  mercury-atlas 4 was an unmanned spaceflight of the mercury program. it was launched on september 13, 1961 at 14:09 utc from launch complex 14 at cape canaveral, florida. a crewman simulator instrument package was aboard. the craft orbited the earth once. 349px|left|thumb|alt=simulator in spacecraft|simulator in spacecraft at this time, nasa was getting increasingly frustrated with the atlas's poor launch record. of four mercury-atlas flights so far, two (ma-1 and ma-3) had been total failures. one (big joe) had been a partial success and the otherwise completely successful ma-2 had experienced propellant slosh problems. in addition, the atlas had not performed well in unmanned programs either as three atlas-able lunar probe launches in 1959&ndash;60 had all failed. the air force was also experiencing problems with military launches as a midas early warning satellite and a samos photoreconnaissance satellite launched with atlasagenas both failed to orbit during 1960. only a few days before the flight of ma4 in september 1961, an atlasagena carrying a samos satellite fell back on the launch pad at vandenberg afb, producing a spectacular explosion. atlas icbm tests at this time were still routinely failing as well.
Project_Mercury Spacecraft_launched_in_1961 Spacecraft_which_reentered_in_1961