WASHINGTON — A software glitch prevented the upper stage of Firefly Aerospace’s Alpha rocket from completing a second burn during a December launch, stranding its payload in a low orbit.

In a Feb. 20 statement, Firefly said an error with the guidance, navigation and control (GNC) software for the upper stage of the Alpha on the company’s “Fly the Lightning” mission Dec. 22 kept the upper stage from firing as planned to circularize its orbit. That left the upper stage and its payload, a Lockheed Martin technology demonstration satellite, in an orbit with a low perigee.

The investigation, which included the company’s own mishap team as well as an independent review, found that the error in the GNC software algorithm “prevented the system from sending the necessary pulse commands to the Reaction Control System (RCS) thrusters ahead of the stage two engine relight.” Firefly didn’t elaborate on the issue, but the RCS thrusters likely would have been used to ensure the stage was in the proper orientation and to settle its tanks so propellant would flow from them into the engine.

“We’re proud of the combined team’s ability to work together to achieve this positive outcome,” Bill Weber, chief executive of Firefly, said in a statement about the investigation. “Looking ahead, the important long-term outcome is the rapid, thorough maturation of Alpha as the dependable one-metric-ton-class rocket the market is demanding.”

Firefly said that it is both correcting the GNC software error and implementing other “process changes” to better detect similar problems in the future. The company said Alpha will be ready for its next launch in the “coming months” but was not more specific.

The mishap stranded the Lockheed Martin satellite in an orbit with an initial perigee of only about 215 kilometers. Lockheed accelerated the tests of the satellite’s antenna technology in what a company executive called a “dramatically compressed mission timeline,” achieving many of the mission objectives within weeks. The satellite reentered Feb. 10, according to a database maintained by The Aerospace Corporation.

While Firefly has not announced a specific return-to-flight date for Alpha, a company executive said earlier this month that Firefly still expected to perform four Alpha launches this year, the same number it projected before the mishap. “We don’t think that’s going to slow us down,” Brett Alexander, chief revenue officer of Firefly, said at the SpaceCom conference Feb. 1.

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...