NASA’s Artemis Launch Postponed Due to Engine Problem on Moon Rocket

The next possible opportunity for takeoff is Friday, Sept. 2, NASA has said. The agency didn’t immediately commit to attempting the flight on that day.

“We don’t launch until it’s right,” NASA Administrator Bill Nelson said. “This is a very complicated machine, a very complicated system.”

Leadership at the space agency said in the run-up to Monday morning that the flight was designed to stress test its deep-space vehicles and warned that technical issues could emerge.

The issue with the engine related to a procedure where staffers route some super-cold propellant into the engines to prepare them for when super-cold fuel flows through them at liftoff, according to a NASA spokeswoman. The engines need to be within a certain temperature range to start them.

Aerojet Rocketdyne Holdings Inc., which made the four main engines on the SLS and upgraded them for the proposed flight, said there are no early indications that Monday’s launch was postponed because of problems with its RS-25 engines, according to a company spokesman.

The SLS rocket is the most powerful rocket that NASA has ever looked to blast off. A spacecraft called Orion sits on top of the rocket, and would travel to the moon during a normal launch. Monday’s scrubbed mission would have sent an uncrewed Orion ship to a lunar orbit and back to Earth over more than 40 days.

Aerojet’s four engines were designed to burn for eight minutes following liftoff, helping to power Orion toward a lunar orbit.

A Boeing Co. spokeswoman didn’t immediately have a comment. The aerospace company developed the SLS rocket’s main stage, a massive body that holds liquid propellant that feeds into the engines.

The rocket includes hardware that NASA has used in operations before. The engines installed on the main stage of the vehicle, including the one linked with a problem, previously helped power rockets used on space shuttle missions.

The SLS rocket, including the boosters on its side, are meant to be jettisoned after their role in missions is over.

SpaceX, meanwhile, has also been developing its own powerful rocket system that aims to handle future deep-space missions, as SLS and Orion are designed to do. The Elon Musk-led company has taken a different approach for some key areas on Starship compared with NASA.

For Starship, SpaceX created a new engine, called the Raptor, to use on the Starship spacecraft and the booster that would blast off from Earth. In February, Mr. Musk said a second version of the Raptor costs about half as much as a prior type but is more powerful.

Starship is also designed to be fully reusable, according to Mr. Musk.

The rocket system hasn’t flown an orbital test yet. Mr. Musk said last week on Twitter that doing so this year was a priority.

The company has faced challenges developing the vehicle, such as a recent explosion under one of the boosters. Space Exploration Technologies Corp., the formal name for SpaceX, didn’t immediately respond to a request for comment.

“Starship is a hard, hard, hard, hard project,” Mr. Musk said at an event organized by The Wall Street Journal last December.

NASA plans to use a version of Starship for its back-to-the-moon missions—the agency plans to use that vehicle to land astronauts on the surface of the moon as soon as 2025. Those astronauts would enter Starship from an Orion craft blasted to lunar orbit by a SLS rocket.

NASA had previously set a two-hour window for the SLS to take off this morning beginning at 8:33 a.m. ET.

The agency and the contractors behind Artemis I, NASA’s name for the mission, and subsequent Artemis missions have faced pressure to get to the launchpad after grappling with technical setbacks that led to cost overruns and delays.

The inspector general at NASA has estimated the Artemis I launch would cost $4.1 billion in production and operational expenses, as would each of the following three flights. The inspector general has described that per-flight cost as unsustainable. NASA officials have said that they are pushing to find cost savings and that the expenses for each mission would fall as more are launched.

Boeing, Lockheed Martin Corp., Northrop Grumman Corp. and other contractors involved in the effort said their companies have taken steps to cut costs.

The Artemis I mission would be the first major launch involving most of the main components that NASA and aerospace companies have assembled to help return astronauts to the lunar surface. No astronauts have reached the moon since 1972, but NASA aims through its Artemis program to make that happen as soon as 2025.

—Doug Cameron contributed to this article.

Write to Micah Maidenberg at [email protected]