NASA’s Space Launch System (SLS) will be the most powerful rocket ever built, with a bark as bad as its bite. The power generated to push SLS toward space will be incredibly loud—so much so that the sound created by its own engines could seriously damage the rocket or injure its crew. In order to protect itself, and its crew, from the damaging acoustics created by its own engines at liftoff, a water suppression system is needed to carry some of that acoustical energy away from the vehicle, and NASA’s Marshall Space Flight Center has recently started the first round of acoustic tests on a scale model of NASA’s SLS.
In order to avoid killing itself from the sound of its own engines, SLS engineers need to understand how low- and high-frequency sound waves affect the rocket on the launch pad—before the rocket is built. The first round of acoustic testing, which began Jan. 16, will help engineers verify the design of the sound suppression system being developed for SLS. The testing, known as the Scale Model Acoustic Test (SMAT), will also provide critical data about how the four RS-25 engines and two enormous solid rocket boosters SLS will be equipped with will affect the vehicle and its crew at liftoff.
“We can verify the launch environments the SLS vehicle was designed around and determine the effectiveness of the sound suppression systems,” said Doug Counter, technical lead for the acoustic testing. “Scale model testing on the space shuttle was very comparable to what actually happened to the vehicle at liftoff. That’s why we do the scale test.”
For the first test last month, engineers used a 5-percent scale model of the SLS core booster, equipped with four liquid oxygen-hydrogen thrusters to simulate the four space shuttle RS-25 engines that will power the core stage of the real SLS. Secured by a thrust plate, side restraints, and cables, the SLS model’s engine-simulating thrusters ignited for five seconds, with the vehicle surrounded by microphones and other instruments to measure the effects acoustic noise and pressure have on it at liftoff.
Several more tests are planned throughout the year, with each test firing being more complex and difficult than the previous. Although the Jan. 16 test focused on the SLS core itself, future tests will include two Rocket Assisted Take-Off (RATO) motors—provided by Alliant Techsystems Inc. (ATK)—to simulate the five-segment solid rocket boosters the real SLS will roar to space on (which will also be provided by ATK).
Meanwhile, as engineers at Marshall carry out acoustic tests on their scale model SLS, preparations to test the actual RS-25 engines for the real SLS at NASA’s Stennis Space Center in Mississippi are picking up pace. This year, Stennis will begin hot-fire tests on an RS-25 engine, and recently a new thrust frame adapter was installed onto the A-1 Test Stand at Stennis in support of the upcoming SLS engine tests.
“This is a big year for Stennis, for NASA and for the nation’s human space program,” said Gary Benton, RS-25 rocket engine test project manager. “By mid-summer, we will be testing the engines that will carry humans deeper into space than ever before.
The first RS-25 engine is set to be delivered to Stennis Space Center A-1 Test Stand in May, with the first RS-25 hot-fire test scheduled for July. Preparations in support of the upcoming engine tests include:
- Completing piping work needed to deliver rocket propellants for tests.
- Installing necessary instrumentation.
- Completing a readiness review in March, followed by early tests of new piping systems.
- Installing equipment needed to accurately measure rocket engine thrust during tests.
- Installing an initial RS-25 engine.
- Completing preliminary tests of installed engine and a new rocket engine test controller.
“During the 30-year run of the Space Shuttle Program, the RS-25 achieved very high demonstrated reliability,” said Garry Lyles, chief engineer for the Space Launch System Program Office at Marshall Space Flight Center. ”And during 135 missions and numerous related engine tests, it accumulated over 1 million seconds — or almost 280 hours — of hot-fire experience. With that kind of reliability, we knew it would be the best engine to power SLS.”
The first reusable rocket engine in history proved its worth during the STS program and will do so again for the SLS—with a few modifications made to the engines. SLS needs more power: For shuttle flights the engines pushed 491,000 pounds vacuum thrust, but for SLS the power level was increased to 512,000 pounds vacuum thrust.
“We need more thrust on the SLS than the shuttle, since we have a heavier payload,” said Mike Kynard, SLS Liquid Engines program manager at Marshall. “The core stage is a good bit larger than the external tank on the shuttle. To accommodate the higher thrust level, we increased the number of engines we had from three to four, and increased the power level of each engine.”
To put the power of the Aerojet Rocketdyne-built RS-25 engines into perspective, consider this:
- The fuel turbine on the RS-25’s high-pressure fuel turbopump is so powerful that if it were spinning an electrical generator instead of a pump, it could power 11 locomotives; 1,315 Toyota Prius cars; 1,231,519 iPads; lighting for 430 Major League baseball stadiums; or 9,844 miles of residential street lights—all the street lights in Chicago, Los Angeles, or New York City.
- Pressure within the RS-25 is equivalent to the pressure a submarine experiences three miles beneath the ocean.
- The four RS-25 engines on the SLS launch vehicle gobble propellant at the rate of 1,500 gallons per second. That’s enough to drain an average family-sized swimming pool in 60 seconds.
ATK successfully completed two key avionics tests recently for the solid rocket boosters which will fly the SLS, and NASA recently selected Teledyne Brown Engineering of Huntsville, Ala., to design, develop, test, evaluate, and certify the SLS Launch Vehicle/Stage Adapter (LVSA). Under a $60 million contract, Teledyne Brown is expected to assemble and manufacture a LVSA structural test article and two flight units, which will be used to connect the rocket’s 27.5-foot diameter core and 16.4-foot diameter interim cryogenic propulsion stages.