The Large Adaptive Reflector: A Giant Radio Telescope with an Aero Twist

A multi-national grouping of radio astronomers has identified the need for a major new instrument, called the Square Kilometer Array (SKA), to be constructed in the coming decade. This giant radio telescope will be 100 times more powerful than any in existence today. The innovative Canadian concept for the underlying design of the telescope, the Large Adaptive Reflector (LAR), is among the best candidates and is well positioned to be adopted by the international community. The LAR is a concept for a low-cost, large-aperture, wideband, radio telescope, designed to operate over the wavelength range from 2mt o 1.4 cm. Theproposed design for the LAR includes two central components. The first is a long focal length, large-diameter parabolic reflector, composed of actuated hexagonal panels, mounted on the ground. The second component is a focal package supported at a height of 500 m by a large helium balloon (aerostat) and a system of three or more taut tethers. The telescope is steered by simultaneously changing the lengths of the tethers with winches (thus changing the position of the feed) and by modifying the shape of the reflector. Simulations have shown that in operating wind conditions, the position of the feed platform can be stabilized to within a few centimetres. This paper gives an overview of the present state of the LAR design, with an emphasis on the airborne subsystem. Construction of a 1/3-scale model of the tethered aerostat subsystem, with a footprint of "only" 0.5 km 2 , is presently underway in Penticton, B.C. It will allow a validation of the underlying design and the study of some fascinating issues in the design and control of this system. Continued on page 240