Delta Differential One-way Ranging (DDOR) is a navigation technique used in interplanetary missions such as our Mars Orbiter Mission. This technique requires co-ordinated observations of the Spacecraft and Reference sources - called Quasars - by two geographically distant Antennas. Correlator is the software that processes these observations and provides accurate Difference-of-time arrival of the signals - on the Insec order - which in turn helps infer the accurate angular position of the Spacecraft for navigation. We have developed the Correlator software indigenously, and it is qualified for Mission Navigation support. Broadly, the Correlator is composed of three modules: Quasar Correlation, Spacecraft Correlation and Theoretical Model Delay Computation. This paper outlines the challenges faced, the design and implementation aspects, and the validated results obtained.
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