End-to-end system test and optical performance evaluation for the Solar and Heliospheric Observatory (SOHO) ultraviolet coronagraph spectrometer (UVCS)

The UVCS is one of the instruments carried by the Solar and Heliospheric Observatory (SOHO), a joint NASA/ESA Spacecraft launched in November 1995. It is designed to perform ultraviolet spectroscopy and visible light polarimetry of the extended solar corona. The primary scientific objectives of the UVCS investigation are to study the physical processes occurring in the extended solar corona, such as: the mechanism of acceleration of the solar wind, the mechanism of coronal plasma heating, the identification of solar wind sources, and the investigation of the plasma properties of the solar wind. The UVCS End-to-End test activities included a comprehensive set of system level functional and optical tests. Although performed under severe schedule constraints, the End-to-End System Test was very successful and served to fully validate the UVCS optical design. All test results showed that the primary scientific objectives of the UVCS Mission were achievable. Following an introductory description of the UVCS Instrument, this paper describes the preliminary UVCS AIV activities, and the rationale for performing the end-to-end system test. The process for the selection of the most appropriate facility for the test is then summarized. The SAO laboratory is then described, as well as the preliminary work that was necessary to be performed to enhance the laboratory test environment. This includes the design, fabrication and installation of a special cryogenically cooled shroud for the vacuum chamber, and upgraded cleanroom facilities. The test philosophy, performance goals, and a summary of the test results are also given.