A functional diagram showing the flow of propellant through an RS-25 engine. Very high flow rates are needed in the main combustion chamber, so the energy to achieve this is generated in upstream combustion "pre-burner" chambers that generate a partial burn to drive the high pressure turbopumps on both the fuel and oxidizer sides. Pressure feeding the preburners is maintained by the low-pressure turbopumps. Routing fuel through the nozzle serves to both cool the nozzle as well as pre-heat the fuel.
<a href="//commons.wikimedia.org/wiki/User:Jkwchui" title="User:Jkwchui">Jkwchui</a>
2011-12-21
<a rel="nofollow" class="external text" href="http://www.shuttlepresskit.com/scom/216.pdf">Main Propulsion System (MPS)</a> (PDF). <i>Shuttle Press Kit.com</i>. Boeing, NASA &amp; United Space Alliance (<span class="mw-formatted-date" title="1998-10-06">6 October 1998</span>). Retrieved on <span class="mw-formatted-date" title="2011-12-07">7 December 2011</span>.