Dynamics and control of a novel radio telescope antenna

This paper presents a mathematical and computer model of the triple-tethered aerostat proposed to support the receiver in a very large radio telescope antenna. The dynamics model considers the system as a set of three (or more) tethers, attached at fixed points on the ground, which come together at a spherical confluence point in which the receiver is located. Also attached to the confluence point is a leash tied to an aerostat overhead. The aerostat provides the necessary lifting force to keep the system aloft. At the ground attachment points, winches pull on the tethers to maintain the confluence point at its desired location. To investigate the performance of this system, we assembled a numerical model of its equations of motion. The tethers and leash were discretized into a number of elements using a lumped mass approach. The effects of cable stiffness, internal damping, gravity and aerodynamic drag as well as winds and turbulence were included in the model. The spherical confluence point and aerostat were modeled to include the effects of aerodynamic forces, as well as gravity and buoyancy. A controller was then developed to control the tether lengths in response to errors in the receiver position from a desired location. The complete system of almost 200 simultaneous first-order differential equations was formulated and solved numerically using a fourth-order Runge-Kutta integration scheme. Numerical experiments on this system indicate that the system can be accurately controlled in the presence of disturbances and that the concept warrants further study.