Mr. Brian Hoff Profile

Brian Hoff

at Alma

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Proceedings Article | 13 September 2012 Paper

66 antennas, up to 16km baselines, 5000m elevation, 28 km from support: the coming challenge of ALMA Observatory antenna group operations and maintenance

Dean Chalmers, Felipe Daruich, Brian Hoff, Cristobal Jara

Proceedings Volume 8448, 844817 (2012) https://doi.org/10.1117/12.927048

KEYWORDS: Antennas, Adaptive optics, Silver, Observatories, Phase modulation, Control systems, Inspection, Reflectors, Oxygen, Roads

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The ALMA Observatory is under construction at 5000 m above sea level on the Chajnantor plateau located in the Atacama Desert, Chile. When complete it will be comprised of 66 parabolic reflector antennas that can be configured in various arrays using a subset of 192 different stations with baselines from 15 to 16,000 m. The Antenna Group in the ALMA Department of Engineering is responsible for maintenance of the antenna mechanical, control and structural systems, antenna relocations and mechanical aspects of astronomical instrumentation exchanges. The large number of antennas, expanse, elevation, weather conditions of the Array Operation Site (AOS) and its distance from the Operations Support Facility (OSF) will make operations and maintenance for the Antenna Group a challenge. Currently, approximately half of the antennas are in place at the AOS and the first period of Early Science is underway. Operational strategies and specialized equipment developed for preventive and corrective maintenance, array reconfiguration and weather event response are being put to the test and revised based on real experience. This paper explains the operational environment, the constraints it imposes, some of the strategies and specialized equipment being developed to reduce reaction time and resources needed to maintain the array and maximize availability for science operations.

Proceedings Article | 6 August 2010 Paper

Characterization of surface tilt of foundations for high-precision radio-astronomic antennas

Brian Hoff, Jose Puga

Proceedings Volume 7733, 77333R (2010) https://doi.org/10.1117/12.857290

KEYWORDS: Antennas, Finite element methods, Chemical elements, Interfaces, Precision measurement, Astronomy, Solids, Thermal effects, Metrology, Amplitude modulation

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The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint project between astronomical organizations in Europe, North America, and East Asia, in collaboration with the Republic of Chile. ALMA will consist of at least 54 twelve-meter antennas operating in the millimeter and sub-millimeter wavelength range. It will be located at an altitude above 5000m in the Chajnantor Plateau in northern Chile. There are 192 antenna foundations under construction at ALMA's Array Operations Site (AOS). Interchangeability between foundations will permit a variety of array configurations. Foundations provide the physical interface to the bedrock, as well as to the underground signal and power cable conduits. To achieve ALMA's precision requirements, the antenna pointing angular error budget is strict with anticipated non-repeatable error on the order of a few arc seconds. This level of precision imposes rigorous requirements on antenna foundations. The objective of this study is to demonstrate the methodology of precision tilt measurements combined with finite element simulation predictions to portray the qualitative nature of the antenna foundation surface deformation. Characteristics of foundation surface tilt have been examined in detail. Although the actual foundation has demonstrated much less resistance to tilt than the finite element representation, the simulation has predicted some key characteristics of the tilt pattern. The large deviations from the ideal have incited speculations into the compliance of materials, ambiguities in the construction, thermal effects and several other aspects described herein. This research has served as groundwork to characterize ALMA's foundation surface behavior on a micro-degree level and to identify subsequent studies to pursue. This in turn has contributed to the diagnosis of antenna pointing anomalies.

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