The Mars 4 orbiter reached Mars on February 10, 1974. Due to a flaw in the transistor 2Т-312 which resulted in its degradation during the voyage to Mars, the retro-rockets designed to slow the craft into Mars orbit did not fire, and Mars 4 flew by the planet at a range of 2200 km. It returned one swath of pictures and some radio occultation data which constituted the first detection of the nightside ionosphere on Mars. It continued to return interplanetary data from heliocentric orbit after the flyby.