Updated at 8 p.m. Eastern.
WASHINGTON — An Atlas 5 rocket successfully launched an Orbital ATK Cygnus cargo spacecraft Dec. 6 after three days of delays, resuming deliveries of essential supplies and experiments to the International Space Station by U.S. companies.
The United Launch Alliance Atlas 5 401 lifted off from Space Launch Complex 41 at Cape Canaveral, Florida, at 4:44 p.m. Eastern time. The Cygnus spacecraft, on a mission designated OA-4, separated from the rocket’s upper stage 21 minutes after liftoff after entering orbit 230 kilometers above the Earth.
The Cygnus spacecraft, named the S.S. Deke Slayton II by Orbital ATK, deployed its solar arrays shortly after entering orbit, and company officials said the spacecraft was in good health as it began a two-and-a-half-day approach to the ISS.
“Everything is basically nominal on board the Deke Slayton II,” said Frank Culbertson, president of Orbital ATK’s Space Systems Group, in a post-launch press conference.
Cygnus, carrying more than 3,500 kilograms of supplies, equipment and experiments for the ISS, is scheduled to arrive at the station early Dec. 9. The station’s robotic arm will grapple the spacecraft and berth it to the Earth-facing port on the Node 1, or Unity, module, the first time that docking port has been used by a cargo spacecraft.
The launch was previously scheduled for Dec. 3, but postponed because of poor weather at the launch site. Winds scrubbed a second launch attempt Dec. 4, and a third attempt Dec. 5 was postponed a few hours before the launch because weather forecasts predicted unfavorable conditions.
With winds gusting close to limits, ULA changed the way it monitored winds for this launch attempt. Vern Thorp, program manager for NASA missions at ULA, said in a pre-launch interview on NASA TV that ULA switched from automated to manual monitoring of wind conditions, and when it monitored wind conditions, to avoid triggering a hold by a wind gust that did not pose an actual hazard to the launch.
The launch is the first for the Cygnus since the October 2014 failure of an Antares rocket shortly after liftoff from Wallops Island, Virginia. Shortly after that failure, Orbital purchased an Atlas 5 launch from ULA to fulfill its contractual requirements to NASA to deliver cargo to the ISS.
The Cygnus cargo includes nearly 1,200 kilograms of crew supplies, topping up stockpiles of consumables there that, in some cases, have started to fall to low levels. Cygnus is also carrying 1,000 kilograms of station hardware, including some spare parts that have also started to drop to low levels on the station.
“We’ve been consuming some of our critical spares,” Kirk Shireman, NASA ISS program manager, said at a Dec. 2 press conference at the Kennedy Space Center. “We are below where we would like to be relative to our on-orbit hardware spares.”
Besides crew supplies and spare parts, the Cygnus is also carrying nearly 850 kilograms of research payloads. Some of those are science experiments studying topics ranging from combustion to fluid dynamics, while others are small satellites that will be later deployed from the station.