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S.S. Deke Slayton II departs International Space Station

Cygnus and Arm

Cygnus was released from the space station on Feb. 19. It will deorbit into the Pacific Ocean on Saturday, Feb. 20. Photo Credit: NASA

After spending more than two months at the International Space Station (ISS), the Deke Slayton II Cygnus cargo ship pulled away from the outpost on Feb. 19 in preparation for disposal in the Earth’s atmosphere.

Controllers at NASA’s Mission Control Center in Houston commanded the station’s robotic Canadarm2 to unberth the Orbital ATK cargo ship earlier in the morning, and position the spacecraft about 30 feet (9.1 meters) below the station. NASA astronaut and the station’s current commander, Scott Kelly, then commanded the arm to release the craft at 6:26 a.m. CST (12:26 GMT) while the pair were flying over the eastern part of Bolivia.


Expedition 46 Flight Engineer Tim Kopra tweets a picture of the soon-to-depart Cygnus cargo ship. It has been attached to the station since December 2015 and will be unberthed by the robotic arm on Feb. 19. Photo Credit: Tim Kopra / NASA

“Goodbye Cygnus,” Kelly said as the spacecraft was thrusting away from the space station. “It was a pleasure having you on board our space station for so long and thanks to all the folks that in Houston, and Dulles especially, that provided us this great vehicle for us. It’s been a pleasure.”

After the release, the Deke Slayton II’s thrusters pushed the craft down and away from the orbiting lab, leaving the station’s ‘Keep-Out Sphere’—a bubble of about 660 feet (200 meters) intended to prevent collisions.

The spacecraft will stay in orbit, moving away from ISS, until Saturday, when its engines will fire two separate times to send it on a destructive course for the atmosphere. From there, Cygnus will burn up over the Pacific.

Cygnus arrived at the orbital complex on Dec. 9, 2015, after being launched atop a United Launch Alliance Atlas V 401 rocket from Cape Canaveral Air Force Station’s Space Launch Complex 41 in Florida three days earlier. Once close to the orbiting lab, it was captured by Canadarm2 and berthed to the nadir port of the Unity module, the first commercial cargo ship to be berthed to that port.

This was Orbital ATK’s return-to-flight mission after the last Cygnus spacecraft was lost in an explosion of the Antares rocket that carried it on October 2014. A return to flight for that rocket is currently planned to take place in late May.

The liftoff weight of the OA-4 Cygnus was some 16,517 pounds (7,492 kilograms)—the heaviest payload ever launched by an Atlas V rocket. It brought with it, among other things, new experiments supporting NASA research in biology, biotechnology, as well as physical and Earth sciences. It also brought up a new life science facility and a microsatellite deployer with the first microsatellite to be deployed from the outpost.

Cygnus spent nearly 72 days attached to the station as the Expedition 46 crew unloaded the more than 7,383 pounds (3,349 kilograms) of supplies. They then reloaded the spacecraft with trash and unneeded equipment.

This was Orbital ATK’s fourth NASA-contracted commercial station resupply mission. The OA-4 Cygnus sported new features that included an extended pressurized container and UltraFlex solar arrays.

Cygnus grappled

Tim Kopra tweeted a close-up image of Canadarm2 holding Cygnus before unberthing. The spacecraft parted ways with the station at 6:26 a.m. CST (12:26 GMT) on Feb. 19. Photo Credit: Tim Kopra / NASA

The next Cygnus cargo mission to launch, dubbed OA-6, is scheduled to launch no-earlier-than March 22—a delay from March 10 due to a black mold contamination issue with cargo bags, which, according to Florida Today, has since been resolved.

OA-6 will also launch atop an Atlas V 401 from the Cape. In addition to food and supplies for the space station, this Cygnus will include a new science payload that will help scientists understand the threat of fire on board vehicles in space. The Spacecraft Fire Safety Demonstration Project, called Saffire, will investigate the spread of fires in microgravity.

The experiment will not be active while Cygnus is berthed to ISS and will only be turned on after the spacecraft is a safe distance away from the outpost.

Three Cygnus spacecraft will be launched with the Saffire experiment: OA-6 in March, OA-5 in June, and OA-7 in October.

Video courtesy of NASA


Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity. You can find him on twitter @TheSpaceWriter.

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