Cygnus NG-18
Video from the International Space Station showed that one of two solar arrays on the Cygnus spacecraft failed to unfold after its launch two days earlier. Credit: NASA TV

Updated 6:15 p.m. Eastern with Northrop Grumman statement.

WASHINGTON — A Northrop Grumman Cygnus cargo spacecraft arrived at the International Space Station Nov. 9 despite having only one of its two solar arrays deployed.

The Cygnus spacecraft, flying the NG-18 cargo resupply mission for NASA, arrived at the station and was grappled by the station’s robotic arm at 5:20 a.m. Eastern. The arm berthed the spacecraft to the station’s Unity module two and a half hours later.

An Antares rocket successfully launched Cygnus Nov. 7, but several hours later NASA reported that one of two solar arrays had failed to deploy after reaching orbit. Northrop said that the spacecraft had enough power from the one deployed solar array to operate the vehicle, but NASA said engineers were studying any issues the undeployed array might have on grappling and berthing the spacecraft.

NASA said in a Nov. 8 statement that it would proceed with having Cygnus approach the station. “Northrop Grumman and NASA made the determination not to deploy the second solar array after initial attempts to deploy it were unsuccessful,” the agency stated.

Video from the ISS showed that while one of the circular arrays, designed to unfold like a fan, deployed as expected, the other appeared to have unfolded only slightly. “The Cygnus team is gathering information on why the second array did not deploy as planned,” NASA stated.

In a statement late Nov. 9, Northrop Grumman blamed the failed deployment of the array on debris from the launch. “During a rocket stage separation event, debris from an Antares acoustic blanket became lodged in one of the Cygnus solar array mechanisms, preventing it from opening,” said Cyrus Dhalla, vice president and general manager of tactical space systems at Northrop Grumman. The company did not explain how the debris got into the mechanism, something the company has not reported happening on previous Cygnus launches.

Cygnus delivered to the station nearly 3,750 kilograms of cargo, including crew supplies, scientific payloads and hardware. That hardware includes a solar array bracket that astronauts Josh Cassada and Frank Rubio will install outside the station on a Nov. 15 spacewalk as part of efforts to upgrade the station’s solar power systems.

Cygnus is scheduled to remain attached to the station until late January, when it will depart the station, loaded with trash, for a destructive reentry.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...