The goal of this thesis is to design a coprocessor expansion board for an On Board Computer (OBC) using Commersial Off The Shelf (COTS) components. This is done in order to meet the increasing demand of more processing power as spacecrafts become more autonomous. After evaluating a number of different options, the LS1046A from ARM was chosen as the processing unit. This would increase the processing power from the current 110 Dhrystone Million Instructions Per Second (DMIPS) to a theoretical 22 560 DMIPS. The schematic was designed in DxDesigner, and after the layout was completed signal integrity simulations were performed in HyperLynx. After modifications to termination resistances, the simulations showed good signal integrity confirming proper routing of the signals. After receiving the manufactured Printed Circuit Board (PCB) with all components mounted, some tests could be performed confirming that the power distribution and the system clock was functioning properly.