Planning lunar observations for satellite missions in low-Earth orbit

Abstract

For Earth-observing satellites in low-Earth orbit, radiometric calibration of the sensors on-orbit is critical for maintaining consistent Earth-view (EV) retrievals as the mission progresses. Many of these satellite instruments use on-board calibration targets, EV sites, and observations of celestial targets in order to perform the sensor characterization. Among the celestial targets, the Moon is widely used across a range of Earth-observing instruments in order to perform radiometric calibration, spatial characterization, and sensor intercomparison. Since many of these instruments use satellite maneuvers in order to bring the Moon into view at a desired time, calculating the time and geometric parameters of the observations is vital for mission planning purposes. We develop a simple tool for planning such observations of the Moon and other celestial targets for instruments in low-Earth orbit based on the SPICE toolkit developed by the Navigation and Ancillary Information Facility at NASA. Given a set of satellite orbital data along with a definition of the instrument coordinates, the tool is designed to provide the timing of observations for an arbitrary view-port direction and a maneuver along an arbitrary axis relative to the spacecraft. The tool can be tested versus known lunar observations for the Aqua and Terra moderate resolution imaging spectroradiometer and the Suomi-NPP and NOAA-20 visible infrared imaging radiometer suite instruments for both roll and pitch maneuvers. We also perform simulations of lunar observations for different instrument configurations, orbits, and maneuver types in order to analyze the change in the potential lunar observations. Finally, we show a simple extension of the tool which can be used for identifying planet and star observations.

Calibrating Geosynchronous and Polar Orbiting Satellites: Sharing Best Practices

“…The first step of lunar calibration is predicting opportunities for viewing the moon through the Space View (SV) port with the spacecraft roll maneuver. The monthly scheduling steps are well described in Wilson's study [53]. After the planned lunar roll maneuver, VIIRS is able to acquire the moon through the SV port near the desired phase angle of −51 degrees.…”

Activities to Promote the Moon as an Absolute Calibration Reference

“…Opportunities for Earth-orbiting satellites to see the Moon are not costly; the Moon is sometimes observed by geosynchronous satellites in cold-space corners [26], LEO satellites can view the Moon periodically by arranging attitude maneuvers [27,28], and flagship satellites usually refrain from frequent large-angle maneuvers, but the Moon can appear unscheduled in the field of view (FOV) of satellites set up with a space-view port [29][30][31]. Such events can be predicted by spatial relations [32].…”