Deorbiting with electrodynamic tethers: comparison between different tether configurations

Electrodynamic tethers have been recently proposed for satellite and rocket upper stage deorbiting to mitigate the debris problem at Low Earth Orbits (LEOs). The deorbiting performance of several electrodynamic tethers, where the electron collection from the ionosphere is obtained with either simple bare wires or bare wires terminated with conducting spherical collectors, was analyzed and compared. Our results indicate that the use of the spherical collectors at the positive termination of the system significantly enhances the deorbiting capabilities of the electrodynamic bare tethers.     

空间绳系组合体拖曳动力学分析及振动控制

空间绳系捕获系统捕获目标物后的组合体在拖曳离轨过程中常产生振动，为此，建立了切向连续推力作用下的空间拖曳绳系组合体面内动力学模型，并对模型进行了横向摆动与纵向振动耦合分析。针对组合体的纵向振动问题提出了一种以张力控制为内环、速度控制为外环的双闭环振动控制策略。进行了振动控制仿真分析，并根据动力学的相似性，建立地面模拟实验系统，仿真与实验结果表明该控制策略可迅速抑制组合体纵向振动、减小系绳冲击并可避免出现系绳松弛现象。     

GEO卫星寿命末期异常情况下离轨控制策略

为及时有效处置卫星寿命末期在轨突发情况,有针对性地做好卫星离轨的各项准备,控制与减小突发异常危害和不良影响,根据离轨控制要求,对异常情况下实施离轨的控制策略进行分析,提出了在燃料受限情况下"小步逼近"的多批次双脉冲离轨控制策略,以及在离轨控制时间受限情况下"大步远离"的短时间大控制量离轨控制策略,并通过仿真对控制策略进行了验证。结果表明,"小步逼近"控制策略能在燃料受限时尽可能地逼近坟墓轨道,"大步远离"控制策略能在较短的时间内将卫星送入坟墓轨道,该策略适用于GEO(Geostationary Earth Orbit,地球静止轨道)卫星寿命末期异常情况下的离轨控制。     

带偏置点的绳系拖拽离轨系统动力学研究

考虑空间拖船利用飞网/飞爪对空间残骸捕获结束后绳系拖拽系统的动力学特性,开展了基于简化的带偏置点构型的建模及仿真研究.首先,捕获后的组合体包括空间拖船、系绳和空间残骸,系绳在空间残骸一端的牵挂点看作偏置点,给出相应的的绳系拖拽系统构型;其次,以降轨离轨过程为例,建立系统能量方程,并根据欧拉-拉格朗日方程给出系统的动力学表达式并估算系绳张紧情况下的平衡点;最后,设定离轨推力,在不同的初始角速度、系绳张紧或松弛以及不同松弛程度条件下,分析绳系拖拽离轨系统的动力学行为.研究表明,空间残骸小的初始角速度和张紧或略微松弛的系绳能够保证安全离轨.     

火箭末级离轨系统中电动力绳系释放条件分析与控制设计

绳系释放过程是电动力绳系火箭末级离轨技术的关键,开展了绳系释放条件分析及控制方案设计。首先,基于"珠式"思想,建立离轨系统绳系释放过程的刚-柔耦合动力学模型。随后,基于数值仿真开展绳系释放条件分析。仿真结果分析发现,释放时火箭末级初始姿态对绳系释放稳定性影响较大,仅靠绳系拉力控制,系统稳定裕度较小,很难保证绳系释放稳定性。据此,进一步提出了一种绳系稳定释放控制方案,并通过数值仿真验证了控制方案的有效性。     

Electric sail,photonic sail and deorbiting applications of the freely guided photonic blade

We consider a freely guided photonic blade (FGPB) which is a centrifugally stretched sheet of photonic sail membrane that can be tilted by changing the centre of mass or by other means. The FGPB can be installed at the tip of each main tether of an electric solar wind sail (E-sail) so that one can actively manage the tethers to avoid their mutual collisions and to modify the spin rate of the sail if needed. This enables a more scalable and modular E-sail than the baseline approach where auxiliary tethers are used for collision avoidance. For purely photonic sail applications one can remove the tethers and increase the size of the blades to obtain a novel variant of the heliogyro that can have a significantly higher packing density than the traditional heliogyro. For satellite deorbiting in low Earth orbit (LEO) conditions, analogous designs exist where the E-sail effect is replaced by the negative polarity plasma brake effect and the photonic pressure by atmospheric drag. We conclude that the FGPB appears to be an enabling technique for diverse applications. We also outline a way of demonstrating it on ground and in LEO at low cost.