The upper and lower modules of the XMM's Structural and Thermal Model (STM) are mated in one of ESTEC's cleanrooms in preparation for alignment, vibration and acoustic testing. ESA's X-ray Multi-Mirror (XMM) high-throughput X-ray spectroscopy mission will be launched by Ariane-5 in 1999. [Image Date: 1998/02] [98.02.005-087]