A satellite bus is the core platform that provides all the essential subsystems a spacecraft needs to function: power generation and storage, attitude determination and control, thermal management, propulsion, command and data handling, and communication with ground stations. The mission-specific instrument or payload is mounted onto the bus, which handles all housekeeping functions.
Standardized commercial buses from manufacturers like Airbus, Northrop Grumman, Ball Aerospace, and York Space Systems significantly reduce development time and cost compared to custom-built satellites. The trend toward modular, mass-produced buses has been essential to the economics of mega-constellations, where hundreds or thousands of identical satellites must be manufactured on an assembly line.