Sun Angles If these camera angles represented sun angle, then for equatorial missions......

(1) At sundown, the robot will generate generous power and cooling by orienting arrays toward the sun. The robot won't experience such low angle in the morning, since landing doesn't occur for an earth-day after lunar dawn. On the Tranquility Trek mission, the robot will experience sundown, but not sunrise.

(2) At all elevations, power and cooling are adequate when the sun impinges from the side or front quarter.

(3) At one earth-day before lunar noon, if the sun impinges from the radiator end, then the robot will turn 180 degrees for better power and cooling. This orients arrays generally toward the sun, and it orients the radiator generally away from the sun. That does not dictate direction of travel, since driving is bi-directional, and off-axis driving azimuth is common. Half-turns are useful for maintaining highest power-to-cooling ratio. Spinning makes no difference at lunar noon, when the sun is top-down. When the sun is overhead, thermal loads are highest, though cooling is still adequate, and solar power is sufficient.

(4) Best power generation occurs when the robot is driving toward a sun that is elevated mid-morning and mid-noon. In that configuration, solar impingement illuminates the entire array, and much of that insolation is at favorable incidence.

From AstroboticBlogPhotos