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

[sferrin]

So...any word on the FAA license? 

Soon.

[jjerjackson]

Wait, what? No more gimbling? Well that's interesting. I'm looking forward to seeing the new flip maneuver.

As I understand it they will gimble, but it will be with electric actuators instead of the current hydraulic.

Respectfully,

James

[joek]

Wait, what? No more gimbling? Well that's interesting. I'm looking forward to seeing the new flip maneuver.

No more hydraulic gimbaling. The new gimbaling is electro-mechanical.

[joek]

In the very beginning of the thread there was a discussion why, in the FCC application, SpaceX wrote of a “Booster touchdown” and a “Ship splashdown”. Back then some people thought that this might suggest an actual landing of a booster on a barge, but ist thought that SpaceX just didn’t pay close attention to their wording. That’s what I still believe as well, but in the light of the new information it makes you wonder whether SpaceX already back then decided against the bellyflop on the first flight

Don't think there is much to read into those tea leaves (or additional Kremlinology required). It leaves SpaceX room to maneuver and is consistent with the PEA...

^c A Starship landing could occur at the VLA, on a floating platform in the Gulf of Mexico, or on a floating platform in the Pacific Ocean. Alternatively, SpaceX could expend Starship in the Gulf of Mexico or Pacific Ocean. Further environmental review of landing at sites not described in this document would be necessary if proposed in the future.
^d A Super Heavy landing is part of a launch, as it would occur shortly after takeoff. Super Heavy could land at the VLA or on a floating platform in the Gulf of Mexico. Alternatively, SpaceX could expend Super Heavy in the Gulf of Mexico. Further environmental review of landing at sites not described in this document would be necessary if proposed in the future.

... if SpaceX made more progress in other areas then we might be seeing different; a lot has changed in the intervening 12 months including (reportedly) pulling back on some test objectives for this first flight.

[StuffOfInterest]

If S24 is going to be doing a bellyflop all the way to the water, has anyone estimated what the terminal velocity will be?

[Vettedrmr]

...SpaceX already back then decided against the bellyflop on the first flight

The "bellyflop" (i.e. the really high AoA) flight regime is required for re-entry; what's being discussed here is whether S24 will attempt the pitch up to vertical for a powered landing or not.

[whitelancer64]

If S24 is going to be doing a bellyflop all the way to the water, has anyone estimated what the terminal velocity will be?

Approximately 75 - 90 m/s, or about 270 - 324 kph / 167 - 200 mph, depending on its angle of attack and the position of the flaperons.

[whitelancer64]

So...any word on the FAA license? 

Soon.

"I want to believe"

Historically, launch licenses for new LVs are only granted a few days before the first launch attempt.

[Oersted]

Maybe I'm a simpleton but I really don't see any interest in this whole discussion of "will they do a belly splash or will they go for a vertical soft landing in the sea"... We'll just see whatever they go for and it will be great no matter what. But I'm obviously in the minority thinking like that!

[StevenOBrien]

"For the first flight test, the team will not attempt a vertical landing of Starship"

https://www.spacex.com/launches/mission/?missionId=starship-flight-test

[Hog]

"For the first flight test, the team will not attempt a vertical landing of Starship"

https://www.spacex.com/launches/mission/?missionId=starship-flight-test

As mentioned in post #747.

[edzieba]

Performing the flip & soft landing means Starship may end up floating in the Pacific neat Kauai. That's a headache for everyone: you now have a huge floating uncontrolled object, with ordinance (the FTS charges) and pressurised elements (headers, any RCS tankage) that may or may not discharge as intended, and may at any time break up from wave action or may drift, depending on uncontrollable weather conditions. Even if a salvage team were standing by with the vessels and equipment needed to drag Starship... somewhere, it'd be no easy task to actually wrangle it safely.

Flipping and soft-landing risks Starship surviving. Not flipping and hitting the water belly-first at terminal velocity mitigates that risk.

[joek]

Historically, launch licenses for new LVs are only granted a few days before the first launch attempt.

Nit: Expect this is a permit (not license). In any case, FAA has historically lagged and not unusual to see nothing published of until after the event. Not holding my breath we will see such from the FAA before this attempt.

[geza]

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

I haven't seen it mentioned already, but S24 will be the last Ship that uses hydraulic gimbeling, so the whole "test like you fly" argument really doesn't apply as far as the flip maneuver goes.  The belly landing eliminates the need to make any particular effort to keep the hydraulic systems operational through the coast phase and re-entry, whereas the "elonerons" (sp?) will be operating off batteries as they will in future Ships.

For me, this is the winning explanation, thanks.

[DanClemmensen]

Performing the flip & soft landing means Starship may end up floating in the Pacific neat Kauai. That's a headache for everyone: you now have a huge floating uncontrolled object, with ordinance (the FTS charges) and pressurised elements (headers, any RCS tankage) that may or may not discharge as intended, and may at any time break up from wave action or may drift, depending on uncontrollable weather conditions. Even if a salvage team were standing by with the vessels and equipment needed to drag Starship... somewhere, it'd be no easy task to actually wrangle it safely.

Flipping and soft-landing risks Starship surviving. Not flipping and hitting the water belly-first at terminal velocity mitigates that risk.

It's a Navy test range. The Navy would probably enjoy having a nice target to sink.

[uhuznaa]

"For the first flight test, the team will not attempt a vertical landing of Starship"

https://www.spacex.com/launches/mission/?missionId=starship-flight-test

Yes, but this is mentioned purely in the context of the launch tower. Also the graphic on this page shows the booster basically doing the boost back burn in the wrong direction. I really wouldn't read too much into these words. Whoever did this page knows more about web design than about rockets.

And anyway it doesn't matter. If they manage to get the thing through all this and to a controlled descent onto the water this test will be more successful than anyone can realistically hope for. I mean, if everything will work out to this extent the landing maneuver will be a piece of cake later.

It's just that we're all stoked up and are looking for anything to talk about... nothing wrong with that too.

[sdsds]

Returning to discussion of possible events early in the test flight timeline:

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

Yes, I see your point and am highly confident SpaceX has extensively analyzed those cases both internally and with external review, particularly from the perspective of safety. If zero or some small number of Booster 7 Raptors lose thrust it seems highly likely the first stage flight profile will proceed on track, with stage separation within some defined "box" of flight parameters (speed, down-range distance, altitude, etc.). My guess is that the vehicle has plenty of performance margin, and even losing thrust from as many as six Raptors (depending on when the events occur) could still result in a "nominal" stage shutdown, perhaps a few seconds later than listed on the timeline. That's not based on any analysis of Booster 7; just on observations about how spaceflight performance margins in general seem to work.

On the pessimistic side, SpaceX must equally have a carefully reviewed plan if all 33 engines shut down early. The likely action would be termination of the entire flight, without attempting to have Ship 24 "escape" off the failed booster. Presumably all the propellant gets burned at altitude and the structural debris impacts in the hazard area. Again total guesswork has me thinking that 10 or more Raptor shutdowns, particularly early in the ascent, lead to this same outcome.

The gray zone for me is thus loss of thrust from 7, 8, or 9 Raptors. Some unexpected common mode failure could lead to this outcome, or a RUD/fratricide event. These seem like cases where one might expect to see Booster 7 burn to depletion yet fail to reach the nominal stage shutdown parameter box. Is this where a Ship 24 escape trajectory that ends with a propellant-depleted splashdown in the Gulf makes sense? Or am I misinterpreting OneSpeed's data?

[TomH]

Historically, launch licenses for new LVs are only granted a few days before the first launch attempt.

You have the implied causality backwards. The more accurate relationship is: Most new LVs are launched within a few days of being granted a launch license.

[TomH]

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?

Neither of you is thinking about the fact that they are landing near a marine sanctuary. If they burn off all the residuals, they can crash with less toxic chemicals. If they did the flip, they'd have more toxins remaining. So you can't definitively say Nope, because you don't know with certainty.

[jpo234]

If they burn off all the residuals, they can crash with less toxic chemicals.

What toxic chemicals?