Exploration Upper Stage - A diagram of the 6 engined S-IV, the 2nd stage of the Saturn I. In comparison to this cluster of RL10A-3 engines, the SLS Block IB 2nd stage, the EUS, will likewise contain a cluster of these engines but will surpass the clustered performance of the above S-IV with just 4 RL10B-2 derived engines and do so without the weight saving common bulkhead of the S-IV.
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