CRS OA 4
CRS OA-4, also known as Orbital Sciences CRS Flight 4 was the fourth successful flight of the Orbital ATK uncrewed resupply spacecraft Cygnus and its third flight to the ISS under the Commercial Resupply Services contract with NASA. With the Antares rocket undergoing a redesign following its failure during the Orb-3 launch, OA-4 was launched by an Atlas V rocket. Following three launch delays due to inclement weather beginning on 3 December 2015, OA-4 was launched at 21:44 UTC on 6 December 2015. With a liftoff weight of 7,492 kilograms (16,517 lb), OA-4 became the heaviest payload ever launched on an Atlas V.