NASA's RS-25 Engines shut down time

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As a follow up to my other question about RS-25's ramp-up time, I was wondering what would be the ramp-down times for the RS-25, i.e. what would be the time that takes to go from 100% thrust to 0% thrust.



Also, were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?










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    5












    $begingroup$


    As a follow up to my other question about RS-25's ramp-up time, I was wondering what would be the ramp-down times for the RS-25, i.e. what would be the time that takes to go from 100% thrust to 0% thrust.



    Also, were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?










    share|improve this question









    $endgroup$














      5












      5








      5





      $begingroup$


      As a follow up to my other question about RS-25's ramp-up time, I was wondering what would be the ramp-down times for the RS-25, i.e. what would be the time that takes to go from 100% thrust to 0% thrust.



      Also, were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?










      share|improve this question









      $endgroup$




      As a follow up to my other question about RS-25's ramp-up time, I was wondering what would be the ramp-down times for the RS-25, i.e. what would be the time that takes to go from 100% thrust to 0% thrust.



      Also, were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?







      nasa sls ssme






      share|improve this question













      share|improve this question











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      share|improve this question










      asked Mar 11 at 18:30









      Mitch99Mitch99

      1648




      1648




















          2 Answers
          2






          active

          oldest

          votes


















          5












          $begingroup$

          (This is all for shuttle, not SLS)



          Running the engine out of propellant was a Big Bad Thing. There were sensors in the External Tank (for hydrogen) and in the orbiter feedlines (for oxygen) that would trigger a shutdown if the sensor registered dry. The placement of the sensors was such that the engine should shut down before they ran out of prop.



          Normally the engines shut down on commands issued by guidance and the system had a small amount of prop remaining. (note: carrying extra prop to orbit wastes payload capacity, carrying too little means you don't go to space)



          (reference)



          Here's some simple linear data for shutdowns from different power levels. This is for the (rather old) FPL version of the SSME (see the taxonomy of the SSME in my answer to Which STS mission raised the normal engine throttle above 100%, and what change to the SSME made that possible?) but should be somewhat representative. It's based on data supplied for use in simulator models at Johnson Space Center. This is chamber pressure data but thrust should be roughly proportionate. Y axis in psi, X axis in seconds.



          enter image description here






          share|improve this answer











          $endgroup$








          • 2




            $begingroup$
            Excellent, thanks! Roughly the same as ramp-up times... Great, I don't need to change my code. However, I now have to put "shut down engine" checks for "fuel level < 1%" instead of " == 0%...
            $endgroup$
            – Mitch99
            Mar 11 at 20:08


















          4












          $begingroup$


          were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?




          Shutdown was commanded when the appropriate trajectory was reached.



          Even in multistage rockets, rocket engines are not run to complete depletion of propellant. The fuel/oxidizer mix ratio must be closely controlled to avoid damage to the engine; if the fuel ran out early the mixture ratio would go ox-rich, increasing combustion chamber temperature. The "trickling" flow of the last little bit of propellant would also produce rough combustion, which could be damaging. As Tristan notes, the turbopump would also be catastrophically damaged if propellant flow trickled.






          share|improve this answer











          $endgroup$








          • 4




            $begingroup$
            Not just that, but if the inlet of a turbopump impeller runs dry, it would overspeed with blinding alacrity.
            $endgroup$
            – Tristan
            Mar 11 at 19:12











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          2 Answers
          2






          active

          oldest

          votes








          2 Answers
          2






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          5












          $begingroup$

          (This is all for shuttle, not SLS)



          Running the engine out of propellant was a Big Bad Thing. There were sensors in the External Tank (for hydrogen) and in the orbiter feedlines (for oxygen) that would trigger a shutdown if the sensor registered dry. The placement of the sensors was such that the engine should shut down before they ran out of prop.



          Normally the engines shut down on commands issued by guidance and the system had a small amount of prop remaining. (note: carrying extra prop to orbit wastes payload capacity, carrying too little means you don't go to space)



          (reference)



          Here's some simple linear data for shutdowns from different power levels. This is for the (rather old) FPL version of the SSME (see the taxonomy of the SSME in my answer to Which STS mission raised the normal engine throttle above 100%, and what change to the SSME made that possible?) but should be somewhat representative. It's based on data supplied for use in simulator models at Johnson Space Center. This is chamber pressure data but thrust should be roughly proportionate. Y axis in psi, X axis in seconds.



          enter image description here






          share|improve this answer











          $endgroup$








          • 2




            $begingroup$
            Excellent, thanks! Roughly the same as ramp-up times... Great, I don't need to change my code. However, I now have to put "shut down engine" checks for "fuel level < 1%" instead of " == 0%...
            $endgroup$
            – Mitch99
            Mar 11 at 20:08















          5












          $begingroup$

          (This is all for shuttle, not SLS)



          Running the engine out of propellant was a Big Bad Thing. There were sensors in the External Tank (for hydrogen) and in the orbiter feedlines (for oxygen) that would trigger a shutdown if the sensor registered dry. The placement of the sensors was such that the engine should shut down before they ran out of prop.



          Normally the engines shut down on commands issued by guidance and the system had a small amount of prop remaining. (note: carrying extra prop to orbit wastes payload capacity, carrying too little means you don't go to space)



          (reference)



          Here's some simple linear data for shutdowns from different power levels. This is for the (rather old) FPL version of the SSME (see the taxonomy of the SSME in my answer to Which STS mission raised the normal engine throttle above 100%, and what change to the SSME made that possible?) but should be somewhat representative. It's based on data supplied for use in simulator models at Johnson Space Center. This is chamber pressure data but thrust should be roughly proportionate. Y axis in psi, X axis in seconds.



          enter image description here






          share|improve this answer











          $endgroup$








          • 2




            $begingroup$
            Excellent, thanks! Roughly the same as ramp-up times... Great, I don't need to change my code. However, I now have to put "shut down engine" checks for "fuel level < 1%" instead of " == 0%...
            $endgroup$
            – Mitch99
            Mar 11 at 20:08













          5












          5








          5





          $begingroup$

          (This is all for shuttle, not SLS)



          Running the engine out of propellant was a Big Bad Thing. There were sensors in the External Tank (for hydrogen) and in the orbiter feedlines (for oxygen) that would trigger a shutdown if the sensor registered dry. The placement of the sensors was such that the engine should shut down before they ran out of prop.



          Normally the engines shut down on commands issued by guidance and the system had a small amount of prop remaining. (note: carrying extra prop to orbit wastes payload capacity, carrying too little means you don't go to space)



          (reference)



          Here's some simple linear data for shutdowns from different power levels. This is for the (rather old) FPL version of the SSME (see the taxonomy of the SSME in my answer to Which STS mission raised the normal engine throttle above 100%, and what change to the SSME made that possible?) but should be somewhat representative. It's based on data supplied for use in simulator models at Johnson Space Center. This is chamber pressure data but thrust should be roughly proportionate. Y axis in psi, X axis in seconds.



          enter image description here






          share|improve this answer











          $endgroup$



          (This is all for shuttle, not SLS)



          Running the engine out of propellant was a Big Bad Thing. There were sensors in the External Tank (for hydrogen) and in the orbiter feedlines (for oxygen) that would trigger a shutdown if the sensor registered dry. The placement of the sensors was such that the engine should shut down before they ran out of prop.



          Normally the engines shut down on commands issued by guidance and the system had a small amount of prop remaining. (note: carrying extra prop to orbit wastes payload capacity, carrying too little means you don't go to space)



          (reference)



          Here's some simple linear data for shutdowns from different power levels. This is for the (rather old) FPL version of the SSME (see the taxonomy of the SSME in my answer to Which STS mission raised the normal engine throttle above 100%, and what change to the SSME made that possible?) but should be somewhat representative. It's based on data supplied for use in simulator models at Johnson Space Center. This is chamber pressure data but thrust should be roughly proportionate. Y axis in psi, X axis in seconds.



          enter image description here







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Mar 11 at 18:49

























          answered Mar 11 at 18:44









          Organic MarbleOrganic Marble

          59.7k3165256




          59.7k3165256







          • 2




            $begingroup$
            Excellent, thanks! Roughly the same as ramp-up times... Great, I don't need to change my code. However, I now have to put "shut down engine" checks for "fuel level < 1%" instead of " == 0%...
            $endgroup$
            – Mitch99
            Mar 11 at 20:08












          • 2




            $begingroup$
            Excellent, thanks! Roughly the same as ramp-up times... Great, I don't need to change my code. However, I now have to put "shut down engine" checks for "fuel level < 1%" instead of " == 0%...
            $endgroup$
            – Mitch99
            Mar 11 at 20:08







          2




          2




          $begingroup$
          Excellent, thanks! Roughly the same as ramp-up times... Great, I don't need to change my code. However, I now have to put "shut down engine" checks for "fuel level < 1%" instead of " == 0%...
          $endgroup$
          – Mitch99
          Mar 11 at 20:08




          $begingroup$
          Excellent, thanks! Roughly the same as ramp-up times... Great, I don't need to change my code. However, I now have to put "shut down engine" checks for "fuel level < 1%" instead of " == 0%...
          $endgroup$
          – Mitch99
          Mar 11 at 20:08











          4












          $begingroup$


          were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?




          Shutdown was commanded when the appropriate trajectory was reached.



          Even in multistage rockets, rocket engines are not run to complete depletion of propellant. The fuel/oxidizer mix ratio must be closely controlled to avoid damage to the engine; if the fuel ran out early the mixture ratio would go ox-rich, increasing combustion chamber temperature. The "trickling" flow of the last little bit of propellant would also produce rough combustion, which could be damaging. As Tristan notes, the turbopump would also be catastrophically damaged if propellant flow trickled.






          share|improve this answer











          $endgroup$








          • 4




            $begingroup$
            Not just that, but if the inlet of a turbopump impeller runs dry, it would overspeed with blinding alacrity.
            $endgroup$
            – Tristan
            Mar 11 at 19:12















          4












          $begingroup$


          were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?




          Shutdown was commanded when the appropriate trajectory was reached.



          Even in multistage rockets, rocket engines are not run to complete depletion of propellant. The fuel/oxidizer mix ratio must be closely controlled to avoid damage to the engine; if the fuel ran out early the mixture ratio would go ox-rich, increasing combustion chamber temperature. The "trickling" flow of the last little bit of propellant would also produce rough combustion, which could be damaging. As Tristan notes, the turbopump would also be catastrophically damaged if propellant flow trickled.






          share|improve this answer











          $endgroup$








          • 4




            $begingroup$
            Not just that, but if the inlet of a turbopump impeller runs dry, it would overspeed with blinding alacrity.
            $endgroup$
            – Tristan
            Mar 11 at 19:12













          4












          4








          4





          $begingroup$


          were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?




          Shutdown was commanded when the appropriate trajectory was reached.



          Even in multistage rockets, rocket engines are not run to complete depletion of propellant. The fuel/oxidizer mix ratio must be closely controlled to avoid damage to the engine; if the fuel ran out early the mixture ratio would go ox-rich, increasing combustion chamber temperature. The "trickling" flow of the last little bit of propellant would also produce rough combustion, which could be damaging. As Tristan notes, the turbopump would also be catastrophically damaged if propellant flow trickled.






          share|improve this answer











          $endgroup$




          were the engines "allowed" to shut down as a result of running out of propellant? Or were they issued a shut down command with some propellant left?




          Shutdown was commanded when the appropriate trajectory was reached.



          Even in multistage rockets, rocket engines are not run to complete depletion of propellant. The fuel/oxidizer mix ratio must be closely controlled to avoid damage to the engine; if the fuel ran out early the mixture ratio would go ox-rich, increasing combustion chamber temperature. The "trickling" flow of the last little bit of propellant would also produce rough combustion, which could be damaging. As Tristan notes, the turbopump would also be catastrophically damaged if propellant flow trickled.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Mar 11 at 19:15

























          answered Mar 11 at 18:42









          Russell BorogoveRussell Borogove

          88.9k3299383




          88.9k3299383







          • 4




            $begingroup$
            Not just that, but if the inlet of a turbopump impeller runs dry, it would overspeed with blinding alacrity.
            $endgroup$
            – Tristan
            Mar 11 at 19:12












          • 4




            $begingroup$
            Not just that, but if the inlet of a turbopump impeller runs dry, it would overspeed with blinding alacrity.
            $endgroup$
            – Tristan
            Mar 11 at 19:12







          4




          4




          $begingroup$
          Not just that, but if the inlet of a turbopump impeller runs dry, it would overspeed with blinding alacrity.
          $endgroup$
          – Tristan
          Mar 11 at 19:12




          $begingroup$
          Not just that, but if the inlet of a turbopump impeller runs dry, it would overspeed with blinding alacrity.
          $endgroup$
          – Tristan
          Mar 11 at 19:12

















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