OA-4, previously known as Orbital-4, was the fourth successful flight of the
Orbital ATKuncrewed resupply spacecraftCygnus and its third flight to the
International Space Station (ISS) under the
Commercial Resupply Services (CRS-1) contract with
NASA.[8][9] With the
Antares launch vehicle undergoing a redesign following its failure during the
Orb-3 launch, OA-4 was launched by an
Atlas V launch vehicle. Following three launch delays due to inclement weather beginning on 3 December 2015, OA-4 was launched at 21:44:57
UTC on 6 December 2015. With a liftoff weight of 7,492 kg (16,517 lb), OA-4 became the heaviest payload ever launched on an Atlas V.[10] The spacecraft rendezvoused with and was berthed to the ISS on 9 December 2015.[6] It was released on 19 February 2016 after 72 days at the International Space Station. Deorbit occurred on 20 February 2016 at approximately 16:00 UTC.[4]
OA-4 was the fourth of eight flights by
Orbital ATK under the
Commercial Resupply Services (CRS-1) contract with
NASA and the inaugural flight of the larger Enhanced Cygnus PCM. The mission was originally scheduled for 1 April 2015.[11] The
Atlas Vlaunch vehicle launched in the 401 vehicle configuration with a four-meter fairing, no solid rocket boosters and a single-engine Centaur upper stage.[8]
In an Orbital ATK tradition, this Cygnus spacecraft was named Deke Slayton II after
Deke Slayton, one of NASA's original
Mercury Sevenastronauts and Director of Flight Operations, who died in 1993. This spacecraft reuses the name Deke Slayton, originally applied to the Orb-3 spacecraft which was lost in an Antares rocket explosion in October 2014.[12]
Manifest
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).
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ).
Cubesats are smaller. Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).