Thermoforming Methods Applied to Radio Reflector Manufacture

Abstract

The first detection of radio waves from an astronomical object was in 1933 by Karl Jansky, when he reported radiation coming from the Milky Way at the Bell Telephone Laboratories. Very important discoveries have been observed using radio telescopes; from the microwave background radiation, one of the most important pieces of evidence for the Big Bang theory, to the latest image of a black hole captured by an international network of radio telescopes called the Event Horizon Telescope. Since astronomical radio sources (i.e. stars, nebulas and galaxies) are very far away, the radio waves that comes from them are very weak, requiring radio telescopes to have large reflective areas to collect enough radio energy to study them. Radio telescopes have typically large parabolic dish antennas, segmented in panels with different surface shape quality requirements proportional to the frequency of the radio signal observed. Different manufacturing methods have been used for microwave antennas. From flat panels made from a metallic mesh forming a gigantic spherical dish like the Arecibo Observarory, to the high precision electroformed panels done for the ALMA submillimetric telescopes. This doctoral dissertation project explores the electromagnetic radiation in the first chapter review, explaining the nature of light and particularly radio waves. It also review the radio telescopes optics, their main components and give some examples, including the ones visited by the author around the USA and Europe. Finally, the author explore different manufacturing methods commonly used in the production of radio reflector panels. On the second chapter, a method derived from Dr. Roger Angel glass slumping technology is explored to manufacture thermoformed reflector panels. The method, consisting of heating up a flat metallic sheet to reduce its yield strength and placing it into an adjustable mold to shape it into the required curvature. The third chapter propose a different method called Electromagnetic Thermoforming, that uses a pancake shaped induction coil to induce eddy currents in a flat panel. This eddy currents heat up the panel and create a electromagnetic force that helps shaping the panel placed on top of a mold. In both cases, the radiative oven and electromagnetic thermoforming, examples panels were produced and compared. Finally, the third chapter relates the proposal made to use the thermoforming methods reviewed in the previous chapter to produce the reflective panels for the Next Generation Very Large Array, promoted by the National Radio Astronomy Observatory. This chapter includes panel design details, including the wind drag and thermal induced deformation, and a production line design to estimate the cost to build a radio telescope prototype.