On Board Data Handling (OBDH) Subsystem

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SAX data management and communication is based on the concept of distributed on-board intelligence:

Intelligent Terminals: Those Subsystems equipped with their own microprocessor-based On Board Computers (OBCs)
Non-Intelligent Terminals

The OBDH is the SubSystem in charge of:

Managing the communication interfaces between the Satellite and the Ground Station
Controlling the environment and status of the on-board non-intelligent Subsystems.
Acting as supervisor of the Satellite processors and Communication Busses.

The OBDH is a fully redundant Subsystem. Together with the OBDH BUS it includes the following units:

Central Terminal Unit (CTU);
Decoder (Dec);
Remote Terminal Unit (RTU);
Tape Recorder Unit (TRU);
Digital Bus Unit (DBU).

Interprocessor communication is based on the ESA Standard RBI protocol and a serial digital bus arbitrated by the CTU.

The OBDH Bus is composed by:

Interrogation Bus for CTU to Terminals communication;
Response Bus for Terminals to CTU transmission of Engineering Data;
Block Transfer Bus for Science Instruments to CTU transmission of Science Data.

The CTU provides the main data handling functions:

Execution of validated commands or their distribution to the local processors.
Acquisition and data formatting for transmission to ground.
Closed loop control of the other Satellite Subsystems and Time distribution.

The CTU also houses the OBDH Software, namely: the Basic Software (BSW) that performs `basic' functions and the Application Software (ASW) which acts as `the on-board mission manager' with the main functions of:

System level operation management
System level failure management
Non-intelligent subsystem failure management

The DBU is the hardware interface between the OBDH BUS and the users; it performs coding/decoding functions.

Communication from/to non-intelligent terminals is performed through the RTU. The Decoder performs the validation and transmission of ground telecommands to the CTU for their distribution to the final end user or directly to the final user for immediate execution in case of High Priority Commands (HPR) for which 64 lines are assigned.

Due to the limited visibility from the Ground Station of about 10 min over 96 min, the TRU provides the capability of storing a large amount of data on board (460 Mbits).

This file was last modified on Wednesday, 02-Sep-1998 17:28:57 CEST by Mauro Orlandini

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