Ground segment

A ground segment consists of all the ground-based control elements of a spacecraft system, as opposed to the space segment and user segment. The ground segment serves to enable control of a spacecraft, and distribution of payload data and telemetry among interested parties on the ground.

The primary elements of a ground segment, discussed in detail below, include:

These ground segment elements are present in nearly all space missions, whether commercial, military, or scientific. They may be located together or separated geographically, and may be operated by different parties. Certain elements may support multiple spacecraft simultaneously.

Mission control centers process, distribute, and perform some analysis of telemetry; they also issue commands, data uploads, and software updates to spacecraft. For manned spacecraft, mission control manages voice and video communications with the crew. Control centers may also be responsible for configuration management and data archival.

There are typically backup sites from which mission control can be maintained if there is a problem at the primary control center which renders it unable to operate, such as a natural disaster; such contingencies are considered in a Continuity of Operations plan.

Control centers may be continuously or regularly staffed by flight controllers. Staffing is typically greatest during the early phases of a mission, and during critical procedures and periods. Increasingly commonly, control centers for unmanned spacecraft may be set up for "lights-out" (or automated) operation, as a means of controlling costs. Flight control software will typically generate alerts regarding significant events – both planned and unplanned – in the ground or space segment that may require operator action.

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