The Meteosat Third Generation sounder satellite, hosting the Copernicus Sentinel-4 mission, has reached its orbit and has been placed under the control of Eumetsat. It is now ready to start commissioning before beginning operations to monitor Earth’s atmosphere from a distance of 36 000 km.

This is another important milestone for the second Meteosat Third Generation sounder (MTG-S1) satellite – and for the future of European weather observation. MTG-S1, developed by the European Space Agency (ESA) with European partners, was launched on 1 July from Cape Canaveral, Florida, on a SpaceX Falcon 9 rocket.

fter more than two weeks in space, the launch and early orbit phase (LEOP) has been successfully concluded. This is a critical period for satellite missions, which begins when they separate from the launch rocket, and concludes when the satellite reaches its final orbit and its direction is stabilised. After LEOP, the satellite is then ready to be commissioned before becoming fully operational.

MTG-S1 ticked all these boxes last week and on Friday, 18 July, the satellite was handed over to the agency responsible for operating the satellite, Eumetsat. The LEOP service provider was Telespazio and LEOP activities were conducted from the Fucino Space Centre, based in the Fucino plateau about 100 km east of Rome, Italy.

The handover comes just over two and a half years after the launch of the first imager satellite for the Meteosat Third Generation family, MTG-I1.

As with MTG-I1, the LEOP was managed by Telespazio, supported by a combined project support team led by ESA and including specialists from ESA, OHB and Thales Alenia Space. Altogether, around 130 people were involved in this tightly coordinated phase, working around the clock from the Telespazio Mission Control Centre in Fucino and the Backup Control Centre in Cannes.

ESA’s Alex Palacios, MTG Satellites Commissioning and Operations Manager, noted that, although the spirit and expertise of the team were familiar, the challenge they faced was different to the LEOP activities for the first MTG satellite.

“Unlike MTG-I1, which launched into a standard geostationary transfer orbit, MTG-S1 was injected into a much more demanding super-synchronous transfer orbit, with an apogee of about 64 000 km, a perigee of 300 km, and an inclination of 21°,” said Alex. “This highly elliptical path required a longer and more complex series of manoeuvres than the first MTG satellite, including five liquid apogee engine burns, to gradually bring the satellite to its final orbit.”

The LEOP for MTG-S1 lasted over 17 days, during which time the satellite was carefully guided, step-by-step, from launch separation to its target orbital slot.

Below, the ESA project support team present in Fucino takes us through the steps of MTG-S1’s LEOP, from launch to geostationary orbit:

From liftoff to first contact

On launch day, the team at Fucino was on console from morning onwards, monitoring the satellite’s configuration and mirroring its onboard software into the LEOP system. After the final countdown, liftoff went smoothly aboard a SpaceX Falcon 9, which accurately delivered MTG-S1 into its planned transfer orbit.

Roughly half an hour after launch, the satellite sent its first signal, received via the Malindi ground station in Kenya, confirming its separation from the launcher.

Immediately following separation, the satellite initiated its automated sequence: pressurising the propulsion system, deploying and locking the solar panels, and orienting itself toward the Sun, reaching the essential ‘power positive’ state that allows it to generate and store energy.

Steering through the transfer orbit

From there, the team activated attitude control systems such as gyroscopes and reaction wheels, and began executing a series of critical burns. These included three perigee-raising manoeuvres and two apogee-lowering manoeuvres, reshaping the orbit until MTG-S1 was coasting in a drift orbit just above the geostationary belt.

During this phase, several other operations were carefully carried out: the Ka-band antenna was deployed, the very antenna that will eventually transmit meteorological data to Earth, and the propulsion system was passivated and vented, since the main engine would not be needed anymore.

Into position and Earth-pointing

The final orbital manoeuvres brought MTG-S1 to its target position at 3.4 °W longitude over the equator. Once there, the satellite was rotated into its operational orientation, switching to Earth-pointing attitude, a defining moment that marked the end of LEOP.

“This milestone wasn’t achieved by luck,” said Alex. “The entire LEOP team had undergone weeks of intensive training, including simulations of a wide variety of potential anomalies, from orbital injection errors and antenna deployment issues to over-pressured fuel systems. That preparation, combined with the lessons learned from MTG-I1’s LEOP, ensured the team was ready to meet any challenge.”

Looking ahead

“LEOP is one of the most demanding phases in a satellite’s life,” noted James Champion, ESA’s MTG Project Manager. “Completing it successfully reflects the professionalism, preparation, and passion of the teams across Europe who brought MTG-S1 safely to orbit.

“Now, the torch passes to the commissioning team, a combined effort from European industry (OHB SE, Airbus and Thales Alenia Space), ESA and Eumetsat, who will begin activating the satellite’s state-of-the-art instruments, paving the way for a new era in weather forecasting and air quality monitoring.”

But for today, we celebrate: MTG-S1 is Earth-pointing, healthy, and exactly where it needs to be to start its next chapter: commissioning.

MTG-S1 and Copernicus Sentinel-4 mission highlights

Source: ESA