This activity was coordinated with scans conducted by the Mercury Dual Imaging System (MDIS) and the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instruments (shown as the wider patterns near the bottom of the image) in order to co-align the instruments and the spacecraft inertial reference frame. The crosshairs show the calculated position of Mercury, while the circle is a fit to the crescent shape of the planet as determined by the MLA measurements. The offset between the crosshairs and the center of the circle is only roughly 0.05 mrad, which is well within the 0.4-mrad field of view (FOV) of the MLA detector, shown in the top left corner of the image. The MLA detector FOV is designed to allow the altimeter receiver to cover the 0.08-mrad-diameter laser spot when the instrument is within a range to the planet of 1800 kilometers (1100 miles), so it produces a somewhat blurry image at the much greater distance of this image. Observations such as this one continue to improve the calibration of the MESSENGER spacecraft and its science payload.
Credit: NASA/Goddard Space Flight Center/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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