Saft powers the weather forecasters' eye in the sky
The dangers of extreme weather events make the satellites that inform our forecasts more important than ever. A vital component of those satellites is the battery.
On March 1st, 2022, America’s National Oceanic and Atmospheric Administration (NOAA) launched its Geostationary Operational Environmental Satellite-T (GOES-T). GOES-T, part of the latest generation of GOES, America’s largest weather satellite system, carries advanced imagery and atmospheric measurement equipment that can map lightning in real time, improve air-quality warnings and even monitor space weather.
We rely on weather forecasts to plan everything from the best time to harvest crops to what to wear to work. And as extreme weather events become more frequent, the early warning provided by satellites is increasingly vital for human safety. These satellites can’t function without batteries, however, which is where Saft comes in. Saft has provided batteries for space use since the 1960s and has powered GOES since 2016.
Batteries to provide energy to satellites during the equinoxes
The first weather satellite was launched in the late 1950s, but today’s weather satellite networks have their roots in the 1970s. They survey the Earth from either a geostationary orbit – staying at a fixed point 36,000 kilometers above the equator – or a polar orbit, in which they circle the planet, passing over both the North and South Poles.
Most of the time they use solar power for key functions, such as the imaging systems that monitor weather patterns and the communications equipment for sending data back to Earth. “The batteries are there for when the satellite is eclipsed when it enters the Earth’s penumbra,” says Dr. Yannick Borthomieu, Saft's Space and Defense product manager.
“Twice a year, around each equinox, a geostationary satellite will be out of sunlight for a little over an hour a day. That only affects about 90 days of the year, but during that time battery power is essential.”
Lighter, smaller, and long-lasting satellites thanks to Saft
A new generation of satellites are also designed to use their battery for some maneuvering. In the past, this was done with chemical engines, powered by a large quantity of fuel carried on the satellite, but it can now be done by plasma engines that draw electricity from the battery. This gives the battery a dual purpose and means the satellite needs less space for fuel.
Weight and size are crucial. Satellite batteries must be able to withstand the shock and vibration of launch, radiation exposure, significant temperature ranges, and work in the vacuum of space, but they must also be small and light. The bigger and heavier they are, the more fuel it takes to get the satellite into space, which adds to the already huge costs. The GOES-T satellite, for example, cost around $350 million to build and an additional $168 million to launch.
That satellite is part of the fourth generation of the GOES series, which is expected to operate until at least 2036, so the battery must be able to operate for just as long. That means an operating life of 20 years or more, and complete reliability. “Saft’s lithium-ion batteries alone have more than two billion cell hours in orbit,” says Borthomieu,” with no failures at all.”
Forecasting weather with Saft’s lithium-ion batteries
Their record of reliability has been built through decades of experience. Saft has been building batteries for space use since the 1960s. The company began making batteries for weather satellites in the 1970s, beginning with the first generation of Meteosat satellites, operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT).
That first generation used nickel-based batteries, which were the standard for about 40 years. When the third generation of Meteosat launches later this year, it will have Saft lithium-ion batteries, which are state of the art. Future satellites will use batteries with a solid electrolyte, rather than a liquid, as in traditional batteries.
These will provide higher energy density in the same size, which is ideal for an industry that is always trying to reduce size and weight. However, Borthomieu says the solid-state batteries are some way off: “Space technology is measured on a Technology Readiness Level scale from one to nine. A seven is ready to fly and a nine is proven in flight. Solid state batteries, at the moment, are at TRL two.”
Lithium-ion batteries will be the norm for a while yet, then. But that is only sensible when reliability is essential. The battery carried by GOES-T, orbiting tens of thousands of kilometers above us, will be helping to forecast our weather for decades to come.