SpaceX Starship : Texas Prototype(s) Thread 21 : Discussion

[Chris Bergin]

New thread (21) for discussion of the Starship prototype being built in Boca Chica, Texas.  Previous posts on these prototypes can be found in these threads:

Discussion 1

Discussion 2

Discussion 3

Discussion 4

Discussion 5

Discussion 6

Discussion 7

Discussion 8

Discussion 9

Discussion 10

Discussion 11

Discussion 12

Discussion 13

Discussion 14

Discussion 15

Discussion 16

Discussion 17

Discussion 18

Discussion 19

Discussion 20

Thread 21 - you're in it!

UPDATES:

SpaceX BFS : Phase 2 - Starship Orbital Prototype(s) - Photos and Updates -3 (Previous)

SpaceX Boca Chica - Production Updates - MASTER Thread (4)

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[cdebuhr]

On one of Mary's latest images of BN3 peeking out from the high-bay (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2242557#msg2242557), I notice a band of external reinforcing stringers ~ 1.5 rings down from the top.  Notwithstanding the bottoms of the GSE tanks, is this the first time we've seen this sort of thing?  I don't recall seeing this before. 

[warp99]

On one of Mary's latest images of BN3 peeking out from the high-bay (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2242557#msg2242557), I notice a band of external reinforcing stringers ~ 1.5 rings down from the top.  Notwithstanding the bottoms of the GSE tanks, is this the first time we've seen this sort of thing?  I don't recall seeing this before.

Good spotting. 

My guess would be that they have used external stringers where there is a bulkhead inside the tank wall. 

These are going to wail like banshees or best case like Pan pipes on descent!

[InterestedEngineer]

On one of Mary's latest images of BN3 peeking out from the high-bay (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2242557#msg2242557), I notice a band of external reinforcing stringers ~ 1.5 rings down from the top.  Notwithstanding the bottoms of the GSE tanks, is this the first time we've seen this sort of thing?  I don't recall seeing this before.

Good spotting. 

My guess would be that they have used external stringers where there is a bulkhead inside the tank wall. 

These are going to wail like banshees or best case like Pan pipes on descent!

I'm not an aeronautical engineer (IANAAE) but my guess is the shockwave at max Q will be far enough out from the skin that the external stringers won't add significant drag near max Q.

I suspect the same goes for the externally stowed grid fins on F9 as well as Super Heavy.

Which makes me start to wonder why all the stringers aren't external, but I should take that to the Engineering thread.

[AC in NC]

On one of Mary's latest images of BN3 peeking out from the high-bay (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2242557#msg2242557), I notice a band of external reinforcing stringers ~ 1.5 rings down from the top.  Notwithstanding the bottoms of the GSE tanks, is this the first time we've seen this sort of thing?  I don't recall seeing this before.

EDIT: StephenOBrien pointed out my error.  I missed you were referring to what's Double circled in Orange


Bridge the gap for me on something I may misunderstand.

Is the Red circled band what you are talking about?  If so, notice these are essentially flat bands rather than, what I thought would be the case, something that stands out meaningfully perpendicular to the tank.  As a layman, I always interpreted stringers as something like "angle iron" or the "hat stringers" we see in the skirt.

So to me, this seems like simply a "reinforcing band" rather than "external stringers" and in that way little different as seen circled in Yellow as compared with the vertical seam scalloped reinforcing strips as shown circled in Green.

[KBK]

On one of Mary's latest images of BN3 peeking out from the high-bay (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2242557#msg2242557), I notice a band of external reinforcing stringers ~ 1.5 rings down from the top.  Notwithstanding the bottoms of the GSE tanks, is this the first time we've seen this sort of thing?  I don't recall seeing this before.

Good spotting. 

My guess would be that they have used external stringers where there is a bulkhead inside the tank wall. 

These are going to wail like banshees or best case like Pan pipes on descent!

Of course, this is done to prevent problem of energetic peaking in the one area. to spread those forces out. it's not specifically or only about flex, but about where energies accumulate, and how to spread that peak out over a larger area. They may even, in the future, if they go forward with keeping it, go for a subtle aspect of a radical discontinuity by making the stringers of unequal non repeating heights or lengths. Such an act would enable a form of force or energetic distribution in a very complex resonance and stressing environment. The more the given vehicle is to be reused then the more important all these minor seeming things become.

[StevenOBrien]

On one of Mary's latest images of BN3 peeking out from the high-bay (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2242557#msg2242557), I notice a band of external reinforcing stringers ~ 1.5 rings down from the top.  Notwithstanding the bottoms of the GSE tanks, is this the first time we've seen this sort of thing?  I don't recall seeing this before.

Bridge the gap for me on something I may misunderstand.

Is the Red circled band what you are talking about?  If so, notice these are essentially flat bands rather than, what I thought would be the case, something that stands out meaningfully perpendicular to the tank.  As a layman, I always interpreted stringers as something like "angle iron" or the "hat stringers" we see in the skirt.

So to me, this seems like simply a "reinforcing band" rather than "external stringers" and in that way little different as seen circled in Yellow as compared with the vertical seam scalloped reinforcing strips as shown circled in Green.

You're highlighting SN16. cdebuhr is referring to the BN3 section, which is behind and to the left of SN16 in the picture.

[Gliderflyer]

It's hard to see, but there are a couple pixels on the booster CAD image that look like they could be those stringers.

https://twitter.com/StarshipGazer/status/1393756816404893698

[cdebuhr]

It's hard to see, but there are a couple pixels on the booster CAD image that look like they could be those stringers.

https://twitter.com/StarshipGazer/status/1393756816404893698

OMG - I just went to the original image in the tweet.  I see what you mean, but damn is that subtle.  I honestly have no idea how some of you here spot things like that.  I figured the external stringers had to be one of two things: 1) reinforcing around the common bulkhead, or 2) reinforcing at the upper bulkhead/gridfins/interstage area.  I'm not sure exactly how much faith to put in these drawings on the labels, but this would seen to argue in favour of option 2.

[cdebuhr]

It's hard to see, but there are a couple pixels on the booster CAD image that look like they could be those stringers.

Those are grid fins.

Nope - zoom in.  I believe he was talking about those faint but distinctly present hatch marks between the grid fins.  I see three of them between the grid fins aligned with the cylinder axis of the vehicle.

Edit I annotated a crop of your picture - see green arrows.

[AC in NC]

Nope - zoom in.  I believe he was talking about those faint but distinctly present hatch marks between the grid fins.  I see three of them between the grid fins aligned with the cylinder axis of the vehicle.

Edit I annotated a crop of your picture - see green arrows.

I'll see myself out now.   

[JS1]

I notice a band of external reinforcing stringers ~ 1.5 rings down from the top.  Notwithstanding the bottoms of the GSE tanks, is this the first time we've seen this sort of thing?  I don't recall seeing this before.

They'd be required due to the extra compressive forces. In sections where you have bulkheads, the bulkheads are meeting the rings at a roughly tangential angle, meaning that the gap between the bulkhead and ring gets tighter and tighter to the point that it's practically inaccessible from one side of the bulkhead. Because it gets so tight, internal stringers, even with their ends bevelled off, can't reach all the way up to the weld, plus actually getting a welder to reach up there is also very challenging without specialised tools.

That leaves a section of ring near the bulkhead weld without any stringer support. With any structure under compressive loads, the longer / skinnier / thinner a beam or plate, etc is, the more susceptible it is to buckling. With Starship the rings are strong enough to handle the compressive loads, but in Super Heavy they're evidently concerned about even these small strips of ring withstanding the compressive forces trying to buckle the rings, and therefore these external stringers are just a simple method of providing the same strength without having to do anything complicated like have stringers that penetrate through the bulkheads, etc.

[darkenfast]

IRT the Booster pic and for the more aeronautical-savvy members: Are those fins realistic for travel in an engine-first direction at the speeds we see for SpaceX first-stage returns? Or perhaps I should ask if the grid-fins can exert enough authority to keep the vehicle under control with those fins as they are? I know swept-forward wings and fins have been done on various research aircraft, but they aren't common.

The reason I am asking is that those fins don't appear to be that heavy. If they work for landing (temporarily), then might SpaceX not pivot to just using them? It wouldn't be the first time they made such a change. Look at how Falcon 9 first stage recovery and handling has evolved.

[Nascent Ascent]

Does SpaceX sub-contract this GSE work to other companies (with requirements, goals, deliverables) or is all this tankage, pipes, towers, concrete, steelwork, etc all designed and managed by SpaceX?

[warp99]

https://twitter.com/starshipgazer/status/1396626650029346822

The technical details of the Heat Exchanger Methane Sub-Coolers:

Interesting these were built in 2019 so planning for the orbital launch pad has been underway for a while and we are starting to see the pieces come together.

[Ocisly]

https://twitter.com/starshipgazer/status/1396626650029346822

The technical details of the Heat Exchanger Methane Sub-Coolers:

Interesting these were built in 2019 so planning for the orbital launch pad has been underway for a while and we are starting to see the pieces come together.

or it's an off the shelf heat exchanger

[warp99]

https://twitter.com/starshipgazer/status/1396626650029346822

The technical details of the Heat Exchanger Methane Sub-Coolers:

Interesting these were built in 2019 so planning for the orbital launch pad has been underway for a while and we are starting to see the pieces come together.

or it's an off the shelf heat exchanger

Designed for cryogenic use at liquid nitrogen temperatures with the required heat capacity and pressure drops. 

That is a very specialised heat exchanger to have four sitting around in stock - based on two being installed and mounting stands for another two.

[Crispy]

IRT the Booster pic and for the more aeronautical-savvy members: Are those fins realistic for travel in an engine-first direction at the speeds we see for SpaceX first-stage returns? Or perhaps I should ask if the grid-fins can exert enough authority to keep the vehicle under control with those fins as they are? I know swept-forward wings and fins have been done on various research aircraft, but they aren't common.

The reason I am asking is that those fins don't appear to be that heavy. If they work for landing (temporarily), then might SpaceX not pivot to just using them? It wouldn't be the first time they made such a change. Look at how Falcon 9 first stage recovery and handling has evolved.

All signs currently point to legs being skipped entirely, in favour of launch tower catching.

[edzieba]

In the final version, maybe.
I would expect the initial booster prototypes to have 'stub legs' similar to those currently on Starship, to allow for landings on flat surfaces. e.g. downrange on a platform as on the plan of record for the first orbital flight, or as a fallback during testing of the booster catcher (retain an extra ton or two of propellant to allow a terminal translate the <50m from catch tower to the existing landing pad). The legs and contingency propellant can be removed once booster catching is ironed out, but the added mass of them for the first few flights is worth not pancaking ~28 Raptors on an otherwise survivable landing.

[darkenfast]

IRT the Booster pic and for the more aeronautical-savvy members: Are those fins realistic for travel in an engine-first direction at the speeds we see for SpaceX first-stage returns? Or perhaps I should ask if the grid-fins can exert enough authority to keep the vehicle under control with those fins as they are? I know swept-forward wings and fins have been done on various research aircraft, but they aren't common.

The reason I am asking is that those fins don't appear to be that heavy. If they work for landing (temporarily), then might SpaceX not pivot to just using them? It wouldn't be the first time they made such a change. Look at how Falcon 9 first stage recovery and handling has evolved.

All signs currently point to legs being skipped entirely, in favour of launch tower catching.

That is what Musk has said that they'd like to do, eventually. First, they'll have to do some landings without the catcher. Second, sometimes the aspirational plan simply turns out to be too hard. SpaceX is very pragmatic about stuff that isn't foundational to the success of the program. Not being reusable is a failure in their book. Not being able to catch a fairing in a net, land a Dragon under power, fly a Falcon 9 first stage back to land from the drone-ship, or build a giant rocket out of carbon fiber, is not a failure. It's a pragmatic change of plan.

So, we have a photo of a picture on some hardware that depicts a Booster, with fins that stick down far enough that the rocket could conceivably sit on them. Are those fins only going to be on boosters that are not recovered, but are splashed? Or, are the fins (perhaps with crush-core extensions), also part of the landing gear for a Booster, Mark I?

The "catcher" concept is fascinating, but I suspect that it is not essential until the flight rate is a lot higher.

Edzieba ninja'd me!