SLS General Discussion Thread 7

[Chris Bergin]

Latest thread, following on from this one:
https://forum.nasaspaceflight.com/index.php?topic=53453.0

Also see: SLS articles:
https://www.nasaspaceflight.com/news/artemis/

L2 SLS:
https://forum.nasaspaceflight.com/index.php?board=48.0

Make sure your posts are worthwhile and don't get into monotonous "I will reply to everything you say and make my point 500 times until it grinds you into the ground" posts.

[jadebenn]

And another one bites the dust.

Anyway, eagerly anticipating seeing Orion on the stack! Not too much longer now!

[Eric Hedman]

And another one bites the dust.

Anyway, eagerly anticipating seeing Orion on the stack! Not too much longer now!

Any idea how long after Orion is added, before the stack gets rolled out to the pad?  The pictures should be spectacular.

[woods170]

In thread number 6 I gave a bit of a history lesson on the technical reasons behind the N1's demise. That included this part:

Had the engines been properly tested during development, than the Soviet engineers would have noticed that shutting down a NK-33 caused a rather substantial fluid hammer effect, capable of rupturing propellant feed lines. That was the primary cause of the loss of the fourth (and last) N1 flight.

Thanks to forum member GreenShrike I was reminded of the fact that N1 flew not with the NK-33 engine, but its predecessor, the NK-15 engine.

[libra]

For all the hate and flaws related to the SLS, two things are sure.

a) if it succeeds, it will be a spectacular light and noise show.

b) if it fails, it will be a spectacular light and noise show.

I wish it to succeeds, of course - NASA never lost a Saturn V, and I'm sure the SLS will fly well. More worried about its future, though...

[woods170]

For all the hate and flaws related to the SLS, two things are sure.

a) if it succeeds, it will be a spectacular light and noise show.

b) if it fails, it will be a spectacular light and noise show.

I wish it to succeeds, of course - NASA never lost a Saturn V, and I'm sure the SLS will fly well. More worried about its future, though...

SLS won't fail. Too much uber-reliable heritage stuff is in there.

[tea monster]

SLS won't fail. Too much uber-reliable heritage stuff is in there.

Is this sarcasm? Maybe you have SLS confused with another program?

On this subject, what are people's opinions of how Boeings recent problems with software and valves on the Starliner could lead to similar problems on SLS's first flight?

[woods170]

SLS won't fail. Too much uber-reliable heritage stuff is in there.

Is this sarcasm? Maybe you have SLS confused with another program?

On this subject, what are people's opinions of how Boeings recent problems with software and valves on the Starliner could lead to similar problems on SLS's first flight?

I was NOT being sarcastic. IMO SLS won't fail in some spectacular launch mishap.

I referred to "uber-reliable heritage stuff" because of this:
Launch mishaps are generally caused by propulsion elements misbehaving. That won't happen on SLS as both the RS-25 and the SRM are thoroughly understood and reliable propulsion elements.
The fact that the SLS SRB is 5 segments vs the shuttle's 4 segments is not enough of a difference to cause some spectacular failure. Nor does the slightly changed recipe of the solid propellant.
The tankage isn't new either. They used the exact same setup from the shuttle ET with the main difference being orthogrid and FSW versus stringers-and-skin. The SRB thrust take out is the same as on ET: at the top with a trust-beam in between the two solids.
Like shuttle the core stage structure takes the main thrust from the RS-25s, albeit via a slightly different load path.
So, lots of commonality in general to the shuttle, particularly for those elements that usually cause havoc on new rockets. I expect a nominal launch to orbit.

[tea monster]

I hope you are right.

As to the 'uber-reliability' of the shuttle hardware that SLS is based on, well, the record isn't as enthusiastic as you are: https://forum.nasaspaceflight.com/index.php?topic=17623.0

[woods170]

I hope you are right.

As to the 'uber-reliability' of the shuttle hardware that SLS is based on, well, the record isn't as enthusiastic as you are: https://forum.nasaspaceflight.com/index.php?topic=17623.0

From RS-25B forward there were NO RSLS aborts. That's the full latter half of the shuttle program having NO RSLS aborts. The RS-25s flying on SLS are of the even later (and even more reliable) RS-25C and RS-25D variants.

The case where a RS-25 stopped working in mid-flight was a one-off, early in the program, with the earlier and less reliable first version of RS-25. Never happened again in the 115 launched that followed after it. So, no concern for the engines flying on SLS.

Foam strikes have no bearing on SLS. APU fires are not a thing either. The two or three that happened were all in the early stages of the shuttle program. Improvements to the APUs prevented repeats of the fires. The APUs on SLS are modified shuttle APUs and thus of the design that flew WITHOUT fires for over 115 missions.

O-ring failures ceased to be a problem after the post-Challenger full SRB joint redesign. From STS-26 forward the prior O-ring problems never repeated themselves. The SLS SRBs are flying with the same post-Challenger joint design. So, no problem expected there.

All supposed reliability problems you pointed at were fixed long ago, in the first half of the STS program. Except for STS-93, which was an outlier due to aging wiring (which you don't have on a brand-new expendable rocket). The need for pins to plug oxidizer ports was eliminated by a injector plate design modification post-STS-93. The RS-25s flying on SLS have that design modification.

The entire second half of the shuttle program showed very high reliability of the propulsion elements and their associated systems. Those very same propulsion elements and systems are being flown on SLS. So, I don't expect catastrophic failures coming from those elements.

If anything causes a SLS launch go wrong I fully expect it to be something else than the legacy elements.

[Khadgars]

And another one bites the dust.

Anyway, eagerly anticipating seeing Orion on the stack! Not too much longer now!

Same!  Has Orion Stage Adapter been installed yet?

[Conexion Espacial]

One of the liquid hydrogen storage tanks (LH2) being built on Launch Pad 39B is nearly complete, the next step is to paint the tank.

[oldAtlas_Eguy]

So will it be finished before the WDR? Or could it delay the WDR occurrence late next month? Or has the WDR slipped out into later in December?

You would want all of your GSE that will be used for a launch to be exercised in a test (WDR) to say that the pad and vehicle are ready for the next step: LAUNCH.

[AS_501]

I thought I read somewhere that the completed stack will be rolled out for pad GSE interface checks, then rolled back to the VAB, then rolled out again for launch.  Correct?  I assume the KSC bus tours will be halted during both roll-outs/back.  Thanks for any info.

[AS_501]

And another one bites the dust.

Anyway, eagerly anticipating seeing Orion on the stack! Not too much longer now!

Same!  Has Orion Stage Adapter been installed yet?

According to SN, the adapter has been installed.
Note:  Still puzzled by NASA's decision to use a dummy motor in the launch escape tower (tower jettison motors will be active).  If there is a launch failure, wouldn't you want to at least recover the Orion capsule?  On the other hand, NASA would have much bigger problems on its hands if there was a launch failure.

[kdhilliard]

...
Note:  Still puzzled by NASA's decision to use a dummy motor in the launch escape tower (tower jettison motors will be active).  If there is a launch failure, wouldn't you want to at least recover the Orion capsule?  On the other hand, NASA would have much bigger problems on its hands if there was a launch failure.

At first that seemed strange to me as well, but I now think it makes a lot of sense.

They will have had to weight the chance of launch failure combined with the benefit of the recovered capsule (and real-life LES test) against the chance of a false alarm from the Emergency Detection System and the resulting loss of launch vehicle and mission.  With an inactive LES, a false EDS alarm can be monitored and later analyzed (perhaps even resolving the issue to the satisfaction of all concerned without reflying the mission), and the mission can continue on to other test objectives.

Starliner's Launch Abort Motors were inactive during OFT-1, and unlike with Artemis-1, they had previously tested ULA's Emergency Detection System on earlier Atlas V flights.

I don't recall the SuperDraco status for DM-1.

[AS_501]

...
Note:  Still puzzled by NASA's decision to use a dummy motor in the launch escape tower (tower jettison motors will be active).  If there is a launch failure, wouldn't you want to at least recover the Orion capsule?  On the other hand, NASA would have much bigger problems on its hands if there was a launch failure.

At first that seemed strange to me as well, but I now think it makes a lot of sense.

They will have had to weight the chance of launch failure combined with the benefit of the recovered capsule (and real-life LES test) against the chance of a false alarm from the Emergency Detection System and the resulting loss of launch vehicle and mission.  With an inactive LES, a false EDS alarm can be monitored and later analyzed (perhaps even resolving the issue to the satisfaction of all concerned without reflying the mission), and the mission can continue on to other test objectives.

Starliner's Launch Abort Motors were inactive during OFT-1, and unlike with Artemis-1, they had previously tested ULA's Emergency Detection System on earlier Atlas V flights.

I don't recall the SuperDraco status for DM-1.

Good points.
Note:  Starliner's abort motors will be armed for OFT-2.

[su27k]

https://twitter.com/jeff_foust/status/1447999228198883333

NASA MSFC director Jody Singer, in opening remarks at the @astrosociety’s von Braun Symposium, says she wanted to show the latest image of SLS as it’s prepared for Artemis-1, but couldn’t get it in time. Instead she shows this pic… from mid-Sept.

Thought: it’s tough to build public interest in a return-to-the-Moon program when the latest image of the rocket that is one of its foundations, being prepared for its first launch, is nearly a month old.

[Coastal Ron]

Not sure where this quote is from in your post...

Thought: it’s tough to build public interest in a return-to-the-Moon program when the latest image of the rocket that is one of its foundations, being prepared for its first launch, is nearly a month old.

...but I wanted to make the observation that the public being excited about the SLS for the Artemis program is like someone being excited about their flight to some far away vacation destination on an airliner. The method of transportation is a means to an end, not the end itself.

Oh, an SLS launch will get press coverage, but SLS supporters shouldn't be expecting the public to sing the praises of the SLS, not when all the video of the astronauts will be from within the Orion MPCV.

Bottom line is that the public will be interested in the return-to-the-Moon program because of what it means to them, not because of the rocket that launched them. And if the public supports the goals of the Artemis program, then the SLS will have a continuing use...

[Vultur]

The method of transportation is a means to an end, not the end itself.

Well, IMO large rockets (like other complex high-energy technologies) are cool in themselves, in one way.

But yes, of course the real attraction is regaining HSF BLEO capability after almost 50 years without it.