95 SYSTEMS: COMMAND AND DATA HANDLING—THE BRAINS OF THE INTERNATIONAL SPACE STATION CHAPTER 5 Table 1. A Summary of the Computers and their Functions on the ISS Multiplexer/ DeMultiplexer Configuration Major Software Functions TIER 1 C&C-1 C&C-2 C&C-3 • Three fully redundant MDMs • All powered on • One operating as Primary • Located internal to US Lab • Process commands from Mission Control Center-Houston and PCS provide telemetry to Mission Control Center-Houston and data to PCS, redundancy management for Tier 2 MDMs, and time management. They also control station modes, software interface to International Partners, and File Transfer management. • Emergency and Vehicle Safing: Execute commands to safe vehicle in response to an emergency event • Manage S-band, Ku-band, ultra-high frequency, audio, video, control high- rate data link, and access mass storage device in support Communications Outage Recorder function • Control Lab Direct Current (DC)-to-DC Converter Units, control RPCM for S0 and External (EXT) MDMs, control rack power based on switch position, execute power and thermal load sheds • Control and coordinate attitude control handovers • Interface to Robotics Work Station TIER 2 Connected to Command & Control Internal (INT)-1 INT-2 • Two fully redundant MDMs • One powered on • One operating as Primary • Located internal to US Lab • Control most Lab RPCMs • Monitor and control of Internal Thermal Control System (ITCS) in Lab/Node 2 including failure and leak detection/response • Atmospheric control, water recovery, fire detection, temperature control • Common Berthing Mechanism (CBM) control and safing EXT-1 EXT-2 • Two fully redundant MDMs • One powered on • One operating as Primary • Located on S0 Truss • High-level control of Solar Array Rotary Joint • High-level control of External Thermal Control System and Thermal Radiator Rotary Joint • Provides high-level control of: Structural Dynamic Measurement System, Common Attachment System, Segment-Segment Attachment System • Control of Mobile Transporter GNC-1 GNC-2 • Two fully redundant MDMs • Both powered on • One operating as Primary • Located internal to US Lab • Provide non-propulsive attitude control by controlling Control Moment Gyros generate and supply pointing data Power Module Control Unit (PMCU)-1 PMCU-2 • Two fully redundant MDMs • One powered on • One operating as Primary • Located internal to US Lab • Monitor and control of Main Bus Switching Units and most Station DC-to- DC Converter Units, provides gateway for PhotoVoltaic Module equipment, provides solar array pointing data, monitor and control of some Lab RPCMs, control RPCM for PL-2 MDM • Control of PhotoVoltaic Control Unit (PVCU) MDMs Payload (PL)-1 PL-2 • Two fully redundant MDMs • Both powered on • One operating as Primary • Located internal to US Lab • Payload software support • Configure, monitor, and control: Automated Payload Switch and Payload Ethernet Hub Gateway Habitation Control Zone (HCZ)† - 1 HCZ-2 • Two fully redundant MDMs • One powered on • One operating as Primary • Located internal to Node 3 • RPCM control • Monitor and control of Node 3 ITCS including failure and leak monitoring • Atmospheric control, water recovery, fire detection, temperature control, regenerative life support systems • CBM control and safing † Initially intended to control the Habitation Module, these MDMs were repurposed after that module was deleted from the program. (continued next page)