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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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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File photo of a previous RS-25 engine test. NASA plans to use the RS-25 on the first flights of the agency’s new Space Launch System. Photo Credit: NASA

One of the leftover rocket engines used during the 30-year Space Shuttle program was tested again today, Feb. 13, 2019, at NASA’s John C. Stennis Space Center in Mississippi.

Known as RS-25 engines, it was formerly called the Space Shuttle Main Engine. Its development began back in the 1960s to be a reusable engine. However, for its use on NASA’s Space Launch System (SLS) they will not be reused and will end up at the bottom of the Atlantic Ocean.

During their tenure with the Shuttle Program, the engines acquired a 99.95 percent success rate.

NASA had planned to use the engines as part of the now-cancelled Constellation Program. When the Ares V rocket was selected to continue as the re-dubbed SLS, the RS-25 was also spared (the announcement of such was made on Sept. 14, 2011) and continues to be tested.

“As we develop a new generation of RS-25 engines, ensuring they continue to remain reliable while reducing costs is a major focus at Aerojet Rocketdyne,” said Aerojet Rocketdyne CEO and president Eileen Drake in an August 2018 statement. “That’s why we’re working hard to drive down costs on the RS-25 by incorporating the most modern and efficient manufacturing techniques.”

For today’s firing, the roughly 8.5-minute test took place just before 4:30 p.m. EST (21:30 GMT) and its main purpose was to further evaluate the flight controller for the engine at a power level of 113 percent.

This comes after a Dec. 12, 2018, test was aborted after about 30 seconds. According to NASASpaceflight, a manual abort command was issued after an anomaly in the data was seen.

Video courtesy of Space Videos

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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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