As part of a three-year test campaign, ESA engineers are trying to evaluate the risk of abandoned satellites with disastrous battery reactions exploding in orbit.
For the “abuse” testing, engineers forced space batteries past the brink of destruction, “through overheating, overcharging, short circuits, and even by shooting them with bullets,” according to the ESA. The end goal is to create technology that remains safely inactive after the mission ends, and doesn’t further add to the space debris problem with an explosion of smaller, more numerous orbital pieces.
“Of more than 250 known satellite explosions that have taken place in orbit, about 10 have been due to batteries,” says François Bausier, ESA power systems engineer who oversees the project. “All the battery explosions in the past were from older technologies that are no longer used for new ESA missions.”
The lithium-ion (Li-ion) batteries currently being used for missions beyond Earth were tested in the bunkers of the Alternative Energies and Atomic Energy Commission (CEA) in France.
“Current lithium-ion batteries for space have never been observed to break up in flight, but they may well explode if thermally, electrically, or mechanically abused. Therefore we’ve subjected them to extremely harsh conditions to simulate what the batteries could encounter once a space mission concludes and a satellite is left drifting in orbit,” Bausier says.
Variations of battery cells and modules were subjected to more than 200 abuse tests. Some were thrown into the gauntlet brand new, while others were aged through simulated space conditions.
The cells’ internal protection systems were tested, mimicking, for example, a scenario of overpressure that affects the internal circuit breakers or venting mechanisms. Other destructive means prodded instances of manufacturing defects, structural failures, internal and external short circuits, overcharging, overheating, insulation issues, and high temperatures when satellites enter orbital sunlight.
“Another abuse method was to simulate a strike by a micrometeoroid or item of space debris,” explains Bausier. “Orbital velocities can exceed 20 km/s; we weren’t able to reach this speed on the ground so decided to use a larger bullet instead—8 mm instead of 0.8 mm. With this configuration the same overall energy was achieved.”