Author Topic: Engine-out capability on the SLS  (Read 6074 times)

Offline Hyperion5

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Engine-out capability on the SLS
« on: 03/25/2013 03:39 PM »
A number of people have been talking about the need for this topic, so I decided to start it.  I've attached a PDF fregate has created, which focuses on a similar capacity HLV with a 6 meter diameter EDS.  What we found, and what the Excel document will clearly show, is which engines are best at handling an engine-out scenario.  The RL-10B-2 clearly comes out a winner over its less efficient and powerful cousin, the RL-10A-4-2, which would exceed its maximum burn time trying to accelerate a heavy payload through TLI.  I thought that given the LRBs and core stage will also have some engine-out capability, that it'd be best to expand this conversation. 

For example, how soon in the flight could the SLS Bloc I's core stage afford to lose an RS-25?  How much does later does this moment arrive on the SLS Bloc IB?  How does adding advanced solids change the engine-out scenario?  Finally, we get to the various liquid rocket boosters under consideration.  Some have very little engine-out capability (twin F-1Bs), while others have a bit more margin (triple AJ-1-E6 engines).  How late in the burn could the boosters afford to lose an engine?  Could they shut down or throttle an opposing engine in time to avoid problems?  Plus, how much more margin would adding LRBs give to the engine-out margins on the core stage or the upper stage?

Anyone want to take a stab at whether or not NASA would keep going forward with a BEO mission if they lost an engine on the SLS Bloc IB's upper stage? 

« Last Edit: 03/25/2013 03:43 PM by Hyperion5 »

Offline sdsds

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Re: Engine-out capability on the SLS
« Reply #1 on: 03/26/2013 03:29 AM »
As always, the devil's in the details. In particular for a stage that participates in ascent, losing thrust from an engine will likely change the disposal location of the stage.

Looking at the SLS configuration with ICPS, launched to a 28.5 orbital inclination (i.e. due East), I believe the intended drop zone for the core is the middle of the Pacific Ocean, with the instantaneous impact point (IIP) trace crossing Africa and possibly Australia. Somewhat obviously when the strap-on boosters are jettisoned the IIP is still close to the Atlantic coast of the U.S., so the vehicle is being powered by the core engines as the IIP crosses those major land masses.

I'm betting that if a core engine fails during a crewed launch before the IIP reaches Africa NASA will shut down the other engines, abort the mission, and recover the crew from the Atlantic. They would do this even if an abort-to-orbit were theoretically still possible on the remaining engines to protect against subsequent engine failures which might result in the core coming down in Africa.

Once the IIP is over Africa they would instead press on, though whether they would then abort into the Indian Ocean is unclear. There's not much population density in Australia, and by then the IIP is moving much faster across the Earth's surface.

Somebody at NASA has almost certainly done this kind of analysis already. Have they shared their results publicly yet?
« Last Edit: 03/26/2013 03:31 AM by sdsds »
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Offline Hyperion5

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Re: Engine-out capability on the SLS
« Reply #2 on: 03/26/2013 04:20 AM »
As always, the devil's in the details. In particular for a stage that participates in ascent, losing thrust from an engine will likely change the disposal location of the stage.

Looking at the SLS configuration with ICPS, launched to a 28.5 orbital inclination (i.e. due East), I believe the intended drop zone for the core is the middle of the Pacific Ocean, with the instantaneous impact point (IIP) trace crossing Africa and possibly Australia. Somewhat obviously when the strap-on boosters are jettisoned the IIP is still close to the Atlantic coast of the U.S., so the vehicle is being powered by the core engines as the IIP crosses those major land masses.

I'm betting that if a core engine fails during a crewed launch before the IIP reaches Africa NASA will shut down the other engines, abort the mission, and recover the crew from the Atlantic. They would do this even if an abort-to-orbit were theoretically still possible on the remaining engines to protect against subsequent engine failures which might result in the core coming down in Africa.

Once the IIP is over Africa they would instead press on, though whether they would then abort into the Indian Ocean is unclear. There's not much population density in Australia, and by then the IIP is moving much faster across the Earth's surface.

Somebody at NASA has almost certainly done this kind of analysis already. Have they shared their results publicly yet?

Wouldn't the experience with the shuttle being of value on this?  Correct me if I'm wrong, but I do believe the Shuttle had exactly one Abort-to-Orbit when it lost an SSME several minutes into the flight.  It may have been still over the Atlantic when it happened.  I'm sure Jim knows the details on that, or possibly Ed Kyle.  Given the SLS is shuttle-derived, would anyone with shuttle knowledge like to summarize when a Shuttle could continue its mission regardless of engine failure?  I have the feeling the SLS' margins will be even more generous, given it has an additional engine. 

Offline 93143

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Re: Engine-out capability on the SLS
« Reply #3 on: 03/26/2013 04:42 AM »
Not directly applicable to SLS, but IIRC J-246 was supposed to be capable of completing its mission if an RL-10 failed to light during ascent and another one also failed to light for TLI.
« Last Edit: 03/26/2013 05:03 AM by 93143 »

Offline sdsds

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Re: Engine-out capability on the SLS
« Reply #4 on: 03/26/2013 05:01 AM »
I do believe the Shuttle had exactly one Abort-to-Orbit when it lost an SSME several minutes into the flight.

You're likely thinking of 51-F. Read the attached write-up from the JSC Space News Roundup. They were headed for a 49.5 inclination orbit. (Not sure why.) That makes for a markedly different IIP trace. It overflies Europe rather than Africa, and then goes south of Australia.
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