Firefly fires Eclipse engine for 226 seconds as Alpha Block II nears

A single Miranda engine burned at full power for 226 seconds—nearly four minutes—as Firefly engineers pushed the power level and the fuel mix through a range of settings. The test is a hard, simple question for the company’s next rocket: can the engine keep running for longer than a normal ascent requires? Firefly says the engine has now completed more than 150 hot-fire tests, but it is moving next into formal qualification before it can be cleared for the first Eclipse vehicle.

Eclipse is Firefly’s planned step into medium-lift launches. The rocket is designed to deliver more than 16 metric tonnes to low-Earth orbit, far beyond the company’s current Alpha launcher. Its first stage is being engineered for reuse, including return-to-launch-site landings that would send the booster back to its original pad after staging. Firefly says the first launch remains on track for next year, while warning that early flights may prioritize reaching orbit and postpone landings until the vehicle has proved itself in space.

At the smaller end of the range, Alpha is getting a substantial redesign. Block II will replace the rocket’s earlier black carbon-fiber finish with a white exterior that forms part of an upgraded thermal protection system. The change follows Alpha’s sixth mission, “Message In A Booster,” which failed after one side of the first stage grew much hotter than expected. The heating reduced structural margins and contributed to an explosion at stage separation.

The new Alpha will also use stretched propellant tanks, increasing the rocket’s height by more than two meters and adding propellant volume. Firefly expects the changes to support heavier payloads or more demanding orbits. The first Block II flight is targeted for the fourth quarter of this year, with a second mission planned in the same quarter.

So what changes, concretely? If Firefly’s timetable holds, customers will get a revised smallsat launcher tested twice in relatively quick succession, while government and commercial missions gain a path toward a larger rocket. Lockheed Martin has extended its Alpha arrangement through 2031, with access to as many as 25 launches. The immediate proof point is still ahead: Block II must show that its thermal upgrades work in flight, and Eclipse must progress from engine testing to a launch and, later, a successful booster recovery.