RESTORE OF AZIMUTHAL ROTATION AXIS
In Italy, in the ’60s and ’70s, the CNR (National Research Committee) ordered to a U.S. company specialized in the sector the construction of two parabolic antennas (radio-telescopes) of 32 meters in diameter,which were installed in Medicina (Bologna) and in Noto (Syracuse), and a parabolic antenna, smaller than 18 meters in diameter, installed in Matera; they constituted an integrated system of radio telescopes for astronomical observation and reception of signals from deep space in the invisible radio frequencies range.
To these antennas, another one has been recently added of 64 meters in diameter, which is currently nearing completion in San Basilio (Cagliari); It’s thus realized the integrated system distributed throughout the national territory, one of the most modern and advanced integrated system of radio telescopes in the world for radio frequencies not only for the equipments it offers, but above all due to the professionalism of the technicians of the current INAF (National Institute for Astrophysics), recognized by the international scientific community.
The parabolic antenna of Noto, in particular, due to the age and the geological conditions of the specific area where it lies, starting few years ago, has shown signs of aging and, in particular, the entire azimuthal rotation system does not guarantee any more the required the accuracy during normal operation; the concrete foundation in which the circular rails are embedded, on which the whole antenna rotates, supported by special 2+2 wheelboxes, the wear developed in time between the rails and the wheels of the same wheelboxes, the mechanical transmissions performing the azimuthal rotation, and a whole series of technical problems of pure mechanical nature led INAF to consider the need for a work of complete restoration of the whole system of azimuthal rotation of the radio-telescope.
The official announcement for the procurement of these works was awarded in July/August 2011 to GALBIATI GROUP, which has taken charge of the entire operation, in collaboration with specialized technicians working at the site of Noto coordinated by A. POINT of Rome; mobile precision measuring instruments are used, and all the production capacities at the workshops in Oggiono (LC) are used together with the super modern control equipment that the company has (dimensional control desk ZEISS 3500 X 6000 X 2500 at controlled temperature, computerized LASER TRACKER). 300 days from the signing of the contract, to carry out the whole operation, were granted to INAF by GALBIATI GROUP.
The raw material, in special Cr Mo alloy steel, for the realization of new rails of the parabolic antenna, had to be procured in the United States, shipped and transported by sea to La Spezia, then to Oggiono for subsequent bending operations (in the required circularity request) and the subsequent mechanical processing to achieve the high accuracy required.
Wheels and azimuthal rotation axes of the antenna are produced from scratch, by using the most modern NiCrMo steel to increase the surface hardness compared to the original wheels, and thus ensure a longer life and reduced wear over time.
Other mechanical dparts, dismantled from the current antenna current, after a careful revision will be reused, provided those eventual minor modifications to optimize their use.
The site in Noto was opened in early September, after implementing the necessary protections for the safety of operators and once acquired all the existing measurements and geometries for comparison with similar theoretical ones envisaged in the project and to compare them with the geometries which will be found at the end works; such measurements carried out with the required accuracy have confirmed the substantial status of breakdown of the whole azimuthal rotation system of the parabolic antenna.
One of the most delicate phases of the entire operation was one relative to the lifting (in safety and with all due cautions) of the entire antenna structure (over 200 tons) by the means of hydraulic jacks appropriately modified for that purpose and properly positioned so as to compensate the position of centre of gravity of the structure itself, not perfectly centred with respect to vertical axis thereof.
Once done, and once stiffened in safety for the entire duration of the recovery operations, both of civil works and of the mechanical details, it has been possible to disassemble the current wheelboxes and connected mechanical transmissions of the antenna; it was then possible the dismantling of special expanded mortars in which, in due course, the worn rails were sunk and thus the dismantling of the rails themselves and the their supporting plates.
In mid-October, on site works were addressed to prepare the implementation of new plates and their alignment, the casting of the new expansive mortar and everything necessary for the installation of the new rails.
At the workshops in Oggiono, new rails, new gears and their accessories were realized, together with all the mechanical parts of the parabolic antenna that were reused (as provided in the technical specifications of the contract); all controlled and pre-assembled at GALBIATI GROUP workshops in the presence of the INAF inspectors before being transported to Noto for the implementation.
GALBIATI GROUP in collaboration with A. POINT has paid maximum attention to all the recovery operations of the azimuthal rotation of the antenna, both at the same site in Note and at the workshops in Oggiono, aand collaboration with managers of INAF resulted positive and proactive under all points of view. It was common task, beyond the mere contractual terms, that the final result came positive and perfectly satisfying to confirm the professionalism acquired by GALBIATI GROUP in the specific field of antennas and radio telescopes, to constitute a more positive reference in addition to the many already acquired and relative to achievements worldwide, and to further increase the so high professionalism in an area as specific and as fascinating as the one of radio astronomy.
It will be our care and concern to update the situation at the time of final re-assembly.