SpaceX Starship : First Flight : Starbase, TX : 20 April 2023 - DISCUSSION

[gemmy0I]

Regarding the apparent lack of a landing burn, my guess is that one (or both) of the following are true:

1. Something in their simulations/modeling has told them conclusively that S24 can't or almost certainly won't successfully pull off the flip-and-burn maneuver. Basically, there's some known deficiency in the design (perhaps structural, but I suspect more likely "plumbing-related", i.e. header-tank/pressurization issues of the sort S15 had) that falls short of the needs of this maneuver, so they left if off the flight plan because they don't expect to learn anything from it. Save it for a future ship (probably S28) that has the necessary design improvements. If true, this would fit neatly with the decision long ago to remove the heat-shield tiles and flaps entirely from S26 and S27 and just fly them expendable. S26 and S27 are from the same design generation as S24, so S28 is their next real opportunity to fix big design issues.

Incidentally, since any design issues in S24 should be shared by S25, if they fly S25, they'll likely use the same flight profile: no landing burn, just focus on testing ascent, re-entry, and atmospheric control through the transonic regime (none of which could be tested with S15 and earlier since they didn't go supersonic).

2. They know that if S24 makes a successful water landing, it'll likely survive the subsequent tip-over, leaving them with a giant, floating stainless-steel whale in the middle of the ocean that they have to dispose of lest it become a marine hazard. Belly-flopping at terminal velocity should guarantee a "clean" breakup (see SN9). They've been through this before with that one Falcon 9 that survived a water landing and had to be demolished with explosive charges by frogmen (not, as the early sensational rumors reported, "used as target practice by the Air Force" ). That kind of operation with human divers in close proximity to a building-sized object "flopping" unpredictably in the waves is surely extremely hazardous - the sort of thing you do when you have no other choice, but you don't want to make a habit of risking when you can avoid it. That's a fast way to get a workers'-comp/wrongful-death lawsuit and a ton of bad publicity.

I'd consider #1 the more likely deciding factor, because I suspect if they thought they could actually get good data on a flip-and-burn landing, they'd try their best to do it (despite the risk of a tricky cleanup; if they expected that to be an issue, there are ways they can mitigate the challenge through engineering, e.g. by leaving the FTS armed and detonating it as soon as the landing burn ends). As we now know, S15's landing burn was far from 100% successful, and its safe touchdown was more of a "fluke" than a true success - so this absolutely remains on their list of things that need to be tested and proven out. I can't imagine them not giving it another shot with S24 unless they didn't think it would teach them anything worthwhile.

[TheRadicalModerate]

They might think that they've fixed the door for max-q stress, but aren't confident about torque on the frame during a flip.

What's the worst that can happen?  The Starship just destroys itself ten seconds earlier.  A belly-flop into the Pacific Ocean at ~100m/s (can't remember the exact number) isn't going to leave much to examine.

[sdsds]

I note with interest the hazard area maps don't seem to cover a case where the booster under-performs but Starship separates and then targets a disposal location in either the mid-Atlantic or Indian Ocean. [...]

If the booster dramatically under-performs, then I'd suggest that SESU will be aborted [...]

Thanks very much for your analysis. It adds quite a bit of clarity to a scenario that seems at best quite murky!

Thinking about the SpaceX test objective priorities, demonstrating stage separation followed by Starship in-flight engine startup seem like items that must be fairly high up the list. Yet even optimistically the lack of flight history for a booster powered by a cluster of Raptor-2 engines makes the likelihood of booster under-performance seem non-negligible.

(Fully recognizing this isn't a "Poll" thread I nonetheless attach a graphic guess at the likelihood of how many booster engines lose thrust — either through commanded shutdowns or RUD/fratricide events — at some time before the intended amount of propellant is expended. The modal value is 8, based on a Poisson distribution with μ = 8.5.)

Sounds like we’ve almost got the ingredients for a good old fashioned frequentist vs. bayesian smack down.

Oh yes, in so many ways!

[envy887]

I note with interest the hazard area maps don't seem to cover a case where the booster under-performs but Starship separates and then targets a disposal location in either the mid-Atlantic or Indian Ocean. [...]

If the booster dramatically under-performs, then I'd suggest that SESU will be aborted [...]

Thanks very much for your analysis. It adds quite a bit of clarity to a scenario that seems at best quite murky!

Thinking about the SpaceX test objective priorities, demonstrating stage separation followed by Starship in-flight engine startup seem like items that must be fairly high up the list. Yet even optimistically the lack of flight history for a booster powered by a cluster of Raptor-2 engines makes the likelihood of booster under-performance seem non-negligible.

(Fully recognizing this isn't a "Poll" thread I nonetheless attach a graphic guess at the likelihood of how many booster engines lose thrust — either through commanded shutdowns or RUD/fratricide events — at some time before the intended amount of propellant is expended. The modal value is 8, based on a Poisson distribution with μ = 8.5.)

Sounds like we’ve almost got the ingredients for a good old fashioned frequentist vs. bayesian smack down.

Oh yes, in so many ways!

The most likely outcomes would seem to be either 0 or 33 the engines shutting down early.

[BenW]

2. They know that if S24 makes a successful water landing, it'll likely survive the subsequent tip-over, leaving them with a giant, floating stainless-steel whale in the middle of the ocean that they have to dispose of lest it become a marine hazard. Belly-flopping at terminal velocity should guarantee a "clean" breakup (see SN9).

They could probably "have it both ways" if they wanted, by attempting the flip maneuver at say 3km altitude, then turning off the engines to ensure that it still impacts the ocean at near-terminal velocity. But agreed that it doesn't make sense to do it if they've predetermined it's incapable, or if the design of S28+ is so different that they wouldn't learn anything by S24/S25 trying it.

[JWC]

Is it possible that these initial prototypes are too heavy?  No landing fuel saves a lot of weight.  The booster being set to 90% thrust affects this as well...

[Kspbutitscursed]

Question:
WEN HOP
Nah just kidding

what are the chances of booster 9 being caught by the chopstix and what are the chances of it being recovered.

[Eer]

Question:
WEN HOP
Nah just kidding

what are the chances of booster 9 being caught by the chopstix and what are the chances of it being recovered.

I believe the answer to both of your questions is zero.

B9 is not flying back to the launch site, so won't be caught by chopsticks.

It looks like from the marine alerts that it will attempt a near landing above water out at sea. We've not seen anything to indicate they plan to tow it back to shore.

[Kspbutitscursed]

Question:
WEN HOP
Nah just kidding

what are the chances of booster 9 being caught by the chopstix and what are the chances of it being recovered.

I believe the answer to both of your questions is zero.

B9 is not flying back to the launch site, so won't be caught by chopsticks.

It looks like from the marine alerts that it will attempt a near landing above water out at sea. We've not seen anything to indicate they plan to tow it back to shore.

did you mean Booster 7
becaus i was talkig about IFT-2

[Herb Schaltegger]

Question:
WEN HOP
Nah just kidding

what are the chances of booster 9 being caught by the chopstix and what are the chances of it being recovered.

I believe the answer to both of your questions is zero.

B9 is not flying back to the launch site, so won't be caught by chopsticks.

It looks like from the marine alerts that it will attempt a near landing above water out at sea. We've not seen anything to indicate they plan to tow it back to shore.

did you mean Booster 7
becaus i was talkig about IFT-2

That's off-topic for this thread. Perhaps consider a different one for that discussion.

[Kspbutitscursed]

Question:
WEN HOP
Nah just kidding

what are the chances of booster 9 being caught by the chopstix and what are the chances of it being recovered.

I believe the answer to both of your questions is zero.

B9 is not flying back to the launch site, so won't be caught by chopsticks.

It looks like from the marine alerts that it will attempt a near landing above water out at sea. We've not seen anything to indicate they plan to tow it back to shore.

did you mean Booster 7
becaus i was talkig about IFT-2

That's off-topic for this thread. Perhaps consider a different one for that discussion.

oops i thought i was  in the discussion thread 25 sorry

[darkenfast]

So the ship is 'landing' horizontally? That's not really a landing and more like a belly flop, right? Is it known why it wouldn't attempt to move vertical and repulsively land?.

If it's a marine sanctuary, there could be a problem with firing engines into the water. But that shouldn't prevent them from igniting to go vertical. They might want to hit horizontal to insure breakup and sinking.

The Ship is landing (or impacting), in a U.S. Navy open-ocean test range north of Hawaii, in very deep water. The Booster, on the other hand is landing somewhere off the south Texas coast, and I'm not sure of what the Marine Sanctuary boundaries are.

[GmP]

Question about the destack that just happened. I was only watching so missed any commentary, but was there an issue at the end that slowed the lowering down? I didn’t see any Twitter comments either. Did I miss anything or are just confused?

[TomH]

The changes to the flight plan may be to eliminate some minor issues that SpaceX feels the FAA is still not satisfied with. Perhaps SX wants to fly and gather what data they can with this rocket while trying to mitigate the FAA's concerns prior to future flights. Perhaps eliminating the SS flip and water landing will allow them to obtain the permit and go fly, as opposed to inconclusive negotiations for an indeterminate amount of time.

[woods170]

The changes to the flight plan may be to eliminate some minor issues that SpaceX feels the FAA is still not satisfied with.

Nope, that's not it. When Gwynne took over some months ago SpaceX did a thorough review of this test flight. Since then a number of test objectives have been moved from this test flight to future ones.

[geza]

The changes to the flight plan may be to eliminate some minor issues that SpaceX feels the FAA is still not satisfied with.

Nope, that's not it. When Gwynne took over some months ago SpaceX did a thorough review of this test flight. Since then a number of test objectives have been moved from this test flight to future ones.

But, why? Flip & landing was already demonstrated by SN15. What was wrong about leaving this maneuver in the flight plan? 

[Herb Schaltegger]

The changes to the flight plan may be to eliminate some minor issues that SpaceX feels the FAA is still not satisfied with.

Nope, that's not it. When Gwynne took over some months ago SpaceX did a thorough review of this test flight. Since then a number of test objectives have been moved from this test flight to future ones.

But, why? Flip & landing was already demonstrated by SN15. What was wrong about leaving this maneuver in the flight plan? 

Planning for it requires software validation, flight dynamics and CFD simulations, and who knows how much other testing and preparatory work. That all takes time and resources away from work on earlier, more significant milestones for this first flight test.

[MichaelBlackbourn]

I think until we see it or don’t on the day no one can say right now. It makes sense they don’t want to clutter the conversation about ‘crash it into the water’ with lingo about landing it. Best to keep the plan simple ‘we’re gonna lose it’ and then do the flip anyway. I doubt how you crash it into the water in the last 500m makes any difference to launch licences.

[wannamoonbase]

...But, why? Flip & landing was already demonstrated by SN15. What was wrong about leaving this maneuver in the flight plan? 

A simple explanation maybe that they consider Starship surviving to make a landing attempt to be a low probability and not worth the effort to include it in the plan.

[WisRich]

Maybe it's a safety issue.  If it were to survive the landing, there might be some residual fuel in the tanks, leaving recovery team members exposed to a potential bobbing bomb.

Just thinking out load.