Rocket Lab Neutron

Neutron is a partially reusable, medium-lift, two-stage launch vehicle under development by Rocket Lab. Announced on March 1, 2021, the vehicle is designed to be capable of delivering a payload of to low Earth orbit in a partially reusable configuration, and will focus on the growing megaconstellation satellite delivery market. First launch is expected after the first quarter of 2026.

Design

Neutron is designed to be partially reusable. The rocket's first stage has a diameter, 4 landing legs and canards, and 2 fairing halves. To maximize reusability, Rocket Lab uses a "hungry hippo" payload fairing design in which, instead of fairings being detached from the first or second stage as is typical in modern rockets, the fairings are integrated with the first stage via hinges. Neutron has two fairing segments mounted in this way. The first stage is powered by 9 oxygen-rich staged-combustion CH4/LOx Archimedes rocket engines.
The second stage of Neutron is completely contained within the Hungry Hippo fairing. It is hung from the separation plane, in that the tank structure of the stage is in tension when under thrust. Like the first stage, its structure is composed of carbon composite. It is powered by one Archimedes engine.
The first stage is intended to propulsively land on a floating landing platform downrange in the Atlantic Ocean named Return on Investment.

Design History

An earlier design of Neutron, included a rocket tall with a -diameter payload fairing. Rocket Lab stated that they intended for the first stage of the vehicle to be reusable, with landings planned on a floating landing platform downrange in the Atlantic Ocean.
On December 2, 2021, Rocket Lab unveiled a revised design for Neutron, featuring a tapered shape with a maximum diameter of. Rocket Lab abandoned opts for a return-to-launch-site reusability profile and on a floating platform. Instead of a conventional payload fairing that is jettisoned and recovered at sea, the fairing is integrated into the vehicle, and opens during stage separation to release the second stage and payload, and then closes before the first stage lands back on earth. The rocket features a unique interstage design where the second stage is "hung" from the first stage structure.
On September 22, 2022, another revised design was unveiled at an investor day, with the first stage engine count increased from seven to nine, and the engine architecture changed from gas-generator to oxygen rich staged combustion. This was done primarily to allow for a lower turbine temperature, while maintaining the same specific impulse. The engine will run with a significantly lower chamber pressure than other similar engines, at the cost of some performance. The number of fairing segments was reduced from four to two.
On July 27, 2023, new concept art on the Rocket Lab website showed a further revised design, with a reduction in the number of payload fairing sections from 4 to 2, redesigned landing legs, and small changes to the overall shape of the rocket. The number of payload fairing sections was reduced in order to allow for simpler fairing opening mechanisms while the landing legs were redesigned in order to be optimized for landings on floating platforms, allowing for an increase in launch availability. The redesigned legs feature a folding mechanism similar to the SpaceX Falcon 9 landing legs.
During the company's earnings call in February 2025, a plan to modify the offshore barge Oceanus were unveiled. When modifications are complete, the ship will be named Return On Investment. The ship will be refit by Bollinger Ship in Louisiana.

Operations

On February 28, 2022, Rocket Lab announced that Neutron will launch from the Mid-Atlantic Regional Spaceport within NASA's Wallops Flight Facility on the eastern coast of Virginia. It was also announced that the company will build a 250,000 square feet manufacturing and operations facility adjacent to the Wallops Flight Facility. Ground was broken for this facility on April 11, 2022., Rocket Lab is planning for the first launch to take place no earlier than July 2025. Test firing of Neutron's Archimedes engine occurred at NASA's Stennis Space Center in Hancock County, Mississippi.
In September 2025, Rocket Lab held a ceremony to mark the launch pad being ready for launch.

Development timeline

Past and future development milestones for Neutron.

Date	Milestone	Status
Q2 2022	Moulds and tooling for Neutron completed
Q3 2022	Full-scale prototype hardware for Archimedes and Neutron being made
Nov 4, 2022	Opening Archimedes test complex at NASA Stennis Space Center
Q4 2022	Pre-burner hotfire Test of Archimedes engine for the first time
Jan 10, 2023	Testing engine ignition on development hardware
Q1 2023	Test stand infrastructure completed for Neutron Stage 2 tank
Aug 8, 2023	First Stage 2 build
Oct 4, 2023	Stage two structural and cryogenic testing
May 6, 2024	First Archimedes development engine built
Aug 8, 2024	First Archimedes engine hot fire
2024	Testing of all avionics and communications devices with critical onboard software and GNC algorithms
NET 2024	Flight mechanisms test program
NET 2025	Stage 1 build
NET 2025	Stage 2 static fire
NET 2025	Stage 1 static fire
Q3 2025	Launch Complex 3 complete
NET 2025	Final integration
Q1 2026	Delivery to Launch Complex 3 for qualification testing and acceptance
NET 2026	Launch

Applications

Neutron is designed to lift up to while expended, while landing the booster downrange and up to with the first stage returning to the launch site. Rocket Lab forecasts Neutron will be able to launch 98% of all payloads launched through 2029. Rocket Lab also intends the design to be able to support constellation deployment, deep space missions, and eventually human spaceflight.
In May 2025, Rocket Lab was awarded an evaluation contract to test for compatibility of Neutron with the USAF Rocket Cargo program for return-to-Earth cargo delivery anywhere on Earth.

Launches

The first flight of Neutron is expected to be in mid 2026.
In September 2025, Rocket Lab planned to launch Neutron three times in 2026, and five times in 2027.

Prospects and market position

According to Rocket Lab, Neutron’s expected debut launch in 2025 also puts the launch vehicle in a strong position to on-ramp onto the U.S. Government’s National Security Space Launch Lane 1 program, an indefinite delivery indefinite quantity contract valued at $5.6 billion over a five-year period. RFPs for the program opened on October 30, 2024 with approved new launch vehicles to be on-ramped to the program in Spring 2025.
In November 2024 Rocket Lab announced that it has signed a multi-launch agreement with a confidential commercial satellite constellation operator to launch a satellite constellation using Neutron. Under the contract, Rocket Lab will launch two dedicated missions on Neutron starting from mid-2026. The missions will launch from Rocket Lab Launch Complex 3 on Wallops Island, Virginia. The launch service agreement for these missions signifies the beginning of a productive collaboration that could see Neutron deploy the entire constellation.