SAFT in cooperation with ESA (European Space Agency) and CNES (French Space Agency) has developed a 3.5 inches diameter NiH2 cell ranging from 36 to 100 Ah.
This development program led to the qualification of the product performed according to ESA specifications on a batch of 15 cells of 90 Ah featuring an energy density of 58.2 Wh/Kg.
The qualification program comprised a pre-vibration sequence with capacity measurement in standard conditions, leak rate measurement at maximum operating pressure, self-discharge and internal resistance determination, a sinusoidal and random vibration sequence followed by a post-vibration sequence to assess the stability of the performances after mechanical solicitations. The qualification sequence also comprises a capacity determination at -20, -5 and 25-C and a characterization of the cells behaviour under realistic GEO conditions.
This test sequence ended with abuse tests comprising over-charge, over-discharge and short-circuit test followed by a destructive physical analysis (DPA) on 2 cells to check the integrity of the internal components after the qualification sequence.
In parallel with the cells test sequence, a qualification test program was conducted on pressure vessels. It consisted in cycling with Hydrogen for a duration of 4 times the GEO life including the number of cycles representative of the use of the battery for station keeping ion thrusters.
These short-term tests are to be followed by life-test cycling on the cells to simulate accelerated GEO conditions on the one hand and advanced conditions for future applications (increased depth of discharge and ion thrusters cycles) on the other.
The results obtained during the short-term test sequence are presented in details and demonstrate the ability of the SAFT NiH2 cells to comply with GEO applications requirements.