Artist rendering of the RS-25 engines and boosters. Engineers will use scale models of the SLS propulsion system to understand heating environments that the base of the vehicle will experience upon ascent. Data from tests on those models will be used for the design of the rocket's base thermal protection system, which keeps major hardware, wiring and — later — crew safe from the extreme heat the boosters and engines create when ignited. Image credit: NASA
The Mission
NASA has put together a highly skilled team of industry and academic partners, including Cockrell School of Engineering assistant professor Charles E. Tinney, to understand what happens when its new RS-25 rocket engine — the first reusable rocket engine in history — is revved up on the launch pad. A total of four RS-25 liquid propellant engines will power the Space Launch System (SLS), which will be NASA’s most powerful rocket to date with the greatest flexibility of any launch system ever built to support any destination, any payload and any mission. Also known as the “superhero,” the rocket’s first test flight is scheduled for 2017.
In collaboration with the NASA Marshall Space Flight Center in Huntsville, Ala., the Cockrell School team is working to analyze and predict the rocket noise and vibrations that RS-25 rocket engines will produce when ignited on the launch pad to ensure that the new SLS rocket, and its payload, can safely make its way to space.
The Problem
Space vehicle engines are designed to perform best at a fixed altitude, which is upward of 100,000 feet, or roughly 19 miles, from sea level where the engines are first ignited. This means that, at launch, space vehicle engines are not operating at optimal performance, which increases the likelihood of ignition problems or catastrophic breakdowns.
Additionally, igniting these engines generates heavy lateral forces against the vehicle, as well as intense sound waves that form from the hot exhaust gas. The force of these sound waves is equivalent to three to four semitrucks (30,000 pounds each) pounding repeatedly into the bottom of the space vehicle. Engineers are tasked with ensuring that the space vehicle can withstand such destructive forces.
The Experiment
Tinney and his team of eight graduate and undergraduate student researchers, from the Department of Aerospace Engineering and Engineering Mechanics, have gone to great lengths to test the performance and safety of the rocket engine under simulated launch conditions. To start, the team built a replica of the RS-25 engine that is roughly one-27th the size of the full-scale engine. The full-scale engine towers more than 14 feet tall and has an exhaust diameter of 8 feet. Since 2011, the team has been accumulating important data by recording and analyzing acoustic events of the RS-25 engine.
The researchers are gaining a better understanding of how the vibrations that form inside these engines during ignition generate sound waves and forces that impact the safety and reliability of space launch vehicles. In March, a crew from Discovery Channel Canada captured the Cockrell School team conducting RS-25 experiments in the school’s one-of-a-kind, echo-free rocket test facility for a segment on the channel’s Daily Planet show.
The Impact
As Cockrell School engineers continue to learn more about the science of engine sound, they will be able to develop methods for reducing the noise and its destructiveness. Beyond safety, another goal of this research is to help engineers develop less bulky rocket designs that can still withstand the forces that come from turning on the engine. And ultimately, Tinney said, this work could lead to lighter and more reliable rockets that cost only a few million dollars, as opposed to hundreds of millions, to launch.
