The axes servo control of optical telescopes and antennas acts in two typical phases: the slew to a new target and the subsequent accurate tracking of the source. Although the tracking error minimization is paramount, a good design of the slewing phase is needed as well. In fact, saturations of velocity and acceleration can easily occur during telescope slew, introducing non-linearities in the control system which may lead to undesired behaviors. Also, sudden accelerations may trigger vibrations of the telescope structure, which may increase the slew time or even prevent a stable target acquisition. In this paper, a command pre-processor is adopted to provide recursively a valid path to reach the assigned target, never exceeding the specified rate and acceleration limits. Different generation methods are considered, with different degrees of smoothness and slewing time. Numerical simulations show their main features in different test cases, for both radio and optical telescopes.
A novel version of digital hardware Italian Tile Processing Module (ITPM) 1.6 has been released for the Low-Frequency Aperture Array (LFAA) component of the Square Kilometre Array (SKA). This back-end includes two plugged-in main blocks, as an analog device , the Pre-ADU board, and an Analog to Digital Unit (ADU), a 6U board containing sixteen dual-inputs Analog to Digital Converters and two Field Programmable Gate Array (FPGA) devices, capable of digitizing and processing 32 RF input signals (50-650 MHz). We present the main features of the upgrade of the board compared to previous versions: there are new and high performance components improving processing capability, mechanical changes matching the design of the housing sub-rack and finally a general reduction of the overall power consumption. The ITPM ADU 1.6 version, now in engineering phase together with its sub-rack system, is currently the last prototype before the design of the industrial line for mass production, necessary for the LFAA deployment. Results of system performances will be presented.
The SKA LOW telescope is an interferometer composed of 512 stations. Each station consists of 256 electronically steered antennas. The Low Frequency Aperture Array is the portion of the SKA-LOW telescope including the antennas and the related electronics. The LFAA signal processing chain amplifies, transports and combines the signals from the antennas composing each station into a coherent beam. Beamforming is performed in the frequency domain, with stringent requirements on bandpass flatness, linearity in a RFI contaminated spectral region, and allowed signal degradation. We adopted an architecture including a highly optimized oversampled polyphase filterbank for channelization, and a distributed network beamformer. The system has been validated as part of the Aperture Array Verification System, a single station operating at the SKA site in Western Australia.
The Square Kilometer Array (SKA) project aims at building the world’s largest radio observatory to observe the sky with unprecedented sensitivity and collecting area. In the first phase of the project (SKA1), an array of dishes, SKA1-MID, will be built in South Africa. It will consist of 133 15m-dishes, which will include the MeerKAT array, for the 0.350-20 GHz frequency band observations. Each antenna will be provided with a local monitor and control system (LMC), enabling operations both to the Telescope Manager remote system, and to the engineers and maintenance staff; it provides different environment for the telescope control (positioning, pointing, observational bands), metadata collection for monitoring and database storaging, operational modes and functional states management for all the telescope capabilities. In this paper we present the LMC software architecture designed for the detailed design phase (DD), where we describe functional and physical interfaces with monitored and controlled sub-elements, and highlight the data flow between each LMC modules and its sub-element controllers from one side, and Telescope Manager on the other side. We also describe the complete Product Breakdown Structure (PBS) created in order to optimize resources allocation in terms of calculus and memory, able to perform required task for each element according to the proper requirements. Among them, time response and system reliability are the most important, considering the complexity of SKA dish network and its isolated placement. Performances obtained by software implementation using TANGO framework will be discussed, matching them with technical requirements derived by SKA science drivers.
Proc. SPIE. 9914, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII
KEYWORDS: Principal component analysis, Zinc, Fourier transforms, Interference (communication), Field programmable gate arrays, Space telescopes, Signal processing, Galactic astronomy, Signal detection, Stochastic processes
SETI, the Search for ExtraTerrestrial Intelligence, is the search for radio signals emitted by alien civilizations living in the Galaxy. Narrow-band FFT-based approaches have been preferred in SETI, since their computation time only grows like N*lnN, where N is the number of time samples. On the contrary, a wide-band approach based on the Kahrunen-Lo`eve Transform (KLT) algorithm would be preferable, but it would scale like N*N. In this paper, we describe a hardware-software infrastructure based on FPGA boards and GPU-based PCs that circumvents this computation-time problem allowing for a real-time KLT.
We present a project aimed at realizing an Italian aperture array demonstrator constituted by prototypical Vivaldi antennas designed to operate at radio frequencies below 500 MHz. We focus on an array composed of a core plus a few satellite phased-array stations to be installed at the Sardinia Radio Telescope (SRT) site. The antenna elements are mobile and thus it will be possible to investigate the performance in terms of both uv-coverage and synthesized resolution resulting from different configurations of the array.
We present the status of the Sardinia Radio Telescope (SRT) project, a new general purpose, fully steerable 64 m
diameter parabolic radiotelescope capable to operate with high efficiency in the 0.3-116 GHz frequency range. The
instrument is the result of a scientific and technical collaboration among three Structures of the Italian National Institute
for Astrophysics (INAF): the Institute of Radio Astronomy of Bologna, the Cagliari Astronomy Observatory (in
Sardinia,) and the Arcetri Astrophysical Observatory in Florence. Funding agencies are the Italian Ministry of Education
and Scientific Research, the Sardinia Regional Government, and the Italian Space Agency (ASI,) that has recently
rejoined the project. The telescope site is about 35 km North of Cagliari.
The radio telescope has a shaped Gregorian optical configuration with a 7.9 m diameter secondary mirror and
supplementary Beam-WaveGuide (BWG) mirrors. With four possible focal positions (primary, Gregorian, and two
BWGs), SRT will be able to allocate up to 20 remotely controllable receivers. One of the most advanced technical
features of the SRT is the active surface: the primary mirror will be composed by 1008 panels supported by electromechanical
actuators digitally controlled to compensate for gravitational deformations. With the completion of the
foundation on spring 2006 the SRT project entered its final construction phase. This paper reports on the latest advances
on the SRT project.