Motion of a space tether system in the atmosphere

The space tether system under consideration consists of two rigid bodies with significantly different ballistic coefficients. Because of this difference one of the bodies acts as a stabilizer for the main body – a spacecraft – during the motion of the tether system in the atmosphere. The investigations are focused on the stability of motion of the tether system in the atmosphere. During its motion in the atmosphere the tether system makes use of torques from aerodynamic forces to maintain a desired orientation. This aerodynamic method of stabilization is passive and does not require energy expenses. Such a tether system can be used to stabilize the motion before landing onto the surface of Earth or other planets with atmospheres. The aerodynamic tether system is helpful for returning payloads from outer space, especially using small landing modules. It is also possible to utilize in the removal of space debris by reducing the altitude of their orbits. By achieving the spacecraft motion stability during descent the tether system enables a reduction in the target landing area at the final stage of the descent. The modelling of motion of the tether system includes two parts – (i) the deployment of the tether system, and (ii) the descent of deployed tether system through the dense layers of the atmosphere. The motion of the deployed tether system is investigated with regard to the terms of its stability. The tether system can be in stable motion even if either or both bodies are statically unstable. The stability of the system is assessed relative to the parameters – the mass, the geometrical dimensions of the bodies and the length of the tether. It is found that increasing the length of the tether, as a controlled part of the deployment process during descent, can provide an additional stabilizing factor for the tether system. The model of the deployment process, based on the model of an elastic tether, represents the tether as a set of nodes with mass and with elastic connections. The control of the deployment is based on the length and the rate of change of the length of the tether. The aerodynamic resistance of the tether and its mass characteristics are both taken into consideration during modelling of the deployment. The described and numerically realized mathematical models allows the parameters for the space tether system motion in the atmosphere to be determined