The tallest single rocket stage NASA has ever flown. The core stage contains four RS-25 engines, their liquid hydrogen and liquid oxygen propellant supply, and the avionics and software that control SLS operation through main engine cutoff. It operates for the entire ~480-second launch — from ground to Earth orbit — reaching speeds of nearly Mach 23.
Five major sections from bottom to top: engine section, liquid hydrogen tank (130 ft tall), intertank, liquid oxygen tank (51 ft tall), and forward skirt. The intertank is the only section bolted rather than welded — providing extra strength to carry booster loads.
The most efficient rocket engine in its class. The RS-25 was formerly the Space Shuttle Main Engine, accumulating over 3,000 starts and 1 million seconds of hot-fire experience across 135 shuttle missions. For SLS, four engines run simultaneously at 109% thrust — higher than the shuttle's typical 104.5%.
Unlike the shuttle, SLS does not recover its RS-25 engines. The core stage altitude and speed at cutoff make recovery impractical without sacrificing payload capacity.
The largest and most powerful solid rocket boosters ever flown. Five-segment design (vs. four on the shuttle), providing 75% of SLS's total thrust for the first two minutes of flight. The larger motor burns about 3 seconds longer and produces 200,000+ lbs of additional thrust compared to the shuttle boosters.
Propellant: polybutadiene acrylonitrile, ammonium perchlorate, and aluminum powder. Each booster generates more thrust than 14 four-engine commercial airliners. The boosters are expended — no parachutes or recovery hardware, saving ~20,000 lbs for additional payload.
The ICPS is a modified Delta Cryogenic Second Stage — proven on 24 ULA Delta IV missions with 100% success. It serves as Orion's upper stage after core stage separation, performing burns to raise the orbit and ultimately fire the Translunar Injection burn that sends Orion to the Moon.
For Artemis II, the ICPS also serves as the proximity operations target — equipped with optical target assemblies on its exterior for Orion's approach practice. After the demo, it deploys CubeSat payloads and performs a disposal burn targeting re-entry above the Pacific Ocean.
The highest SLS element, connecting the ICPS to Orion. Made of lightweight aluminum, it contains a diaphragm that prevents hydrogen gas from entering the spacecraft during launch. For Artemis II it carries four CubeSat secondary payloads and a centerline docking target for the proximity operations demo.
Three redundant flight computers in the core stage forward skirt each use three microprocessors running the same software. 256 MB RAM per computer. Distributed avionics connect all elements — engines, boosters, ICPS — with the core stage serving as the "brain." For Artemis II, vehicle performance data is also transmitted to the crew in Orion for the first time.
Human-rating certification for ICPS with new emergency detection system (proven on Atlas V / Starliner)
Booster separation motors rotated 15° for better core stage clearance; separation 4 seconds earlier
Core stage power distribution control unit updated to resolve timing issues
Strakes added to intertank flanking booster attach points to reduce airflow-induced vibrations
ICPS RL10B-2 upgraded to RL10C-2 with dual-engine igniter and debris-containment netting
New 1.25-million-gallon LH₂ storage tank at Pad 39B enables 24-hour turnaround between attempts
ICPS Teflon seals added to LH₂ and LOX umbilicals for safer propellant operations
Flight Safety System adds time delay to allow crew escape via Launch Abort System
Orion Stage Adapter updated to carry 4 larger CubeSats (vs. 10 smaller on Artemis I)