The MESSENGER Visible and Infrared Spectrograph: Design, calibration, and analysis of lunar observations

The subjects of this thesis are the design analysis, calibration, and use of the Visible and Infrared Spectrograph (VIRS). This device is one component of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument for MESSENGER, NASA's first orbiting mission to the planet Mercury. Science goals and the typical limitations of spaceflight instrumentation combine to shape the VIRS design. A summary of these competing factors is presented along with raytrace simulations which detail the optical imaging performance. Careful ground calibration of scientific instruments is critical to the analysis of returned flight data. The laboratory calibration experiments which quantify VIRS characteristics are described and the results presented. Mercury has been shown to possess composition and surface properties similar to those of the Moon. In an effort to validate the performance of VIRS, reflectance spectra of the Moon were acquired with an engineering model of the device from a ground-based telescope. These measurements are shown to be consistent with data sets from other ground-based observations and observations from the Clementine spacecraft. The ability of VIRS to accurately measure spectra from compositionally distinct materials is demonstrated. TiO2 is an important indicator of rock type on the Moon. It is hypothesized that an ultraviolet color ratio may provide a direct measure of TiO2 abundance. This metric, as calculated from the ground-based lunar measurements of the VIRS engineering model, is found to provide a simple, linear association with TiO2 content. One year after the MESSENGER spacecraft was launched, an Earth-swingby maneuver provided an in-flight calibration opportunity for the flight, VIRS. Disk-integrated lunar spectral radiance is compared with extrapolated nearside measurements from other investigators.