Final RS-25 Engines From the Space Shuttle Era Now Ready to Serve the Artemis IV Mission

RS-25 rocket engine 20 photos
Photo: Aerojet Rocketdyne
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NASA is all about reusing leftover hardware from previous space programs because it helps it save time and money on the new ones. But in few such cases was NASA as good at doing that than it is in the Artemis program.
America's second Moon exploration program is well underway, having been kickstarted by the launch of the first uncrewed mission back in 2022. We should have had the second flight of the program, and the first crewed one, take off this year, with the first Artemis Moon landing initially planned for 2026.

Sadly, both missions were pushed back by a year or so, but that doesn't mean work on getting more missions ready, especially the more distant ones, isn't accelerating.

I said earlier that NASA is a master at reusing existing hardware, and the Artemis program more than proved that. The rocket that supports the program, the massive Space Launch System (SLS), uses, for instance, some engines called RS-25.

The hardware is made by Aerojet Rocketdyne, and the units were initially meant to serve the Space Shuttle program. Also called  Space Shuttle Main Engine, these things were attached in groups of three to the backs of each Shuttle to give the launch rocket's two boosters help get it off the ground. Together, the three RS-25s generated 1.2 million pounds of thrust while burning liquid propellant.

Aerojet Rocketdyne produced quite a lot of these engines for the Shuttles, and when the program was scrapped in 2011 plenty of them were left standing and in usable state. Instead of throwing them away, the company and NASA set them aside for future use.

Artemis IV Block 1B Details
Photo: Aerojet Rocketdyne
The opportunity to get them to work arose when NASA imagined the SLS. The RS-25s proved to be the perfect choice for the Moon mega-rocket because, in a nutshell, they were "the most reliable, efficient, high-performance engines ever built."

The Artemis I mission I mentioned earlier left our world pushed by the four RS-25 engines strapped to the core stage and the two solid rocket boosters of the SLS. The powerplants used back then were not from the unused group of engines, but were units that had previously been flown on the Space Shuttle.

Artemis II, which at the time of writing is scheduled to take a crew of four people on a trip around the Moon, will use RS-25s as well. Two of them have already seen action on previous Shuttle missions, while the other two will be new.

NASA will continue to use this already-made RS-25 engines up to the Artemis V mission. Scheduled for 2029, this mission and the ones after it will rely on the same kind of powerplants, only newly-produced and specifically imagined for the new program.

That means Artemis IV, planned for 2028, will be the last to use Shuttle-era engines. And the company making them announced this week it has already completed upgrading the hardware for its use in the SLS.

You see, even if they are the best of their kind ever made, the RS-25s needed a series of upgrades for them to be able to power the SLS. Changes included the fitting of new flight computers, ones that are capable of withstanding the higher temperatures they have to survive so close to the solid rocket boosters.

Artemis SLS
Photo: NASA
The hardware will also get to power a new breed of rocket. Whereas missions I through III rely on a kind of SLS called Block 1, missions V through IX will use the Block 1B. Although the same as before in terms of core stage, booster design, and major components, the 1B will bring increased capabilities.

More to the point, the rocket will use a more powerful second stage. It currently relies on a single RL10 made by the same Aerojet Rocketdyne, but on the upgrade, it will be backed by four of them.

When in crewed version, the SLS would thus be able to carry 38 metric tons of payload all the way to cislunar space, a serious increase over the 27 metric tons the Block 1 is capable of transporting. When operating in cargo mode, Block 1B will be able to send 42 metric tons of cargo to the Moon.

There will also be a new universal stage adaptor installed above the upper stage, and that should provide 24 percent more volume for cargo than "an industry-standard five-meter-class payload fairing."

Aerojet says it completed work on the final Space Shuttle-era engines to be used on the SLS at the Stennis Space Center in Mississippi. It will now focus on the creation of brand-new RS-25 engines, the ones that will be used to power the Artemis program past the fifth mission.

The improved variants of the powerplants should not only be cheaper to make (by about 30 percent compared to the Shuttle version), but they should also deliver more power.
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About the author: Daniel Patrascu
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Daniel loves writing (or so he claims), and he uses this skill to offer readers a "behind the scenes" look at the automotive industry. He also enjoys talking about space exploration and robots, because in his view the only way forward for humanity is away from this planet, in metal bodies.
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