ALOS Data Users Handbook

ALOS Data Users Handbook3.3 Overview of Spacecraft Bus Instruments3.3.1 Telemetry, Tracking and Command (TT&C)Telemetry, tracking and command subsystem (TT&C) is an instrument to receive command signals from groundstation directly or via DRTS, and to distribute to each subsystem after demodulating and decoding the signals.TT&C also transmits telemetry data of each subsystem directly or via DRTS to the ground station after taking,editing, recording and modulating the data. TT&C has a function to relay ranging signals as well as light loadmode function and autonomous/automatic function.For the first time as Earth observation satellites developed by JAXA, A CCSDS protocol is used for TT&C, andstandard of MIL-1553B is adopted for databus.3.3.2 Electrical Power Subsystem (EPS)The important jobs of ALOS's EPS are to accept the electrical power as much as 7,000W generated by SolarArray Paddle (PDL) at the dayside orbit, to provide that electrical power to ALOS's components, and to chargeBatteries (BAT) for use at the nightside orbit.Other jobs of EPS are electrical power suppliment for deployment of PDL, PALSAR and DRC antenna afterALOS - H-IIA separation, electrical and thermal maintenance of BAT, and electrical protection of ALOS'scomponents against excess current generated on PDL.EPS consists of the following components:• Power Control Unit (PCU)• Battery Charge Control Unit (BCCU)• Battery (BAT)• Ordnance Controller (ODC)• Reconditioning Load (RCL)• Shunt Dissipater (SHNT)3-23