Just seconds after liftoff on October 28, 2014, an Orbital Sciences rocket exploded, destroying 5,000 pounds of space station supplies. No one was onboard, thankfully, but the blast took out part of the Wallops Flight Facility in Virginia.
The two independent assessments point to an explosion in one of the engines' liquid oxygen turbopump, but what caused the explosion remains unclear. NASA chalks it up to either poor engine design, debris in the engine, or a manufacturing defect. Orbital says a manufacturing defect is the most likely explanation.
Orbital has since switched engines from the AJ-26 engine to the Russian-made RD-181, and aims to resume ISS resupply launches with Antares next year.