Systems engineering efforts in the construction of the Canadian hydrogen observatory for radio-transient detectors

The Canadian Hydrogen Observatory for Radio-transient Detectors (CHORD) will consist of 640 six-meter diameter antennas made of fiberglass composite material. The antennas will be fabricated and assembled at the Dominion Radio Astrophysical Observatory (DRAO) in Kaleden, BC, Canada, managed by the National Research Council of Canada (NRC). NRC has developed composite based single piece reflector technology over the past decade. A high degree of dimensional repeatability is key for CHORD to meet its scientific goals. This begins by manufacturing highly stable and repeatable dish molds. Subsequently, highly repeatable dishes are manufactured, components are assembled, and antennas are precisely positioned in the CHORD array. In this paper we present the antenna mechanical system, production of the antenna, top-level requirements, error definitions and verification plan, performance verification plan, and quality management plan. Since the antennas are made of composites, formulating an error budget is critical to keep track of the error allocations due to process induced errors, tooling and mold errors, and surface distortions due to gravity, wind and temperature variation. In addition, an overall pointing budget has been prepared to allocate the effect of mechanical misalignment, wind, foundation movement and other sources, etc. A Monte Carlo simulation of 1000 antennas provided the error stack up and expected precision values. A detailed verification plan is presented. Finally, the quality engineering plans are in place so that the manufacturing facility can ensure the production of the repeatable antennas through a quality assurance program. An acceptance sampling of the antennas will be conducted for metrology-based verification. A robust quality management plan is also in place to safeguard repeatability of the antenna production. The antennas will be accompanied by production data-cards, which enlist the critical configuration and process data about the antenna production and assembly operations. At the end of the pipeline, these antennas will go through verifications and acceptance tests to validate that performance requirements are met.