An experimental geodetic satellite orbits Earth and is equipped with a retroreflector consisting of two flat mirrors joined at a 90∘ 90^\circ\,90∘ angle.
An incident light ray strikes Mirror 1 with an angle of incidence of 35∘35^\circ35∘.
State the angle of reflection of the ray at Mirror 1.
Calculate the angle of incidence of the reflected ray when it strikes Mirror 2, and explain why the final reflected ray from Mirror 2 is parallel to the incident ray.
Ground stations aim laser pulses at the satellite's retroreflector to measure its distance.
Show that the average distance to the satellite is 6000 km.
The round-trip travel time of the laser pulses varies over the course of the satellite's 12-hour orbit.
Suggest what can be deduced about the satellite's orbit from the variation shown in the graph.
Very precise measurements over several years show that the average round-trip travel time increases by a tiny fraction of a microsecond each year. What further information does this give about the orbit of the satellite?
