The Mariner Mars '71 mission was planned to consist of two spacecraft on complementary missions, but due to the failure of Mariner 8 to launch properly, only one spacecraft was available. Mariner 9, launched on May 30, 1971, combined mission objectives of both Mariner 8 (mapping 70 % of the Martian surface) and Mariner 9 (a study of temporal changes in the Martian atmosphere and on the Martian surface). For the survey portion of the mission, the planetary surface was to be mapped with the same resolution as planned for the original mission, although the resolution of pictures of the polar regions would be decreased due to the increased slant range. The variable features experiments were changed from studies of six given areas every 5 days to studies of smaller regions every 17 days.    The scientific objectives of the ultraviolet spectroscopy experiment for the Mariner Mars '71 orbital missions were divided into two categories: (1) ultraviolet cartography, the mapping of the surface and lower atmosphere in the ultraviolet spectral region; and (2) ultraviolet aeronomy, the study of the composition and structure of the upper atmosphere using the techniques of ultraviolet spectoscopy. The ultraviolet cartography measurements were accomplished by pointing the spectrometer at the illuminated disk of Mars. The upper atmospheric measurements required the use of different geometries in order to view the upper atmosphere and to discriminate against the bright, lower atmosphere of Mars.

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