As the International Space Station's (ISS's) various habitable modules are placed in service on orbit, the need to provide for sustaining engineering becomes increasingly important to ensure the proper function of critical onboard systems. Chief among these are the environmental control and life support system (ECLSS) and the internal thermal control system (ITCS). Without either, life on board the ISS would prove difficult or nearly impossible. For this reason, a ground-based ECLSS/ITCS hardware performance simulation capability has been developed at NASA Marshall Space Flight Center (MSFC). The ECLSS/ITCS sustaining engineering test bed will be used to assist the ISS program in resolving hardware anomalies and performing periodic performance assessments. The ISS flight configuration being simulated by the test bed is described as well as ongoing activities related to its preparation for supporting ISS Mission 5A. Growth options for the test facility are presented so the current facility can be upgraded to enhance its capability for supporting future Station operations well beyond Mission 5A. Test bed capabilities for demonstrating technology improvements of ECLSS hardware are also described.