Image Credit: ESA–David Ducros, 2017, CC BY-SA IGO 3.0.
Batteries on the International Space Station (ISS)
In January 2017 two astronauts on the ISS went for spacewalks to upgrade power storage batteries outside the station. Nickel-hydrogen batteries originally designed specifically for space stations and satellites had been used during the first battery installation. They had reached the end of their lifespan and were replaced by more modern lithium-ion batteries which will be in service until the ISS is decommissioned 2024.
The advantage of nickel-hydrogen batteries was their long lifetime withstanding large numbers of charge-discharge cycles. But they were sensitive to ”battery memory” meaning they could loose part of their capacity if not charged and discharged completely during each cycle. The main task of the ISS batteries is to store the energy produced by the solar panels during its 45 minutes in sunlight. This electricity is used during the following 45 minutes in darkness wich the ISS passes through with every orbit.
Lithium-ion batteries have a much higher energy density than nickel-hydrogen batteries. Therefore, one lithium-ion battery can replace two nickel-hydrogen batteries, despite being smaller and lighter. In addition, lithium-ion batteries do not show a battery memory effect, but they are more sensitive to overcharging and need to be protected against it. They also typically have a lower lifespan than nickel-hydrogen batteries, but the lithium-ion batteries for the ISS have been specifically designed for 60000 charge-discharge cycles, i.e. a ten year lifespan.
Batteries on Satellites and Space Crafts
Just like the ISS, space crafts and satellites need access to energy when being in the shadow of a planet. Therefore, they normally also carry batteries for the storage of energy produced by sun light. Batteries are also needed to kick-start operating systems before the solar panels are unfolded. In addition, rockets rely on the use of high-power batteries for autonomous operation during the launch into space.
Some space crafts like ESA`s Huygens probe run with non-rechargreable batteries (lithium sulphur dioxide batteries) when solar panels are impractical. Space crafts venturing very far from the sun like the Cassini mission to Saturn or New Horizons to Pluto by NASA depend on electricity from so-called radioisotope thermoelectric generators (RTGs) instead of solar panels or batteries. These produce electricity from the decay of radioactive plutonium.
During the early days of space flight, nickel-cadmium batteries were used for energy storage. However, they were soon supplanted by the nickel-hydrogen technology described above. These are now in turn slowly replaced by lithium-ion batteries. Their biggest advantage for space travel is the high energy density meaning they can store a lot of energy at a low weight and small volume. One major challenge regarding the use of lithium-ion batteries in unmanned space flight is their sensitivity towards the extremely low temperatures in space. Another problem is the long battery lifespan of 1000 to 33000 cycles required in space missions which can take up to 15 years. Despite these obstacles work is ongoing to improve the lithium-ion battery technology for further applications in space.