Determination of Shadowing On the Lunar Surface Using a Lunar-Celestial Equatorial Coordinate System

Future human exploration of the lunar surface will depend on the ability to predict and model conditions for survivability during Extra-Vehicular Activity (EVAs). Estimating first-order astronaut metrics during EVAs, such as space suit temperature, transportation rover power requirements, suit heater power requirements, etc..., is necessary for the design of future space suits, transport vehicles, and other technologies involved in manned lunar surface operations. These metrics can be derived from knowledge of the locations of shadows cast by surrounding terrain for a given region of interest on the Moon. If shadow locations are known over time, they can also be used for estimation of thermal and power metrics for any technical, robotic, or solar-powered mission components on the lunar surface. Calculation of shadows based on exact sun position for lunar equatorial regions necessitated use of a Moon-centered celestial coordinate system. A Lunar-Celestial Equatorial Coordinate System is analogous to the Earth Equatorial coordinates in celestial geometry. Rather than considering the position of the Sun relative to the Moon by first comparing lunar orientation with the relative position of the Earth, this use of Moon- centered coordinates allows consideration of the path of the Sun in the sky as seen from the Moon. This enables local sun angles to be calculated in a horizontal coordinate system, just as they are for determining Sun position on the Earth. Thus, local Sun angles may be readily determined for a given time at a given point on the lunar surface, and trigonometric relationships can be used in conjunction with accurate surface elevation maps to determine whether that point is in shadow. Application of this technique can provide characterization of shadowing over any desired EVA path or exploration area of interest over time, making it possible to include thermal and power analysis of potential surface assets in a model.