The primary spacecraft structure containing power, temperature control, and directional thrusters of the satellite that provides locations for the payloads.
Sources:
NIST IR 8401
from
NASA/TP-20210021263
NIST IR 8441
from
NASA/TP-20210021263
The infrastructure of a space platform typically consisting of the basic physical structures, mechanisms, and subsystems for propulsion, power, thermal control, attitude determination and control, and TT&C (telemetry, tracking, and command) communications and processing.
Sources:
NIST IR 8270