WASHINGTON – An upgraded upper stage for the Space Launch System rocket has undergone an in-depth review, allowing prime contractor Boeing to begin manufacturing hardware.
Boeing announced on December 21 that the Exploration Upper Stage (EUS) of the SLS has completed a critical design review with NASA. That review confirmed the design of the EUS, allowing Boeing to continue developing the stage, including hardware manufacturing.
The EUS will be used on the Block 1B variant of SLS, replacing the Interim Cryogenic Propulsion Stage (ICPS) used on the first Block 1 version of the SLS and based on the Delta 4 upper stage. The EUS will have larger tanks and use four Aerojet Rocketdyne RL10 engines.
The Block 1B will provide better performance than the Block 1. While the Block 1 can place 27 tons on a translunar injection trajectory, the SLS Block 1B will increase that performance to 38 tons. That will enable SLS Block 1B missions launching Orion spacecraft to carry additional “co-manifested” payloads, such as components for the Lunar Gateway.
“EUS has been designed for manned flight from the outset, and the additional lift capacity provided with the EUS requires fewer flights to enable a sustainable human presence in deep space faster and safer,” said Steve Snell, EUS- program manager at Boeing, in a statement.
However, the Block 1B version of SLS won’t fly until the mid-2020s. The first three SLS missions will be of the Block 1 variant and use the ICPS. This would drive out the SLS Block 1B debut after 2024, subject to any changes to the schedule of Artemis missions and the possible use of the SLS to launch Europa Clipper.
Without needing the EUS in the short term, NASA tried to slow its development. In the budget request for the fiscal year 2021, it was proposed to postpone the final design of the SLS block 1B. “While the SLS Block 1B configuration with the Exploration Upper Stage (EUS) remains an important future capability, the significant performance and cost challenges facing NASA’s prime contractor, Boeing, in completing the Core Block 1 phase, which NASA and his contractors are concentrating. in the short term on the successful completion of the Block 1 SLS and the reliable manufacturing of flight systems, ”said the budget proposal.
However, Congress has continued to provide funding for EUS. The fiscal year 2021 omnibus spending bill, passed by Congress on Dec. 21, mandated NASA to spend at least $ 400 million on the development of Block 1B, “ including the Exploration Upper Stage and associated systems, including related systems. facilitation, in support of an SLS Block 1B mission available for launch in 2025 in addition to the planned Block 1 missions for Artemis 1 through Artemis 3. “
A NASA authorization law, passed by unanimous agreement in the Senate on Dec. 18, went even further and mandated NASA to continue “developing the Exploration Upper Stage for the Space Launch System with a planned availability that will is sufficient for use on the third launch of the Space Launch System. ”The bill will not be passed by the House in this Congress, but Senate supporters see it as a starting point for a new NASA authorization bill next year.
Meanwhile, testing of the core stage for the first SLS mission continues at the Stennis Space Center. NASA said it conducted a wet dress rehearsal of the SLS core stage on Dec. 20, loading it with liquid hydrogen and liquid oxygen propellants. This is the penultimate test of the overall Green Run test campaign, with the final test being a full static fire test of the stage’s four RS-25 engines.
NASA halted an earlier attempt at the wet dress rehearsal on Dec. 7, when the temperature of the liquid oxygen flowing at the core stage was slightly higher than required. NASA said they would make changes to testing procedures, rather than the stage itself, to fix the problem.
“Looking at the data first, we indicate that the stage performed well during propellant loading and replenishment,” said NASA, but noted that the exercise countdown, which had to stop 33 seconds before ignition, instead of them stopped a few minutes less. “The team is evaluating data to determine the exact cause of the early shutdown,” NASA said in a brief statement, noting that the problem did not appear to lie with the core stage itself.