Manned flights

All of the six crewed Mercury flights were successful, though some planned flights were canceled during the project. The main medical problems encountered were simple personal hygiene, and post-flight symptoms of low blood pressure. The launch vehicles had been tested through uncrewed flights, therefore the numbering of crewed missions did not start with 1. Also, there were two separately numbered series: MR for “Mercury-Redstone” (suborbital flights), and MA for “Mercury-Atlas” (orbital flights). These names were not popularly used, since the astronauts followed a pilot tradition, each giving their spacecraft a name. They selected names ending with a “7” to commemorate the seven astronauts.