The regional coverage satellite constellations are in demand for fulfilling earth observation needs of specific user regions of interest as opposed to global coverage thus enhancing the revisit period for the area. In this paper, we present a few key mission aspects of the regional coverage constellation designed and operated by the Indian Space Research Organization (ISRO) in low earth orbit. ISRO developed three X-Band Synthetic Aperture Radar (SAR) Earth Observation satellites and placed them in three inclined orbit planes to enhance the Indian region's coverage. This is India's first inclined orbit constellation designed for remote sensing applications in low earth orbit. The satellites were built around a standard bus carrying a Synthetic Aperture Radar payload with a deployable Radial Rib Antenna (RRA). They were designed to achieve a high agility capability. As SAR sensors are capable of all-weather, day, and night imaging; thus, most suitable in inclined orbits where the illumination conditions vary continuously for imaging. Though the inclined orbits provide more revisit opportunities to the region of interest, their characteristics pose challenges in mission design and operations. Though the mission design and planning involved a host of elements, this paper brings out the details of a few key mission analysis elements, planning aspects and operations that were critical in the course of various mission phases. The mission analysis included mission-specific requirements like launch windows selection for the constellation and reference attitude generation specific to inclined orbit geometry. Mission planning had to take care of Radial Rib Antenna (RRA) deployment requirements which were very critical for the mission, apart from taking care of individual subsystem requirements. The SAR payload data product quality and targeting accuracy are very sensitive to the satellite image point range (vis-a-vis SAR operation data window). Extensive post-launch calibration activity was carried out to meet all these mission requirements and data product specifications. The challenge was in fixing the payload beam alignment and fixing the uncertainties in onboard and ground computations. The paper also describes the methods of fixing all possible error sources affecting the high-resolution SAR payload performance.

中文翻译：

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区域覆盖高度敏捷SAR卫星的任务运行管理：几个关键方面


区域覆盖卫星星座需要满足特定用户感兴趣区域的地球观测需求，而不是全球覆盖，从而延长该区域的重访周期。在本文中，我们介绍了印度空间研究组织（ISRO）在近地轨道设计和运营的区域覆盖星座的几个关键任务方面。 ISRO开发了三颗X波段合成孔径雷达（SAR）地球观测卫星，并将它们放置在三个倾斜轨道平面上，以增强印度地区的覆盖范围。这是印度第一个专为近地轨道遥感应用而设计的倾斜轨道星座。这些卫星是围绕一个标准总线建造的，该总线携带合成孔径雷达有效载荷和可部署的径向肋状天线（RRA）。它们旨在实现高敏捷性。由于SAR传感器能够全天候、昼夜成像；因此，最适合照明条件连续变化的倾斜轨道进行成像。尽管倾斜轨道为感兴趣区域提供了更多重访机会，但其特性给任务设计和操作带来了挑战。尽管任务设计和规划涉及许多要素，但本文详细介绍了在各个任务阶段过程中至关重要的几个关键任务分析要素、规划方面和操作的细节。任务分析包括特定于任务的要求，例如星座的发射窗口选择和特定于倾斜轨道几何形状的参考姿态生成。 除了考虑各个子系统的要求外，任务规划还必须考虑对任务非常关键的径向肋状天线（RRA）部署要求。 SAR 有效载荷数据产品质量和目标精度对卫星图像点范围（相对于 SAR 操作数据窗口）非常敏感。进行了广泛的发射后校准活动，以满足所有这些任务要求和数据产品规格。挑战在于修复有效载荷光束对准以及解决机载和地面计算中的不确定性。本文还描述了修复影响高分辨率 SAR 有效载荷性能的所有可能误差源的方法。