The EV-CPDS is basically a frame containing 3 CPDS units like the "IV-CPDS" which is used inside the Station. Normally, one is pointed forward (in the direction ISS is travelling), one is pointed in the reverse or "anti-velocity" direction and one points straight up ("zenith") away from Earth. A small part of the time ISS will be in "X-pop" mode where the station will be rotated somewhat around the vertical axis in order to increase the efficiency of the solar collectors.

Particle Angle Detection Basics At right, only two of the 3 X,Y postition planes are shown. Note that strips run horizontally on one side and vertically on the other side of a thin silicon chip. When a high energy particles passes through, a charge pulse is produced in only one X and one Y strip, giving the location of the penetration. Simple geometry of the penetration location in two planes gives the direction angles of the particle. The amplifiers (triangle shapes) and multiplexer electronics for each row or column are contained in a single chip developed by the CERN acclerator people in Europe. The multiplexed signal output (two for each detector plane) is analyzed by on-board electronic circuits and the results recorded for each particle event.