This paper reports on the design and manufacture of C-band multi-Watt optical fibre amplifiers for satellite laser communications. Three module types have been developed and are presented, outputting optical power of 1W, 3W and 5W respectively. A modular design was adopted for the amplifier so that it can be scaled to different power levels and achieve cost-effectiveness and mass manufacturing, thus enabling application in satellite constellations. Radiation testing demonstrates the robust performance against ionizing radiation levels found in LEO and GEO orbits. All degradations are within system requirements and are recoverable in operation by changing the operational parameters, whilst still complying with end of life power consumption and component de-rating specifications. The amplifiers are able to deliver >1W, >3W and >5W output power at 1550 nm for 100 krad TID based on the measurements performed. An environmental test campaign has demonstrated the robustness of the 5W module against sine and random vibration. Additionally, thermal cycling in vacuum has been performed on an optical breadboard, demonstrating a stable optical output, verifying the robustness of the optical design. G and H unit design and AIT space processes are capable of delivering robust and qualified fibre optic units for deployment in satellite laser communication missions.