topography. MCAP does not equip a tracking mirror due to strict weight limitations and captures images at solar phase angles of around 15 degrees, where the reflected light is sufficient to achieve high signal-to-noise ratios.
The engineering model (EM) of the MCAP was completed, and we conducted functional and performance verification and environmental tests. During these tests, several problems were identified, including stray light generation, but all of these problems have been resolved. We also conducted imaging tests using several carbonaceous meteorites as Phaethon simulants and confirmed that the reflectance spectra of these meteorites were obtained correctly. At the time of this writing, MCAP is in the process of confirming the design of its proto flight model (PFM), and the PFM is expected to be manufactured soon.
The images of (3200) Phaethon for scientific objectives will be taken around the closest approach during the flyby. In this phase, automatic asteroid tracking using the TCAP images will be conducted by controlling the tracking mirror of TCAP and the spacecraft's rolling motion.
TCAP is a panchromatic camera designed to observe the global shape, semi-global features, and local surface features of (3200) Phaethon. To conduct these observations, TCAP is equipped with a tracking mirror capable of changing the boresight direction and keeping the asteroid in the field of view of TCAP throughout the flyby. The key specifications of TCAP include a focal length of 787.7 mm, aperture of φ114.0 mm, field of view of 0.81 deg × 0.81 deg, and IFOV (FOV per pixel) of 7 μrad/pixel. TCAP also serves as the optical navigation camera for flyby observation, and these specifications are essential for both scientific imaging and the successful execution of the flyby imaging sequence. Given that the angular velocity at the closest approach is around 4.1 deg/s, which exceeds the capacity of spacecraft attitude control alone, the use of a tracking mirror is imperative. Achieving high pointing accuracy and stability is crucial to maintaining the asteroid within the field of view of TCAP and capturing images without motion blur. The apparent diameter of (3200) Phaethon is calculated to be around 0.69 deg at the closest approach, assuming a diameter of 6 km for (3200) Phaethon, whereas the field of view of TCAP is 0.81 deg × 0.81 deg. Therefore, TCAP requires high pointing accuracy to establish tracking while keeping the asteroid in the field of view. Additionally, high pointing stability is essential to capture images of Phaethon without introducing blurring.
An engineering model (EM) of TCAP was manufactured, and basic functional and performance tests confirmed compliance with the requirements. Subsequently, environmental tests were conducted, but during the impact test, a problem was identified with the bend mirror of the tracking mirror module. At the time of this writing, improvements to the mirror adapter are underway, and testing will resume shortly.
MCAP is a multiband camera with wavelengths of 425, 550, 700, and 850 nm. The focal length, aperture, field of view, and IFOV are 99 mm, φ20.8 mm, 6.5 deg × 6.5 deg, and 54 μrad/pixel, respectively, for all bands (Focal length varies slightly with band). MCAP has multiple optical systems and sensors to capture images in all bands simultaneously. MCAP employs branching optical systems that separate incident light into two imaging sensors using a dichroic prism. As a result, four bands can be covered with two branching optical systems. Although the spatial resolution of MCAP is inferior to that of TCAP, comparing images taken by MCAP with the high spatial resolution images from TCAP allows for understanding the correlation between surface materials and topography. MCAP does not equip a tracking mirror due to strict weight limitations and captures images at solar phase angles of around 15 degrees, where the reflected light is sufficient to achieve high signal-to-noise ratios.
The engineering model (EM) of the MCAP was completed, and we conducted functional and performance verification and environmental tests. During these tests, several problems were identified, including stray light generation, but all of these problems have been resolved. We also conducted imaging tests using several carbonaceous meteorites as Phaethon simulants and confirmed that the reflectance spectra of these meteorites were obtained correctly. At the time of this writing, MCAP is in the process of confirming the design of its proto flight model (PFM), and the PFM is expected to be manufactured soon.