Exploration Upper Stage
| Manufacturer | Boeing |
|---|---|
| Country of origin | US |
| Used on | SLS Block 1B |
| General characteristics | |
| Height | not to exceed 18 m (60 ft) |
| Diameter | 8.4 m (28 ft) |
| Propellant mass | up to 129,000 kg (285,000 lb) |
| Engine details | |
| Engines | 4 RL10-C |
| Thrust | 440 kN (99,000 lbf) |
| Fuel | LOX/LH2 |
The Exploration Upper Stage (EUS) is being developed as a large second stage for Block 1B and Block 2 of the Space Launch System (SLS), replacing Block 1's Interim Cryogenic Propulsion Stage. It will be powered by four RL10 engines burning LOX/LH2 to produce a total of 440 kN (99,000 lbf) thrust. As of February 2015[update] the SLS Block 1 is baselined to be able to bring 70 metric tons into low Earth orbit (LEO), while the SLS Block 1B is baselined at 105 metric tons. The EUS is expected to fly on the second launch of SLS scheduled for 2021.
The Block I configuration of SLS will have the ability to insert 70 metric tons into low Earth orbit (LEO) using Shuttle-derived 5-segment Solid Rocket Boosters and a core stage powered by four RS-25 engines. Its second stage, the ICPS, will be considered part of the 70 t payload and on EM-1 it will be placed, along with the Orion crew capsule, on a 1,800 km by -93 km suborbital trajectory to ensure safe disposal of the core stage. At apogee, the ICPS will perform an insertion burn to raise the perigee and put itself and Orion into a stable orbit, and will later perform a translunar injection burn to send the uncrewed Orion capsule on a circumlunar excursion.
To improve on the 70 metric ton Block 1, NASA considered a Block 1A upgrade which would replace the Shuttle-heritage boosters with advanced solid or liquid boosters, and a Block 1B upgrade which would develop an improved second stage. This improved stage was originally named the Dual Use Upper Stage (DUUS, pronounced "duce") but was later renamed the Exploration Upper Stage (EUS) due to DUUS sounding like a profanity in Japanese.
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