Author Topic: Why is it so hard to develop a restartable SSME?  (Read 2092 times)

Offline tnphysics

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Why is it so hard to develop a restartable SSME?
« on: 10/24/2009 06:58 PM »
Why is it so hard to develop a restartable SSME?

Offline Jim

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Re: Why is it so hard to develop a restartable SSME?
« Reply #1 on: 10/24/2009 07:03 PM »
Why is it so hard to develop a restartable SSME?

Because it was not made to be.  It is a head started engine.  The start box is not easy to achieve in orbit. 
The engine will have issues with water still in it for restart since it relies on drying on the ground.

It is like trying to make a gasoline engine into a diesel engine.

Offline clongton

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Re: Why is it so hard to develop a restartable SSME?
« Reply #2 on: 10/24/2009 07:47 PM »
It is like trying to make a gasoline engine into a diesel engine.

That's actually not that far off for a comparison Jim.
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I started my career on the Saturn-V F-1A engine

Offline Danny Dot

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Re: Why is it so hard to develop a restartable SSME?
« Reply #3 on: 10/25/2009 03:05 AM »
It is like trying to make a gasoline engine into a diesel engine.

That's actually not that far off for a comparison Jim.

"Integrator" has the answer, but I forgot what it was.  The summary is airstart could be done, but restart was a show stopper.  This drove the Ares I to a J-2.

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Offline NASAForm1676

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Re: Why is it so hard to develop a restartable SSME?
« Reply #4 on: 10/25/2009 04:22 AM »
For the restartable application what makes SSME great is also its downfall.  Its great combination of specific impulse/thrust (that are driven by the higher than usual chamber pressure) requires turbo pumps and plumbing that need special preparations for the start.   It can't tolerate ullage.  It requires head pressures in the prop lines for the spin up.  There is an entire infrastructure dedicated to starting STS SSME on the ground. Now imagine packing all that infrastructure up into a tiny box inside on a stage somewhere for the 'on/off' version.
« Last Edit: 10/25/2009 04:26 AM by NASAForm1676 »

Offline A_M_Swallow

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Re: Why is it so hard to develop a restartable SSME?
« Reply #5 on: 10/25/2009 08:26 AM »
Does this summarize down to the SSME needs several starter motors and they weight more than the main engine?  Also the total mass produces something that is too heavy to fly.

Offline NASAForm1676

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Re: Why is it so hard to develop a restartable SSME?
« Reply #6 on: 10/25/2009 08:37 AM »
Well, helium pumps are also 'motors' in a way. 

Yes, making SSME into restartable is like strapping a whole bunch of pumps and extra plumbing fittings and other crap and technicians onto a rocket for an engine *start* in the air/vacuum, leave alone *Re-Starts*
« Last Edit: 10/25/2009 08:40 AM by NASAForm1676 »

Offline Jim

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Re: Why is it so hard to develop a restartable SSME?
« Reply #7 on: 10/25/2009 11:25 AM »
For the restartable application what makes SSME great is also its downfall.  Its great combination of specific impulse/thrust (that are driven by the higher than usual chamber pressure) requires turbo pumps and plumbing that need special preparations for the start.   It can't tolerate ullage.  It requires head pressures in the prop lines for the spin up.

That is the start box

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