Production of rocket engines has traditionally been a labour-intensive process, resulting in very high unit costs. The thrust chamber of the Saturn V’s F1 first stage engine was composed of individual tubes carrying coolant propellant which were manually brazed together in a total of 900 metres of joins, each of which had to be inspected for flaws. The number of engines produced (65 flew on Apollo and Skylab launches) was insufficient to justify automating this slow and costly manufacturing process. The RL10 upper stage engine used on the Atlas V and SLS launchers, which is around the size of a truck engine (2.15 metres in diameter and mass of 301 kg) costs around US$ 17 million each.
The advent of additive manufacturing (“3D printing”) and, in particular, the ability to fabricate metal parts by a variety of methods such as electron-beam melting, allows forming structures impossible to create by conventional machine tool processes. A variety of companies are now developing and manufacturing 3D printed rocket engines, and Rocket Lab’s Rutherford engine, of which 399 have flown to date on Electron launchers, is largely 3D printed by laser powder bed fusion.