ISRO Satellite Centre (ISAC) is the lead centre of the Indian Space Research Organisation in the development and operationalisation of satellites for communication, navigation and remote sensing applications. In all these spacecrafts, highly advanced embedded systems carryout variety of mission critical functions. Each of these embedded systems house heterogeneous Processor and Embedded Software Combinations to carry out their functionalities. As per existing practices, testing of on board software to confirm its functioning takes place only when the software is integrated with its associated hardware. On the contrary, by a technique called the Software in Loop Simulation (SILS) test method, the on-board software can be fully tested in a software simulated dynamic environment without Hardware. This method of flight software validation is demonstrated in MARS ORBITER MISSION for AOCE, TCP, SSR, BDH software. The results very well demonstrate the effectiveness of the technique in early performance prediction and assessment of on-board software. This validation philosophy will be followed for all future spacecrafts. In a development, environment where software requirements are too complex and requirement changes are to he incorporated even during final stages of development, this technique offers an excellent solution in fully validating on board software at source code level before it gets integrated with target hardware. This additional validation step not only improves software quality but also enhances productivity and reduces system turnaround time.
