What are the chances that SLS fails its first launch?

[TheRadicalModerate]

I guess that’s fair in a general waterfall vs something more agile type of way. But even in classic waterfall development cycles you still have iterations. It’s not like the FSW requirements are the same ones they started with 10 years ago. The cycles are slowerand they don’t go through as many as other more modern dev methodologies, but they still iterate.

You're basically making a statement that waterfall works, which is obviously true.  But the problem with waterfall iteration is that major requirements changes require going through the entire requirements/function spec/design spec/implementation/test design/test process again, which leaves you open to a variety of pathologies:

1) The people who wrote all of these documents originally and then used them to implement stuff have probably left, which means that the regression bugs have bit rot, and fixing code with bit rot is much more likely to generate a cascade of new regression bugs.

2) Because the cycles between releases are longer (which in turn is caused by the waterfall documentation and review tail), when regressions surface, they impact more code, and the chance of fixing them in such a way that all the impacted code is fixed is reduced.

I'm not starry-eyed about Agile or any other iterative methodology.  You can still make bad designs, and you can still have regressions that get fixed stupidly.  But all the stuff that enables Agile in the first place--living specs that are use-case driven, better version management tools, deployment integrated into the development process--increases the sheer speed at which you can efficiently turn a version over.  That higher cadence makes regressions much less likely to have big impacts, which in turn keeps the test plan from going off into the weeds when stuff happens that nobody had envisioned.

As for the new CSECs they’ve been hotfired a lot more often than the core stage has so if anything you should feel less nervous about them.

There's a big difference between hotfiring something in a test cell at exactly 1g and 1bar and controlling an engine at multiple g's and fractions of a bar, with different vibrational and GN&C characteristics.  But when you come right down to it, an RS-25 may be a plumber's nightmare, but it's not exactly a cutting-edge control problem any more.  I'm not that nervous about the controller software, simply because it's a pretty well bounded problem.

[zubenelgenubi]

Moderator:
Keep the discussion civil and on-topic. Posts deleted.

[SpaceCadet1980]

Moderator:
Keep the discussion civil and on-topic. Posts deleted.

Please clarify what exactly is off topic and uncivil. I seem to have 2 posts deleted, one was a continuation of the discussion of how waterfall/agile relates to SLS. I can understand that being ruled off topic for this thread, but not why only my post and not the one I replied to was deleted.

The other post was replying to a post from Khadgars essentially explaining why I found his post uncivil, yet his uncivil post was not removed (I did not report his post, since the explanation was too long for the tiny report box). I don't get the standard you are using here. Did you perhaps delete that post for referencing a post that was edited/removed by the original author after I pointed out the religious connotation of what they said?

[Vahe231991]

Given that the fourth WDR test of the SLS rocket for the Artemis 1 mission was largely successful in terms of seeing both stages of the rocket fueled despite a liquid hydrogen leak at the QD of the core stage, it's highly unlikely the SLS would fail its first launch.

[pathfinder_01]

Given that the fourth WDR test of the SLS rocket for the Artemis 1 mission was largely successful in terms of seeing both stages of the rocket fueled despite a liquid hydrogen leak at the QD of the core stage, it's highly unlikely the SLS would fail its first launch.

I wouldn't have that much faith in any rocket that passed a WDR. A WDR is supposed to simulate what happens before launch....any rocket that has failed generally failed in flight and of course passed launch.

[Overwatchfan123]

The risk of LOV, LOM, and LOC all go down when the SRBs separate two minutes after launch, and this is because the SRBs are more dangerous than liquid fuel.

[Jim]

Given that the fourth WDR test  of the SLS rocket for the Artemis 1 mission was largely successful in terms of seeing both stages of the rocket fueled despite a liquid hydrogen leak at the QD of the core stage, it's highly unlikely the SLS would fail its first launch.

A WDR does not ensure flight success.   It is only provides schedule risk reduction and crew training.  Any problems uncovered in a WDR would be uncovered during the first countdown and with its associated delays caused by resolving those delays.

[Jim]

The risk of LOV, LOM, and LOC all go down when the SRBs separate two minutes after launch, and this is because the SRBs are more dangerous than liquid fuel.

Not necessarily true.

[ZachS09]

The risk of LOV, LOM, and LOC all go down when the SRBs separate two minutes after launch, and this is because the SRBs are more dangerous than liquid fuel.

Not necessarily true.

Exactly. What if there’s a premature shutdown of one or more of the RS-25s? Will there be enough power to limp into orbit in case of that event?

[jadebenn]

The risk of LOV, LOM, and LOC all go down when the SRBs separate two minutes after launch, and this is because the SRBs are more dangerous than liquid fuel.

Not necessarily true.

Exactly. What if there’s a premature shutdown of one or more of the RS-25s? Will there be enough power to limp into orbit in case of that event?

SLS has T-0 single engine out capability. Would be LOM, but it could limp to LEO.

Single engine out after SRB separation is less severe. More than one might trigger an abort, depending on the timing and severity.

[Hog]

The risk of LOV, LOM, and LOC all go down when the SRBs separate two minutes after launch, and this is because the SRBs are more dangerous than liquid fuel.

Not necessarily true.

Exactly. What if there’s a premature shutdown of one or more of the RS-25s? Will there be enough power to limp into orbit in case of that event?

SLS has T-0 single engine out capability. Would be LOM, but it could limp to LEO.

Single engine out after SRB separation is less severe. More than one might trigger an abort, depending on the timing and severity.

The paper I'm guessing Jadebenn is referencing.

[Vahe231991]

Given that the fourth WDR test  of the SLS rocket for the Artemis 1 mission was largely successful in terms of seeing both stages of the rocket fueled despite a liquid hydrogen leak at the QD of the core stage, it's highly unlikely the SLS would fail its first launch.

A WDR does not ensure flight success.   It is only provides schedule risk reduction and crew training.  Any problems uncovered in a WDR would be uncovered during the first countdown and with its associated delays caused by resolving those delays.

The September 2022 cryogenic fueling test was intended to reduce risks with loading LH₂ into the SLS core stage before launch, and despite minor damage to the foam insulation resulting from Hurricane Ian, the first SLS launch went smoothly. 

[whitelancer64]

Given that the fourth WDR test  of the SLS rocket for the Artemis 1 mission was largely successful in terms of seeing both stages of the rocket fueled despite a liquid hydrogen leak at the QD of the core stage, it's highly unlikely the SLS would fail its first launch.

A WDR does not ensure flight success.   It is only provides schedule risk reduction and crew training.  Any problems uncovered in a WDR would be uncovered during the first countdown and with its associated delays caused by resolving those delays.

The September 2022 cryogenic fueling test was intended to reduce risks with loading LH₂ into the SLS core stage before launch, and despite minor damage to the foam insulation resulting from Hurricane Ian, the first SLS launch went smoothly.

Wet Dress Rehearsals - sometimes many of them - have been done for every major rocket ever launched.... Many of which failed on their first launch.  Ground tests and rehearsals are meant to find issues and fix them before they become problems on launch day, but they can't find everything.