To know the distance separating MOM and Earth we make use of radio waves.
The time taken by the radio signal to go to MOM and come back is indicative of the distance between MOM and Earth. MOM is presently about 35 lakh km away from Earth and it takes about 23 seconds for the radio waves to go and come back at the speed of light (about 3 lakh km per second).
That’s as simple as saying ( speed x time )/2 = distance.
The rather obscure jargon for this simple distance calculation is the term called ‘range’
