Following the same model as several other launch companies (RocketLab, SpaceX), Relativity used a single engine design (Aeon) on Terran 1, with nine Aeon engines on the booster, and a single vacuum-optimized Aeon engine on the upper stage. Terran 1 was built entirely from 3D-printed parts, including tanks, engines, bulkheads, and all other parts of the booster and second-stage.
Terran 1 was abandoned after its first launch, with the company pivoting to the more powerful Terran R. This occurred during a time in the industry when dedicated smallsat launchers were experiencing market pressure. Before cancellation, there was discusion of replacing the nine Aeon engines on the first stage with a single Aeon-R engine; this option was ultimately not pursued.
