1960-07-29 USA Mercury Atlas MA-1

MA-1 launch cover with Goldcraft cachet, postmarked Port Canaveral, July 29, 1960.
Mercury-Atlas 1 (MA-1) was the first attempt to launch a Mercury capsule at Cape Canaveral on July 29, 1960. The spacecraft was unmanned and carried no launch escape system. The Atlas rocket suffered a structural failure 58 seconds after launch at an altitude of approximately 30,000 feet (9.1 km) and 11,000 feet (3.4 km) down range. The vehicle exploded on its way through max q and all telemetry signals ceased. Because the day was rainy and overcast, the booster was out of sight from 26 seconds after launch, and it was impossible to see what happened.

MA-1 launch cover with PAFB postmark July 29, 1960.
The mission was to conduct a suborbital test flight and reentry of the spacecraft. The capsule carried live separation rockets, but dummy retrorockets. Several other systems were not installed, including the cabin pressurization system and the astronaut couch. A number of Mercury engineers had voiced their objection to the launch because the weather would prevent observation of the flight. Some witnesses claimed to have heard an explosion, but this could not be verified. The capsule continued transmitting until it impacted the ocean, approximately 6 miles downrange. Salvage brought the capsule, Atlas booster engines and LOX vent valve to the surface from the ocean floor. The engines showed no sign of damage except some deformation from impact with the ocean, but the vent valve and a still-attached segment of piping had noticeable fatigue cracks.

(Reference from Mercury-Atlas 1)