Not XLing
A record supply load won’t reach the International Space Station as scheduled
The problem arose early Tuesday when the spacecraft’s main engine shut down earlier than expected.
Sep 16, 2025 7:13 pm
63
File photo of a previous Cygnus spacecraft at the International Space Station, showing the vehicle’s main engine.
Credit:
NASA
File photo of a previous Cygnus spacecraft at the International Space Station, showing the vehicle’s main engine.
Credit:
NASA
Text
settings
Story text
Size
Small
Standard
Large
Width
*
Standard
Wide
Links
Standard
Orange
* Subscribers only
Learn more
Minimize to nav
A problem with the main engine on Northrop Grumman’s Cygnus XL spacecraft will keep it from delivering 11,000 pounds of supplies and experiments to the International Space Station as scheduled on Wednesday.
In a statement released Tuesday afternoon, NASA said ground teams are evaluating backup plans that might still allow the Cygnus spacecraft to reach the space station, just not on schedule. The problem arose early Tuesday when the spacecraft’s main engine shut down earlier than expected during two burns to boost the ship’s orbit for its rendezvous with the ISS, according to NASA.
Officials didn’t release any other details about the engine problem, but all other systems on the Cygnus XL spacecraft are performing as designed, NASA said. The agency said a new arrival date and time at the space station is “under review.”
Seeking another way
The Cygnus XL spacecraft launched Sunday at 6:11 pm ET (22:11 UTC) aboard a SpaceX Falcon 9 rocket from Cape Canaveral Space Force Station, Florida. A series of main engine burns was supposed to bring the spacecraft from the orbit the Falcon 9 released it in to an orbit matching the altitude of the ISS.
The mission was on track to arrive at the station early Wednesday. Unlike SpaceX’s Dragon crew and cargo ships, which fly themselves to automated dockings at the station, the Cygnus must be captured by the lab’s Canadian-built robotic arm. NASA astronaut Jonny Kim was set to use the arm to capture the Cygnus spacecraft as it flew within 30 feet of the complex. The robotic arm would then place the spacecraft on an attachment port on the station’s Unity module for a stay of up to six months.
This is Northrop Grumman’s 22nd cargo mission to the space station under a multibillion-dollar commercial resupply contract with NASA. All but one have successfully reached the station. This mission has taken on greater importance than a typical cargo delivery flight after engineers discovered damage to a Cygnus spacecraft that was supposed to launch earlier this year.
The damage occurred during the shipment of the spacecraft’s pressurized cargo module from its manufacturer in Italy. While Northrop Grumman hopes to repair the module and launch it on a future flight, officials decided it would be quicker to move forward with the next spacecraft in line for launch this month.
This is the first flight of a larger model of the Cygnus spacecraft known as the Cygnus XL, measuring 5.2 feet (1.6 meters) longer, with the ability to carry 33 percent more cargo than the previous Cygnus spacecraft design. With this upgrade, this mission is carrying the heaviest load of supplies ever delivered to the ISS by a commercial cargo vehicle.
The main engine on the Cygnus spacecraft burns a mixture of hydrazine and nitrogen tetroxide propellants. This mixture is hypergolic, meaning the propellants ignite upon contact with one another, a design heralded for its reliability. The spacecraft has a separate set of less powerful reaction control system thrusters normally used for small maneuvers, and for pointing the ship in the right direction as it makes its way to the ISS.
If the main engine is declared unusable, one possible option for getting around the main engine problem might be using these smaller thrusters to more gradually adjust the Cygnus spacecraft’s orbit to line up for the final approach with the ISS. However, it wasn’t immediately clear if this was a viable option.
Unlike SpaceX’s Cargo Dragon spacecraft, the Cygnus is not designed to return to Earth intact. Astronauts fill it with trash before departure from the ISS, and then the spacecraft heads for a destructive reentry over the remote Pacific Ocean. Therefore, a problem preventing the spacecraft from reaching the ISS would result in the loss of all of the cargo onboard.
The supplies on this mission, designated NG-23, include fresh food, hardware for numerous biological and tech demo experiments, and spare parts for things like the space station’s urine processor and toilet to replenish the space station’s dwindling stocks of those items.
Space Reporter
Stephen Clark
Space Reporter
Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.
63