SWOT

The Surface Water and Ocean Topography satellite, commonly known by its acronym SWOT, is a scientific Earth-observation payload operating in low Earth orbit. Launched in December 2022 and built by Thales Alenia Space for NASA, SWOT represents a major step forward in humanity's ability to observe and quantify the water that covers and courses across our planet's surface. Tracked in the LowEarth catalog under NORAD ID 54754 and international designator 2022-173A, the spacecraft remains operational in orbit as of this writing.

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Mission and Purpose

Water is both the defining feature of Earth as a planet and one of the most critical resources for civilization, yet the global picture of how surface water moves, accumulates, and changes over time has historically been incomplete. Rivers, lakes, reservoirs, wetlands, coastal zones, and the open ocean have each been studied with various instruments and methods, but never with a single unified, high-resolution, globe-spanning survey. SWOT was conceived specifically to close that gap.

The satellite carries a radar altimeter system designed to measure the precise height of water surfaces — not just in broad strokes, but at a level of detail fine enough to resolve relatively small water bodies and narrow river channels. This capability allows scientists to estimate river discharge rates, track changes in lake and reservoir volumes, and study how water stored on land responds to seasonal cycles, drought, and long-term climate shifts. These are not trivial questions: freshwater availability is directly tied to agriculture, human health, and ecosystem function across every inhabited continent.

The ocean component of the mission is equally ambitious. The surface of the sea is not flat; it rises and falls in subtle but scientifically meaningful ways that reflect the distribution of heat, salt, and currents beneath. Measuring ocean surface topography at high resolution enables researchers to map mesoscale and sub-mesoscale ocean features — eddies, fronts, and currents — that play an important role in the global redistribution of heat and carbon. Previous satellite altimeters generally measured ocean height along narrow ground tracks, leaving substantial gaps between measurements. SWOT's wide-swath radar technology greatly expands the spatial coverage achievable in a single pass, providing something far closer to a true two-dimensional image of the ocean surface.

SWOT is a collaborative international undertaking. NASA serves as the primary operator, with the French space agency CNES (Centre National d'Études Spatiales) as the principal partner. The Canadian Space Agency and the UK Space Agency also contributed to the mission. This kind of multi-agency partnership is well established in Earth science, and it reflects both the global relevance of the science and the substantial cost and complexity of building and operating a spacecraft at this level of capability.

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Orbit and Tracking

SWOT orbits Earth in a near-circular low Earth orbit with an apogee and perigee both at approximately 898 km, indicating a nearly perfectly circular trajectory. At that altitude, the satellite completes one orbit every 102.8 minutes, circling the globe roughly 14 times per day. Its orbital inclination is 77.6°, a high-inclination path that enables the spacecraft to observe the vast majority of the Earth's surface, including high-latitude regions where significant freshwater storage occurs in glaciers, ice sheets, and snow cover.

The combination of altitude and inclination is well suited to the mission's goals. At 898 km, the satellite is high enough to achieve broad swath coverage and a favorable repeat ground track, allowing it to revisit the same locations on a regular cycle — essential for monitoring how water bodies change over time. The high inclination ensures that coverage extends well into the polar regions without requiring a true polar or sun-synchronous orbit, though it does mean the very highest latitudes near the poles are not observed.

From a tracking perspective, SWOT is a substantial object in low Earth orbit. With a mass of approximately 2,000 kg, it is a mid-to-large class spacecraft. Objects of this size at this altitude are generally trackable by ground-based radar networks and are cataloged systematically by the 18th Space Defense Squadron, which maintains the authoritative registry of Earth-orbiting objects from which the NORAD catalog ID is derived.

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Design and Operators

SWOT was manufactured by Thales Alenia Space, a Franco-Italian aerospace company with a long track record in building satellite platforms and scientific payloads. The spacecraft has a launch mass of approximately 2,000 kg, placing it in a class of satellite that requires a medium-to-large launch vehicle to reach orbit.

The satellite lifted off on December 15, 2022, at 19:00 Eastern Standard Time. It was launched from the United States, with NASA serving as the operating agency on behalf of the international partnership. The spacecraft's registration is under the United States, consistent with NASA's role as prime operator.

The core instrument aboard SWOT is the Ka-band Radar Interferometer, known as KaRIn, which is the technology that enables the wide-swath altimetry that distinguishes this mission from previous radar altimeters. Rather than measuring water height along a single nadir track, KaRIn uses two antennas separated by a long boom to capture height data across a wide swath on either side of the satellite's ground track. This interferometric approach is the key innovation that makes SWOT's two-dimensional water surface mapping possible. Additional conventional nadir altimetry instruments are also carried aboard, providing continuity with the historical record of ocean surface height measurements established by earlier missions such as TOPEX/Poseidon and the Jason series.

The satellite's structure and thermal systems were designed to operate reliably in the radiation and thermal environment of low Earth orbit at roughly 900 km altitude — well below the inner Van Allen radiation belt, which reduces but does not eliminate radiation exposure considerations for electronics and solar arrays.

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Scientific Significance

The data SWOT is designed to produce has implications across several scientific disciplines and practical domains. In hydrology, the ability to estimate river discharge from space — without relying solely on sparse networks of in-situ stream gauges, which are unevenly distributed and declining in number in many parts of the world — is potentially transformative. Regions with limited ground-based monitoring infrastructure, including much of the developing world, stand to benefit substantially from satellite-derived water data.

In oceanography, the fine-scale mapping of sea surface height allows researchers to study ocean dynamics at scales that were previously difficult or impossible to observe globally from space. Small eddies and fronts that are nonetheless important for ocean mixing, biological productivity, and the transport of heat and gases had been largely invisible to earlier altimetry systems. SWOT's measurements are expected to improve ocean circulation models and, by extension, climate models that depend on accurate representation of ocean heat transport.

For water resource management, SWOT offers data that can support monitoring of reservoirs and lakes critical to human water supplies and hydroelectric power generation. The capacity to track surface water storage changes from orbit, with near-global coverage, provides a new tool for understanding and responding to water scarcity, flood risk, and the impacts of changing precipitation patterns.

The mission also contributes to the long-term record of sea level change. By measuring ocean surface topography at high resolution and tying those measurements to the established altimetry record, SWOT extends and enriches a decades-long observational dataset that is central to understanding global sea level rise — one of the most consequential measurable consequences of ongoing climate change.

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Current Status

As of the time of catalog entry, SWOT remains in orbit and has not undergone decay or reentry. The spacecraft's 2022-173A designation places its launch firmly in the recent era of Earth observation, and it is actively registered as an operational payload. Mission status details beyond the orbital parameters recorded in the tracking catalog are not publicly documented in this database entry; observers interested in the operational status of the science instruments or data production should consult NASA or CNES mission pages directly.

In terms of orbital stability, the near-circular orbit at 898 km is relatively stable over medium timescales, experiencing only limited atmospheric drag compared to satellites at lower altitudes. Without regular orbit-maintenance maneuvers, a satellite at this altitude would remain in orbit for a very long period before natural decay brought it back into the denser atmosphere, though SWOT carries propulsion systems capable of performing station-keeping and orbit-adjustment maneuvers as needed to maintain its science orbit.

SWOT occupies a distinctive place in the history of Earth-observing satellites as one of the first missions explicitly designed to provide a global, high-resolution inventory of surface water — a resource whose careful measurement is increasingly urgent in a changing climate. Its data products are intended to be freely available to the international scientific community, consistent with the open-data policies of NASA and CNES.