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Synergistic Air Breathing Rocket Engine (SABRE) can use standard, lightweight aluminum alloys because the inflow of air keeps the engine at a cool enough temperature to keep the aluminum below its melting point. Since ramjets don't have a downstream turbine blades, they can operate at higher, more efficient temperatures, closer to 3900°F (2150°C). These higher temperatures require titanium or other specialized alloys and order to prevent melting or structural damage.