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  Shuttle main engines at 104 percent?

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Author Topic:   Shuttle main engines at 104 percent?
jasonelam
Member

Posts: 443
From: Monticello, KY USA
Registered: Mar 2007

posted 03-12-2008 09:59 PM     Click Here to See the Profile for jasonelam   Click Here to Email jasonelam     Edit/Delete Message   Reply w/Quote
I have an interesting question that has boggled my mind for quite some time as a space enthusiast, and I haven't received a good answer about this, so here goes:

During a launch, I have always heard the call for "Go at Throttle Up", and also noticed that the engines are at 104% of rated thrust during launch and for most of the way uphill. Why wouldn't the engines be at 100%? Does this cause more wear and tear to the engines? I have also been told that in the event of an abort the engines would throttle up to 109% of thrust. How is it possible for an engine to have more throttle than it should?

I know this may be a simple question, but is one that has boggled me for years. Thanks!

Robert Pearlman
Editor

Posts: 27328
From: Houston, TX
Registered: Nov 1999

posted 03-12-2008 10:27 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
The percentage level does not indicate actual power (as would be reasonable to assume) but rather rated output.

The SSMEs are rated to provide 375,000 pounds of thrust at sea level. However, through the combination of upgrades and certification, the SSMEs are capable of providing more thrust than the baseline.

When a higher percentage is cited, it refers to levels that are above the 375,000-lb. mark. Or, to quote NASA:

quote:
The main engines can be throttled over a range of 65 to 109 percent of their rated power level in 1-percent increments. A value of 100 percent corresponds to a thrust level of 375,000 pounds at sea level and 470,000 pounds in a vacuum. A value of 104 percent corresponds to 393,800 pounds at sea level and 488,800 pounds in a vacuum; 109 percent corresponds to 417,300 pounds at sea level and 513,250 pounds in a vacuum.

Tom
Member

Posts: 1275
From: New York
Registered: Nov 2000

posted 03-13-2008 03:07 PM     Click Here to See the Profile for Tom   Click Here to Email Tom     Edit/Delete Message   Reply w/Quote
And just to add one more bit of information, since STS-95, the main engines actually are throttled up to 104.5% thrust.

Aztecdoug
Member

Posts: 1330
From: Huntington Beach
Registered: Feb 2000

posted 03-13-2008 04:27 PM     Click Here to See the Profile for Aztecdoug   Click Here to Email Aztecdoug     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Robert Pearlman:
However, through the combination of upgrades and certification, the SSMEs are capable of providing more thrust than the baseline.

The members of Spinal Tap would be proud to learn that NASA has developed the proverbial 11.

------------------
Kind Regards

Douglas Henry

Enjoy yourself and have fun.... it is only a hobby!
http://home.earthlink.net/~aztecdoug/

Mr Meek
Member

Posts: 348
From: Chattanooga, TN
Registered: Dec 2007

posted 03-13-2008 06:35 PM     Click Here to See the Profile for Mr Meek     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Aztecdoug:
The members of Spinal Tap would be proud to learn that NASA has developed the proverbial 11.
They'll be disappointed, though, by the failure of their letter campaign to get the first Orion test article christened "Big Bottom".

WSTFphoto
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posted 03-19-2008 08:46 PM     Click Here to See the Profile for WSTFphoto   Click Here to Email WSTFphoto     Edit/Delete Message   Reply w/Quote
I think they got it right in the movie "Space Balls" with ludicrous speed.

All times are CT (US)

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