|Country of origin||United States |
|Application||First- and second-stage engine |
|Propellant||LOX / liquid methane|
|Thrust, vacuum||200,000 lbf (890 kN) (Vacuum version)|
|Thrust, sea-level||165,000 lbf (730 kN) |
|Throttle range||100% - 50%|
|Specific impulse, vacuum||329s (SL)|
365s (Vac version)
Archimedes is a liquid-fuel rocket engine burning liquid oxygen and liquid methane in an oxidizer-rich staged combustion cycle. It is designed by aerospace company Rocket Lab for its Neutron rocket.
Archimedes was presented on December 2, 2021 in a webcast by Rocket Lab CEO Peter Beck. It was presented as a fully reusable, gas generator engine using LOX and methane as propellant, a departure from the company's previous Rutherford, which is electrically pump fed. He then stated that it had a thrust of 1 MN (220,000 lbf) and 320 seconds of specific impulse. The same day, the Neutron page on Rocket Lab's website was updated specifying the thrust of the seven Archimedes used on the first stage as 5,960 kN (1,340,000 lbf) at sea level and a maximum thrust of 7,530 kN (1,690,000 lbf) and the upper stage's single vacuum optimized Archimedes at 1,110 kN (250,000 lbf). It is expected to have its first hot-fire test during 2022.
In an interview published on CNBC website, Mr. Beck stated that Archimedes would be manufactured in New Zealand and its very simple design had "all the things you want when you have to build an engine that can be reused over and over again.” In the September 21st, 2022 Investor Day Presentation, the engine design had changed to an oxidizer-rich staged combustion cycle. The presentation stated that the sea level version would have a maximum thrust of 730 kN (160,000 lbf) with a vacuum isp of 329s and would be able to throttle to a 50% of maximum thrust.
Meanwhile the vacuum optimized version, would have a maximum thrust of 890 kN (200,000 lbf), an isp of 367s and the same throttling capabilities of 50% of maximum thrust. It was also implied, but not confirmed, that the engine would be built in the Virginia, USA factory. It was disclosed they would use the Stennis Space Center A-3 Test stand for development testing. They expected to start preburner testing in that or following quarter, hopefully starting full engine testing at Stennis before 2023 ends, and hoped to be able to launch in 2024. 
Archimedes is presented as a highly reusable liquid-propellant engine using methane and liquid oxygen in a oxidizer-rich staged combustion cycle. There are both sea-level and vacuum variants. The engine is mostly 3D printed, with some of the biggest 3D printers in the world. The rationale for the cycle change from the original gas generator was that they could not get the performance they needed through all the throttle points that a reusable rocket needs, without pushing the turbine temperature and other factors beyond their preset limits. By changing to the higher performing cycle but with lower performance requirements, they were able to lower temperatures and other stress factors and increase margins everywhere, making reusability much more attainable.