Spaceflight Insider

New ‘brain’ for RS-25 engine is no technological flashback to the ’80s

sls_launch_closeup_engines_at_liftoff_NASA image posted on SpaceFlight Insider

Image Credit: NASA

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.

controller on RS-25 rocket engines at Stennis Space Center building 9101 NASA photo posted on SpaceFlight Insider

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.

Aerojet Rocketdyne facilitites at Stennis Space Center Mississippi photo credit Jason Rhian SpaceFlight Insider - Copy

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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Reader Comments

Awesome engine. Makes the SpaceX Merlin look like the cheap junk it is.

The RS-25, while producing 2.3 million pounds of thrust in a vacuum, only has a thrust-to-weight ratio of ~ 66. The Merlin 1D, while only producing 1/3rd the thrust has a thrust-to-weight ratio of ~ 150. Instead of using old technology RS-25, why not design a new engine?

Well, you did not quote the thrust right and why design a new engine when it one of the best in the world as it is? Kerosene is an obsolete technology- especially in the upper stages. SpaceX infomercials will not change the Isp numbers.

The situation with the improvements to the SSME/RS-25 is hardly new. With a handful of exceptions (e.g. the RS-68 for the Delta IV and the Merlin-series engines for Falcon), most of the large American-built engines that have flown on American launch vehicles over the last several decades have been incrementally modified versions of rocket engines that were originally developed during the 1950s and 1960s. Over time they are upgraded to take advantage of advances in materials, electronics and manufacturing techniques to improve their performance, reliability and manufacturability.

Mentioning the Merlin series of low thrust kerosene burners alongside hydrogen burning state of the art technology is just another page in the New Space mob playbook. Yes, rocket engines are just updated versions of earlier models just like piston engines in cars are. But placing kerosene in the same category as hydrogen is not an honest comparison at all. Kerosene is an obsolete propellent. The years of incessant New Space mob infomercials claiming kerosene is somehow superior are a prime example of how the public is being lied to. The best mix of propulsion technology is the Solid Rocket Booster in the lower stages and hydrogen in the upper.

Gary Church, mentioning that Merlin-series of engines is one of the few totally new, large rocket engines developed in recent decades in the US for use on launch vehicles (without any additional commentary pro or con, I might add) hardly makes one part of this “New Space mob” you seem to be obsessed about for whatever reason. It is a simple statement of FACT… nothing more. Please direct your diatribes elsewhere.

I don’t believe this is your website. YOU take it elsewhere.

Large engine? The Merlin design is from the 60’s, very low thrust which is why so many have to be used. Large is what the 5 segment SRB is at 3.6 million pounds of thrust.
That would be about 17 times the thrust of the Merlin. Uh-huh.
The amazing thing about SpaceX is that so many have been duped by their scam.

There is a reason why a new engine is not being developed. The RS-25 is being used because it is a proven powerplant, and it keeps some of the old Space Shuttle program infrastructure going. Maybe in time a newer design might be used!

The recent news articles claiming a “critical need” for a new kerosene engine are a scam. The RS-25 is awesome with performance in upper stages far beyond anything burning kerosene is capable of. Just as the 5 segment SRB has no competition on this planet for lower stage performance. We don’t need any new engines. But SpaceX does and cannot afford hydrogen.

Mr. Church, can you please post your educational and professional credentials please, to allow the public to properly evaluate your “expertise” on rocket engine design…, such as it is? It would be most enlightening to us “layman” who have Aerospace Engineering degrees, and have worked for Rockwell, McDonnell Douglas, and yes, SpaceX over the past 35+ years. Is it possible that there’s more to life than just Isp values, when cost per pound to orbit is considered?

No thanks. It is obvious to all except those who are unhappy with what is being said that when someone demands credentials they should not even be commenting on an open forum. What I said is the truth so your only resort is an attempt to intimidate and demean. Typical New Space mob tactic.

RP-1 rocket engines like SpaceX uses are cheaper than hydrogen rocket engines mainly because the turbopumps for a hydrogen engine are fiendishly difficult to engineer and have to be about 10 times more powerful than the pumps for a kerosene engine because hydrogen is so less dense. But if you want that over 400 seconds of Isp that is what is required. In an upper stage this higher Isp number makes a huge difference. The arguments concerning kerosene versus hydrogen were settled long ago when Mr. Brown conceded that Abe Silverstein was right and attributed the success of the Moon shot to adopting hydrogen for the upper stages of the Saturn V instead of going with the easier and less expensive kerosene engines. It is all part of space history- and completely ignored/denied by the New Space mob. Consider the Atlas which is now dependent on a brand new kerosene engine- and that is a scam. Why? Because solid rocket boosters have no moving parts to speak of and are the most efficient engineering solution to getting a stack out of the atmosphere. Kerosene is obsolete. Unless you happen to be an “entrepreneur” who can only afford it, or a company that has been buying surplus Russian engines and making a profit off them. The Atlas needs something to replace the good deal second hand Russian engine and hype in the media is an attempt to get the taxpayer to foot the bill. Scam after scam and because of the demise of a well informed public they are getting away with it.

The cost per pound “screaming cheap” argument does not hold water when the under-the-table NASA support given to SpaceX is taken into account and the fact that without the ISS and lots of tax dollars there would be no SpaceX.

Mr. church I’m a little confused, are your saying that the Atlas V is using surplus engines? I’m sure the the RD-180 that the Atlas is currently using are made specifically for ULA. Obital science’s Antares was usung surplus NK-33/AJ-26’s and are now switching to brand new RD-181’s.
Your statement about the Saturn V is also a little perplexing, yes it did use hydrogen in the upper stages, but the first stage was a kerosene.
The RS-25 is an amassing engine for sure, but as the article points out it is an old engine that is in need of modernization.

Your facts are purposely skewed and inaccurate. I don’t have the time to expose your disinformation. This is what always happens when anyone criticizes SpaceX. A person who is not a space buff and just looking for the truth will never get anything but deception and obfuscation from these New Space infomercials. It’s sad.

What facts do I have wrong?

“-are your saying that the Atlas V is using surplus engines?”

Unless you happen to be an “entrepreneur” who can only afford it, or a company that has been buying surplus Russian engines and making a profit off them. (Note I said nothing about Atlas V, you did)

“-now switching to brand new RD-181′s.”

(There is no RD-181 yet)

And yes, the Saturn V did use a kerosene first stage. But the Shuttle SRB was far more powerful and had no moving parts to speak of; arguably superior to the F-1 since the SRB’s were reusable. As for the RS-25 being “old”, the design of the Merlin is much older.

You are attempting to pick apart my comment and make me appear ill-informed and that is typical of the kind of obfuscation and underhanded deception the New Space mob constantly practices.

Many thanks. Your reply quoting second-hand arguments and irrelevant generalities about NASA’a judgment speaks volumes about your direct practical experience in the Aerospace Industry (which is evidently zero). Luckily, those who actually have the knowledge and skill to build functional rockets and spacecraft are leading the way to the future of space exploration, rather than the armchair pundits who’s only experience was playing with Estes model rockets when they were kids (which I did as well). Being the “space authority” that you are, perhaps Elon will send you a postcard when he gets to Mars…, or not. I’d say that’s enough time wasted having a battle of wits with an unarmed person. Have a nice day.

Ad hominem is all you got. Could not refute a single thing I wrote. It is always the same with you Musk groupies.

I would say the reason Elon and SpaceX aren’t pursuing hydrogen engines is due to hydrogen being not ideal for long missions. A Mars mission would be roughly three years round trip and in that time the hydrogen would have had a high probability of damaging components of the rocket. Now SpaceX has core goals of lowering costs and getting humans to Mars so they decided it was in their best interest to not pursue development of hydrogen engines. Cost and Lifespan > higher ISP.

SpaceX however knows that kerosene is not the end all either. Methane would increase isp over kerosene and would potentially give a better life cycle for the rocket.

I don’t know why your downing the Merlin engine so much, but it suits the goals of the falcon 9 rocket. And it may soon go down in history for reusability. So haters gonna hate.

“A Mars mission would be roughly three years round trip and in that time the hydrogen would have had a high probability of damaging components of the rocket.”

Not buying that one. Even if it made any sense, chemical propulsion is useless for any human deep space missions; nuclear energy is required. And that is far beyond the ability of any “entrepreneur” peddling hobby rockets.

Mars is the facade and behind it is the real game: LEO tourism. That’s the scam and these New Space infomercial comments flood any forum where the truth is exposed.

Yes they do, however, the past week was Christmas and much of our staff – are volunteers and were out for the holiday.
Jason Rhian – Editor, SpaceFlight Insider

Apparently the commenting rules don’t apply here any longer…..

The deluded sycophants and rabid Musk worshipers of the New Space mob eventually drag down every forum allowing the truth to be told about their tourist scam. They patrol the internet looking for any criticism of their demigod and if they can’t cyberbully a critic into silence they bury the conversation in a tower of Babel. Shrill demands for credentials to demean and intimidate, then ever cruder insults; it is what they have done for years and everyone has given up and just let them have the floor. Newcomers believe all the New Space propaganda is the truth. It’s disgusting.
I have absolutely no respect for any of them and show them no courtesy at all anymore.

So, Gary Church: Assuming you’re smart enough to drive a car, you should now convert your car to run on nitro-methane. It’s so much more powerful that gasoline is obsolete. Of course it’s 10 times as expensive as gasoline, will corrode your fuel lines, it’s more dangerous in a crash and your engine will only last 150 miles instead of 150,000 but gasoline is obsolete, right?

Hydrogen is so much more difficult to handle, so much more expensive and due to its density requires larger rockets with bigger tanks. This increases the ground infrastructure costs as well. If you’re trying to win a high value race or get the absolute maximum to another planet, use the better fuel. If all you’re doing is going to the corner store or low earth orbit, use the family car or the Falcon.

Same old New Space infomercial. Joe the space plumber explains how it is all so easy. Puh-leez.

I try to give back as good as I get Mr. Rhian. I am not a fan of “New Space” and make it a point to illustrate my views with as much colorful language as the rules allow. When others start handing me subtle insults because of my position and making inferences about my intelligence I take it for what it is. In my experience their arrogance leads them to believe they are entitled to bully and insult anybody who disagrees with them. What they can get away with I should be able to. Moderators usually dislike a “troublemaker” and try to warn that person out of their hair. I am not trying to cause trouble- just stating my views as enthusiastically as the New Space fanatics do. I greatly appreciate the opportunity to discuss and expound on the information your site displays. Thank you for your warning and happy holidays.

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