The Wikipedia page for NASA Flight director Holly Ridings contains a portrait with two other STS-117 mission flight directors. The caption there says:
Flight directors for the STS-117 mission in June 2007. Annette Hasbrook (ISS Orbit 1), Kelly Beck (ISS Orbit 2 & lead) and Holly Ridings (ISS Orbit 3).
Question: Why would different Shuttle orbits have different mission directors?