Sun-synchronous orbit (SSO)
Sun-synchronous orbit (SSO) is a type of low Earth polar orbit in which satellites are in sync with the Sun. As such, this allows satellites to pass over the same part of Earth at nearly the same time each day. Objects in SSO fly at altitudes between 372 and 497 miles (600-800 km) and travel at speeds reaching 4.66 miles per second (7.5 km/s), says ESA.
In SSO, satellites have a perpetual view of the Sun, which is great for making solar observations. And because Sun-synchronous satellites pass over the same spot each day, the downlinking of data is a cinch. NASA’s solar surveying Hinode satellite and Earth-observing Aqua satellite currently work in SSO.
SSO is “necessary for science because it keeps the angle of sunlight on the surface of the Earth as consistent as possible, though the angle will change from season to season,” NASA says. “This consistency means that scientists can compare images from the same season over several years without worrying too much about extreme changes in shadows and lighting, which can create illusions of change.” An absence of Sun-synchronous satellites would make it “impossible to collect the kind of consistent information required to study climate change,” according to the space agency.
