Cygnus CRS OA-4 Cygnus CRS OA-4, also known as Orbital ATK CRS-4 and CRS Orb-4, was the fourth successful flight of the Orbital ATK uncrewed resupply spacecraft Cygnus and its third flight to the International Space Station 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, OA-4 became the heaviest payload ever launched on an Atlas V. The spacecraft rendezvoused with and was berthed to the ISS on 9 December 2015. It was released on 19 February 2016 after 72 days at the station. Deorbit occurred on 20 February at approximately 16:00 UTC.