Northrop Grumman’s Cygnus XL cargo ship, carrying more than 11,000 pounds of equipment and supplies for the International Space Station, suffered two premature engine shutdowns Tuesday, forcing flight controllers to interrupt a carefully planned rendezvous and delay the ship’s arrival at the outpost.
It was not immediately known what went wrong or when the spacecraft might be able to complete its rendezvous, assuming flight controllers can resolve the problem and develop an alternative “burn plan.”
NASA 
“Early Tuesday morning, Cygnus XL’s main engine stopped earlier than planned during two burns designed to raise the orbit of the spacecraft for rendezvous with the space station,” NASA said in a blog post. “All other Cygnus XL systems are performing normally.”
No other details were provided.
The Cygnus was launched Sunday from Cape Canaveral atop a SpaceX Falcon 9 rocket. The cargo ship was released from the booster’s upper stage as planned, kicking off a precisely planned sequence of rendezvous rocket firings to catch up with the space station.
Unlike SpaceX’s cargo Dragon and Russian Progress freighters, which carry out autonomous dockings at their respective ports, the Cygnus was designed to be captured by the station’s robot arm and pulled in for berthing.
The Cygnus XL capture had been planned for Wednesday morning, but it’s now on hold while engineers work to understand the problem and develop an alternate rendezvous plan.
“The Cygnus XL will not arrive to the space station on Wednesday, Sept. 17, as originally planned, with a new arrival date and time under review,” NASA said in its blog post.
A Progress launched last week successfully docked at the station Saturday. The Cygnus XL launch was a long-awaited milestone for Northrop Grumman after an earlier Cygnus was damaged during transit from a subcontractor in Europe to Cape Canaveral. That vehicle is still grounded pending analysis and repairs.
Sunday’s launch was the third of at least four SpaceX flights purchased by Northrop Grumman while the company recovers from the transit setback and presses ahead with work to develop a new booster of its own.
SpaceX 
And it was the maiden flight of the Cygnus XL, so named because the upgraded cargo ship has been lengthened to carry more cargo to the station per flight.
“We’ve been partnering with Northrop Grumman on this update, and we’re excited that Northrop is ready to deliver this incredibly beneficial increase in capacity,” Dina Contella, deputy manager of the space station program for NASA, said before launch. “It’s about 1.6 meters (5 feet) longer and it carries about 2,600 additional pounds more cargo.”
For its first flight, the XL ship is loaded with more than five-and-a-half tons of needed spare parts, research material and crew supplies, including holiday treats for the station crew.
“The (Cygnus) is packed with consumables, like nitrogen, oxygen, food and toilet parts, and it has a large number of spare parts that are required for systems like, for example, our urine processor,” said Contella. “We’re stocking up on these items since we were short over the past year, and we’d like to have a good reserve for the future.”
NASA pays for cargo delivery flights using Cygnus and Dragon spacecraft. To date, SpaceX has successfully carried out 32 Dragon resupply missions while Northrop Grumman has completed 20 successful flights not counting the current mission.
Both companies suffered one in-flight failure each due to launch mishaps early in the commercial resupply program.
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