Take a look at your current devices. Can you imagine swapping that smartphone for a gigantic cellphone from the 1980s? Surfing the Internet with dial-up speed? Working out to your favorite music with a cassette player?

Today’s technology is better, faster and more innovative. People have to keep up with the rapidly changing times, and so does the “brain” for the RS-25 rocket engine.

The engine controller unit on the RS-25 — formerly known as the space shuttle main engine — helped propel all of the space shuttle missions to space. It allows communication between the vehicle and the engine, relaying commands to the engine and transmitting data back to the vehicle. The controller also provides closed-loop management of the engine by regulating the thrust and fuel mixture ratio while monitoring the engine’s health and status.

Just like the ever-evolving computer, the engine controller unit needed a “refresh” to provide the capability necessary for four RS-25 engines to power the core stage of NASA’s new rocket, the Space Launch System (SLS ), to deep space missions. The core stage, towering more than 200 feet tall with a diameter of 27.6 feet, will store cryogenic liquid hydrogen and liquid oxygen that will feed the vehicle’s RS-25 engines.

The engine controller unit allows communication between the vehicle and the engine, relaying commands to the engine and transmitting data back to the vehicle. Engineering model controllers are being tested at the Marshall Center and Stennis Space Center.
Photo Credit: NASA / MSFC

“You can’t put yesterday’s hardware on today’s engine, especially since many parts of the shuttle-era engine controller unit aren’t even made anymore,” said Russ Abrams, avionics subsystem manager in the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Marshall manages the SLS Program for the agency. “We need the most updated control systems for this engine to meet SLS specifications and take us to places we’ve never been before in space.”

Controller development is based heavily on the recent development experience with the J-2X engine controller. An engineering model RS-25 controller is being tweaked and tested at Marshall. At one of the center’s test facilities, engineers are simulating the RS-25 in flight, using real engine actuators, sensors, connectors and harnesses.

A second engineering model controller and RS-25 engine also recently were installed on the A-1 test stand at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. Pending final preparation and activation work, the engine test series is anticipated to begin in 2015.

“NASA and its partners have been working very hard to evolve this crucial piece of hardware and software for the RS-25, and we look forward to seeing it tested on the A-1 stand very soon,” said Johnny Heflin, deputy manager of the SLS Liquid Engines Office at Marshall. “This is an exciting time for everyone involved with this project.”

The RS-25 and controller work are a collaborative effort between NASA and prime contractor Aerojet Rocketdyne of Sacramento, California.

The first flight test of the SLS will be configured for a 70-metric-ton (77-ton) lift capacity and carry an uncrewed Orion spacecraft beyond low-Earth orbit to test the performance of the integrated system. As the SLS evolves, it will be the most powerful rocket ever built and provide an unprecedented lift capability of 130 metric tons (143 tons) to enable missions even farther into our solar system.

The RS-25 is produced by Aerojet Rocketdyne. Photo Credit: Jason Rhian / SpaceFlight Insider

This article originally appeared on NASA’s website and can be viewed here: RS-25

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BAY ST. Louis, MS — 2015 is off to a hot start for NASA’s Space Launch System (SLS). The RS-25, the powerful engine that will propel America’s next heavy-lift rocket into deep space completed its first test of the new year in a blaze of glory. On Jan. 9, at the agency’s Stennis Space Center, engineers conducted a test fire of the RS-25 engine. Attached to the A-1 test stand, the RS-25 fired for 500 seconds, allowing crews to collect critical data needed to analyze the engine’s controller unit and inlet pressure. Four RS-25 engines will power the mighty SLS on future missions to an asteroid and even Mars.

“This first hot-fire test of the RS-25 engine represents a significant effort on behalf of Stennis Space Center’s A-1 test team,” said Ronald Rigney, RS-25 project manager at Stennis. “Our technicians and engineers have been working diligently to design, modify and activate an extremely complex and capable facility in support of RS-25 engine testing.”

The RS-25 engine, formerly responsible for powering the space shuttle, will power NASA’s Space Launch System. Photo Credit: NASA

Any space aficionado may recognize the RS-25 engine as the one responsible for powering the space shuttle.  Recently, the “brain” of the RS-25 underwent an upgrade. The “brain”, otherwise known as the engine controller unit, enables communication between the vehicle and the engine, relaying commands to the engine and transmitting data back to the vehicle. Also providing closed-loop management of the engine by regulating the thrust and fuel mixture ratio while monitoring the engine’s health and status, the updated controller will use updated hardware and software configured to operate with the new SLS avionics architecture.

“We’ve made modifications to the RS-25 to meet SLS specifications and will analyze and test a variety of conditions during the hot fire series,” said Steve Wofford, manager of the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, where the SLS Program is managed. “The engines for SLS will encounter colder liquid oxygen temperatures than shuttle; greater inlet pressure due to the taller core stage liquid oxygen tank and higher vehicle acceleration; and more nozzle heating due to the four-engine configuration and their position in-plane with the SLS booster exhaust nozzles.”

More upgrades will have to be completed prior to further testing in April of this year.  Systems to be upgraded include the high pressure industrial water system, which provides cool water for the test facility during a hot fire test. A total of eight tests are on the books, totaling 3,500 seconds, for the current development engine. Later on, another development engine will undergo 10 tests, totaling 4,500 seconds. The second test series will include the first test of new flight controllers, labeled as green running.

Close-up view inside the A-1 test stand during a hot fire test of the RS-25 engine. Photo Credit: NASA

The first flight test of the SLS, currently estimated for 2018, will feature a configuration for a 70-metric-ton (77-ton) lift capacity and is intended to carry an uncrewed Orion spacecraft beyond low-Earth orbit. This will be a true test of the integrated system’s performance. SLS will continue to be upgraded, in order to provide an unprecedented lift capability of 130 metric tons (143 tons) and enable missions even farther into our solar system.

NASA currently has 16 flight engines in its fleet, as well as two development engines for ground testing. Engineers have performed extensive analysis to understand how the engines will work for SLS, and will continue analyzing the integrated design with the help of detailed data collected from the hot fire testing.

“The RS-25 is the most efficient engine of its type in the world,” said Steve Wofford, manager of the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center, in Huntsville, Alabama, where the SLS Program is managed. “It’s got a remarkable history of success and a great experience base that make it a great choice for NASA’s next era of exploration.”

An RS-25 SSME undergoing testing. Photo Credit: Aerojet Rocketdyne

The agency has an existing contract with Aerojet Rocketdyne (Rocketdyne), prime contractor for the RS-25, and Stennis engineers are starting the process of adapting the engine to meet SLS performance expectations with this engine testing. When powering the shuttle, the RS-25 routinely operated at 491,000 pounds of thrust. On SLS, it will operate at 512,000 pounds of thrust for the first four flights. Before launch, the four engines in the SLS core stage will encounter colder liquid oxygen propellant temperatures and a colder engine compartment in the SLS core stage.

Beginning at engine and booster ignition, the engines will encounter higher propellant inlet pressure and greater exhaust nozzle heating due to differences in the SLS design. Future testing will be designed to subject the engine to the higher thrust and greater cooling conditions it will experience with SLS. Together, NASA and Rocketdyne plan to start producing new RS-25 engines for future flights, and will further adapt and modify the engine design as part of continuing efforts to make the engines more powerful and more affordable.

“We had identified significant cost and time saving ideas for the RS-25 before the shuttle program ended,” Wofford said. “We see many opportunities for process and manufacturing savings with the change to an expendable engine and the maturation of technologies, such as 3D printing and structured light scanning.”

Initially, the team will produce six new engines, and once the design and manufacturing process has been streamlined, more RS-25 engines are expected to be produced. The RS-25 is expected to be the engine that will be powering space exploration for decades to come.

Video courtesy of NASA

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Engineers from NASA’s Marshall Space Center in Huntsville, Alabama are collaborating with  the Buffalo, New York based company CUBRC Inc. to conduct a series of tests that will provide important information about the heating conditions at the base of the space agency’s Space Launch System (SLS) rocket. As NASA works to get this new heavy-lift booster off the ground and into the skies – these latest tests should assist in the agency’s efforts.

The NASA engineers have been working with CUBRC to design and build 2 percent scale models of SLS propulsion system. The tests will use models of the SLS’s two five-segment solid rocket boosters and four core-stage RS-25 engines and a 6.5 foot tall scale model of the entire rocket. The models are fired for brief durations of about 50-150 milliseconds per test.

“There’s a lot of complex work that goes in to such a short-duration test,” said Manish Mehta, lead engineer for the SLS Base Heating Test Program at Marshall, where the SLS Program is managed for the agency. “The timing of the propulsion systems and shock tunnel have to be precise. Although this test program has been technically challenging, there’s no heritage data that we can fall back on to predict SLS base environments because this vehicle has never been flown before”

“There are four engines and two booster rocket plumes that are firing into the base,” Mehta added. “This results in highly complex flow physics, which is not something you can develop analytically and predict very accurately.”

Two-percent scale models of the SLS solid rocket boosters and core stage RS-25 engines. Photo Credit: NASA/MSFC

Testing of the scale models will provide information on the heating conditions that the base of the SLS will experience during both planned and unplanned flight events.  Data from the series of tests will be used to verify flight hardware design environments and set specifications for the thermal protection system of the rocket’s base. The system will protect the rocket’s  systems and crew from the extreme heat created by the engines during liftoff and ascent.

Testing of the core stage in normal launch scenarios was  conducted first, followed by testing of the entire SLS model in early January. The full-stack configuration had 200 heat flux and pressure sensors inside the aft section of the rocket for data collection. Over 30 test cases out of a planned total of 85 have been performed. The test series, which began in August 2014, is scheduled to conclude early this summer.

The test program takes advantage of new technologies that weren’t available during the development of previous human space flight programs, such as high-speed visible light and infrared cameras, laser diagnostics and new designs of model propulsion systems to more accurately simulate full scale rocket engines.

It’s great to be working on hardware and stretching our engineering skills on coming up with solutions to technical issues we’ve experienced along the way,” said Mehta. “I think we’ve done well.”

Artist rendering of the RS-25 engines and boosters powering the liftoff of the SLS from the pad. Image Credit: NASA

It took about a year and a half to design and build the models to flight specifications. For the test series the models are loaded with propellant, pressurized with oxygen and hydrogen lines and ignited inside of one of CUBRC’s  shock tunnels. The shock tunnels replicate both supersonic and hypersonic flight conditions, simulating environmental conditions  that the rocket will experience during ascent including temperature, pressure and velocity.

“We like to say we’re duplicating a flight test on the ground,” said Aaron Dufrene, technical lead at CUBRC. “What’s great about the design of these models is we can run them dozens, even hundreds, of times and reuse most all of the hardware every single time.”

“That’s why NASA historically started doing this short-duration testing technique,” added Mark Seaford, a Marshall engineer who works on the test project. “Since you are testing at a much smaller scale, in this case 2 percent, the heating goes up at the throat of the nozzles. We can’t run it for a substantial length of time or the hardware would be compromised under the heat. We really had to challenge ourselves in the design process to get the right materials to minimize that risk.”

The first flight test of the SLS will launch an uncrewed Orion spacecraft beyond low-Earth orbit to test the performance of the integrated system. The flight test, which will use the 70 metric ton (77 ton) lift capacity configuration  of the SLS, is scheduled for 2018.

Video courtesy of NASA

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NASA and Aerojet Rocketdyne have agreed to resume production of the RS-25 engine for use on the agency’s Space Launch System (SLS). Image Credit: NASA

On Monday, Nov. 23, NASA and Aerojet Rocketdyne (Rocketdyne) announced a $1.16 billion contract for Rocketdyne to resume production of the RS-25 engines that helped power the Shuttle to orbit for 30 years. The engines will now be used to power the agency’s new super heavy-lift vehicle, the Space Launch System (SLS), and it’s Orion capsule, to the Moon, Mars and beyond.

On Shuttle, three RS-25’s, which were reconditioned and reused, were attached to the aft end of the orbiter. For SLS, four RS-25’s will be required for each flight, and the engines will not be recovered and reused.

NASA has 16 flight-ready RS-25’s in storage at its John C. Stennis Space Center (SSC) in south Mississippi. These engines will be used on the first four SLS flights. However, for subsequent flights, additional engines will be required.

SLS RS-25 flight engine mission assignments. Photo Credit: Aerojet Rocketdyne

According to NASA, the new contract runs from November of this year through September of 2024, and only “restarts [Rocketdyne’s] production capability including furnishing the necessary management, labor, facilities, tools, equipment and materials required for this effort, implementing modern fabrication processes and affordability improvements, and producing hardware required for development and certification testing.” However, the contract does allow for a future modification which would enable NASA to actually order six new flight engines.

SpaceFlight Insider speaks with Rocketdyne’s Jim Paulsen on Aug. 13. Photo Credit: Aerojet Rocketdyne

Jim Paulsen, vice president, Program Execution, Advanced Space and Launch Programs at Rocketdyne, explained that the “RS-25 engines designed under this new contract will be expendable with significant affordability improvements over previous versions. This is due to the incorporation of new technologies, such as the introduction of simplified designs; 3-D printing technology called additive manufacturing; and streamlined manufacturing in a modern, state-of-the-art fabrication facility.”

The first SLS launch, Exploration Mission 1 (EM-1), an uncrewed test flight around the Moon, is scheduled for 2018. The first crewed flight, Exploration Mission 2 (EM-2), is schduled for no later than 2023, and NASA intends to fly SLS once a year thereafter, budget permitting.

Click here to view Rocketdyne’s video news release regarding new RS-25 production.

Video courtesy of NASA / Aerojet Rocketdyne

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NASA engineers conduct a successful test firing of RS-25 rocket engine No. 2059 on the A-1 Test Stand at Stennis. The hot fire marks the first test of an RS-25 flight engine for NASA’s new Space Launch System vehicle. (Click to enlarge) Photo Credit: NASA/SSC

Work on NASA’s Space Launch System (SLS) reached another milestone on March 10, 2016, when Aerojet Rocketdyne test fired the RS-25 engine at the Stennis Space Center in Mississippi. This is the first flight engine for the SLS and the first one to be tested for a full duration of flight. Designated E2059, the engine fired for 500 seconds while bolted firmly to the test stand.

“This rocket will take humans farther and faster into the Solar System than we have ever traveled and increase our capability of making exciting new discoveries by launching large astronomical observatories and other scientific missions,” said Eileen Drake, Aerojet Rocketdyne CEO and president.

RS-25 engine No. 2059 arrives at the A-1 Test Stand at Stennis Space Center on Nov. 4, 2015. (Click to enlarge) Photo Credit: NASA/SSC

Stennis Space Center, located north of New Orleans, is home to some of NASA’s most advanced test stands. The site is the largest rocket testing facility providing services to over 30 different agencies, government entities, and private businesses such as Blue Origin. Stennis is also where all the Space shuttle main engines, a close relative of the RS-25, have been tested. The use of the site made sense due to the existing engine infrastructure.

“It is always a good day at NASA and Aerojet Rocketdyne when you feel the rumble of the Earth as the RS-25 engine comes to life,” said Drake. “This test is the first test of the new controller on a flight engine, demonstrating true adaptability and continuation of technology insertions for this workhorse engine.”

While testing of the new controller for the RS-25 was the primary objective, several other objectives were also completed. In conditions similar to what the hardware will experience in flight, Aerojet Rocketdyne tested the calibration of engine and facility flowmeters and the operation of a rebuilt high-pressure fuel pump.

“Mission success is our driving factor, which is why testing each engine is critical to ensure the safety of the astronauts and cargo that will fly on SLS,” added Drake.

While this RS-25 engine is the first flight article to undergo testing, Aerojet Rocketdyne racked up over 3,700 seconds of engine firing time last year. Those tests involved the first RS-25 development engine. Testing of these engines is critical as they are exposed to extreme conditions during the flight profile. Pressures inside the engine can exceed 7,000 pounds per square inch (492.15 kg/cm²). Beyond that, the engine must operate with temperature swings from –423 °F (–252 °C) to over 6,000 °F (3,315 °C).

Engine E2059 is scheduled to be used on the second flight of the SLS in the bottom core stage. That flight is currently scheduled for 2021. Additional engines, slated for testing from now through 2017, will be used for the 2018 inaugural Exploration Mission-1 launch.

Aerojet Rocketdyne is the prime contractor for the RS-25 core stage engines that will be used to propel SLS on its eight-minute climb into space. They are also currently developing the AR1 – an engine being considered as a replacement for the Russian-built RD-180 engines used on the Atlas V.

Video Courtesy of NASA Stennis

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The latest development test of the RS-25 engine occurred July 29 at NASA’s Stennis Space Center. Photo Credit: NASA

After an early shutdown some two weeks ago, NASA and Aerojet Rocketdyne successfully hot-fired a development RS-25 engine. The full-duration test involved engine 0528 and lasted 650 seconds.

The engine roared to life in the afternoon of July 29 on the A-1 test stand at NASA’s Stennis Space Center in Mississippi. The RS-25, previously known as the Space Shuttle Main Engine, is being repurposed for use on the Space Launch System (SLS).

The July 14 firing of the same engine, 0528, lasted only 193 seconds due to a problem with the A-1 test stand. Photo Credit: NASA

“When we send astronauts to deep space destinations, including Mars, we want them to be riding on the safest, most reliable launch vehicle, which is why we are testing the RS-25 engine under multiple scenarios to ensure America’s next heavy-lift rocket will have the performance needed to take our astronauts deeper into space,” Aerojet Rocketdyne CEO and President Eileen Drake said in a news release.

Testing is required for these engines because, even though they have flown into space before with the Space Shuttle, they will be operating in more extreme conditions.

“During the flight, the RS-25 engines will endure more heat, pressure and thrust on SLS than on the Space Shuttle,” said Jim Paulsen, vice president for NASA programs at Aerojet Rocketdyne.

Four RS-25 engines will fly at the bottom of the SLS core stage at 109 percent power level, compared to the 104.5 percent when operated on the Space Shuttle. Additionally, they will be closer to the two side-mounted Solid Rocket Boosters. On top of that, the taller core stage will result in a higher pressure on the fuel inlet system on each engine.

The firing comes after the July 14 early shutdown of the same engine. However, according to a NASA media release, that was due to a minor problem with the test stand and not the RS-25.

The test lasted about 193 seconds. According to a report by NASASpaceflight, at the recent NASA Advisory Council, NASA Exploration Systems Development Deputy Associate Administrator Bill Hill said the shutdown was due to a low-pressure indication on the line that feeds industrial water to and cools the flame trench. He said that indicated there was a leak somewhere. Teams fixed the problem earlier this week.

There are three more scheduled firings in the current series – the next scheduled for Aug. 18. According to NASA, the tests are focused on a new engine controller and higher operating parameters.

“Stennis is our go-to site to put our engines through rigorous testing; this is where we assemble and test our RS-25, RS-68 and AR1 engines,” Drake said, “Mission success is our number one priority and testing at Stennis is critical to providing the nation with next generation propulsion capabilities.”

Video courtesy of NASA Stennis

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An artist’s concept of Orion docked with a nuclear thermal-engined Mars Transfer Vehicle. Image Credit: NASA

NEW ORLEANS — Before wowing onlookers with the sights and sounds related to testing an RS-25 engine, NASA sought to educate members of traditional and social media outlets about agency and industry efforts related to the Journey to Mars.

However, before the agency can begin sending ships and crew beyond Earth’s neighborhood, they must first complete the rocket and spacecraft that will enable that journey. A televised panel discussion with NASA personnel started the day with a status update of the Space Launch System (SLS), accompanied by a discussion of the challenges the agency must consider in reaching the Red Planet with a crewed mission and the efforts underway to overcome them.

The structural test article for the Orion crew access tunnel on display at Michoud. Photo Credit: Curt Godwin / SpaceFlight Insider

Bill Hill, NASA’s deputy associate administrator for Exploration Systems Development, outlined the progress the agency is making with SLS.

Exploration Mission 1 (EM-1), the maiden launch of the SLS, is still on-track for a late 2018 liftoff and will send the Orion spacecraft on a distant retrograde orbit around the Moon. It will be the only mission to use the Interim Cryogenic Propulsion Stage (ICPS). The pressure vessel for that Orion craft has already been delivered to Kennedy Space Center (KSC) in Florida.

“I would have preferred for [the mission] to have been called EFT-2,” Hill said, in an apparent nod to the experimental nature of Orion’s previous mission on Exploration Flight Test 1 (EFT-1).

Notably, though not related, Hill also mentioned it is NASA’s ultimate goal to turn over the International Space Station to commercial entities at the end of the agency’s commitment in the mid-2020s.

Lara Kearney was also on-hand to explain some of the changes in the Orion spacecraft following its maiden flight in December 2014 atop a Delta IV Heavy.

Kearney, NASA’s Orion Crew and Service Modules manager, noted the spacecraft has evolved from 31 separate structural pieces for the EFT-1 mission to seven for the EM-1 flight. Not only has the number of structural components been significantly reduced, but nearly 1,000 pounds (453 kilograms) of mass has been removed from the spacecraft.

Prior to visiting the Vertical Assembly Center, where the world’s largest spacecraft welding tool is nearing completion of the flight article for the mammoth liquid hydrogen tank for the SLS core stage, SLS Stages Element Manager Steve Doering allowed for a small detour to see the completed structural test article for the tank.

NASA’s Steve Doering discusses the process of making the SLS core stage liquid hydrogen tank. Photo Credit: Curt Godwin / SpaceFlight Insider

Currently undergoing installation of sensors, the 130+ feet (∼40 meters) long tank will eventually be shipped to NASA’s Marshall Space Flight Center (MSFC) in Huntsville, AL, where it will be subjected to simulated flight loads in a recently-constructed test stand so that the design can be validated.

Beyond simply discussing the progress of SLS and Orion toward EM-1, NASA also provided access to propulsion experts.

To date, all human-rated spacecraft have relied on chemical propulsion, whether it be solid fuel, cryogenic, semi-cryogenic, or hypergolic. However, there is a theoretical limit to the efficiency one can expect out of those more traditional methods: approximately 450 seconds of specific impulse (I_sp). I_sp measures the change in momentum delivered per unit of propellant consumed by the engine. One can roughly equate this to the fuel economy rating of an automobile.

Due to the inherently more efficient nature of a nuclear thermal rocket engine – originally tested more than fifty years ago as part of the NERVA (Nuclear Engine for Rocket Vehicle Application) program – there is renewed interest in the practical use of the technology for deep space missions. The NERVA tests showed an efficiency level of 850 seconds I_sp – nearly twice that of the RS-25.

Tony Kim, project manager for nuclear propulsion at NASA’s Marshall Space Flight Center, is in the early conceptual design phase for a restart of the program and is confident that efficiencies can be increased to 1,000 seconds I_sp.

Kim, an emphatic supporter of nuclear thermal engines, posits that such an engine would be safe to launch and would be much safer for astronauts as it would reduce total flight time on a Mars mission by 3 to 4 months, directly reducing the amount of time the crew would be exposed to potentially harmful radiation, both from the sun and from interstellar sources. Such an engine would only use 5.5 pounds (2.5 kilograms) of low-enriched uranium on a round-trip mission to the Red Planet, in addition to its liquid hydrogen propellant.

Though nominally a topic of public derision, Kim asserts now is the time to resume work on a nuclear thermal engine and he feels the public is ready.

“We understand nuclear power,” Kim said when asked about his rationale.

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RS-25 engine № 0528 tested at NASA’s Stennis Space Center (SSC) on August 18, 2016, in preparation for the SLS. Photo Credit: Curt Godwin / SpaceFlight Insider

BAY ST. LOUIS, Miss. — This past week, on August 18, SpaceFlight Insider was on hand at NASA’s Stennis Space Center (SSC), in south Mississippi, for the latest RS-25 engine test in preparation for its use in the agency’s new super heavy-lift vehicle – the Space Launch System (SLS).

Guests watch as RS-25 № 0528 unleashes a torrent of steam at Stennis’ A-1 test stand. Photo Credit: Scott Johnson / SpaceFlight Insider

Rain in the area caused some concern as to whether the test would proceed as scheduled. However, Rick Gilbrech, SSC Director, explained that “a shower this morning had me a little edgy, but, as long as we don’t have any lightning, we’re ok.”

The test, one in a series on engine № 0528, an unflown Shuttle-era developmental engine, took place as scheduled at 5:10 p.m., local time, in SSC’s A-1 test stand. The firing lasted for the planned 420 seconds, and all reports indicate that the test was successful.

Prior to the test, SpaceFlight Insider had the opportunity to speak with Steve Wofford, manager of the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center (MSFC), concerning the timing of the test.

“This is a target time test. It’s usually an events based thing,” explained Wofford. “You proceed to test whenever inlet conditions are right. You condition the engine, you condition the facility, all day, and when it’s ready, you test.”

Wofford also explained that this test would involve no gimbaling of the engine and that controllers were aiming test conditions at the “edge of the start-box today. Not corners, but [the] edge of the start box – so it’s high pressure, nominal temperature.”

Prior to the test, NASA had announced that controllers would throttle the engine between 80 percent and 111 percent. SpaceFlight Insider asked Wofford if on-site observers would be able to distinguish between the thrust levels.

“Most definitely,” Wofford stated. “We’re going to be doing a lot of throttling today, and you can tell the difference in the pitch, and the loudness, between high power levels and lower power levels. And […] if the wind blows the sound to you, it’ll sound a lot louder. But, yeah, high power levels are most definitely louder.”

Wofford also explained that one aspect of the firing was continued testing of the new engine controller, or “brain”: “The new RS-25 controller that we’re making was derived from the J-2X controller. So, the J-2X controller was kind of a stepping stone to this RS-25 controller. The RS-25 engine has a much, much more sophisticated control system than the J-2X because it’s a more complicated engine cycle. So, we had to build that extra functionality into the RS-25 controller.”

SLS Engine Operating Environment

Steve Wofford, SLS Engine Manager, discusses the August 18, 2016, test. Image Credit: NASA TV

Later, Wofford addressed the differences between Shuttle and SLS RS-25 engine operating environments.

“It’s a lot different, particularly in terms of thermals and acoustics,” explained Wofford. “We’ve got models that predict that environment. But, the big differences are you’ve got four engines in a cluster now, instead of three. And, on Shuttle, the three engines were kind of tucked up out of harm’s way. Now, they’re right at the exit plane, and co-planer, with the solids. So, it’s very, very different.”

Wofford further explained that “we’ve got models that predict that we can handle that environment, but that’s a big part of why we’re going to run this stage test [– the SLS core stage “Green Run” –] next year. So, we’re going to instrument the heck out of the engines to gather data, all sorts of data, in terms of temperature, pressure, flow, and acoustics, in that stage test environment.”

“There’s some extra insulation on the nozzles to protect them from that different thermal environment,” Wofford continued. “The vast majority of the nozzle is cool; it’s got hydrogen running through it. Some of it is not cool – the structural path and the drain lines are not cool – and they’ve got extra insulation.”

Future RS-25 Testing

On upcoming RS-25 testing, Wofford responded: “We’re going to run a lot more tests on 0528. We’re going to run, […] counting today, six more tests in this series, on this engine, and then two tests on flight engines for SLS. And then, following that, we’ll be certified for flight with SLS, so we can kind of stand down the test program to certify for flight. Then, following that, in the fall of next year, we’re going to be moving into a development test series for our new engines – for our affordability changes.”

And, when asked about testing of the “flight” versions of the new RS-25 engine controller, Wofford responded: “That’ll be in the fall. That’ll actually be the second flight model controller – the first one will be the qualification unit – that’ll be [brought] out of the laboratories […] controller FM-1 will never fly. It’s a lab unit. Controller FM-2 will fly on EM-1 [and will be tested] in the fall.”

Future RS-25 Production

NASA has 16 (14 of which are previously flown) Shuttle-era RS-25 “flight” engines in storage at SSC. These engines will be installed on the SLS core stages, four at a time, and flown on missions EM-1 through EM-4.

SLS RS-25 flight engine mission assignments. Photo Credit: Aerojet Rocketdyne

Missions subsequent to EM-4 will require new engines. As a result, NASA signed, in 2015, a $1.16 billion contract with Aerojet Rocketdyne for the production of six (four “flight” and two “certification”) additional RS-25s.

“We’ve started work on the future engines,” said Wofford. “Number one, we’re re-starting production lines that have been idle for as long as twenty years, so that’s no small feat in itself. Number two is to continue to get more time and explore how the engine handles the new SLS propellant engine conditions [at] colder and higher pressure.”

RS-25 engine № 0528 test at SSC on Aug. 18, 2016. Photo Credit: Curt Godwin / SpaceFlight Insider

“The other thing is there’s some obsolescence changes that we’ve had to make for these, and there’s some parts that we couldn’t make again if we wanted to, particularly some of the electronics.”

Wofford continued, “But, the really exciting category is the affordability changes. We’re taking advantage of forty years worth of manufacturing lessons learned, advances in technology, like 3-D printing […]. We need to ‘move’ the world’s most complex rocket engine to make it much, much more affordable for this expendable application.”

When asked about the benefits of new 3-D printing, or additive manufacturing (AM), technology, Wofford stated that “it can help a lot […] we have upwards of forty parts that we’re going to be making via additive manufacturing. Some of the really, really difficult, expensive, time-consuming parts to make, we’re going to be making by additive – a lot cheaper, a lot faster.”

“Some of the ducts that we’re going to be using on the engine are going to be made by AM,” explained Wofford. “For instance, you can make a duct by AM that has a lot of complex geometry, and a lot of complex bends in it, whereas before, that would have to be made in multiple pieces, with welds in them, now you can make one monolithic piece. As an engineer, a weld is a built-in brittle discontinuity that I don’t like – one piece is better.”

However, and despite advances in technology, SLS is a Shuttle-heritage design, conceived to take advantage of existing architecture and hardware.

“We have to kind of tread a thin line. It has to have the same form, fit, and function, and fit in [the] same hole that it did before,” explained Wofford. “You’re somewhat constrained in that regard because you’re retrofitting new parts into in an existing engine. But, given that, we’re still doing lots of redesigns that do meet that form, fit, and function requirement.”

Potential RS-25 Cost-Savings

Wofford was also asked about potential cost-savings associated with new RS-25 production, as compared with Shuttle-era production: “33 percent is our target and we’re on track to make that […]. We would be there, at the 33 percent, on the third or fourth engine […]. It’s high pay-off. When you integrate that 33 percent, over time with four engines per vehicle, […] it’s [a] really good return on our investment.”

Video Courtesy of NASA Stennis

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A drone captures never-before-seen views of a test firing of an RS-25 engine at NASA’s Stennis Space Center. Photo Credit: NASA

Engineers at NASA’s Stennis Space Center near Bay St. Louis, Mississippi, conducted a test of the RS-25 engine on the A-1 Test Stand. In addition to collecting performance data on the engine that will help power the new Space Launch System (SLS) rocket, a NASA drone revealed never-before-seen imagery of the more than six-minute-long firing.

The test was conducted by Aerojet Rocketdyne and Syncom Space Services personnel. Aerojet Rocketdyne is NASA’s prime contractor for the RS-25 engines. Syncom Space Services is the prime contractor for Stennis facilities and operations.

“The RS-25 is a remarkable engine that continues to undergo testing at Stennis to ensure that the Space Launch System rocket will have the performance necessary to safely take our astronauts into deep space,” said Aerojet Rocketdyne CEO and President Eileen Drake.

A drone captures never-before-seen views of a test firing of an RS-25 engine at NASA’s Stennis Space Center. (Click to enlarge) Photo Credit: NASA

Views of the test stand came from an overhead drone, which captured the re-purposed Space Shuttle-era engine firing in action for the first time from above the A-1 stand.

“Never before has drone technology been used to give us a bird’s-eye view of our engine test,” Drake said.

Development engine No. 0528 ran for 380 seconds (about 6 minutes, 20 seconds) allowing engineers to monitor various engine operating conditions. According to NASASpaceflight, the engine was throttled to 109 percent of the originally designed power level for 205 seconds, 100 percent for nine seconds, and 80 percent for 118 seconds.

This was the 12th test of the RS-25 to confirm it meets the added requirements and performance beyond what was needed to support the Space Shuttle program.

The test is another step in the development of the rocket that will eventually launch humans beyond low-Earth orbit for the first time since 1972. Four RS-25 engines, along with a pair of five-segment solid rocket boosters, will power the SLS at launch on deep space missions to the Moon or Mars.

The engines for the first four SLS flights will be former Space Shuttle Main Engines, which were also tested at Stennis.

“The RS-25 engine continues to perform flawlessly, which is a testament to the dedication and hard work of the hundred of employees across the country supporting this program,” said Dan Adamski, RS-25 program director at Aerojet Rocketdyne.

Engineers are conducting an ongoing series of tests this year on both development and flight engines to ensure the design, outfitted with a new controller, can perform at higher levels under a variety of conditions and situations. The engine controller unit controls the internal engine functions during the flight and enables proper communication between the SLS and the RS-25.

According to NASASpaceflight, three more firings of engine 0528 are planned – one on March 24, April 27, and May 16 – before it is removed for other engines to be tested. There is an option for a fifth test on the engine in June if needed. After that, flight engines will begin firing on the stand.

Stennis is also preparing its B-2 Test Stand for the core stage of the first SLS flight, known as Exploration Mission 1. The testing will involve installing the flight stage on the stand and firing its four RS-25 engines simultaneously.

EM-1 is expected to launch in 2018 to send an uncrewed Orion spacecraft into a distant retrograde orbit around the Moon. However, NASA is currently studying the feasibility of adding people to the first mission, which would likely delay EM-1 by at least a year.

Video courtesy of NASA’s Marshall Center

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An RS-25 rocket engine is tested at NASA’s Stennis Space Center in Mississippi, the 13th such test for NASA’s new Space Launch System. Photo Credit: NASA

The powerful RS-25 engine that will be used on NASA’s new super-heavy-lift Space Launch System (SLS) underwent its 13th test March 23, 2017, at NASA’s Stennis Space Center in Bay St. Louis, Mississippi.

An RS-25 being tested at NASA’s John C. Stennis Space Center. Photo Credit: NASA / Aerojet Rocketdyne

The RS-25 engine

Formerly known to many as the Space Shuttle Main Engine (SSME), an RS-25 burns liquid hydrogen (LH2) and liquid oxygen (LOX). During the shuttle era, each produced produce 491,000 pounds (2,184 kilonewtons) of vacuum thrust while running at 104.5 percent of the rated thrust.

Three at a time, these engines helped launch all 135 Space Shuttle missions into orbit.

SLS, however, will need a bit more power, and part of this testing is to evaluate its durability at its new power level, which is now 109 percent of rated thrust resulting in 512,000 pounds (2,277.5 kilonewtons) of vacuum thrust.

Additionally, the RS-25 will experience other conditions that will be more extreme than during a Space Shuttle flight.

“The engines for SLS will encounter colder liquid oxygen temperatures than shuttle, greater inlet pressure due to the taller core stage liquid oxygen tank and higher vehicle acceleration, and more nozzle heating due to the four-engine configuration and their position in-plane with the SLS booster exhaust nozzles,” said Steve Wofford, manager of the SLS Liquid Engines Office at NASA’s Marshall Space Flight Center, following the first test of the SLS engines in 2015.

Unlike during the Space Shuttle era, the SLS engines will not be reused since the booster will not be recovered. There are currently 16 former Space Shuttle engines at the Stennis facility for use on the first SLS launches. After that inventory is exhausted, however, new engines will be built using modern techniques and materials to lower the cost of producing an expendable version of the RS-25.

The March 23 engine test lasted for approximately 500 seconds which simulated the actual burn time the engines will operate during an SLS launch.

The engine controller

Aerojet Rocketdyne technicians inspect the new controller on the RS-25 development engine. Photo Credit: Aerojet Rocketdyne

This firing also included a test of a new SLS engine controller that not only operates the engine, taking commands from the SLS flight computers and translating it to the engine, but also monitors the health and performance of the engine and communicates that back to the flight computers.

The new controller has 20 times more processing power than the Space Shuttle engine controllers it replaces. Increased reliability has been built into it and it weighs 50 pounds (22.7 kilograms) less than its shuttle counterpart.

“Just think about all the advances in computing technology and electronics that have occurred over the recent years, we’ve been able to include those advances into the controller,” said Dan Adamski, RS-25 program director at Aerojet Rocketdyne. “We’ve been able to increase the processing speed, add memory and greatly improve the reliability of the entire controller communication network.”

This particular controller, once the test data certifies its performance, will be installed on one of the four flight engines that will propel the SLS on its maiden flight.

Four RS-25 engines, providing over two million pounds of thrust, along with two five-segment solid rocket boosters will provide the power to lift the SLS off the pad and into orbit.

Currently, the maiden flight of the SLS is tentatively scheduled for late in 2018. That launch will send an uncrewed Orion spacecraft on a journey to orbit the Moon to test all of its systems.

However, following a directive from the Trump administration, NASA is investigating the requirements needed to put a crew on that first launch. If a crewed mission becomes a reality, the extra time needed to ready the flight will push it into 2019, if not later.

Video courtesy of NASA

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Aerojet Rocketdyne tests the third RS-25 flight controller on a developmental engine at NASA’s Stennis Space Center on July 25, 2017. Photo & Caption Credit: NASA

Propulsion hardware testing for NASA’s Space Launch System (SLS) continues at Stennis Space Center in Mississippi. Aerojet Rocketdyne just completed its third 500-second test of the controller unit for the RS-25 main engine on July 25.

The brains of the operation

Before they began their new lives as core stage engines for SLS, the liquid hydrogen/liquid oxygen RS-25s were the main engines for NASA’s Space Shuttle. In that role, three RS-25s were clustered at the tail end of the orbiters. For SLS, a four-engine cluster will be positioned at the aft end of the core stage at the same level as the SRBs.

This will be a new thrust, thermal, and control environment for these legacy engines. Given the changes to the engine’s mission and the advances in avionics made since their first test firing in 1975, the RS-25s are getting the equivalent of a brain transplant.

The engine controller Aerojet Rocketdyne tested provides precise control of the engine’s operation and internal health diagnostics. It also allows the engine to communicate with SLS and human controllers on the ground. During launch and flight, the controller communicates with the SLS flight computers, receiving critical commands, returning engine status data, and making real-time corrections to turbopump speeds, combustion pressures, and thrust and propellant mixture ratios as needed.

“Achieving the optimum thrust and mixture ratio is crucial for creating an extremely efficient rocket engine,” added Dan Adamski, RS-25 program director at Aerojet Rocketdyne. “The RS-25 is the most efficient booster engine in the world, which is why it is the right engine for human exploration of deep space.”

NASA tested the first flight controller on the A-1 Test Stand at Stennis in March of this year, the second in May. After reviewing the test data, the first two controllers were designated for use on SLS. Tuesday’s single-engine, 500-second test concentrated on controlling and monitoring the engine’s thrust and mixture ratio precision operation.

Coming attractions

The controller tested on July 25 is slated to be used on the inaugural flight of SLS, Exploration Mission (EM) 1, scheduled for 2019. EM-1 will send an uncrewed Orion spacecraft around the Moon and return it safely to Earth. Once NASA has four flight-ready engines, the SLS program will be able to start testing the RS-25s in four-engine clusters on Stennis’ B-2 Test Stand.

Video courtesy of NASA

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August 9, 2017, RS-25 engine test at NASA’s John C. Stennis Space Center in Mississippi. Photo Credit: NASA

On Wednesday, August 9, NASA and Aerojet Rocketdyne conducted a 500-second test of an RS-25 developmental engine at the agency’s Stennis Space Center (SSC) in Mississippi. The test was used to validate the fourth upgraded engine controller required for the first flight of the Space Launch System (SLS).

The RS-25, formerly known as the Space Shuttle Main Engine (SSME), is being reused for SLS; however, the engine controller – the “brain” of the engine – has been redesigned to reduce weight, to use less power, and to improve reliability.

SLS will be powered by four RS-25 engines, along with a pair of five-segment solid rocket boosters (SRB‘s).

The first flight of SLS, Exploration Mission-1 (EM-1), is expected to take place in 2019. It will propel the Orion capsule on a three-week uncrewed mission to a distant retrograde orbit around the Moon.

Video courtesy of NASA

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NASA capped off summer with a 500-second hot-fire test of a fifth RS-25 engine flight controller unit on the A-1 Test Stand at its Stennis Space Center near Bay St. Louis, Mississippi, on Aug. 30, 2017. Photo Credit: NASA

The final test of the RS-25 engine for the new Space Launch System (SLS) took place on August 30, 2017, at Stennis Space Center near Bay St. Louis, Mississippi. The 500-second hot-fire test is the fifth of the RS-25 engine flight controller unit on the A-1 test stand.

Four RS-25 engines will be integrated with the SLS rocket with the Orion spacecraft during the first test flight, Exploration Mission-1 (EM-1). A controller communicates with the SLS flight computers to ensure that the engines are performing at accurate levels. The new flight controllers are a critical component of engine modification.

During tests, the controllers are installed on a developmental RS-25 engine, which is then fired in the same method. The test is another step closer toward the United States’ mission to return to human deep-space exploration missions. NASA launched a series of summer tests beginning at the end of May, followed by three additional tests.

The four engines generate a combined 2 million pounds-force (8,900 kilonewtons) of thrust at liftoff. With the boosters, total thrust at liftoff will exceed 8 million pounds-force (35,590 kilonewtons). The RS-25 engines designated for use on the initial SLS missions are former Space Shuttle Main Engines, modified to provide the additional power for the larger, heavier SLS rocket.

On the SLS, expendable versions of the engine will provide thrust for the vehicle’s core stage. While engines on the Space Shuttle ran at 491,000 pounds-force (2,184 kilonewtons) of vacuum thrust, the power level was increased for the SLS to 512,300 pounds-force (2,279 kilonewtons) of vacuum thrust to augment the vehicle’s heavy-lift capability.

A total of 16 RS-25 engines are stored at Stennis. The tests, which began in 2015, are conducted by a team of NASA, Aerojet Rocketdyne, and Syncom Space Services engineers and operators.

Video courtesy of NASA

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An Aerojet Rocketdyne technician inspects the 3-D printed pogo accumulator assembly on an RS-25 development engine at the Aerojet Rocketdyne facility located at NASA’s Stennis Space Center. Photo & Caption Credit: Aerojet Rocketdyne

NASA and Aerojet Rocketdyne have conducted the final RS-25 hot-fire test of 2017 at their Stennis Space Center in Mississippi. The six-minute, 40-second test was conducted at Stennis’ A-1 Test Stand. The test also continued the development of components that utilized additive manufacturing, more commonly known as “3-D printing”.

The test conducted today was known as a “green-run test” and utilized a 3-D printed RS-25 flight controller part. This was the eighth RS-25 test of the year and the sixth flight controller overall to be tested for NASA’s Space Launch System (SLS) rocket.

The SLS is the U.S.’ next launch vehicle designed to send crews to the Moon and perhaps, one day, Mars. The flight controller tested is about the size of a beach-ball and is called a POGO accumulator assembly. This part is used as a kind of “shock absorber” which will dampen vibrations, or oscillations, which are caused by the rocket propellants as they flow down the fuel system between the launch vehicle and the engine itself.

“This test demonstrates the viability of using additive manufacturing to produce even the most complex components in one of the world’s most reliable rocket engines,” Eileen Drake, CEO and president of Aerojet Rocketdyne said via a release issued by the company. “We expect this technology to dramatically lower the cost of access to space.”

NASA’s launch vehicle fabrication partners across the U.S. are working to develop and produce components and flight hardware for this new rocket using techniques like additive manufacturing or 3-D Laser Printing.

It is hoped that this will help replace the 16 RS-25 engines that are currently being used (or planned for use). These are, essentially, modified leftover engines from the Space Shuttle Program. It is hoped that the use of 3-D printed components will allow for the costs of producing these elements to be lowered.

NASA has stated that the 3-D printed component performed as expected.

At present, the first SLS flight will be Exploration Mission 1, or EM-1, which will be an unmanned test flight of the Orion Multi-Purpose Crew Vehicle on an uncrewed lunar orbital test flight. The following flight will be EM-2 which will be the first crewed mission to the Moon since Apollo 17 flew to the Moon in December of 1972. It is hoped that EM-2 will take place in the 2022–2023 time frame.

“As Aerojet Rocketdyne begins to build new RS-25 engines beyond its current inventory of 16 heritage shuttle engines, future RS-25 engines will feature dozens of additively-manufactured components,” said Dan Adamski, RS-25 program director at Aerojet Rocketdyne via a company-issued release. “One of the primary goals of the RS-25 program is to lower the overall cost of the engine while maintaining its reliability and safety margins. Additive manufacturing is essential to achieving that goal.”

The A-1 and A-2 test stands were created during the Apollo era to test the J-2 engines for the Saturn V Moon rockets second stage known as the S-II.

Video courtesy of NASA Stennis

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Archive image of prior RS-25 test, Feb. 22, 2017 , Shown from the viewpoint of an overhead drone. Photo Credit: KSC Unmanned Aerial Systems Team

NASA and Aerojet Rocketdyne conducted another successful test firing of the Space Launch System’s core stage main engine, the RS-25, on Jan 16 2018.

The 14 foot (4 meter) tall engine was attached to NASA’s Stennis Space Center’s A-1 test stand where it was hot fired for six minutes and five seconds. When propelling the SLS on its missions to the Moon and beyond, these engines are planned to fire for about eight and half minutes. This marks the second successful test for the engine in just over a month with a six minute and 40 second firing having occurred on Dec. 13 2017.

RS-25 rocket engines at NASA’s Kennedy Space Center in Florida. Photo Credit: Jason Rhian / SpaceFlight Insider

“Aerojet Rocketdyne is playing a vital role in the nation’s effort to expand the frontiers of humankind. This test is the latest example of our steady progress, not only toward EM-2 but also toward putting the nation’s exploration program on a sustainable path for the future,” said Eileen Drake, Aerojet Rocketdyne’s CEO and president via a company-issued release.

This particular test qualified the engine controller that will be used on the third engine of the second planned flight of the SLS (EM-2), currently scheduled to be a crewed trip around the Moon. The SLS main core is designed to use four RS-25 engines producing just over 2 million pounds of thrust paired with two 5 segment Solid Rocket Boosters (SRBs – produced by Orbital ATK) propelling it at liftoff.

The RS-25 engine is fueled by a mixture of Liquid Hydrogen (LH2) and Liquid Oxygen (LOX), earlier versions of the engine helped power NASA’s now-retired fleet of Space Shuttle orbiters off the pad for more than 30 years.

A total of 16 Space Shuttle Main Engines are being upgraded for use on the SLS. Improvements to the engine include a new controller, which is  essentially the engine’s brain. With substantially increased processing power and a decrease in weight, the engine controller is being prepared to be ready to take SLS through its first flights. In addition, engine thrust has been increased by 21,000 pounds to a total of 512,000 pounds.

Unlike with the shuttle, where the engines were reused, the SLS engines will be single-use as the core stage will not be recovered.

This test also marked the second successful demonstration of the pogo accumulator assembly, which is designed to dampen vibrations that could result in stability issues during flight. The pogo accumulator is NASA’s largest additive manufactured (3-D-printed) rocket engine component used in the retooled RS-25.

Additive manufacturing is planned to play a key role in Aerojet Rocketdyne’s efforts to reduce the production costs of future versions of the RS-25 by as much as 30 percent.

More testing of the RS-25 is scheduled to be conducted this year to test components and to qualify more of the new flight controllers so they are ready for future SLS missions.

“We ended 2017 with a successful engine test in December and have now maintained that momentum into 2018,” said Dan Adamski, RS-25 program director at Aerojet Rocketdyne. “Future testing this year will continue to add to the program’s inventory of flight controllers and will bring additional development hardware into the test program to demonstrate design, manufacturing and affordability improvements. Our pogo accumulator assembly is just one of the first of these efforts to be hot-fire tested.”

The first flight of the Space Launch System, Exploration Mission 1, is currently scheduled for some time in 2019 will be an uncrewed flight to the Moon.

Video courtesy of NASA Stennis

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Aerojet Rocketdyne RS-25 rocket engine controller test Feb. 1, 2018. Photo Credit: NASA

On Feb. 1, 2018, a team of engineers at NASA, Aerojet Rocketdyne and Syncom Space Services engineers and operators test-fired the RS-25 engine conducted a test firing at the Stennis Space Center near Bay St. Louis, Mississippi.

With this test fire, all four of the RS-25 engines which will be used in the Space Launch System (SLS) have been tested for the second flight of the new rocket.

“We are thrilled to mark another important step toward humankind’s first foray beyond low Earth orbit since 1972,” said Eileen Drake, Aerojet Rocketdyne CEO and president via a company-issued release.

The test firing occurred at Stennis’ A-1 test stand. Flight controller ECU-11 was installed on the RS-25 engine for the test, and engine E0528 was fired under conditions that duplicated an actual launch. The RS-25 engines are actually modified Space Shuttle Main Engines (SSMEs), and a major part of the modification is the flight controller, which allows the engine to communicate with the SLS rocket, monitoring and communicating engine operation and the status of its internal functioning.

During a typical test, the engine is throttled to various test levels in order to duplicate different specific scenarios that occur during a launch. This allows engineers to compile data on the engine’s performance.

RS-25 flight controllers have already been installed on the engines that will fly on the SLS core stage for Exploration Mission 1, the mission that will fly the Orion Multipurpose Crew Vehicle on an unscrewed flight beyond the Moon.

If all goes as planned, Exploration Mission 2 will carry humans beyond Low Earth Orbit (LEO) for the first time since 1972.

The Feb. 1 test included a 3D-printed pogo accumulator assembly. It was the third test of the 3D-printed component. NASA and private industry have been utilizing 3D printing, both on the International Space Station and in experimental satellites, to reduce construction costs, as well as to open up new methods of space construction.

Now that all of the four RS-25 engines have been test fired, the core stage for the first SLS mission is next to be tested at Stennis. In that test, all four engines will be fired simultaneously.

At launch, the SLS is designed to utilize its RS-25 engines and two solid rocket boosters (produced by Dulles, Virginia-based Orbital ATK), producing an estimated total 8 million pounds of thrust.

Exploration Mission 1 is currently scheduled to lift of from Kennedy Space Center’s Launch Complex 39B on Sept. 5, 2018. With Exploration Mission 2 is slated to take place sometime in 2022 and is supposed to be the first time that astronauts leave somewhere for other than low-Earth orbit, in this case lunar orbit, for the first time since Dec. 1972’s Apollo 17 mission.

“This is the third of four scheduled tests to confirm not only the functional performance of the Pogo, but also to verify the structural margins and capabilities,” said Dan Adamski, Aerojet Rocketdyne director for the RS-25 program. “All the data gathered to date has matched up very well with our predictions.”

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An RS-25 engine undergoes a test at NASA’s Stennis Space Center. Photo credit: NASA

Engineers at NASA’s Stennis Space Center conducted a test of the Space Launch System’s (SLS) RS-25 engine, pushing the design to the highest level ever recorded for the powerhouse previously used to send Space Shuttles into orbit. The Aerojet Rocketdyne-manufactured engine reached a peak output of 113 percent of rated power during the Feb. 21, 2018, firing at the coastal Mississippi site.

Aerojet Rocketdyne’s Owen Brayson highlight’s the 3-D-printed pogo accumulator assembly on the RS-25. Photo credit: Aerojet Rocketdyne

Testing the limits

The firing took place at the A-1 test stand where Engine 0528, a development article being used by NASA and Aerojet Rocketdyne to evaluate new hardware and software, was pushed to 113 percent of rated power for 50 seconds of the 260-second test to explore the limits of the design.

“Increased thrust requirements for the RS-25 are just one of the many changes in the SLS rocket’s performance that will facilitate our nation’s deep space exploration goals and objectives,” said Aerojet Rocketdyne’s RS-25 program director, Dan Adamski, in a press release issued by the company. “While we can analytically calculate engine performance and structural capabilities at these higher power levels, actually demonstrating that performance with an engine hot fire provides the added confidence that these engines will meet all specification requirements demanded of SLS.”

During their previous life as Space Shuttle Main Engines, RS-25 engines regularly ran at 104.5 percent of rated power while pushing Space Shuttles into orbit. Once the storied spacecraft were retired, 16 of the reusable engines were left over. They will be used on the first four flights of SLS (four per launch) and run at 109 percent.

Because the SLS is expendable, the current stock of engines will be depleted by flight four. According to Aerojet Rocketdyne, new RS-25s are being developed under its restart program to be used for SLS flight five and beyond. Those will fly at 111 percent. 

Testing to 113 percent will allow engineers to discover how the RS-25 and its components react at higher levels.

The RS-25 engines were designed more than 40 years ago for a specific power level during development, which engineers considered 100 percent. Over the decades, the design was refined and upgraded. Rather than revising documentation, the initial 100 percent mark was kept, with ratings over that marking higher power levels.

An artist’s rendering of an SLS Block 1 rocket on the launch pad at night. Four RS-25 engines and two five-segment Solid Rocket Boosters will power it toward orbit. Image Credit: NASA

Beyond evaluating the engine at higher throttle levels, this test also saw the inclusion of both an RS-25 flight controller and a 3-D-printed pogo accumulator assembly. The RS-25’s flight controller, or “brain,” will communicate with the SLS’s flight computers to relay the health and performance of the engine during the powered phase of its flight.

The pogo accumulator assembly, however, marks the largest component of the engine to be manufactured via a 3-D printing, or additive manufacturing, process. The use of this modern technique eliminates more than 100 welds on the vibration-reducing component, shortening production time by more than 80 percent, according to NASA.

“With modern fabrication processes, including additive manufacturing, the ‘next generation’ of the RS-25 will have fewer parts and welds, reducing production time as well as costs,” said Carol Jacobs, RS-25 engine lead at Marshall Space Flight Center, in a news release issued by the space agency.

These solo engine evaluations are precursors to the SLS core stage’s full-up hot fire test—also called the “Green Run”—during which all four RS-25 engines will undergo a flight-duration firing. This test will mimic the output levels expected on a nominal flight and will certify the hardware for use on Exploration Mission 1 (EM-1) in 2020. The uncrewed flight will validate the rocket and the Orion crew vehicle before carrying astronauts on EM-2 no earlier than 2023.

This test is the latest in a line of evaluations of the super heavy-lift vehicle’s development.

“One of the key features of SLS is its versatility to support human and robotic missions, launching spacecraft, habitats and astronauts to a variety of deep space destinations,” said Eileen Drake, CEO and president of Aerojet Rocketdyne, in the company’s release. “The lifting power of the SLS will permit NASA to get bigger payloads to distant planets more quickly than any other launcher operating today.”

Video courtesy of NASA

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An RS-25 rocket engine ignites for an engine controller test conducted at NASA’s Stennis Space Center on Sept. 25, 2018. Photo Credit: Matt Haskell / The Aerospace Geek

STENNIS SPACE CENTER, Miss. — Aerojet Rocketdyne tested a leftover Shuttle Space Main Engine, redubbed the RS-25, at NASA’ Stennis Space Center in Mississippi. The test marked the latest step in the space agency’s efforts to send crews deeper into space than has ever been attempted before.

The window for today’s test opened at 2 p.m. CDT, with the engine coming to life at 3:31 CDT (18:31 GMT). All total, the engine was active for about 500 seconds.

The RS-25 used a mixture of cryogenic liquid hydrogen and oxygen to demonstrate that the heritage hardware could fire at 109 percent thrust. Today’s test was held to certify a flight controller that is planned for use on the RS-25. 

NASA plans to use the RS-25 on the first flights of the agency’s new Space Launch System. Photo Credit: Matt Haskell / The Aerospace Geek

Between eight to ten tests are carried out annually at Stennis. However, SLS does not require any of these tests to be completed prior to taking to Florida’s skies on its first planned voyage – Exploration Mission 1 (EM-1). The rocket’s maiden flight is currently scheduled to take place in 2020.

A backup set of engines are available should one of their components become damaged or an anomaly was discovered during a core stage test.

“The first set of engines is set and ready to go, they’ve already been put on the core stage (of SLS) and tested as a whole assembly at the B-2 stand,” Stennis Space Center’s Deputy Director of the Engineering Test Directorate, Gary Benton told SpaceFlight Insider. “Right now we’re working on a second set, which could be used on the second flight (EM-2) or as a spare set for the first flight.”

Elements of the RS-25 emerged in the 1960s, with the engine’s “official” development starting in the 1970s in the lead up to the Shuttle Program. After NASA’s fleet of shuttle orbiters was retired in 2011, some of the SSMEs that remained were re-tasked to fly on SLS. Unlike on shuttle, these engines will not be reused.

The RS-25 is a modified version of the Space Shuttle Main Engine. Photo Credit: Matt Haskell / The Aerospace Geek

The photos within this article were captured by Matt Haskell with The Aerospace Geek

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NASA plans to use the RS-25 on the first flights of the agency’s new Space Launch System. Photo Credit: Matt Haskell / The Aerospace Geek

STENNIS SPACE CENTER, Miss — Aerojet Rocketdyne tested one of its legacy Space Shuttle Main Engine in preparation for use on NASA’s Space Launch System on Tuesday, Sept. 25, 2018. The A1 Test Stand weathered an eight minute test fire at 109 percent throttle starting at 3: 15 p.m. EDT (19:15 GMT). Photos courtesy: Matt Haskell / The Aerospace Geek

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Aerojet Rocketdyne RS-25 rocket engines at NASA’s Kennedy Space Center in Florida. Photo Credit: Jason Rhian / SpaceFlight Insider

The flight controllers for the first planned flights of NASA’s massive Space Launch System (SLS) rocket are now in the hands of those refurbishing the RS-25 engines that will help power the SLS’ first stage.

Aerojet Rocketdyne took possession of the Honeywell-produced hardware late last month (October of 2018). The flight controllers help guide the RS-25 as they propel the SLS aloft.

In essence, these controllers “talk” with SLS and handle an array of other tasks such as monitoring the health and performance of the engines and regulating their thrust levels.

“The RS-25 program continues to achieve important milestones as we work toward the initial round of flights of America’s newest exploration rocket,” said Eileen Drake, Aerojet Rocketdyne CEO and president via a company-issued release. “We look forward to continuing to outfit the 16 engines remaining in our inventory from the shuttle with these upgraded controllers.”

Aerojet Rocketdyne now has 18 of the new controllers. This includes a spare, a qualification unit and 16 flight units. Aerojet Rocketdyne is currently putting these components through their paces with the latest test taking place on Oct. 31. During which the ground test-article of the RS-25 flared to life during a test that ran just shy of eight and-a-half minutes (this marked the 13th test of one of the new flight controllers).

The RS-25 is a modified version of the Space Shuttle Main Engine, which was used during the 30 years NASA’s now-retired fleet of orbiters were in service. As one might imagine, systems that can trace their lineage back to the 60s require a 21st Century upgrade. Each RS-25 is capable of producing an estimated 512,000 pounds of thrust at altitude.

The four RS-25s that have been selected for use on SLS’ maiden flight, Exploration Mission 1, are at NASA’s Stennis Space Center located in Mississippi. If everything goes as advertised EM-1 should take to Florida’s skies in 2020 from Kennedy Space Center’s Launch Complex 39B.

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