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Aerojet Rocketdyne tests third SLS engine controller

SLS: Aerojet Rocketdyne RS-25 flight controller test on July 25, 2017.

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



Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.

Reader Comments

Interesting how NASA needs to hype RS-25 engine test like it’s the cat’s meow. ARJ does this for every RS-68 and SpaceX does this so often and regularly you could set your watch to it. I guess when you’re not flying you need to show something.

The “modern” controller which is from J-2X, which itself is from RS-68 originally replaces the SSMEC Block II also from Honeywell. This thing rocked redundant Motorola 68K processors that would top out at 20Mhz making your Raspberry Pi look like a graphics workstation by comparison. Defiantly needed to be upgraded.

NASA is amazing I also dream to work with NASA but I think I can only dream about it. I think NASA should its main focus on how to keep our world safe against natural disasters and should avoid such risk of tech which leads to natural disaster. Keeping everyone safe should be a number one priority.

Protection from natural disasters is a worthy goal. However, the National Aeronautics and Space Administration is an agency created to research flight and space exploration. Avoiding “tech” would defeat its entire purpose. The Earth observations provided by NASA have given us an enhanced awareness of global warming, but NASA cannot be eesponsible to protect the world from any disasters associated with those climate changes.

I think NASA is going to do secret experiments.

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