WASHINGTON — The European Space Agency says the first launch of the Ariane 6 remains on track for the middle of 2024 despite an aborted test of the rocket’s upper stage.

In a Dec. 19 statement, ESA said it successfully completed a test of an Ariane 6 prototype called combined test loading, or CTLO3, at the spaceport in Kourou, French Guiana, Dec. 15. In the test, the rocket’s core and upper stages were loaded with propellants and went through a practice countdown that concluded with a four-second firing of the core stage’s Vulcain 2.1 engine.

CTLO3 also demonstrated what ESA called “extreme ignition conditions and degraded modes of liftoff” as well as abort modes that required unloading propellants from the rocket with “very limited control resources.”

“The rehearsal was very well executed, and the countdown ran exactly as planned,” ESA said in a Dec. 19 statement, calling the test a complete success. “The launch operations for Ariane 6 are mastered, we are ready to go.”

However, a test of the upper stage eight days earlier was not a complete success. A hot-fire test of the upper stage, called HFT-4, at a facility in Lampoldshausen, Germany, was aborted two minutes into the test when “some parameters had gone beyond predetermined thresholds,” ESA said in a statement.

The HFT-4 test was intended to test how the upper stage would perform in “extreme and unexpected conditions” rather than those expected in a normal flight. ESA said the cause of the abort is under investigation, with an update expected in mid-January.

ESA first revealed the problem with HFT-4 at a Dec. 14 briefing after a meeting of the ESA Council. “There are no signs that it will delay the announced inaugural flight date,” said Toni Tolker-Nielsen, ESA director of space transportation. ESA announced Nov. 30 a launch period of between June 15 and July 31 for the first Ariane 6.

ESA reiterated that in its statement. “We are confident that these investigations will not impact the schedule to Ariane 6 inaugural flight,” it said of the HFT-4 abort.

Some tests of the launch system will continue into early 2024. ESA said tests are planned at the end of January of the disconnection system for umbilicals at the launch pad for fueling the rocket. The flight hardware for the first Ariane 6 launch is scheduled to arrive in Kourou in mid-February.

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...