Abstracts:Among all of the offered methods to determine the attitude of a spacecraft, in this research, three optimal algorithms solving the Wahba problem algebraically due to their simplicity of implementation are examined. Furthermore, this study elucidates the sources of attitude determination errors and aims to enable Attitude Determination and Control Subsystem (ADCS) engineers to choose a suitable microprocessor to implement the attitude algorithm. This research tends to show the difference in interpretation of attitude knowledge errors arising from both Model-in-the-Loop (MIL) and Processor-in-the-Loop (PIL) simulations. To this aim, we conduct PIL tests on two different kind of microcontrollers, one of which is a 32-bit and the other is a 16-bit one. We compare the performance of algorithms in MIL with the two PILs resulting from 16- and 32-bit architectures and inspect the source of accuracy reduction. Finally, we conclude the best algorithm regarding implementation and the round-off errors arising from that. In addition, the execution time of methods is checked in order to evaluate prescribed solutions based on this criterion.