Aerodynamic control would have been provided via a total of seven flight control surfaces, the wingtip rudders, trailing edge elevon/air brakes, and a body-mounted flap; these surfaces would have been controlled via quadruplex-redundant digital flight controls and actuated via triplex-redundant hydraulics. Mission management would have been performed via three general-purpose computers, a monitoring computer, and three digital databuses. Electrical power was to be provided by a motor that would have used liquid oxygen-liquid hydrogen along with ten US-built fuel cells. The environmental control and life support systems supply pressurisation of the cabin, along with air, water, and warmth, to support the crew for a maximum of 40 days, although may have been potentially extendable to enable 90 day missions. For autonomous operations, "Hermes" was to have been able to operate for up to one month, and would be able to remain docked with an orbiting space station for a maximum of 90 days.