Airborne Composites, The Netherlands, is selected as contractor for the delivery of 25 12 meter diameter CFRP Back Up Structures for the ALMA project in Chili. This 6 year contract is awarded by Vertex Antennentechnik GmbH in Duisburg, Germany.
The Atacama Large Millimeter Array, or ALMA, is an international collaboration to develop a world-class telescope array to study the universe from a site in the foothills of Chile"s Andes Mountains. Each of ALMA"s antenna dishes will measure 12 m wide. The ALMA antennas will be movable.
At its largest, the array will measure 14 km, and at its smallest, only 150 m. ALMA"s location in the Atacama Desert is one of the highest, driest places on Earth, making it ideal for astronomical research at sub-millimeter wavelengths and frequencies up to 950 GHz, which are absorbed by atmospheric moisture. ALMA will be located in this specific desert of northern Chile on the high-altitude (5000m) Zona de Chajnantor, east of the village of San Pedro de Atacama in Chile. When completed (in 2011), ALMA will be the largest and most capable imaging array of telescopes in the world.
In March, 2000, Vertex Antennentechnik started the design and manufacturing of the ALMA prototype antenna. This antenna was installed at the ALMA Test Facility (ATF) on the VLA site in New Mexico in November 2002.
The ALMA Test Facility (ATF) serves two purposes: it is the test bed upon which the ALMA prototype antennas are evaluated and it serves as a platform for ALMA prototype instrumentation and software testing. Each of the two prototype antennas (US and Europe) has been evaluated using a uniform set of criteria which gauge their relative performance. The evaluation of the two ALMA prototype antennas is concluded in May 2004.
The supporting structure (BUS) of the primary structure has the shape of a symmetrical parabolic, composed of 24 identical segments composed out of carbon fiber and aluminum honeycomb sandwich segments. The design is optimized for maximum temperature stability (minimum CTE).
The Airborne program will start with a material qualification program involving various tests e.g. compression, strength in different fiber directions, including 3 & 4 point bending. The next step will be creation of a 3D CAD model of the segments master mould by the Airborne engineering department. 3D laser measurement has to confirm that the shape of the mater mould will be within the required tolerances. The negative mould will be made with tooling prepreg and manufactured by Airborne with autoclave cure process. The manufacturing process of the BUS segments consists of cutting and labeling the prepreg with an automated prepreg cutter, hand lay-up in the CFRP mould and co-curing ribs and stringer panels flat autoclave tables. A separation layer between the prepreg and the honeycomb is part of the configuration, in order to achieve the necessary corrosion protection. Curing will be done in an autoclave (2.65m x 13.5m). All rib and stringer panels will be CNC machined before bonding into the segments. After trimming of the segments, the CFRP tubes with INVAR inserts and ribs are bonded into the segments.
The CFRP center hub of the BUS will be produced with the winding machine of Airborne, as will also the CFRP tubes in the segments. The quadrapod structure is produced by using prepreg materials and curing in a dedicated oven system. This structure exists of 4 segments of 4,5 x 5,5 m connected together into a CFRP center headpart. The last step is the integration of the back-up structure followed by a 3D measurement of the entire structure as part of the client approval. All CFRP components will be containerized and shipped by sea to be installed on the Atacama Desert in Chili.
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