[One] problem with legacy hardware, built by traditional contractors such as Orbital ATK and Aerojet Rocketdyne, is that it's expensive. And while NASA has not released per-flight estimates of the expendable SLS rocket's cost, conservative estimates peg it at $1.5 to $2.5 billion per launch. The cost is so high that it effectively precludes more than one to two SLS launches per year.
[...] [The RL-10] engines, manufactured by Aerojet Rocketdyne, are also costly. (Ars understands that NASA paid an average of $17 million for each RL-10 engine for the maiden Exploration Upper Stage vehicle). So in October, to power the EUS, the space agency issued a request for information to the aerospace community for "a low cost drop-in replacement engine to minimize program cost." According to the document [fbo.gov], the initial set of four engines would be needed in mid-2023 to prepare for the third flight of the SLS rocket, known as Exploration Mission-3.
Then, after an extension of the deadline for responses beyond mid-November, NASA revised the RFI on December 1. The revised document [fbo.gov] no longer seeks a "drop-in replacement" for the RL-10 engine, rather it asks for a "low-cost replacement engine." Although this seems like a subtle change, sources within the aerospace industry indicated to Ars that it is significant. According to NASA, it was done to increase the number of responses.
[...] That would probably include Blue Origin's BE-3U engine, which the company plans to use for its upper stage on the New Glenn heavy lift rocket. This is a modified version of the BE-3 engine that powers the New Shepard rocket, which has now flown successfully [arstechnica.com] seven times. Blue Origin has previously marketed the BE-3U to Orbital ATK for its Next Generation Launch System, which is looking for an upper stage engine. A single BE-3U provides about 120,000 pounds of thrust, which exceeds the 100,000 pounds of thrust provided by four RL-10 engines.
Just cancel SLS [nextbigfuture.com] and give that money to SpaceX, Blue Origin, or anybody willing to launch competitively.
Related: Maiden Flight of the Space Launch System Delayed to 2019 [soylentnews.org]
First SLS Mission Will be Unmanned [soylentnews.org]
Commercial Space Companies Want More Money From NASA [soylentnews.org]
Trump Space Adviser: Mars "Too Ambitious" and SLS is a Strategic National Asset [soylentnews.org]
Boeing CEO Says His Company Will Carry Humans to Mars Before SpaceX [soylentnews.org]
President Trump Signs Space Policy Directive 1 [soylentnews.org]