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NASA's RS-25 Engines shut down time

Which STS mission raised the normal engine throttle above 100%, and what change to the SSME made that possible?NASA's RS-25 EnginesHow did they solve Saturn V pogo oscillation problems?Why were the two Quindar tones so close in frequency and not apodized?Theoretical Max G forces on Shuttle Launch?Was 39A built with a rocket much larger than the Saturn V in mind?Has budgetary support for Juno been extended, or is it running out?How does the Space Shuttle's SSME engine's thrust vary after ignition?Did InSight take a “mean left” turn on its way to Mars? Is it an out-of-plane maneuver?To what extent was Apollo program training specific to each mission?Did NASA tell the Skylab astronauts to “Stop running around!”?NASA's RS-25 Engines

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?

nasa sls ssme

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asked Mar 11 at 18:30

Mitch99Mitch99

845

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add a comment | 

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?

nasa sls ssme

share|improve this question

asked Mar 11 at 18:30

Mitch99Mitch99

845

New contributor

Mitch99 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

add a comment | 

$begingroup$

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?

nasa sls ssme

share|improve this question

asked Mar 11 at 18:30

Mitch99Mitch99

845

New contributor

Mitch99 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this question

asked Mar 11 at 18:30

Mitch99Mitch99

845

New contributor

Mitch99 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked Mar 11 at 18:30

Mitch99Mitch99

845

New contributor

Mitch99 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked Mar 11 at 18:30

Mitch99Mitch99

845

New contributor

Mitch99 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked Mar 11 at 18:30

Mitch99Mitch99

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2 Answers
2

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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.

share|improve this answer

edited Mar 11 at 18:49

answered Mar 11 at 18:44

Organic MarbleOrganic Marble

58.7k3161251

$endgroup$

• 
  
  
  

  
  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
  

  
  
  
  

add a comment | 

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

edited Mar 11 at 19:15

answered Mar 11 at 18:42

Russell BorogoveRussell Borogove

87.7k3294377

$endgroup$

• 
  
  
  

  
  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
  

  
  
  
  

add a comment | 

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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.

share|improve this answer

edited Mar 11 at 18:49

answered Mar 11 at 18:44

Organic MarbleOrganic Marble

58.7k3161251

$endgroup$

• 
  
  
  

  
  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
  

  
  
  
  

add a comment | 

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.

share|improve this answer

edited Mar 11 at 18:49

answered Mar 11 at 18:44

Organic MarbleOrganic Marble

58.7k3161251

$endgroup$

• 
  
  
  

  
  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
  

  
  
  
  

add a comment | 

$begingroup$

(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.

share|improve this answer

edited Mar 11 at 18:49

answered Mar 11 at 18:44

Organic MarbleOrganic Marble

58.7k3161251

$endgroup$

share|improve this answer

edited Mar 11 at 18:49

answered Mar 11 at 18:44

Organic MarbleOrganic Marble

58.7k3161251

answered Mar 11 at 18:44

Organic MarbleOrganic Marble

58.7k3161251

answered Mar 11 at 18:44

Organic MarbleOrganic Marble

58.7k3161251

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

edited Mar 11 at 19:15

answered Mar 11 at 18:42

Russell BorogoveRussell Borogove

87.7k3294377

$endgroup$

• 
  
  
  

  
  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
  

  
  
  
  

add a comment | 

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

edited Mar 11 at 19:15

answered Mar 11 at 18:42

Russell BorogoveRussell Borogove

87.7k3294377

$endgroup$

• 
  
  
  

  
  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
  

  
  
  
  

add a comment | 

$begingroup$

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

edited Mar 11 at 19:15

answered Mar 11 at 18:42

Russell BorogoveRussell Borogove

87.7k3294377

$endgroup$

share|improve this answer

edited Mar 11 at 19:15

answered Mar 11 at 18:42

Russell BorogoveRussell Borogove

87.7k3294377

answered Mar 11 at 18:42

Russell BorogoveRussell Borogove

87.7k3294377

answered Mar 11 at 18:42

Russell BorogoveRussell Borogove

87.7k3294377