Historical
Invocon developed the External Wireless Instrumentation System (EWIS) to provide long-term structural dynamics measurements of the International Space Station (ISS) solar array trusses while deployed on-orbit. Due to the rotating joints that allow the solar arrays to track the sun throughout the orbit, installing wired sensors was prohibitively expensive and complex. The wireless interface to EWIS has enabled NASA to integrate the desired instrumentation at a reasonable cost late in the ISS module assembly process with minimal impacts to the vehicle and without having to sacrifice performance. When commanded, EWIS data acquisition units acquires highly-synchronized micro-g measurements from 10 triaxial accelerometers distributed along the truss and forward this information via Radio Frequency communication into the ISS, where it is downlinked to controllers at Mission Control. Additionally, both a continuous monitoring mode for recording dynamic events and a cycle counting algorithm for continuous tracking of structural fatigue have been implemented. Invocon was responsible for generating and executing all qualification and acceptance test plans and procedures for EWIS under a subcontract to Boeing Houston. Testing was performed at Invocon, NASA Johnson Space Center, and other outside test facilities. The EWIS system components interface with multiple ISS vehicle electrical systems, including 120V power, Mil-Std-1553 for time distribution, the OpsLAN for data transfer, and the ISS Fileserver and Space Station Computer (SSC) laptop computers for system control. All system interfaces were verified through analysis and testing.
