A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is an orbit arranged so that it precesses through one complete revolution each year, so it always maintains the same relationship with the Sun.
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👉 Sun-synchronous orbit in the context of Aqua (satellite)
Aqua (EOS PM-1) is a NASA scientific research satellite in orbit around the Earth, studying the precipitation, evaporation, and cycling of water. It is the second major component of the Earth Observing System (EOS) preceded by Terra (launched 1999) and followed by Aura (launched 2004).
The name "Aqua" comes from the Latin word for water. The satellite was launched from Vandenberg Air Force Base on May 4, 2002, aboard a Delta II rocket. Aqua operated in a Sun-synchronous orbit as the third in the satellite formation called the "A Train" with several other satellites (OCO-2, the Japanese GCOM W1, PARASOL, CALIPSO, CloudSat, and Aura) for most of its first 20 years; but in January 2022 Aqua left the A-Train (as Cloud Sat, CALIPSO and PARASOL had already done) when, due to its fuel limitations, it transitioned to a free-drift mode, wherein its equatorial crossing time is slowly drifting to later times, from its tightly controlled orbit.
In this Dossier
- ⭐ Core Definition: Sun-synchronous orbit
- 👉 Sun-synchronous orbit in the context of Aqua (satellite)
- Sun-synchronous orbit in the context of A-train (satellite constellation)
- Sun-synchronous orbit in the context of Sentinel-3
- Sun-synchronous orbit in the context of Svalbard Satellite Station
- Sun-synchronous orbit in the context of Polar Satellite Launch Vehicle
Sun-synchronous orbit in the context of A-train (satellite constellation)
The A-train (from Afternoon Train) is a satellite constellation of four Earth observation satellites of varied nationality in Sun-synchronous orbit at an altitude that is slightly variable for each satellite.
The orbit, at an inclination of 98.14°, crosses the equator each day at around 1:30 pm solar time, giving the constellation its name (the "A" stands for "afternoon") and crosses the equator again on the night side of the Earth, at around 1:30 am.
Sun-synchronous orbit in the context of Sentinel-3
Sentinel-3 is an Earth observation heavy satellite series developed by the European Space Agency as part of the Copernicus Programme. As of 2024, it consists of 2 satellites: Sentinel-3A and Sentinel-3B. After initial commissioning, each satellite was handed over to EUMETSAT for the routine operations phase of the mission. Two recurrent satellites, Sentinel-3C and Sentinel-3D, will follow in approximately 2026 and 2028 respectively to ensure continuity of the Sentinel-3 mission.
Each Sentinel-3 satellite is designed to operate for seven years in a sun-synchronous low-Earth orbit. The satellites use multiple sensors to measure topography, temperature, marine ecosystems, water quality, pollution, and other features for ocean forecasting and environmental monitoring.
Sun-synchronous orbit in the context of Svalbard Satellite Station
Svalbard Satellite Station (Norwegian: Svalbard satellittstasjon) or SvalSat is a satellite ground station located on Platåberget near Longyearbyen in Svalbard, Norway. Opened in 1997, it is operated by Kongsberg Satellite Services (KSAT), a joint venture between Kongsberg Defence & Aerospace and the Norwegian Space Centre (NSC). SvalSat and KSAT's Troll Satellite Station (TrollSat) in Antarctica are the only ground stations that can see a low altitude polar orbiting satellite (e.g., in Sun-synchronous orbit) on every revolution as the Earth rotates. As of 2021, the facility consists of 100 multi-mission and customer-dedicated antennas which operate in the C, L, S, X and K bands. The station provides ground services to more satellites than any other facility in the world.
Customers with their own installations include the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the National Oceanic and Atmospheric Administration (NOAA). The station also reads and distributes data from the Japanese Hinode solar research satellite. The facility has seen a large increase in smaller customers after 2004, when the Svalbard Undersea Cable System started providing a fiber Internet connection. Concessions for downloading are only issued to civilian satellites, yet some data has been indirectly used by armed forces. There is a disagreement as to whether this constitutes a breach of the Svalbard Treaty.
Sun-synchronous orbit in the context of Polar Satellite Launch Vehicle
The Polar Satellite Launch Vehicle (PSLV) is an expendable medium-lift launch vehicle designed and operated by ISRO. It was developed to allow India to launch its Indian Remote Sensing (IRS) satellites into Sun-synchronous orbits, a service that was, until the advent of the PSLV in 1993, only commercially available from Russia. PSLV can also launch small size satellites into Geostationary Transfer Orbit (GTO).
Some notable payloads launched by PSLV include India's first lunar probe Chandrayaan-1, India's first interplanetary mission, Mars Orbiter Mission (Mangalyaan), India's first space observatory, Astrosat and India's first Solar mission, Aditya-L1.