Up until 2015 the rate at which cube satellite missions achieved full mission success was only 44.1% for any organizations rst mission (academic or corporate), the success rate increases to only 62% for cube satellites launched as a second mission. This thesis suggests that there are two main sources for the high failure rate:​ improper veri cation, and the common use of COTS components and their reliability in a space environment. The thesis provides a means of increasing mission assurance through the use of physics of failure reliability estimation models that incorporate the intrinsic and extrinsic failures of thermal mechanical e ects as well as radiation e ects on EEE components, a design methodology is also presented that incorporates reliability modeling as well as thorough software and hardware in loop testing to prevent failure due to improper veri cation. The environment and reliability models are calculated for the on board command and data handling system of the ECOSat- II cube satellite being developed by the University of Victoria ECOSat team using NX Siemens for thermal FEA modelling, SPENVIS for radiation environment, and MATLAB for reliability calculation.