MTG-S1

MTG-S1, catalogued under NORAD ID 64723 and carrying the international designator 2025-143A, is a European atmospheric-monitoring satellite launched on 30 June 2025. Officially designated Meteosat 13 upon entering operational service, it occupies a geostationary orbit above the Earth and forms part of two overlapping European space programmes: the Meteosat Third Generation (MTG) series operated by EUMETSAT, and the Copernicus Sentinel-4 constellation developed under the European Union's broader Earth observation initiative. It is the first of two planned Meteosat Third Generation-Sounder spacecraft and simultaneously serves as the first operational node of the Sentinel-4 system.

Mission and Purpose

The satellite's primary role is atmospheric sounding — the systematic profiling of chemical and physical properties within Earth's atmosphere, particularly over Europe and neighbouring regions. Sentinel-4A/MTG-S1 is designed to support continuous monitoring of air quality, tracking the distribution and concentration of trace gases such as ozone, nitrogen dioxide, sulphur dioxide, and aerosols. This data serves both near-real-time operational forecasting and longer-term climate research, feeding into the Copernicus Atmosphere Monitoring Service (CAMS) and other data pipelines used by meteorological agencies, environmental regulators, and researchers across Europe and beyond.

The Copernicus programme, funded and coordinated at the European Union level with significant involvement from the European Space Agency (ESA), is the world's largest civil Earth observation programme by scope. Within that framework, the Sentinel satellite families each address specific observational needs. The Sentinel-4 configuration is distinctive in that its instruments are not hosted on a dedicated free-flying platform but rather integrated as a payload aboard the MTG-S spacecraft — an arrangement that allows the sounder satellite to benefit from EUMETSAT's established infrastructure for geostationary meteorological operations while simultaneously fulfilling Copernicus data requirements.

Beyond air quality, the satellite's sounder heritage means it contributes to numerical weather prediction by providing atmospheric temperature and humidity profiles with higher vertical resolution than is achievable from imager satellites alone. This positions MTG-S1 at the intersection of operational meteorology and environmental monitoring, a dual mandate that reflects the converging priorities of European space policy over the past two decades.

Orbit and Tracking

MTG-S1 occupies a near-perfect geostationary orbit, with a tracked apogee of 35,799 km and a perigee of 35,791 km — a difference of only 8 km, indicating a very low eccentricity and a nearly circular path around Earth. Its orbital period is 1,436.2 minutes, extremely close to the roughly 1,436-minute sidereal day that defines the geostationary condition, meaning the satellite completes one orbit in very nearly the same time it takes Earth to rotate once relative to the fixed stars. Its inclination is 0.6°, a small but non-zero figure suggesting the satellite may be in an early operational phase before full stationkeeping has brought it to a precisely equatorial plane, or that this represents its nominal maintained inclination. True geostationary satellites nominally target 0° inclination; small residual inclinations are common in practice.

From the ground, a geostationary satellite at this altitude appears essentially stationary against the backdrop of stars when viewed from any fixed point on Earth's surface within its visibility cone. MTG-S1 is tracked in the LowEarth catalog under NORAD ID 64723 with the COSPAR designation 2025-143A, and its orbital elements are regularly updated to reflect stationkeeping manoeuvres and any positional adjustments made by the operations team. Because geostationary satellites maintain a fixed angular position relative to Earth's surface, ground station pointing is straightforward once the longitude slot is known, and continuous contact is possible without the need for antenna tracking systems to slew across the sky.

At an altitude of approximately 35,800 km, MTG-S1 sits at the outermost edge of the operational geostationary belt, well above the medium-Earth orbit radiation belts and in a region where the space environment, while still subject to solar energetic particle events and cosmic radiation, is well characterised. The mass of the satellite is not publicly recorded in the current orbital catalog.

Design and Operator

MTG-S1 was manufactured by Thales Alenia Space, the Franco-Italian aerospace company with extensive experience in large telecommunications and Earth observation platforms. Thales Alenia Space has served as prime contractor for multiple generations of European meteorological satellites, and its involvement in the MTG programme represents a continuation of that role into the third generation of the Meteosat series.

The satellite is operated by EUMETSAT, the European Organisation for the Exploitation of Meteorological Satellites, an intergovernmental body whose membership spans the majority of European states. EUMETSAT's mandate centres on the continuous delivery of meteorological and climate data from geostationary and polar-orbiting platforms, and it operates the ground infrastructure necessary to command, control, and receive data from the MTG constellation. The transition of MTG-S1 from its launch designation to its operational name, Meteosat 13, follows EUMETSAT's established naming convention under which satellites receive their Meteosat number only after commissioning is complete and the spacecraft has been accepted for service.

The MTG-S class is architecturally distinct from its companion MTG-Imager (MTG-I) spacecraft, which carry wide-field cameras for rapid full-disc imaging. The sounder variant instead hosts high-spectral-resolution infrared and ultraviolet-visible-near-infrared spectrometers designed to discriminate between atmospheric layers. This division of labour between imager and sounder satellites within the same constellation allows EUMETSAT to offer a more comprehensive observational product suite than any single multi-instrument platform could efficiently provide. The two satellite types are intended to operate in coordination, with their data streams merged at the ground segment level.

Programme Context and Significance

The Meteosat Third Generation programme represents a major step forward in European geostationary meteorological capability, succeeding the second-generation Meteosat series that had provided continuous coverage since the early 2000s. The inclusion of an atmospheric chemistry and composition mission — the Sentinel-4 component — within the MTG architecture is a relatively novel integration, reflecting the expanding scope of what operational meteorological agencies are expected to deliver. Historically, detailed atmospheric composition monitoring was the domain of research satellites; embedding this capability within an operational geostationary asset represents a maturation of that science into routine service.

For the Copernicus programme specifically, MTG-S1/Sentinel-4A fills a gap in temporal coverage. Polar-orbiting Sentinel satellites, including those in the Sentinel-5 family, revisit any given location approximately once per day at best. A geostationary sounder, by contrast, can observe the same region of Europe continuously throughout daylight hours, capturing the evolution of pollution episodes, ozone patterns, and aerosol events in near-real-time. This high-revisit atmospheric chemistry data is of direct relevance to air quality forecasting services and to the enforcement of environmental regulations that require evidence of transboundary pollution transport.

The launch on 30 June 2025 and the satellite's continued presence in orbit mark the completion of a development programme that spanned many years of engineering, procurement, and international coordination between the European Commission, ESA, EUMETSAT, and the industrial supply chain. MTG-S1 is expected to have an operational lifespan consistent with other geostationary meteorological satellites in its class, providing continuity of service well into the 2030s, though the current orbital catalog does not record a planned end-of-life or decommissioning date.

A second MTG-S spacecraft is planned to follow, ensuring redundancy and long-term continuity. Together, the two sounder satellites are intended to provide an unbroken observational record that supports both operational services and climate data records requiring consistent, calibrated measurements over multi-decadal timescales.

Current Status

As of the information reflected in the current catalog entry, MTG-S1 remains in orbit, stationed in its geostationary position. Its orbital parameters — an apogee of 35,799 km, a perigee of 35,791 km, an inclination of 0.6°, and a period of 1,436.2 minutes — are consistent with an active, stationkept geostationary payload. The mission type and operational status are not detailed in the publicly available catalog record at this time. EUMETSAT, as the operating authority, is the primary source for updates on commissioning progress, data availability, and the formal declaration of operational service under the Meteosat 13 designation.

Observers and researchers wishing to follow the satellite's positional status can do so through the LowEarth tracking platform using NORAD ID 64723. Because geostationary satellites are effectively fixed relative to the Earth's surface, positional monitoring is of less operational significance than for low-Earth orbit objects, but regular catalog updates ensure that any orbital manoeuvres or anomalies are reflected in the element sets available for mission planning and interference avoidance purposes.