Surveillance Direction System 
Satellite Data System 
System Design Specification 
Software Design Standards 
Short Data Service 
Software Design Specification 
Steering Damping System 
Switched Data Service 
Shuttle Dynamic Simulator 
Safety Data Sheet 
Secure Digital Switch 
Shuttle Data Systems 
Shuttle Dynamic Simulation 
Software Development Specification 
Software Development System 
Switched Digital Service 
Synchronous Data Set 
Satellite Discriminating Sensor 
Scientific Data System 
SDH Data Sub-network 
Sensor Display System 
Shock Dampening System 
Signal Dependent Stereo 
smart distributed system 
solar disk sextant 
Speech Digit Signalling 
Submerged demineralizer system 
Sysops Distribution System 
Sample Delivery System 
Sample Distribution System