The Apollo spacecraft power generation and distribution system was both complex, involving fuel cells, DC-to-AC inverters, and multiple batteries, and highly redundant, essentially allowing itself to be re-wired in flight to work around failed components. This was put to the test after an oxygen tank explosion in the service module of Apollo 13 en route to the Moon caused massive damage to the electrical power and life support systems needed to get the crew back alive. Loss of electrical power took down the instrumentation needed by flight controllers on the ground to figure out what had happened and devise a way to use what remained operational to save the crew, requiring a delicate balance using the remaining power of the spacecraft’s dying systems as the clock was running out.