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The Ars Technica article Rocket Report: A new Delta 2, Blue Origin inks with NASA, a fiery Falcon Heavy says:

Boeing seeks to ship SLS core stage by the end of 2019. With a renewed emphasis from the Trump administration on completing the large Space Launch System rocket for a 2020 flight, NASA and prime contractor Boeing have reworked the final assembly plan for the first SLS Core Stage to bring its scheduled completion date back to the end of 2019, NASASpaceFlight.com reports.

Skipping the Green Run test likely ... We hear that NASA Administrator Jim Bridenstine will be briefed at the end of this week on this plan to accelerate development, which likely will recommend skipping a "Green Run" test of the full core stage at Mississippi's Stennis Space Center. There are risks to this, both political (from Mississippi's delegation) as well as technical due to the problems such an all-up test firing may uncover. Still, if NASA has any chance to launch the SLS rocket in 2020, it must make difficult decisions and trade risk.

I found the NASA Spaceflight article NASA Stennis wrapping up B-2 Stand activation for SLS Green Run testing which talks about a Green Run project, but most of the article is about resting a deluge system rather than a static launch test.

Question: What exactly will/would be the "Green Run test" for SLS?

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According to NASA:

A green run is the first time the engines are assembled into a single configuration with the core stage and fired at nearly full-power. This will test the compatibility and functionality of the system to ensure a safe and viable design.

NASASpaceFlight provides a bit more detail:

[The SLS Green Run test] will essentially fly the Core Stage in place on the test stand through a nominal, eight-minute launch and ascent. Green Run test activities will involve several firsts, including the first cold flows, the first full tanking, and the first hot fire of the four RS-25 engines integrated with the Core Stage propulsion system.

Lastly, Jim Bridenstine's remarks during the FY 2020 budget request hearing answers the question while also describing an alternative currently being studied:

When we talk about a green run test, we're talking about basically building the core stage of the rocket with all four engines all at the same time and then running the whole rocket (minus the side boosters) for a period of eight minutes. The question is, is that necessary? Could we test each engine individually, at very high off-nominal conditions, to eliminate either as much risk or almost as much risk as we would if we ran the full green run? That could save six months of schedule, depending on how we do it.

On a separate note, I'd be interested in learning the etymology of the term, since I've only seen it used in reference to the SLS Core Stage.

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    $\begingroup$ I'm 99.44% sure that skipping this test is a bad idea. $\endgroup$ – uhoh Apr 21 at 23:37
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    $\begingroup$ Repeating, of course $\endgroup$ – Tran Situ Apr 22 at 0:28
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    $\begingroup$ This sounds very much like the plan for the failed Soviet Moon rocket, N-1. Rush the schdule, skip stand tests and go straight to launch. Didn't work well that time - N-1 failed all 4 attempted flights. Rushing things under political pressure is incompatible with good engineering practices in a fields as complex as rocketry. $\endgroup$ – Lesser Hedgehog Apr 22 at 1:12
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    $\begingroup$ "Green run" has been used for decades. It simply means testing of a new component/engine. Green as in "green recruit" for a new soldier. It was used every time a new / rebuilt SSME was tested. "SSC was responsible for flight green run testing of the SSME, as well as assembly and refurbishment of development engines. " nasa.gov/sites/default/files/files/3HO.pdf $\endgroup$ – Organic Marble Apr 22 at 17:44
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    $\begingroup$ I've only heard it used in reference to testing at Stennis. $\endgroup$ – Organic Marble Apr 23 at 11:16

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