5:15 PM - 7:15 PM
[PPS03-P17] Development Status of the DESTINY+ Onboard Cameras for Flyby Imaging of (3200) Phaethon and Other Small Bodies
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 small-class mission led by JAXA/ISAS, scheduled to be launched in 2028. DESTINY+ will flyby the near-Earth asteroid (3200) Phaethon, known as an active asteroid and the parent body of the Geminid meteor shower. 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.
DESTINY+ also plans multi-flybys to small bodies other than Phaethon, and TCAP and MCAP will carry out flyby observations of these bodies. TCAP and MCAP were originally designed to be optimized for flyby observations of Phaethon but will be used for flyby observations of other objects to the extent possible, basically in the same way as for Phaethon. Prior to the Phaethon flyby, a small body flyby is planned to aim for flyby validation (i.e., validation of tracking imaging during the flyby), and the near-Earth asteroid Apophis, which has attracted much attention in terms of planetary defense, is considered as a candidate target object.
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 engineering model (EM) of TCAP was once completed more than a year ago, but the mirror of the tracking mirror module detached during impact tests. To address this problem, the mirror adaptor was improved to increase the adhesive strength, but this led to a degression in the surface accuracy of the mirror. Thus, we are considering the possibility of polishing and evaporation coating of the mirror surface after adhering to the adaptor. Although the above problems remain, the TCAP EM has been subjected to an environmental test (qualification test), which confirmed that no other major problems arose. Having resolved the remaining issues, we will proceed to the critical design review (CDR) of the proto-flight model (PFM).
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. 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.
The PFM of MCAP was designed based on the results of the validation with the engineering model, and the production of the PFM was almost complete at the time of writing this manuscript. Focus adjustment of the PFM is underway, and the focus is being adjusted so that the amount of signal of point source images is constant, independent of positional variations at the sub-pixel level. This is necessary to improve the accuracy of the onboard sensitivity calibration using stars. The environmental tests for PFM (proto-flight tests) will be conducted after the focus adjustment is completed.
DESTINY+ also plans multi-flybys to small bodies other than Phaethon, and TCAP and MCAP will carry out flyby observations of these bodies. TCAP and MCAP were originally designed to be optimized for flyby observations of Phaethon but will be used for flyby observations of other objects to the extent possible, basically in the same way as for Phaethon. Prior to the Phaethon flyby, a small body flyby is planned to aim for flyby validation (i.e., validation of tracking imaging during the flyby), and the near-Earth asteroid Apophis, which has attracted much attention in terms of planetary defense, is considered as a candidate target object.
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 engineering model (EM) of TCAP was once completed more than a year ago, but the mirror of the tracking mirror module detached during impact tests. To address this problem, the mirror adaptor was improved to increase the adhesive strength, but this led to a degression in the surface accuracy of the mirror. Thus, we are considering the possibility of polishing and evaporation coating of the mirror surface after adhering to the adaptor. Although the above problems remain, the TCAP EM has been subjected to an environmental test (qualification test), which confirmed that no other major problems arose. Having resolved the remaining issues, we will proceed to the critical design review (CDR) of the proto-flight model (PFM).
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. 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.
The PFM of MCAP was designed based on the results of the validation with the engineering model, and the production of the PFM was almost complete at the time of writing this manuscript. Focus adjustment of the PFM is underway, and the focus is being adjusted so that the amount of signal of point source images is constant, independent of positional variations at the sub-pixel level. This is necessary to improve the accuracy of the onboard sensitivity calibration using stars. The environmental tests for PFM (proto-flight tests) will be conducted after the focus adjustment is completed.