Is it possible to integrate Electric Propulsion thrusters effectively on Very Low Earth Orbit Microsatellites?

本报告介绍了为研究在极低地球轨道（<200公里）微型卫星（质量<125千克）上有效使用电推进的可行性而开展的工作。其目的是提供一种20-100公斤重的高性能卫星，适用于各种飞行任务，在轨道上的寿命至少为一年，在160公里的高度运行遥感卫星有许多好处。成像仪离目标越近，成像仪就越小，从而有可能使用超小型卫星（<30公斤），从而降低尺寸和成本。与500公里处的卫星相比，甚低地球轨道卫星可以实现焦距的3倍减少以及RF功率的高达30倍减少，同时显著提高下行链路数据速率。总的来说，这可能会导致总成本降低10倍。由于在这些低高度的空气密度增加，卫星会受到更大的阻力，这通常会导致它在几个月内脱离轨道。使用电力推进系统来对抗增加的阻力可以实现增加的操作寿命。欧洲航天局的重力场和稳态海洋环流探测器（GOCE）证明了这一点，该探测器在燃料耗尽之前使用电力推进器维持了55个月的260公里轨道高度，如上所述，人们对使用小于200公里的轨道感兴趣，这比GOCE低得多，因为它具有更高的大气密度，因此阻力更大。因此，有必要对阻力和轨道进行建模，以便了解与轨道的其他扰动相比，空气密度在这一高度上所起的更大作用。一旦确定了阻力水平，就可以选择电力推进的类型。为了帮助进行选择，进行了推进类型与使命类型的映射。利用直接模拟蒙特卡罗技术对超小型卫星的阻力进行建模，然后将其与标准轨道建模技术相结合，确定电推进装置的大小。

This describes work to investigate the feasibility of using Electric Propulsion on Ultra Low Earth Orbit (<200km) Microsatellites (mass <125kg) effectively. The aim is to provide a highly capable satellite in the 20-100 kg range, applicable to a wide range of missions which could achieve a lifetime of at least one year in orbit.Operating a remote sensing satellite at 160km has many benefits. The closer the imager is to a target, the smaller this imager can be, leading to the possibility of using nanosatellites (<30kg) with consequent size and cost reductions. Compared to a satellite at 500 km, a Very Low Earth Orbit Satellite may achieve 3x reduction in focal length as well as up to 30x reduction in RF power with a significantly improved downlink data rate. Altogether this could lead to a 10x reduction in the overall cost.Due to increased air density at these low altitudes a satellite experiences larger drag forces which would normally cause it to de-orbit within a few months. An increased operational lifetime can be achieved using an electric propulsion system to combat the increased drag. This was demonstrated by the European Space Agency's (ESA) Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) which sustained an orbital altitude of 260km using electric propulsion for 55 months before running out of fuel.As described above, there is an interest in using orbits of less than 200km, considerably lower than GOCE, which have a higher atmospheric density and therefore higher drag. It was therefore necessary to model both the drag and orbit in order to understand the increased role that the air density played at this altitude in comparison to other perturbations of the orbit. Once the level of drag was established, the type of electric propulsion could be selected. A mapping of propulsion types to mission types was performed to aid this selection process. Modelling of the drag for the nanosatellite was achieved using direct simulation Monte Carlo techniques and this was then combined with standard orbit modelling techniques to size the electric propulsion unit.