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Preliminary Design of the Australian Ska Pathfinder (Askap) Telescope Control System J.C Proceedings of ICALEPCS2009, Kobe, Japan TUD001 PRELIMINARY DESIGN OF THE AUSTRALIAN SKA PATHFINDER (ASKAP) TELESCOPE CONTROL SYSTEM J.C. Guzman, CSIRO/ATNF, Sydney, Australia Abstract candidate core site. This region has been identified as The Australian SKA Pathfinder (ASKAP) is a 1% ideal for a new radio observatory. The population is very Square Kilometre Array (SKA) pathfinder radio small and hence there is a lack of man-made radio signals telescope, comprising of 36 12-metre diameter reflector that would otherwise interfere with weak astronomical antennas, each with a Focal Plane Array consisting of signals. approximately 100 dual-polarised elements operating at ASKAP will be mainly a survey telescope carrying centimetre wavelengths and yielding a wide field-of-view systematic (unattended) routine observations of the entire (FOV) on the sky of about 30 square degrees. ASKAP is southern sky. However a small amount of time will be currently under construction and will be located in the allocated for targeted observations. For more information remote radio-quiet mid-west region of Western Australia. about ASKAP project visit [3]. It is expected to be fully operational in 2013. Key Major challenges in terms of software development are: requirements for the ASKAP control system include: • Support for remote operations: Science operations control and monitoring of widely distributed devices, and main control room will be located in Sydney handling of a large number of monitoring points (approx. (~4,000 km from Boolardy). Technical/maintenance 150,000), accurate time synchronisation and remote semi- operations and data processing will be located in automated operations. After evaluating several software Geraldton. technologies we have decided to use the EPICS • Very large data flow: ASKAP will produce approx. framework for the Telescope Operating System and the 10 TB/hr of visibility data (full spectral resolution). Internet Communications Engine (ICE) middleware for Thus we cannot afford to store raw observed data. the high-level control message bus. This paper presents a • Parallel and distributed processing is vital: There is a preliminary design of the ASKAP control system as well need to run calibration and imaging pipelines in High as describing why we have chosen EPICS and ICE and Performance Computers (HPC). how both technologies fit in the overall ASKAP software • Limited computing staff: Approximately 60 FTE architecture. planned for mid-2006 to 2013. ASKAP THE PROJECT ASKAP SOFTWARE ARCHITECTURE The future of cm and m-wave astronomy lies with the Our Architecture Goals Square Kilometre Array (SKA), a telescope under The philosophy behind our system decomposition into development by a consortium of 19 countries. The SKA software components took into account three priorities: will be 50 times more sensitive than any existing radio Majority of components should be deployed in facility. A majority of the key science for the SKA will be • Geraldton. Only the strictly necessary functionality addressed through large-area imaging of the Universe at should be deployed in Boolardy because frequencies from 300 MHz to a few GHz. For more maintenance and support is more difficult and costly information about SKA, visit [1] and [2]. at the remote site. ASKAP is a next generation radio telescope on the Narrow interfaces: Services provided by each strategic pathway towards the staged development of the • component should be well defined and as simple as Square Kilometre Array (SKA). ASKAP has four goals, possible. Dependencies between components should namely: be minimal. • To carry out world-class, groundbreaking Loosely coupled: The ASKAP software system must observations directly relevant to the SKA Key • be flexible and scalable both in terms of Science Projects development, deployment and maintenance. • To demonstrate and prototype the technologies for Requirements are expected to change as more is the mid-frequency SKA, including field-of-view learned about the system, the science that will be enhancement by focal-plane phased arrays on new- done with it, and the manner in which the system technology 12-metre class parabolic reflectors will be operated. A key to fulfilling this goal is loose • To establish a site for radio astronomy in Western coupling, where dependencies are minimised and Australia where observations can be carried out free modifications have minimal effect on the system as a from the harmful effects of radio interference. whole. At a minimum, components should be loosely • To establish a user community for SKA. coupled in terms of hardware platforms, ASKAP will be located in Boolardy, a remote outback programming languages (C++, Java and Python) and mid-west region of Western Australia, approximately 400 even its implementation. km northeast of Geraldton and 800 km north of Perth. The location also corresponds to the Australian SKA Status Report 343 TUD001 Proceedings of ICALEPCS2009, Kobe, Japan Figure 1: Top-level logical view of the ASKAP system. The red boxes group the components commonly known in other projects as the Monitoring and Control (M&C) System. clear that nowadays many technologies exist that provide Logical View this type of communication infrastructure. These We have decomposed the ASKAP software system into technologies are commonly known as middleware. Our several top-level components as shown in Figure 1: requirements for the middleware are: • Executive: Responsible for orchestrating an • Multiplatform: both client and/or server running in observation. Linux and MacOSX. • Scheduler: Responsible for scheduling the • Language bindings for C++, Java and Python. observation for execution by the Executive • Support for request/response type of communication. component. • Support for publish/subscribe type of • Telescope Operating System (TOS): Responsible for communication. monitor and control of the physical telescope. This • Promote loose coupling. component will be deployed in Boolardy. • Support for fault tolerance (replication, etc.). • Central Processor (CP): Responsible for processing • Open source. observations into scientific products. • Mature project. • Data Service: Responsible for permanent and Three alternatives were evaluated in early 2009: temporary storage of data shared by the online Apache Tuscany ([4]), Apache ActiveMQ ([5]) and ICE components. ([6]) The Apache Tuscany project looks promising and • Monitoring Archiver: Responsible for archiving fulfils many of the requirements listed above but it was monitoring data generated in the system. found too immature for our needs, in particular the • Logging: Responsible for log messages generated in support for C++ bindings ActiveMQ and ICE fulfil many the system. of the requirements of our message bus. However, we • Alarm Management System: Responsible for have selected ICE over ActiveMQ primarily because of managing/escalating alarm conditions in the system. its Interface Definition Language (IDL). The benefits of • Operator Display: Responsible for presenting a User having a strict IDL are: Interface for control and monitoring of the • Eliminates ambiguity. instrument by an operator. • Avoids us having to define our own IDL between • Ephemeris Service: Responsible for providing software components. ephemeris. • Avoids us having to build our own bindings between • Radio Frequency Interference (RFI) Service: the programming language and the IDL. Responsible for identifying any RFI, which may Another reason that pushed ICE over ActiveMQ for us impact the execution of the observation. was that many of our interfaces appear to be best suited to an object oriented model. Top-level Message Bus The communication between software components is done through a message bus, as shown in Figure 1. It is Status Report 344 Proceedings of ICALEPCS2009, Kobe, Japan TUD001 THE TELESCOPE OPERATING SYSTEM • Presents a unified interface to high-level control (TOS) (easier integration). • Provide common software for hardware subsystems TOS Responsibilities developers. The main functions of the TOS are: The evaluation report also presented some limitations of EPICS: • Provides a narrow interface to other components mainly involved in observations. • It is mainly used for soft real-time control system (suggested maximum control loop rate via Channel • Coordinates the operation of many distributed and heterogeneous hardware subsystems. All hardware Access is 20 Hz). This is not an issue for us since subsystems are located in Boolardy and include: hard real-time is done via hardware. Antenna drives, receivers, local oscillators, digitisers, • Limited data types in Channel Access protocol. For beamformers, correlator, event generators, time and ASKAP there is no requirement to have a single signal distribution and environmental sensors software framework for the entire data flow system. (weather, lightning, power generator, humidity, room Complex data types are needed at the top-level temperature, etc.). where we will use a different communication middleware (ICE). • Coordinates the correct time synchronisation between hardware subsystems. • Very “narrow” client/server API with no support of request/response-type of communication. This is not • Captures telescope monitoring data and generates the visibility’s meta-data for data processing by CP an issue for us since the operation of the control component. Publishing of meta-data is synchronised system is mainly asynchronous. with integration cycle. • Handles safety operations with the instrument
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