The Space Shuttle stack, comprised of the Orbiter, External Tank, and Solid Rocket Boosters, occupies the center of the patch in launch configuration. The United States flag overlays the stack to represent the contribution of the Space Shuttle to America's space program. The trajectory around the Earth depicts the orbital phase of the Shuttle's mission, while the thin layer of atmosphere symbolizes the ascent and entry phases. The 25 stars on the orbiter wing denote its Mach 25 reentry velocity. The top of the patch features the designations of the six named vehicles, which are further represented by the six rays emanating from the sun. The names Challenger and Columbia are set apart to memorialize the loss of those vehicles, as fourteen stars surround the Earth to honor the crewmembers of those missions.