MA

Atlas Propulsion System

The Atlas launch vehicle had a unique 'stage-and-a-half' propulsion system, where the sustainer stage was powered by a central liquid fueled engine with two similar jettisonable booster engines to the sides. Rocketdyne LR101 verniers were added for jaw, pitch and roll control.

Atlas-A, B and C used the MA-1 system with Rocketdyne LR43-NA-3 booster and LR43-NA-5 sustainer engine, the later which Atlas-A lacked. Atlas-D/LV-3 upgraded to MA-2 replacing the sustainer engine with the LR105-NA-3 and the boosters with the LR89-NA-3. Atlas E and F kept the LR105 and LR89, but upgraded both to NA-5. SLV-3 and Atlas-H further developed into the MA-5 with both engines moving to NA-7.

The MA-5 was kept by Atlas-G and Atlas-I. Atlas-II changed this by keeping the stage-and-a-half system but swapping out the LR-NA engines with RS-56-OBAs for the boosters and an RS-56-OSA for the sustainer. Atlas-III moved away from the stage-and-a-half setup and replaced the main stage propulsion with the RD-180.