The Space Shuttle Main Engines did their job 135 times. The technology was actually designed back in the 1970's but proved over and over again that it was ahead of its time. The SSME is still the most powerful, efficient rocket engine ever.
It's success is why NASA's next rocket to take humans to space, the SLS, will also use the shuttle main engines that are still in inventory. The engine now referred to as RS-25.
"So, RS-25 is a wonderful engine. It's a technological marvel, unmatched in safety and reliability," said Steve Wofford, the Liquid Engine Office Manager for SLS. The engine has been tested over the years for more than a million seconds without a single problem. NASA still has 16 of the engines to work with and would love to make more of them.
They are, however, expensive at some 50-million dollars a copy. To help that situation, there's an engine upgrade in the works. "Specifically for producibility and affordability improvements for the engine," said Wofford.
The upgrade includes getting rid of some 700 of the engines more than 7,000 parts, and manufacturing some of those parts using the most modern techniques. Technicians and engineers at Marshall Space Flight Center are hard at work using 3-D printing to make parts that formerly required costly, time-consuming casting.
3-D printing uses a laser beam to melt metal power in thin layers one on top of another. Just like a layer cake the layers add up to make a substantial creation. The cost and time savings usually about half.
The RS-25 is being improved, and those doing the work will tell you that it's worth it. "We'll be able to fly this engine indefinitely," said Steve Wofford.
"They really are the most efficient rocket engine that was ever built. Many people have tried to match the fuel efficiency and it's never happened," said Kathryn Crowe who's in the Propulsion Systems Vehicle Integration Office.
Ultimately the upgrade is trying to cut the cost of the engines by a third, and the 5-year manufacturing time by a year. The reason for the still high cost and long manufacturing cycle, is the fact that the engine is so good, because it's so complex. Also it's rated to carry humans to space and that means engineering tolerances are in the thousandths of an inch.
The RS-25 engine has had multiple upgrades over the years, but the others were all for safety and reliability. This time as we said, it's for cost and ease of manufacturing.