A “space system” refers to a set of components, including spacecraft, ground stations, and communication networks, that work together to accomplish a specific mission or set of missions in space. The components of a space system are designed to perform various functions such as earth observation, communication, navigation, and scientific research.
Space systems are generally defined to consist of five segments: space, launch, ground, link, and user. The individual segments are defined in the following sections.
Space Segment
This is the spacecraft in the system – either individual or a constellation. The satellite bus provides the structure and supporting subsystems – including power, communications, thermal control and attitude/orbit control – to support the payload (the equipment that actually performs the spacecraft’s mission). A single satellite may carry multiple payloads and payloads may serve many customers.
Launch Segment
The launch segment in a space system refers to the various components and activities involved in the process of launching a spacecraft from the Earth’s surface into orbit or beyond. This includes the launch vehicle, payload, ground support equipment, launch site infrastructure, and the procedures and personnel required to execute a launch.
User Segment
User segment capabilities can be hand-held, or mounted in vehicles, on maritime vessels and in aircraft, e.g., GPS receivers, Starlink user terminals, satellite telephones.
Link Segment
The link segment is the communications network that connects the other segments and includes both the electromagnetic spectrum and cyber considerations. Note that the link segment includes ground to space, space to space, and ground to ground network connections.
Ground Segment
The ground segment is the ground-based infrastructure and associated services or support mechanisms and personnel critical to the functioning of the space system, such as satellite monitoring and control, uplink and downlink ground stations and mission operations centers