These machines and system/process designs may be simple or complex, inexpensive or expensive, luxuries or essentials. Items such as kitchen food mixer, the auto-mobile, heating/air-conditioning systems, nuclear power plants, practical autonomous and tele-operated robotics, and interplanetary space vehicles would not be available today were it not for the mechanical engineer. Important areas in which mechanical engineers work at this time also have to do with the use of solar, wind, and tidal energy and of cogeneration from wastes for domestic and industrial uses.