The Instrument is the main design driver for a simulator. For Earth Observations missions there are 4 main types of instruments: Passive Opticals, Active Microwaves, Passive Microwaves and Active Opticals [Ref]:
Main type of instruments for EO missions.
The Module is a stage of the simulation chain. The simulation chain of any Earth Observation end-to-end simulator can be divided into 6 basic Modules.
The Modules compose the Reference Architecture.
Each Module is composed by Blocks. A Block is a unit of software that performs one functionality, for example the Orbit Block, the Attitude Block, the Line-of Sight Block, etc. The Blocks are the “bricks” of the simulation chain.
