I was reading the press release for the recent test firing of the RS-25 engine No. 2059 at Stennis Space Center and I came across the quote:

The next time rocket engine No. 2059 fires for that length of time, it will be carrying humans on their first deep-space mission in more than 45 years.

To me this implies that the next time this engine will be used is in around 8 (maybe more) years time when they use SLS to launch astronauts on the Asteroid Redirect Mission (ARM).

Why is there such a delay in using this engine (which has flown several Shuttle missions before) again? Or is it an incorrect statement that they have made in this press release?

  • $\begingroup$ Are you asking why it's going to be 8 years before our next manned mission beyond LEO, or why the engine hasn't flown since the space shuttle was retired? $\endgroup$ Mar 15, 2016 at 14:40
  • $\begingroup$ I am asking why the engine used for the first test fire of an SLS main engine isnt going to be used on the first actual launch of an SLS vehicle. To me it seems strange that they are holding it back for a manned mission into "deep space". $\endgroup$
    – Dean
    Mar 15, 2016 at 14:42
  • $\begingroup$ From that same press release: "Following today’s firing, Stennis and Aerojet Rocketdyne will conduct a development engine series to test new flight engine controllers and will continue to test RS-25 flight engines." So presumably some of the other engines to be tested will go into the first SLS flights. $\endgroup$ Mar 15, 2016 at 14:45
  • $\begingroup$ Yeah, they have 16 left from the STS so I imagine they have refurbished all those and will want to test fire all of them first. It would be understandable if they were reusable, then this particular engine could be flown on several SLS missions, but they're not, so why wait so long to launch an already working engine? $\endgroup$
    – Dean
    Mar 15, 2016 at 14:48

1 Answer 1


Edit: my original answer was incorrect. NASA has already allocated engines to specific launches:

In May 2014, NASA allocated four engines for the first launch of SLS: ME-2045, ME-2056, ME-2058, and ME-2060. Around the same time, they were wrapping up preparations on the SSME engine test stand.

In May 2014, NASA also selected 4 contingency engines for SLS EM-1: ME-2047, ME-2059, ME-2062, and ME-2063.

There was a series of test fires of development engines (to test the new engine controller, for example).
ME-2059 was the first flight engine to be tested in this new configuration, this served as a calibration run of the new configuration. The other engines will also be tested, then there'll be a test of the entire first stage.

If ME-2059 is not needed in its contingency role, it'll be used for SLS EM-2.

In early 2015, the plan was to test the EM-1 engines first. I don't know what has changed that, maybe something as simple as scheduling of the upgrade work to the various engines. There have also been delays in getting the test stand ready.


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