Rocket Lab Neutron

Neutron is a medium-lift two-stage launch vehicle under development by Rocket Lab. Announced on 1 March 2021, the vehicle is designed to be capable of delivering a payload of 13000 kg to low Earth orbit in a partially reusable configuration, and will focus on the growing megaconstellation satellite delivery market. The vehicle is expected to be operational sometime in 2025. It uses LOX and liquid methane propellant on both stages of the vehicle.

Design
An earlier design of Neutron, featured at the initial unveil in March 2021, featured a rocket 40 m tall with a 4.5 m-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 2 December 2021, Rocket Lab unveiled a revised design for Neutron, featuring a tapered shape with a maximum diameter of 7 m. Rocket Lab abandoned plans for landing Neutron on a floating platform, instead opting for a return-to-launch-site reusability profile. 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 the 22nd of September 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. They have also reduced the number of fairing segments from four to two.

On the 27th of July 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.

Operations
On 28 February 2022, Rocket Lab announced that Neutron will launch from the Mid-Atlantic Regional Spaceport (MARS) 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 11 April 2022. , Rocket Lab is planning for the first launch to take place no earlier than 2024. Test firing of Neutron's Archimedes occurred at NASA's Stennis Space Center in Hancock County, Mississippi.

Development timeline
Past and future development timeline of Neutron.

Applications
Neutron can lift up to 15000 kg while expended, 13000 kg while landing the booster downrange and up to 8000 kg 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.