A planned Mars mission that ended in a spectacular failure occurred on this day in history.
Mars 1969B, or Mars 2M No.522, was launched by the Soviet Union onboard a Proton rocket on April 2nd, 1969. The goal of the spacecraft was to take pictures of the Red Planet with a variety of cameras onboard, as well as take other readings with scientific instruments.
However, moments after launch, an engine caught fire and the rocket came back down on the launch complex less than a minute after takeoff. The fuel leak and rocket debris actually blocked the people working on the launch from getting out for a time. This, along with the failure of Mars 1969A, meant that the Soviets could send attempt to send no more probes to Mars for a couple more years. Meanwhile, the United States saw mostly success with their Mariner program to Mars.