Mariner 3 (together with Mariner 4 known as Mariner-Mars 1964) was one of two identical deep-space probes designed and built by the Jet Propulsion Laboratory (JPL) for NASA's Mariner-Mars 1964 project that were intended to conduct close-up (flyby) scientific observations of the planet Mars and transmit information on interplanetary space and the space surrounding Mars, televised images of the Martian surface and radio occultation data of spacecraft signals as affected by the Martian atmosphere back to Earth.

[1][2] Although the launch was initially successful, there was a separation issue and Mariner 3 stopped responding when its batteries ran out of power.

Unsure of the exact problem, ground controllers issued a command to turn off the rate gyros to conserve power while they worked to figure out what had happened.

The ground controllers next considered firing Mariner 3's midcourse correction engine to blow off the shroud, but they ran out of time.

Even if the shroud could be removed, the mission would have failed, since the low velocity meant that Mariner 3 would miss Mars by several million miles.