Conversion of a Telecommunications Antenna into a Radio Telescope: Laser Scanner Measurements of Optics and Dish Surface Quality of a Cassegrain Antenna
Abstract
A number of countries have identified redundant large telecommunications antennas (TA) and indicated their intention to convert them into radio telescopes (RT). As the efficiency of a parabolic dish radio telescope depends on its surface quality and optical alignment, a careful assessment of these properties should be undertaken before conversion. Here, as a case study, we describe a laser scanning (LS) procedure we developed and used for the Warkworth 30m Cassegrain antenna. To investigate gravity-induced mechanical deformation of the antenna surfaces and structure, we conducted measurements at elevation angles ranging from 6 to 90 degrees. The ability of a laser scanner to survey its nominal 4π steradian surroundings allows for simultaneous study of the main and subreflectors, readily permitting a dynamic investigation of variation of the telescope optics as elevation changes occur. In particular, the method we present here allows determination of the surface quality of both main and subreflectors, the displacement between centers of the reflectors, their relative rotations and focal length variation as a function of elevation angle. We discuss details of settings, measurements, data processing and analysis focusing on possible difficulties and pitfalls. In our case study, no significant elevation-dependent surface deformation of the reflectors was observed, with the overall standard deviation of the postfit residuals varying between 1.0 and 1.7mm as elevation angle changes from 90∘ to 6∘, respectively. We, therefore, conclude that in our case both the main reflector and the subreflector, as well as the telescope optics, remain unaffected by gravitational deformation within the accuracy of the measurements, a conclusion that can possibly be extended to the similar class of TA currently considered for conversion.
- Publication:
-
Journal of Astronomical Instrumentation
- Pub Date:
- 2019
- DOI:
- 10.1142/S2251171719500107
- Bibcode:
- 2019JAI.....850010R
- Keywords:
-
- Radio telescope;
- optics;
- telecommunications antenna;
- gravitational deformation;
- laser scanner;
- principal component analysis