Very low Earth orbits (VLEO), typically classified as orbits below approximately 450 km in altitude, have the potential to provide significant benefits to spacecraft over those that operate in higher altitude orbits. This paper provides a comprehensive review and analysis of these benefits to spacecraft operations in VLEO, with parametric investigation of those which apply specifically to Earth observation missions. The most significant benefit for optical imaging systems is that a reduction in orbital altitude improves spatial resolution for a similar payload specification. Alternatively mass and volume savings can be made whilst maintaining a given performance. Similarly, for radar and lidar systems, the signal-to-noise ratio can be improved. Additional benefits include improved geospatial position accuracy, improvements in communications link-budgets, and greater launch vehicle insertion capability. The collision risk with orbital debris and radiation environment can be shown to be improved in lower altitude orbits, whilst compliance with IADC guidelines for spacecraft post-mission lifetime and deorbit is also assisted. Finally, VLEO offers opportunities to exploit novel atmosphere-breathing electric propulsion systems and aerodynamic attitude and orbit control methods. However, key challenges associated with our understanding of the lower thermosphere, aerodynamic drag, the requirement to provide a meaningful orbital lifetime whilst minimising spacecraft mass and complexity, and atomic oxygen erosion still require further research. Given the scope for significant commercial, societal, and environmental impact which can be realised with higher performing Earth observation platforms, renewed research efforts to address the challenges associated with VLEO operations are required.

中文翻译：

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极低地球轨道对地球观测任务的好处

极低地球轨道 (VLEO)，通常被归类为高度低于约 450 公里的轨道，与在更高高度轨道运行的航天器相比，它有可能为航天器提供显着的好处。本文对 VLEO 中航天器操作的这些好处进行了全面的审查和分析，并对那些专门适用于地球观测任务的好处进行了参数调查。光学成像系统最显着的好处是轨道高度的降低提高了类似有效载荷规格的空间分辨率。或者，可以在保持给定性能的同时节省质量和体积。同样，对于雷达和激光雷达系统，可以提高信噪比。其他好处包括提高地理空间定位精度，通信链路预算的改进，以及更大的运载火箭插入能力。与轨道碎片和辐射环境的碰撞风险可以证明在低海拔轨道上有所改善，同时也有助于遵守 IADC 的航天器任务后寿命和脱轨准则。最后，VLEO 为开发新型吸气式电力推进系统以及空气动力学姿态和轨道控制方法提供了机会。然而，与我们对低热层、空气动力阻力、提供有意义的轨道寿命同时最大限度地减少航天器质量和复杂性的要求以及原子氧侵蚀的理解相关的关键挑战仍然需要进一步研究。鉴于重要的商业、社会、