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NASA.s Double Asteroid Redirection Test (DART) mission will hit Dimorphos comma the satellite in the binary near-Earth asteroid system (65803) Didymos in late September 2022 for a controlled asteroid impact experiment. We request 19 orbits to observe the DART impact ejecta for a total duration of three weeks to characterize its morphology and temporal evolution comma and to constrain the mass comma velocity and velocity distributions comma particle size and size frequency distributions of the ejecta. Impact is a common and important process naturally occurring in all planetary systems and plays an important role in the evolution of planetary objects. The DART mission is the first experiment to demonstrate asteroid impact hazard mitigation by using a kinetic impactor comma with its primary objective being to measure the momentum transfer efficiency during asteroid impact on a realistic asteroid scale. Although HST has observed naturally occurring impacts in the past comma the DART impact is the first asteroid impact with precisely known impactor properties and a considerable amount of detailed knowledge about the target and impact site. Therefore comma the proposed observation will both greatly improve our knowledge about impacts on asteroids comma and significantly strengthen the coordinated global observing campaign organized by the DART investigation team. HST is the only observing facility that is capable of high-resolution comma high sensitivity imaging of the full extent of the DART ejecta for the full duration of ejecta development and dissipation.

美国国家航空航天局（National Aeronautics and Space Administration, NASA）的双小行星重定向测试（Double Asteroid Redirection Test, DART）任务，将于2022年9月下旬撞击双近地小行星系统(65803)迪迪摩斯（Didymos）的卫星迪摩斯（Dimorphos），以开展受控小行星撞击实验。我们申请19个轨道的观测时长，总为期三周，用于观测DART撞击产生的喷流，以表征其形态学特征与时间演化过程，同时限定喷流的质量、速度及速度分布、粒径与粒径频率分布。撞击是所有行星系统中普遍存在的重要自然过程，对行星天体的演化具有关键作用。DART任务是首个通过动能撞击器验证小行星撞击减灾技术的实验，其核心目标是在真实小行星尺度下，测量小行星撞击过程中的动量传递效率。尽管哈勃空间望远镜（Hubble Space Telescope, HST）过去曾观测过自然发生的撞击事件，但DART撞击是首次已知撞击器参数精确、且对靶标与撞击位点拥有大量详细认知的小行星撞击实验。因此，本次申请的观测计划既能极大拓展我们对小行星撞击过程的认知，也能显著强化DART研究团队统筹组织的全球协同观测活动。哈勃空间望远镜是唯一能够在喷流形成与消散的全周期内，对DART喷流的完整范围开展高分辨率、高灵敏度成像的观测设施。