NASA’s SLS (Space Launch System) Moon rocket demonstrated eye-watering performance and precision during its inaugural flight in November 2022. An upgraded system now in development, known as the SLS Block 1B, will be even more powerful and capable. This new Block 1B configuration will bring significant improvements in SLS payload capacity and versatility, supporting more robust programs in human exploration and scientific discovery.
The SLS Block 1B features improvements including newly manufactured versions of the shuttle-derived RS-25 first-stage engine and the Exploration Upper Stage (EUS), which is equipped with four RL10 engines to deliver more punch than the current single-engine Interim Cryogenic Propulsion Stage (ICPS) used on the first three Artemis missions. NASA and L3Harris Technologies are making important progress on both fronts.
RS-25: First Reusable Rocket Engine
For example, NASA and L3Harris in July completed the Design Certification Review for the new production RS-25 engines. Current SLS versions use reusable RS-25 engines remaining from NASA’s Space Shuttle program, which flew 135 missions over three decades before retiring in 2011.
“At the end of the Space Shuttle program, NASA had 16 engines in its inventory, which is enough for four SLS flights,” said Mike Lauer, RS-25 program director, Aerojet Rocketdyne, L3Harris. “To power the flights that follow, our team was challenged to design and build a modernized version of the RS-25 that is more affordable and better performing without sacrificing the engine’s outstanding reliability.”
RS-25 Enhancements
The new production engines boast a 30% cost reduction compared to those used in the Space Shuttle program. Additionally, they are engineered to operate at 111% of their rated thrust level—an increase from the 104.5% thrust level during the Shuttle era and 109% thrust level for the initial four Artemis missions. This added thrust translates to more than 990 additional pounds of payload to the Moon and a corresponding increase in payload to various deep space destinations.
L3Harris has revitalized supply chains and qualified new processes and suppliers to begin building these new, more affordable engines. Several components were redesigned to make them easier to produce and thus more affordable. Key upgrades include:
- The Pogo Accumulator Assembly, which enhances flight stability by dampening engine pressure oscillations, is now additively manufactured, or 3D printed, reducing the number of manufacturing welds by 78%.
- The main combustion chamber is now assembled using hot isostatic pressing, a bonding technique that cuts fabrication cost and schedule in half.
- The new engine controller offers 20 times the processing power of its predecessor and also is lighter and more reliable, with expanded functionality.
- The nozzle, which endures extreme temperatures and pressures during operation, was redesigned for modernized fabrication, improved assembly and an 80% reduction in parts and welds.
- Flex hoses replace complex internal flex joints on the legacy engines.
- 3D-printed parts are also used in other components including ducts, valve housings and ball shafts, and the turbine manifold, yielding significant reductions in machining, welds and cycle time.
The upgraded RS-25 engines were put through their paces during 69 hot-fire tests at NASA’s Stennis Space Center in Mississippi to ensure they meet the new performance demands of the SLS Block 1B.
“When we fly, we want to see the engine perform perfectly,” Lauer said. “When we test, we’re testing to the extreme limits of operation to ensure the engines can complete the mission with plenty of margin to spare.”
The test series included hot-firings under scenarios including different inlet conditions, high-power, low-power, emergency shutdowns, and with hydraulics in the on and off modes, Lauer said. It also demonstrated engine performance under off-nominal conditions, which is critical to the flight safety of the vehicle.
“Successfully completing this rigorous test series earlier this year is a testament to the outstanding work by the RS-25 design and development team,” added Lauer. “We accumulated about 34,000 seconds of hot fire test time between the development, retrofit, and certification tests, demonstrating these new engines are ready to safely launch astronauts to the Moon and beyond.”
Exploration Upper Stage
Meanwhile, NASA and EUS contractor Boeing also are progressing on the new SLS upper stage, a major upgrade from the ICPS being used on the first three Artemis missions. The EUS features four L3Harris -built RL10 engines, substantially enhancing the SLS’s already formidable lift capability. The EUS will provide 97,000 pounds of thrust during translunar injection, a significant increase from the ICPS’s nearly 25,000 pounds of thrust. This additional power translates to a 40% increase in payload capacity, allowing NASA to send over 83,000 pounds for crewed missions to the Moon in a single launch and 93,000 pounds for a potential SLS cargo variant. For longer missions to the planets, mission planners can use the SLS power to carry larger, heavier spacecraft or substantially shorten travel times.
True Potential of SLS
The new RS-25 engines and EUS are a major first step in unlocking the full potential of SLS – the most capable rocket ever designed to support the most ambitious missions to deep space.
With the Block 1B, NASA will be able to launch directly into deep space astronaut crews with co-manifested payloads, such as landers, rovers and research modules. Scientists can look forward to sending larger, more complex instruments into space, including advanced large-aperture telescopes, and to launch space probes that venture further into our solar system to deliver more science sooner. The national security community can take advantage of rideshare opportunities aboard SLS Block 1B missions.
“With the evolved Block 1B version of SLS, you’re looking at potential breakthroughs in planetary science, astrophysics, as well as insights into the origins of life and the potential for life on other worlds,” Lauer said. “Block 1B is crucial for the next step in deep space exploration, especially because it doesn’t have to stop or refuel. The SLS and Orion system are the only vehicles in existence that can carry people directly to the Moon and beyond and safely bring them back to earth. ”
Beyond the Block 1B version, NASA is developing the eventual Block 2 rocket with substantially greater payload performance to enable more complex and deep space exploration journeys to Mars.
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