OA-4, previously known as Orbital-4, was the fourth successful flight of the Orbital ATK uncrewed resupply spacecraft Cygnus and its third flight to the International Space Station (ISS) under the Commercial Resupply Services (CRS-1) contract with NASA.

With a liftoff weight of 7,492 kg (16,517 lb), OA-4 became the heaviest payload ever launched on an Atlas V.[9] The spacecraft rendezvoused with and was berthed to the ISS on 9 December 2015.

[7] In an Orbital ATK tradition, this Cygnus spacecraft was named Deke Slayton II after Deke Slayton, one of NASA's original Mercury Seven astronauts and Director of Flight Operations, who died in 1993.

[11] The mission was the first flight of the enhanced variant of Orbital ATK's Cygnus spacecraft, capable of delivering more than 3,500 kg (7,700 lb) of essential crew supplies, equipment and scientific experiments to the International Space Station (ISS).

Total cargo: 3,349 kilograms (7,383 lb)[5][12] Total cargo with packing material: 3,513 kg (7,745 lb) Media related to Cygnus 5 at Wikimedia Commons