Yesterday, NASA Stennis successfully completed a hot fire test of Aerojet Rocketdyne RS-25 a.k.a SSME. It was noted in the webcast before the test started that they were testing the 'engine controller'. I also read about testing the new 3d printed 'pogo' for the engine.

  1. What are these components and what function do they serve? Why have a test dedicated to these?

Looking at the live test video one could gather they tested for about 7 mins in which the back pressure area of blue radiation or the first shock was noticably varying, which would imply variable thrusting.

  1. So, while doing that how did they exactly test the two components? What data were they looking for?

  2. How does passing this test pave way for further tests that are planned, ultimately to the EM-1 mission?


1 Answer 1


The engine controller is a computer mounted on the SSME which monitors and controls the engine. It, for example, takes throttle commands as a % of power level from the vehicle and translates them into control commands for the engine valve control loops. The SLS engine controller is a new hardware device and presumably new software as well.

The pogo accumulator is a spherical tank charged initially with helium and later with GO2 which acts as a standpipe and provides the capability to damp out oscillations in the LO2 feed system.

You can read about the shuttle era pogo system here and the engine controller here

Pogo accumulator drawing enter image description here

It makes sense to hotfire an engine after incorporating changes. I have no detailed information on the test objectives, but they would have been testing the engine controller hardware and software in an operational environment. Same for the pogo accumulator hardware.

  • $\begingroup$ Looks good, thanks! I still can't get any response from even the main site ksc.nasa.gov or even science.ksc.nasa.gov Could it be blocked internationally? Is it supposed to be public? i.sstatic.net/CrZnG.png $\endgroup$
    – uhoh
    Jan 18, 2018 at 7:34
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    $\begingroup$ It's working here, so I am not sure what is going on. I'm away from home so don't have access to own library. The links are to the space shuttle press reference manual; there are several copies of it, even pdf'ed, on the internet, but may have the same restrictions. $\endgroup$ Jan 18, 2018 at 7:51
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    $\begingroup$ This is a link to the manual on a different NASA website. spaceflight.nasa.gov/shuttle/reference/shutref/… $\endgroup$ Jan 18, 2018 at 7:53

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