Atlas-Able 4 launcher
Pioneer P-1 was a space probe intended to be launched into Lunar orbit. There it would study the space environment between the Earth and the Moon, as well as advanced spacecraft control from Earth and also included a newer television camera system.
Unfortunately, during a launcher test at the cape, the Atlas rocket exploded on the pad and caused tremendous damage, but luckily no one was killed or injured. Fortunately, the probe had not yet been placed onto the rocket at the time of the explosion! P-1 was later used for the P-3 mission.