MUSTANG 2 is a 223 element focal plane that operates between 75 and 105 GHz on the 100 meter Green Bank Telescope. It shares many of the science goals of its predecessor, MUSTANG, but will have fifteen times the sensitivity and five times the field-of-view. Angular scales from 900 to 60 will be recovered with high fidelity providing a unique overlap between high resolution instruments such as ALMA and lower resolution single dish telescopes such as ACT or SPT. Individual TES bolometers are placed behind feedhorns spaced by 1.9λ f and are read out using a microwave SQUID multiplexing system.
EtherCAT (Ethernet for Control Automation Technology) is gaining wide spread popularity in the automation
industry as a real time field bus based on low cost, Ethernet hardware. EtherCAT maximizes use of 100Mbps Ethernet
hardware by using a collision free ring topology, efficient Ethernet frame utilization (> 95%), and data exchange "on the
fly". These characteristics enable EtherCAT to achieve Master to Slave node data exchange rates of > 1000 Hz.
The Green Bank Telescope, commissioned in 2000, utilizes an analog control system for motion control of 8
elevation and 16 azimuth motors. This architecture, while sufficient for observations at frequencies up to 50GHz, has
significant limitations for the current scientific goals of observing at 115GHz. Accordingly, the Green Bank staff has
embarked on a servo upgrade project to develop a digital servo system which accommodates development and
implementation of advanced control algorithms.
This paper describes how the new control system requirements, use of existing infrastructure and budget
constraints led us to define a distributed motion control architecture where EtherCAT real-time Ethernet was selected as
the communication bus.
Finally, design details are provided that describe how NRAO developed a custom EtherCAT-enabled motor
controller interface for the GBT's legacy motor drives in order to provide technical benefits and flexibility not available
in commercial products.
MUSTANG is a 90 GHz bolometer camera built for use as a facility instrument on the 100 m Robert C. Byrd
Green Bank radio telescope (GBT). MUSTANG has an 8 by 8 focal plane array of transition edge sensor
bolometers read out using time-domain multiplexed SQUID electronics. As a continuum instrument on a large
single dish MUSTANG has a combination of high resolution (8) and good sensitivity to extended emission
which make it very competitive for a wide range of galactic and extragalactic science. Commissioning finished
in January 2008 and some of the first science data have been collected.
The Penn Array Receiver (PAR) is a camera designed for rapid, high angular resolution imaging at 90 GHz (3.3 mm). When installed on the 100 m Green Bank Telescope it will have a 32" × 32" field of view and 8" resolution. PAR has an eight by eight planar array of superconducting Transition Edge Sensor bolometers. Currently it is in the commissioning phase and after that it will become a user instrument capable of mapping a 5' × 5' area of sky to a noise level of 40 μJy in one hour.
The enterprise architecture presents a view of how software utilities and applications are related to one another under unifying rules and principles of development. By constructing an enterprise architecture, an organization will be able to manage the components of its systems within a solid conceptual framework. This largely prevents duplication of effort, focuses the organization on its core technical competencies, and ultimately makes software more maintainable. In the beginning of 2003, several prominent challenges faced software development at the GBT. The telescope was not easily configurable, and observing often presented a challenge, particularly to new users. High priority projects required new experimental developments on short time scales. Migration paths were required for applications which had proven difficult to maintain. In order to solve these challenges, an enterprise architecture was created, consisting of five layers: 1) the telescope control system, and the raw data produced during an observation, 2) Low-level Application Programming Interfaces (APIs) in C++, for managing interactions with the telescope control system and its data, 3) High-Level APIs in Python, which can be used by astronomers or software developers to create custom applications, 4) Application Components in Python, which can be either standalone applications or plug-in modules to applications, and 5) Application Management Systems in Python, which package application components for use by a particular user group (astronomers, engineers or operators) in terms of resource configurations. This presentation describes how these layers combine to make the GBT easier to use, while concurrently making the software easier to develop and maintain.