If I'm travelling to the moon or any other object I can record my speed relative to that object just fine and through similar processes record the distance to the object at any given time along my journey. My speed can be deduced by simple Doppler measurements. My distance can be deduced by the total time it takes to do a single measurement of my speed. Why do you think you need a 3rd observer to do this?
Take for instance an AEW&C plane. Their radar lets the operators know the vector of the object which includes the distance to an object and that object's direction and speed relative to the AEW&C plane. Sure the radar system can do further calculations and say how fast, far and what direction objects are travelling with regard to a point on the ground but that is an additional transformation that the system performs. The measurements of AEW&C always start out relative to the AEW&C plane itself.