ALMA ANTENNA KEY SPECIFICATIONS Operational Experience of the European ALMA antennas S. Stanghellini, R. Laing, S. Rossi, W. Wild European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany SURFACE PERFORMANCE INTRODUCTION The European Southern Observatory (ESO) provided 25 high-precision 12 metre diameter antennas to the international ALMA project. After a design and protoyping phase, the AEM Consortium (European Industrial Engineering, Italy, MT-Mechatronics, Germany, and Thales Alenia Space, France and Italy) assembled, commissioned and delivered the 25 units from 2010 to 2013 at the ALMA Site in Chile. Surface accuracy less than 25 μm for all antennas independent of temperature. This poster summarizes 5+ years of accumulated operations experience of the European ALMA antennas. ALMA ANTENNA KEY SPECIFICATIONS 10.9 μm 13.7 μm The antenna specifications are set for efficient submillimetre imaging from a harsh high altitude site, maximizing availability and allowing remote operation. REMOTE OPERATION Full remote access to all antenna subsystems Remote restart after power failure Remote maintenance Sub-Reflector mechanism lubrication Azimuth and Elevation friction checks Tiltmeter Alignment check Antenna balancing Key measures to ensure redundancy include Software automatically excludes failing drive system segments Multiple encoder reading heads 11.3 μm 13.1 μm Fig. 1 Surface maps derived from holography. (a) primary surface of DA41 after setting at the OSF. (b) as (a), but after two years of operation at the AOS. (c) Surface map of DA41 for the full optics (primary and secondary) derived from astroholography at 230GHz. (d) As (c), but for antenna DA43. Overall surface accuracy error: < 25 µm rss Absolute Pointing error: < 2.0 arcsec Offset and tracking pointing errors: < 0.6 arcsec within 2 degrees and 15 minutes Fast switching error over 1.5 degree and 2.0 sec: < 0.6 arcsec On the fly mapping: scan at 0.05 deg/sec with error < 1.0 arcsec Solar observation capability System Level MTBF (Mean Time Between Failure): > 3 years Surface stability to be maintained over 5 years, including transport. RELIABILITY Key measures to promote high reliability at 5000m Careful selection of electronic components High altitude analysis to take into account lower air pressure and reduced air cooling shorter creepage distance for electrical components Despite these measures the full reliability specification has not been met. HVAC and Antenna Control Unit improvements are ongoing. MAINTENANCE MANUAL The S1000D standard, common in the aeronautic industry but new in astronomy, proved to have limitations in the field. The Atacama Large Millimeter/submillimeter Array (ALMA) is an international partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan, together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile.