Updated 1 March 2012 Mechanical design and integration of the support structure for the Reionization And Transients InfRared instrument RATIR Alejandro Farah *a , J. Jesús González a , Alexander S. Kutyrev b , Gennadiy Lotkin b , Alan M. Watson a , Nathaniel R. Butler c , William H. Lee a , Michael Richer d , Eduardo López d , David Clark d , Gerald Cabak e , Ori D. Fox b , David A. Rapchun b , Carlos Román-Zúñiga d , Leonid Georgiev a a Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 70-264, 04510, Mexico, D.F., Mexico; b NASA Goddard Space Flight Center, MS 665, Greenbelt, MD, USA; c School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA; d Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 106, 22800, Ensenada, Baja California, Mexico; e University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064, USA; * farah@astro.unam.mx ABSTRACT In this article we present the mechanical design and the manufacturing of the support structure for the Reionization And Transients InfraRed (RATIR) camera. The instrument is mounted at the f/13 Cassegrain focus of the 1.5-meter Harold Johnson telescope of the Observatorio Astronómico Nacional at San Pedro Mártir ( OAN/SPM) in Mexico. We describe the high-level requirements and explain their translation to the mechanical specifications and requirements. We describe the structural finite-element analysis and the boundary conditions, loads, and general assumptions included in the simulations. We summarize the expected displacements, rotations and stresses. We present the optomechanical components and the elements used to attach the instrument to the telescope. Finally, we show the instrument installed on the telescope. Keywords: design, manufacturing recommendations, integration 1. BRIEF DESCRIPTION AND REFERENCES The RATIR instrument was designed and constructed by the University of California, the Universidad Nacional Autónoma de México, and the NASA Goddard Space Flight Center 1-5 . The instrument is intended to obtain photometry in riZYJH filters of gamma-ray bursts identified by the Swift and Fermi satellites. When not observing gamma-ray bursts, RATIR will be used by the wider Mexican astronomical community. The instrument was recently mounted at the f/13 Cassegrain focus of the 1.5-meter Harold Johnson Telescope of the OAN/SPM and us currently undergoing commissioning and testing. In this paper we describe the mechanical support structure of the instrument and the mounts for the two warm dichroics. 2. MECHANICAL DESIGN The optical design of RATIR was carried out using the Zemax ® software and the mechanical design using SolidWorks ® . The format used for the translation between them was IGES format (Initial Graphics Exchange Specification) due the absence of direct link between Zemax and SolidWorks. We recommend avoiding excluding ray traces of the beam