20 years in space and still in orbit, thanks to Saft

In March 2004, the first telecommunications geostationary satellite was launched, powered by a Saft lithium-ion battery. 20 years later, it’s still in orbit, 36,000 kilometers above the earth. Here’s a report on this epic space story.  

Today, when lithium-ion (Li-ion) batteries are mentioned, everyone thinks of smartphones, laptops, tools for home improvement or gardening, and electric vehicles. But few people think of batteries designed for use in space, powering the satellites that meet our daily telecommunications and weather forecasting needs.  

Let’s take a look back. It all started more than 20 years ago. The year was 1996. The CNES (French national center for space studies) and the ESA (European Space Agency) financed the first telecommunications satellite program, whose power was provided by a Li-ion battery – a major first for the application of this type of battery. Its name? Stentor, which in French stands for “Satellite de Télécommunications pour Expérimenter les Nouvelles Technologies en Orbite,” and in English means, “telecommunications satellite for testing new technologies in orbit.” Saft, a partner of the CNES since the beginning of space exploration in 1966, was naturally chosen to manufacture the battery, a true technological feat at the time. The challenge matched the project’s pioneering ambition, with the first industrial application of a several-kilowatt lithium-ion battery in a satellite.  

A design brief specific for space application 

At Saft, the R&D teams focused on perfecting the best battery for space: a Li-ion battery that met the extremely precise requirements of the design brief. “The satellite was launched by a rocket, which required specific mechanical, acoustic, and shock-resistant characteristics during takeoff. It would function in a total vacuum, which necessitated a completely sealed system. It would be subjected to extreme temperatures, ranging from minus 150 to 200 degrees Celsius on the satellite’s surface, depending on its position to the Sun. This placed constraints on the heat management plan. It also had to be resistant to solar radiation. Lastly, the Saft battery had to supply the electricity needed to power the satellite during the eclipse periods over its 12-year lifespan. These were the specifications in 1996,” said Yannick Borthomieu, who was then head of the development department for components and batteries for space application and is now the product manager for the ADP (Aerospace, Defense & Performance) division at Saft. He went on to say, “the reliability had to be excellent given that any repairs to the satellite in geostationary orbit were practically impossible.”  

Fifty employees at the Saft Poitiers and Bordeaux sites were involved in this innovation 

The Saft teams quickly assigned roles to contribute to the project. In Poitiers, R&D worked at full capacity to develop a battery that responded to all the requirements of this application. In Bordeaux, Saft converted its battery production pilot line for electric cars – this was before 2000 when electric cars had yet to find their market – into a satellite battery production line.  

In 2000, only four years after the start of the program, everything was ready. Unfortunately, the telecommunications satellite, which would have assessed and validated the battery technology in orbit, was lost after the mid-flight explosion of the Ariane launcher on December 11, 2002. 

A collective, multi-partner adventure 

While the projected plan for demonstrating the technology in orbit experienced a critical failure, which at that time could have resulted in stopping this evolution in battery technology, the manufacturers, who firmly believed in the excellence of the Saft technology, supported the project. The three partners managed to convince the satellite operators to install a Li-ion battery. “We were able to convince the operator Eutelsat to make a bid. The insurers, who were also involved, were informed of the risks connected with the technology change but did not apply significant premiums to this high-stakes, high-level project,” Yannick Borthomieu said.  

The major moment came on March 15, 2004: from the Baikonur base, the 4,250-kilogram Eutelsat W3A satellite, powered by the Li-ion battery, was launched 36,000 kilometers. The satellite’s name refers to its position at 3 degrees west of the Greenwich meridian. Its mission was scheduled for 12 years. Today, 20 years later, W3A continues to orbit the earth. A mission going beyond all expectations!  

Circling for over 20 years!  

Even though the Li-ion battery has powered the W3A satellite for more than 20 years, it does not run continuously. The battery provides “nighttime” power when the satellite goes behind the earth and sits in the shade of the blue planet where the sun can no longer shine on it. This energy powers the platform and ensures the telecommunications satellite’s operations (antennas, transponder), which provide telemetry readings and operational monitoring from the ground. In the “daytime” phase, the solar panels produce the energy needed to power the satellite and recharge the batteries at the same time. 

At the start of the mission, Saft monitored the battery performance every year, then every five years. No anomalies or deviations from the initial objectives have been reported in the past 20 years. The battery manufacturing experts and satellite developers worked on the battery’s use during the mission, thus defining the depth of discharge (DOD) used to guarantee the W3A’s lifespan. This DOD corresponds to the energy consumed by the battery during each eclipse phase. The battery’s total degradation over the course of the mission was projected at a maximum of 12%. In 2019, after 15 years in use, the battery’s health status proved much better than projected with a loss of less than 2%.  W3A’s mission has therefore been extended.  

Due to the exceptional performance demonstrated by W3A over 20 years, Yannick Borthomieu and the Saft teams convinced all of the world’s satellite producers and operators to choose Li-ion batteries.

The field of application for lithium-ion batteries appears to be endless, on land, at sea, in the air, and in space!  

Astronomical figures 

• Weight of the Eutelsat W3A satellite: 4250 kg 

• Battery capacity: 240 Ah 

• Battery weight: about 170 kg 

• Battery power: about 8.5 kW 

• Number of satellites powered by Saft lithium-ion batteries over the past 20 years: 383.