Last update: November 18th, 2019 at 5:00 am
NASA monitors the health of our planet with a constellation of satellites. The Aqua satellite, shown at top, uses the Latin name for water, and it carries a suite of sensors specially designed for observing all parts of Earth’s water cycle, including water on land, in the oceans, and in the atmosphere. Aqua follows a kind of polar orbit known as a Sun-synchronous orbit, which means it crosses the equator at the same local time during each pass. Aqua’s orbit ascends from south to north during the daylight hours, crosses near the North Pole, circles around Earth’s nighttime side, and crosses near the South Pole to return to the daytime side.
Aqua passes over Earth’s equator between 1:30 and 1:45 p.m. local time on each daytime orbit. This precise timing of orbits ensures that Aqua takes consistent measurements of Earth system processes, enabling scientists to make valid comparisons between data observed on different dates. But polar-orbiting satellites are influenced by the gravity of both the Sun and the Moon, which can pull them off their intended course into an east-west-leaning orbit. To compensate for these gravitational pulls, engineers at Aqua’s Mission Conrol Center at NASA Goddard Space Flight Center must give the satellite orbit the occasional tune-up. For a look at one such tune-up, see the Earth Observatory feature story Flying Steady: Mission Control Tunes Up Aqua’s Orbit.
Credit: NASA images by Reto Stöckli (Aqua satellite) and Jeff Schmaltz, MODIS Rapid Response (global view). Caption by Michon Scott.