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I am developing a FSX-based space flight simulator FSX SpacePort. I've been trying to get the detailed specs on NASA's RS-25 engine, namely, what were the ramp-up times for this engine? As in, how long did it take from ignition to full thrust?

Thanks!

Organic Marble
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Mitch99
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1 Answers1

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A good assumption is that the startup sequence is very similar to the SSME. Here is some SSME startup data showing the time you asked about from the Rocketdyne Pocket Data Book. Eventually the SLS will be using RS-25Es which are somewhat different from the SSME, but my guess is that the start sequence won't change much if at all.

enter image description here

The hashed field is test experience, the solid lines are the ICD requirements.

Organic Marble
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  • Awesome! Exactly what I was looking for! Thank you! – Mitch99 Mar 10 '19 at 23:33
  • @Mitch99 Since you're new to the site: If this answer is what you were looking for, please mark it as correct by clicking the gray checkmark beside it. And upvote if you have a mind to. – Organic Marble Mar 10 '19 at 23:36
  • Got it, thanks!! – Mitch99 Mar 11 '19 at 00:05
  • So - since it takes ~4 seconds to get them to 100% thrust, do they then ignite them at T -4:00 seconds, and they count T -0:00 the time all of them are roughly at 100%, the SRBs get lit, and it's a "mission start"? – Mitch99 Mar 11 '19 at 00:14
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    I only know about shuttle, but there the start command was send at ~T-5 seconds, which gave time for the SSMEs to light, the "twang" to settle, and then the SRBs lit at, yes, T-0. SLS won't have the "twang" to deal with because its engines are axially mounted. – Organic Marble Mar 11 '19 at 00:16
  • How long after SRB light are the hold-downs fired? – Russell Borogove Mar 11 '19 at 00:57
  • @RussellBorogove The SRB igniters and the charges that blow the nuts on the hold down posts were fired simo. https://spaceflight.nasa.gov/shuttle/reference/shutref/srb/ignition.html – Organic Marble Mar 11 '19 at 01:01
  • @OrganicMarble Wow -- I guess they had a lot of confidence in the consistency of the initial thrust curve for the SRBs. – Russell Borogove Mar 11 '19 at 02:12
  • @OrganicMarble, "Twang" - I am assuming, oscillation due to their off-longitudinal axis orientation? Also - would you know about the ramp-down rates? As in, how long did it take to thrust down from 100% down to 0%? – Mitch99 Mar 11 '19 at 05:44
  • Shutdown is a bit more complex because you don't always start from the same power level. If you'd like to ask a new question, I can dig up some info. – Organic Marble Mar 11 '19 at 12:24
  • Just to clarify - is the y-axis 'percent of rated power level'? I'm having a hard time reading it! – Jack Mar 11 '19 at 18:55
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    That's correct. – Organic Marble Mar 11 '19 at 18:57
  • @Mitch99 as a side-note, while it's good to mark an answer as "accepted" if the answer provided is a perfect match, it can also dissuade additional answers. If the answer you got didn't fully answer your question, wait a little bit before accepting it as others may still give a more complete answer, or an answer to supplement the original. (This obviously doesn't apply here as Mr. Marble's answer was great). – Magic Octopus Urn Mar 11 '19 at 19:00
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    @MagicOctopusUrn you are correct of course, but the one time - the one time - that Johnny Robinson actually accepted one of my answers, you posted this, he took off the acceptance, and never accepted another one. sigh – Organic Marble Mar 11 '19 at 19:02
  • @OrganicMarble oh-- Maybe it'd be better to not say that then, I can remove it :). It was the standard on my other site though codegolf.stackexchange.com. Even I struggle to remember to mark answers as accepted and often have to go back to do it in large batches. I'd never "unaccept" an answer though, that's slightly rude. – Magic Octopus Urn Mar 11 '19 at 19:11
  • No, I'm not bitter. Not at all! Ha ha! Seriously, you are absolutely right. – Organic Marble Mar 11 '19 at 19:14
  • And, it wasn't even you @MagicOctopusUrn who did it. It was "Bear". So please accept my apologies. – Organic Marble Mar 11 '19 at 20:00
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    @OrganicMarble not a biologist eh-- if you can't tell a bear and an octopus apart ;P? Nothing to apologize for-- sounded like something I'd do hah. – Magic Octopus Urn Mar 12 '19 at 14:11