When rocket scientists were first tasked with creating rockets powerful enough to punch through Earth's atmosphere and travel into space, they didn't have to invent a new method of engineering. Rather, they started with what they knew already worked: automobile mechanics.
Similar to car engines, rocket engines require the same basic ingredients to generate power: fuel, air and a spark.
The team at Aerojet Rocketdyne has upgraded the 16 Space Shuttle Main Engines that remained in NASA's inventory following the end of the agency's shuttle program. Now known as RS-25s, these mighty engines have been upgraded with new, advanced controllers and other improvements to support the first four flights of NASA's Space Launch System (SLS) rocket in support of the agency's Artemis program. The first test flight, known as Artemis I, took place in November 2022 when the SLS rocket launched the human-rated Orion spacecraft on a 1.4 million mile journey around the Moon and back.
"Those who work in the engineering field have been building on the work of their predecessors since Imhotep designed the Pyramid of Djoser in ancient Egypt around 2600 BC," said Aerojet Rocketdyne RS-25 Program Director Doug Bradley. "For instance, during the origins of the space age, early rocket scientists leveraged many concepts and practices that were learned throughout the automotive industry."
While the flight-proven RS-25 is certainly among the most advanced engines in the world, the basic way it operates would be familiar to any car enthusiast. Similar to typical internal combustion car engines, rocket engines like the RS-25 ignite a mix of fuel (liquid hydrogen) and an oxidizer (liquid oxygen) to create hot exhaust gases. In a car engine, these gases push a piston that turns a crankshaft attached to an axle. The rotating axle turns the wheels to propel the car forward. In a rocket engine, the escaping hot gases produced by combustion push against the engine nozzle to produce thrust that propels the rocket.
Rocket engines also use intricate injector assemblies to introduce propellants into the combustion chamber. These assemblies function similarly to fuel injection systems used on car engines.
Another similarity between rocket engines and car engines is their use of turbomachinery. Exhaust pressure and heat from a rocket engine's preburner is used to spin up downstream turbopumps similar to the way a turbocharger on some car engines creates additional horsepower using the hot-gases generated by the engine's exhaust. Commercial automobile turbochargers operate at an inlet pressure of 20-30 psi, whereas the preburner-turbopump assembly in the RS-25 engine operates at upwards of a whopping 5,500 psi.
"Turbochargers were invented in the early 20th century as a means to increase the power of diesel engines," Bradley added. "I don't doubt that that the engineers designing the first rocket engine turbopumps would have studied the concepts underlying those early turbochargers and how they could be applied to rocket engines."
There are a lot of similarities between rocket engines and car engines; however, one major difference is that a single Aerojet Rocketdyne RS-25 engine produces more than 500,000 pounds of thrust (roughly 12 million horsepower). The RS-25's high pressure fuel turbopump, which is about the size of a car engine and is used to pump fuel to the engine's combustion chamber, generates 70,000 horsepower alone. For comparison, the average car engine produces less than 300 horsepower, and top fuel dragsters, which are among the fastest cars in the world, produce 11,000 horsepower.
One of the most challenging feats in the automotive racing industry is building a car to race in the renowned 24-hours of Le Mans endurance race. Cars are pushed to the limits of technical capability, exceeding 200 mph while jetting around the 8.5 mile long Circuit de la Sarthe for 24 hours straight.
Building rocket engines that can safely propel astronauts along with thousands of pounds of payload into space at more than 20 times the speed of sound is Aerojet Rocketdyne's equivalent to Le Mans. Billions of dollars, years of hard work and, most importantly, human lives are on the line if something were to go wrong during a rocket launch. Fortunately, the expertise and experience of the team ensures that RS-25 engines have unparalleled reliability.
During each launch of the SLS, four RS-25 engines will generate more than 2 million pounds of combined thrust as they burn for just over 8 minutes and consume more than 90,000 gallons of propellant. The good news is that thanks to its use of liquid hydrogen and liquid oxygen, the only exhaust coming from the RS-25 engines is clean, superheated water vapor (steam) with zero carbon emissions!
"It's a privilege to be a part of the Aerojet Rocketdyne team that is designing, manufacturing, assembling and testing these incredible rocket engines," concluded Bradley. "Watching the first SLS launch during the Artemis I mission, with the help of our powerful RS-25 engines, took my breath away. We are truly at the dawn of a new era of human deep space exploration."