The main job of a star tracker is to snap images of the surrounding star field so that the spacecraft can internally calculate its orientation in space. It completes this task many times per minute. The accuracy of each of LADEE’s instrument’s measurements depends on the star tracker calculating the precise orientation of the spacecraft.
“Star tracker cameras are actually not very good at taking ordinary images,” said Butler Hine from NASA’s Ames Research Center in Moffett Field, California. “But they can sometimes provide exciting glimpses of the lunar terrain.”
Given the critical nature of its assignment, a star tracker doesn’t use ordinary cameras. Star trackers’ lenses have a wide-angle field of view in order to capture the night sky in a single frame.
The images shown here were acquired February 8, 2014, while LADEE was carrying out atmospheric measurements. The series of five images were taken at one-minute intervals and caught features in the northwestern hemisphere of the Moon. LADEE was traveling approximately 60 miles (100 kilometers) per minute along its orbit. All images were taken during lunar night, but with earthshine illuminating the surface.
The initial image captured the smooth-floored crater Krieger, about 14 miles (23km) in diameter, on the horizon, with 4-mile-wide (7km) Toscanelli in the foreground.
The second image shows Wollaston P, about 2.5 (4km) diameter, near the horizon and the southeastern flank of the lunar mountain Mons Herodotus.
The third image caught a minor lunar mountain range, Montes Agricola, which is northwest of the large bright crater Aristarchus, as well as the flat-floored crater Raman, about 6 miles (10km) diameter.
Image four in the series captured Golgi, about 4 miles (6km) in diameter, and 3-mile-wide (5km) Zinner.
The final image views craters Lichtenberg A and Schiaparelli E in the smooth mare basalt plains of Western Oceanus Procellarum, west of the Aristarchus Plateau.
The star trackers will operate while LADEE continues to measure the chemical composition of the atmosphere, collect and analyze samples of lunar dust particles in the atmosphere, and hope to address a long-standing question: Was lunar dust, electrically charged by sunlight, responsible for the pre-sunrise glow above the lunar horizon observed during several Apollo missions? And who knows? The star trackers may help answer that question.