round-trip light time

[Monty]

the elapsed time it takes for a signal to travel from Earth to a spacecraft (or other body) and back to the starting point

[Tjalfdyed 0]

Round-trip light time is the total time it takes for a beam of light to travel from a source to a target and then back to the original source. This concept is commonly used in astronomy and space exploration to calculate distances between celestial bodies or spacecrafts, and it is based on the constancy of the speed of light.