Rocket Lab has delayed the maiden flight of its Neutron launch vehicle to no earlier than 2027 after discovering manufacturing defects in the carbon fibre first-stage propellant tank, the company's latest setback in developing a medium-lift rocket built around composite materials.
The problem traces to the forward dome of the Stage 1 tank, which was produced using Rocket Lab's in-house Automated Fiber Placement machine. After the composite was cured in an autoclave, inspection revealed tiny air pockets, known as voids, in newly thickened sections of the dome. Thicker carbon composite is harder to cure cleanly because heat and pressure must force resin through the layers and expel trapped air. Voids can compromise structural strength, and the domes did not meet Rocket Lab's standards.
Chief executive Peter Beck said the company was very close to achieving the correct process on its first attempt and that the issue had been replicated in testing, meaning the cause is now understood. The time needed to resolve it has pushed the debut to no earlier than 2027. The broader target window is intended to avoid the repeated schedule adjustments that followed earlier launch dates.
The setback follows a more dramatic failure earlier in the year. On the night of 21 January, the first full-size Stage 1 qualification tank ruptured during hydrostatic testing, in which the tank is filled with water and pressurized. That article had been built by a third-party company using manual hand-layup, a slower and less consistent process adopted as a schedule workaround while Rocket Lab commissioned its own large Automated Fiber Placement machine. Beck attributed the rupture to the third-party hand-layup process used on that specific tank.
Switching to the automated machine allowed Rocket Lab to remove joints and inserts left by the manual process and to add thicker carbon composite in the forward and aft domes. That change, however, introduced the curing challenge now being addressed. Rocket Lab next plans to build the forward dome, analyse it for defects, and assemble a new Stage 1 tank that will undergo the same testing as the article that ruptured in January. Beck has said the first two milestones are expected before the end of the year, with assembly and testing in the first quarter of 2027. Further detail on the Flight 1 launch date is expected only after those steps.
Carbon fibre's appeal for rocket builders is its extremely high strength-to-mass ratio: a kilogram of the material is stronger than a kilogram of aluminium or steel. For reusable or small-lift vehicles, every kilogram saved on the primary structure can be reallocated to payload, allowing the same rocket and propellant load to carry heavier satellites. Rocket Lab's Electron, the most active vehicle in its class with almost 100 flights and a 96 percent success rate, became the first carbon fibre rocket to reach orbit in 2018. Firefly Aerospace's Alpha and Isar Aerospace's Spectrum also use the material.
But composite manufacturing is complex. Engineers must balance fibre grade, the proportion of fibre to resin, and the orientation of individual plies, which are laid in varying directions to handle different flight loads. Manual hand-layup is slow and prone to human error, while Automated Fiber Placement is faster and more consistent but requires significant upfront investment in tooling.
Rocket Lab is not alone in confronting these difficulties. Neutron, along with Firefly Aerospace and Northrop Grumman's Eclipse, is part of a small group of vehicles attempting composite medium-lift designs. SpaceX originally planned to build the vehicle now known as Starship from carbon fibre before switching to steel, citing cost, repairability, high-temperature performance, and the fact that steel gains strength at cryogenic temperatures. Temperature resistance also matters for re-entry vehicles, since a more heat-tolerant base material can support a lighter heat shield, offsetting some of carbon fibre's mass savings.
The delay leaves Rocket Lab's medium-lift ambitions tied to a manufacturing process it is still refining, with the next tank build and test campaign serving as the clearest signal of whether the 2027 target holds.