ALMA
Manufacturing 25 antennas for the largest astronomical telescope that helped capture the first image of the black hole
Project Name: ALMA: Atacama Large Millimeter Array
Project summary: Manufacturing 600 high-precision back-up structures (BUS) segments for 25 antennas in the ALMA array
Client: Vertex Antennentechnik GmbH
Duration: 2006-2011
Project Description
In 2011, the ALMA array of 66 antennas began scientific observations of electromagnetic radiation from space to discover the cosmic origins. The high-precision radio telescopes are positioned on a 5,000 meter elevation in the Atacama Desert of northern Chile under extreme environmental conditions. Airborne was selected as one of the international partners to develop and produce high-precision components for this ambitious project. In the period 2006-2011 we manufactured the back-up structures (BUS) for 25 of the antennas in the ALMA array. The BUS is a crucial part of the telescope as it supports and maintains the shape of the reflector surface.
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- Sandor Woldendorp
- Business Unit Director - Aerospace
Customer requirements
The requirements for the BUS were very high because of the environmental conditions at 5,000 meters height in the Chilean desert. The antennas could not deform more than 25 μm under heavy wind loads, large temperature changes or gravity. That meant the BUS needed to be very stiff and thermally stable in form – which could not be met with a metal design. Therefore, the BUS is made from a carbon fiber composite (CFRP) sandwich structure. Also the sub reflector support structure is made of CFRP. Furthermore, the BUS should not degrade under the very cold and dry environmental conditions at this altitude with high UV light levels.
Working process
The BUS consists of 24 segments (pie pieces) with a very high stiffness to weight ratio and a very low thermal expansion coefficient. Since the dimensional stability of the BUS is very important, the dimensional accuracy and the repeatability of the stiffness properties should be the same for all segments. The total of 25 x 24 = 600 BUS segments needed to be manufactured in a time frame of 5 years. Every segment needed to undergo thorough inspection to rule out any defects, as repair or maintenance at a height of 5,000 meters in the desert is both difficult and expensive.
Result
Airborne designed all of the tooling, developed and optimised production processes and produced the 600 large components that were needed to build 25 antennas. A special manufacturing line was set-up and every process step of the BUS was optimized with the investment in special tooling, a large 5-axis milling machine, and a laser tracker for measuring in order to be able to guarantee an accurate segment. Most of the tooling was made from CFRP, designed and manufactured in house in order to have the same low thermal expansion coefficient as the BUS segments itself. This was needed to meet the stringent dimensional tolerances. Every segment was milled with a high accuracy 5-axis milling machine and measured with a laser tracker to ensure the right dimensions of the segments. Quality checks were implemented at every process step to ensure a defect free segment.
The entire project was completed in time. The ALMA antennas are operating perfectly, helping in the understanding of cosmic origins.
The successful collaboration between Airborne and Vertex has led to another joint assignment: the design and manufacturing of the Mirror Support Structures for two new telescopes: the CCAT-prime and SOLAT telescopes. These two next-generation telescopes will be able to facilitate even more unprecedented scientific observations, due to the innovative crossed-Dragone optical design and very high mirror surface accuracy.
