European weather and atmosphere observation is entering a new, advanced phase. Following its launch on July 1, 2025, from Cape Canaveral, Florida, the Meteosat Third Generation Sounder satellite (MTG-S1), which also carries the Copernicus Sentinel-4 mission, has successfully reached its intended geostationary orbit at an altitude of 36,000 kilometers. After the critical launch and early orbit phase (LEOP), control of the satellite was handed over to Eumetsat, the European Organisation for the Exploitation of Meteorological Satellites, on Friday, July 18. This moment marks the beginning of preparations for the commissioning of a system that will fundamentally change the way we forecast weather and monitor air quality.

A revolution in observing the Earth from space

The MTG-S1 satellite is not just another satellite in a series; it is the carrier of a revolution in meteorology. Unlike previous satellites that provided two-dimensional images (imagers), MTG-S1 is a "sounder." This means it is equipped with instruments that can scan the atmosphere in three dimensions, providing detailed vertical profiles of temperature and humidity. This capability will allow meteorologists to look inside atmospheric layers and detect signs of instability long before clouds even form. The main instrument, the Infrared Sounder (IRS), will scan Europe every 30 minutes, offering unprecedented data that will significantly improve so-called "nowcasting" – the short-term prediction of extreme weather events such as severe storms, hail, and heavy rainfall. This provides valuable extra time for issuing warnings and taking protective measures.

In addition, MTG-S1 carries the Sentinel-4 instrument as part of the Copernicus programme. This is a hyperspectral spectrometer that will monitor the concentrations of key trace gases and aerosols over Europe and North Africa every hour. Data on ozone (O3), nitrogen dioxide (NO2), sulphur dioxide (SO2), and formaldehyde will be crucial for more accurate air quality forecasts, which have a direct impact on public health, as well as on understanding climate change and atmospheric pollution.

A complex journey to geostationary orbit

The journey of the MTG-S1 satellite to its final destination was extremely demanding and lasted more than 17 days. After being precisely delivered into orbit by a SpaceX Falcon 9 rocket, the launch and early orbit phase (LEOP) began, a critical period in which the satellite is placed on its trajectory and stabilized. Unlike the first satellite in this series, MTG-I1, which was launched into a standard geostationary transfer orbit, MTG-S1 was placed in a much more demanding, so-called super-synchronous transfer orbit. This highly elliptical path, with its farthest point (apogee) at approximately 64,000 km and its closest (perigee) at just 300 km from Earth, required a longer and more complex series of maneuvers. The team on the ground had to perform five precise burns of the main engine to gradually shape the orbit and bring the satellite to the target altitude of 36,000 km above the equator.

This method, although more complex, allows for a more efficient change in the orbit's inclination and ultimately saves the satellite's precious fuel, which extends its operational lifespan. Every step of this process was closely monitored and guided from the Fucino space centre in Italy.

European cooperation and expertise at work

The successful positioning of the MTG-S1 satellite is the result of outstanding cooperation and expertise from teams across Europe. The project was led by the European Space Agency (ESA), which developed the satellite in collaboration with industrial partners such as OHB SE and Thales Alenia Space. The critical LEOP phase was the responsibility of the Italian company Telespazio, which managed the operations from its Fucino control centre, located about a hundred kilometers east of Rome. About 130 experts from various agencies and companies participated in this coordinated operation, working around the clock to ensure that every maneuver was flawless. Support was also provided by experts from the backup control centre in Cannes. Alex Palacios, head of MTG satellite commissioning and operations at ESA, emphasized that the team, although experienced after the launch of the first MTG-I1 satellite, faced new challenges due to the more complex orbit. Weeks of intensive training and simulations of various anomalies, from orbit injection errors to antenna problems, ensured that the team was prepared for every possible scenario.

Key steps from launch to operational position

The entire process of bringing the satellite into an operational state can be divided into several key phases. It all began with a flawless liftoff on July 1. About half an hour after launch, the Malindi ground station in Kenya received the first signal, confirming that the satellite had successfully separated from the rocket. Immediately thereafter, MTG-S1 initiated an automated sequence: it activated its propulsion system, deployed its solar panels, and turned towards the Sun to achieve a "power positive" state, meaning it began to produce and store its own energy. The next step was the activation of the attitude control systems, such as gyroscopes and reaction wheels. This was followed by a series of five key engine burns – three to raise the perigee and two to lower the apogee – which gradually made the elliptical orbit circular. During this phase, the Ka-band antenna, crucial for transmitting the vast amount of meteorological data to Earth, was also successfully deployed. After the main engine completed its task, the propulsion system was passivated. Final maneuvers brought the satellite to its target position at 3.4 degrees west longitude above the equator, where it was rotated into its final, operational orientation with its view directed towards Earth. This officially concluded the LEOP phase.

What's next: Preparing for a new era of meteorology

With the handover of control to Eumetsat, one chapter has ended, and another begins – the commissioning phase. In the coming months, a joint team of experts from European industry (OHB SE, Airbus, and Thales Alenia Space), ESA, and Eumetsat will carefully activate and calibrate the sophisticated instruments on the satellite. This is a delicate process to ensure that the data the satellite sends will be accurate and reliable. James Champion, MTG Project Manager at ESA, pointed out that the successful completion of LEOP reflects the professionalism and passion of the teams that safely brought MTG-S1 into orbit. Now, as he says, "the baton is passed to the commissioning team," which will prepare the ground for a new era in weather forecasting and air quality monitoring. Today is celebrated as a great success: the MTG-S1 satellite is healthy, stable, and exactly where it needs to be, ready for its next, crucial chapter.

Source: European Space Agency