It what seems like a paradox, ESA engineers have been blowing up batteries in hopes of cleaning up space debris. In a series of severe "abuse" tests at the test bunkers of France's Alternative Energies and Atomic Energy Commission (CEA), lithium-ion batteries designed for space satellites were tortured as part of the Clean Space initiative's three-year project to better understand catastrophic battery failures and prevent battery explosions in derelict spacecraft.
Space debris is a major problem threatening our ability to operate in Earth orbit, and one of the key factors in creating such debris are the batteries installed in now-defunct satellites. According to ESA power systems engineer François Bausier, there have been over 250 known satellite explosions, with about 10 of these due to batteries.
The problem is that batteries generate electricity through electrochemical reactions and old batteries, especially older designs, can explode if they are overstressed, subjected to impacts, or simply start producing gas inside of their casings. If a battery explodes, it can destroy the satellite, send it into a new orbit, or directly expel particles that, though tiny, could endanger other spacecraft as they travel at hypersonic velocities. Though lithium ion batteries are safer than others, they are not completely safe.
"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," says Bausier. "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."
Over 200 destruction tests were conducted on a variety of battery types, including cells and multiple-cell modules. Some of these batteries were new and others were repeatedly charged and discharged to artificially age them. In addition, the tests included other components, including internal circuit breakers and venting systems. The tests took place in an inert atmosphere to simulate the vacuum of space, but ESA says that satellites themselves often provide oxidizers in various forms that can support destructive reactions.
The torture tests came in a variety of forms. These included short-circuiting the batteries to simulate both circuit and structural failures, overcharging them, overheating, and over-discharging to determine if this could make the batteries "passive" or safer.
"Another abuse method was to simulate a strike by a micrometeoroid or item of space debris," says Bausier. "Orbital velocities can exceed 20 km/s. We weren't able to reach this speed on the ground, so [we] decided to use a larger bullet instead – 8 mm instead of 0.8 mm. With this configuration, the same overall energy was achieved."
Based on these tests, ESA recommends that batteries on decommissioned satellites should be completely discharged and disconnected from the solar panels before retirement, and that the craft should be configured to keep the batteries at as even a temperature as possible. In addition, new batteries should be better designed to handle space conditions and satellites built to avoid explosions.
Under international regulations, decommissioned spacecraft orbiting below an altitude of 200 km (125 mi) must be designed to deorbit within 25 years of deactivation and must remain switched off until reentry.
Source: ESA