AeroCube-4 Captures Images of the Moon’s Shadow
One of Aerospace’s CubeSats captured a photo of the moon’s shadow on Earth’s surface during the solar eclipse that occurred on Nov. 3.
This solar eclipse began at 11 a.m. UTC and lasted for about two hours, with the shadow of the moon tracing a thin path that began in the Atlantic near Bermuda, crossed the ocean in a southeasterly direction, and ended over central Africa.
The image shows the umbral and penumbral shadows of the moon. The dark center of the circle—the umbra—is 50-100 km wide, and the penumbra extends another 100+ km beyond that. The image was taken while the shadow was passing over the Atlantic ocean south of Liberia and the Ivory Coast.
The photo was taken by the 1.0 kilogram AeroCube-4 satellite that Aerospace built and operates to support the Space and Missile Systems Center Development Planning Directorate. AeroCube-4 was launched in September 2012, has been on orbit for over 13 months, and has captured over 2000 images of the Earth’s surface.
It is possible to calculate the orbital motion of the moon, and the corresponding paths of solar eclipses, many centuries into the future or past. For CubeSats in low earth orbit, however, orbital forecasts are precise only for days or weeks, at best. In the four weeks leading up to the solar eclipse of Nov. 3, orbital forecasts showed that AeroCube-4 would fly close enough to the eclipse path to obtain photographs of the moon’s shadow on the Earth’s surface.
The Aerospace PicoSat team developed an imaging plan for the eclipse, including timing and pointing instructions. The plan was uploaded to the satellite the day before the eclipse and executed autonomously as the satellite flew closest to the shadow. At the time the photo was taken, AeroCube-4 was west of the moon shadow, flying in a northeasterly direction. The view in the photo is toward the southeast, with part of the West African mainland visible at the top of the image.
The photo was taken using the AeroCube-4 fisheye lens, which has a field of view greater than 180 degrees. Visual distortion due to the fisheye is exaggerated in the image towards the edges of the photo. On the outermost perimeter of the photo, parts of the lens casing are also visible.
AeroCube-4 used an Earth nadir sensor, sun sensors, and magnetometers to provide attitude knowledge and three miniature reaction wheels to provide 3-axis attitude control for pointing the camera toward the shadow of the moon.