The validation tests conducted on the Control/Structures Interaction (CSI) Computer System (CCS)/Remote Interface Unit (RIU) is discussed. The CCS/RIU consists of a commercially available, Langley Research Center (LaRC) programmed, space flight qualified computer and a flight data acquisition and filtering computer, developed at LaRC. The tests were performed in the Space Structures Research Laboratory (SSRL) and included open loop excitation, closed loop control, safing, RIU digital filtering, and RIU stand alone testing with the CSI Evolutionary Model (CEM) Phase-0 testbed. The test results indicated that the CCS/RIU system is comparable to ground based systems in performing real-time control-structure experiments. Sparks, Dean W., Jr. Langley Research Center ACCEPTABILITY; AIRBORNE/SPACEBORNE COMPUTERS; COMPUTER COMPONENTS; FEEDBACK CONTROL; FLIGHT CONTROL; REAL TIME OPERATION; DATA ACQUISITION; DIGITAL FILTERS; SPACECRAFT ELECTRONIC EQUIPMENT; SPACECRAFT STRUCTURES...