OA-9 Cygnus leaves ISS
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OA-9 Cygnus as seen during its arrival at the ISS on May 24, 2018. Credit: NASA
Following two months attached to the International Space Station, the ninth Cygnus resupply spacecraft was unberthed and released from the orbiting outpost to perform a secondary two-week free-flight mission.
The Northrop Grumman (formerly Orbital ATK) OA-9 Cygnus was unberthed in the early-morning hours of July 15, 2018, before being released at 8:37 a.m. EDT (12:37 GMT). Upon departure the cargo ship and ISS were flying 407 kilometers above the southeastern border of Colombia. Expedition 56 flight engineers Serena Aunon-Chancellor of NASA and Alexander Gerst of the European Space Agency (two of six people residing at the outpost) were at the controls of the station’s 57.7-foot (17.6-meter) robotic Canadarm2 and commanded it to release the vehicle.
“It was really cool watching Cygnus depart,” said Expedition 56 Flight Engineer Serena Aunon-Chancellor of NASA to Mission Control in Houston. “[It was] almost a little surreal to watch a cargo vehicle like that depart the station and then to see it from a distance and just think this was just a normal day at the office.”
The OA-9 Cygnus, named S.S. J.R. Thompson, was launched to the outpost on May 21. After a three-day trek, the spacecraft rendezvoused with the ISS and came within about 10 meters of the outpost’s Destiny laboratory module. Using Canadarm2, the then Expedition 55 crew captured the freighter. Several hours later, the arm was used to maneuver the ship to the Earth-facing port of Unity to be berthed.
Over the course of its 52-day stay at the ISS, its 3,400 kilograms of cargo was unloaded and then reloaded with some 3,000 kilograms of unneeded equipment for eventual disposal by burning up over the Pacific Ocean.
A view of the OA-9 Cygnus with Soyuz MS-09 docked in the background. Credit: NASA
Several days before unberthing operations were underway, a unique task was performed by Cygnus—a test of the spacecraft’s reboost capability. It was the first time a commercial vehicle performed this task, which is typically handled by Russian Progress spacecraft.
At 4:25 p.m. EDT (20:25 GMT) July 10, Cygnus’s main engine was fired for about 50 seconds. Although brief, it still raised the altitude of about 90 meters, according to NASA.
The space station flies some 400 kilometers above Earth. However, there is still a tiny amount of atmospheric particles that constantly slow the 400-metric-ton outpost down, gradually lowering its orbit. If reboosts every few months are not performed, eventually the station would fall out of the sky.
Reboosts of the station were performed by the now-retired NASA’s space shuttles many times during the construction phase of the outpost between 1998 and 2011. Since then, Russia’s Progress spacecraft has been the primary vehicle to raise the orbit of the ISS. Additionally the European Space Agency’s Automated Transfer Vehicle, which just like the space shuttle has since been retired, also helped with reboosts.
The Zvezda service module, which was launched in 2000, also has a fuel reserve and can raise the orbit of the space station. But as it is limited, it is reserved for use only when a visiting vehicle is unable to perform the task.
While the OA-9 Cygnus’s ISS mission is complete, it won’t perform a deorbit burn until July 30. That two-week free-flight will be used to deploy six CubeSats using an external NanoRacks deployer attached to the spacecraft. Once complete, Cygnus will be commanded to deorbit over the southern Pacific Ocean to burn up safely.
The next Cygnus is currently planned for late November 2018. However, the exact date will flex over the coming months as the visiting vehicle schedule works to accommodate not only the comings and goings of the Russian Soyuz and Progress spacecraft, but also a Japanese Kounotori cargo spacecraft in September as well as the first uncrewed test flights of the Commercial Crew Program as early as Fall 2018.
NOTE: While this article was written by Derek Richardson, it was originally published at SpaceFlight Insider. Feel free to head over there to read all the stuff they write about!
