Author Topic: Developing the BFS - Phase 1 Big Falcon Hopper (BFH) Discussion - THREAD 2  (Read 314277 times)

Offline jpo234

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Can anyone been tell if they are using a common dome or if there are 2 independent tank domes?

Images from yesterdays drone footage seem to show a common bulkhead.
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline jpo234

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"Moreso than any other single part, the most confusing aspect of Starhopper has to be the apparent condition of its steel tank domes, distinctly covered with a patina of impurities like rust, dirt, dust, and grime." https://www.teslarati.com/spacex-starship-hopper-tank-bulkhead-installation-launch-landing-pad-progress/

Could they be planning to use cryogenic bladders inside the rough, dirty steel tanks?

Or... just clean it?
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline strato1

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Can anyone been tell if they are using a common dome or if there are 2 independent tank domes?

Images from yesterdays drone footage seem to show a common bulkhead.


Thanks.  I see the lower methane and there is a "head #3" photo.  Couldn't tell if they had a separate one for LOX.

Offline strato1

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This pic was taken on 1-16-19 when the large sections were being moved. A couple sections had some pieces of lumber on them. So perhaps it was a piece of lumber that fell?

Zooming in I get 1.0 in holes spaced at 2D.  (20 segments of the outer dome, 12 segments of the inner)

Offline su27k

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Well there's still a bunch of stuff laying around.

- The top dome (and its cap)
- the arced members near the top dome (maybe its interface stiffener to the cylinder?)
- Some 3' tubes
- anything else?

I must have missed something, thats what you get for traveling I guess.

1: Do we know its a common bulkhead design to begin with? The hopper doesnt need top notch mass efficiency. I must have missed that info.

2: If it is a common bulkhead design, why does everyone assume that whats inside the hopper is a common bulkhead? Wouldnt it make sense to have a few meters of engine space and above that the tanks? Would fit with what we see.

We don't know it's a common bulkhead, but pixel counting shows:
1. The water tower part of the hopper body is 12m high
2. The dome is about 3m high
3. The dome inside the water tower has its edge ~3m away from the water tower upper edge
4. This leaves 6m between the lowest point of the dome and the lower edge of the water tower

So:
1. If it's not common bulkhead design, and we're seeing the lower dome for the upper tank, then the lower tank only has 6m to use, even if we put two dome next to each other for the lower tank, the lower dome of the lower tank would be at level with water tower's lower edge, there wouldn't be space for engines.
2. If we're seeing is the lower dome of a common bulkhead design, its lowest point is 6m away from the water tower's lower edge, that seems to be way too much space just for the thrust structure and engines.

Offline Johnnyhinbos

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Well there's still a bunch of stuff laying around.

- The top dome (and its cap)
- the arced members near the top dome (maybe its interface stiffener to the cylinder?)
- Some 3' tubes
- anything else?

I must have missed something, thats what you get for traveling I guess.

1: Do we know its a common bulkhead design to begin with? The hopper doesnt need top notch mass efficiency. I must have missed that info.

2: If it is a common bulkhead design, why does everyone assume that whats inside the hopper is a common bulkhead? Wouldnt it make sense to have a few meters of engine space and above that the tanks? Would fit with what we see.

We don't know it's a common bulkhead, but pixel counting shows:
1. The water tower part of the hopper body is 12m high
2. The dome is about 3m high
3. The dome inside the water tower has its edge ~3m away from the water tower upper edge
4. This leaves 6m between the lowest point of the dome and the lower edge of the water tower

So:
1. If it's not common bulkhead design, and we're seeing the lower dome for the upper tank, then the lower tank only has 6m to use, even if we put two dome next to each other for the lower tank, the lower dome of the lower tank would be at level with water tower's lower edge, there wouldn't be space for engines.
2. If we're seeing is the lower dome of a common bulkhead design, its lowest point is 6m away from the water tower's lower edge, that seems to be way too much space just for the thrust structure and engines.
Humm, so Nomadd pointed out that the arc sections laying stacked up next to the dome appear to be a smaller diameter.

And the common and separate bulkhead theories both seem to have spacing issues.

And there’s large center holes on the domes.

And there are sections of Jefferies Tubes laying around.

Sooo... what about concentric spheres, one holding methane (outer) and one holding LOX (inner)? Build the inner sphere atop a descender tube the penetrates the bottom of the outer sphere. It could also fit just below the upper leg bracing and then the top dome of the outer sphere above the bracing.

I hate suggesting it - I sound like a wild speculator, which I am not fond of being. But...?
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Offline jpo234

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Well there's still a bunch of stuff laying around.

- The top dome (and its cap)
- the arced members near the top dome (maybe its interface stiffener to the cylinder?)
- Some 3' tubes
- anything else?

I must have missed something, thats what you get for traveling I guess.

1: Do we know its a common bulkhead design to begin with? The hopper doesnt need top notch mass efficiency. I must have missed that info.

2: If it is a common bulkhead design, why does everyone assume that whats inside the hopper is a common bulkhead? Wouldnt it make sense to have a few meters of engine space and above that the tanks? Would fit with what we see.

We don't know it's a common bulkhead, but pixel counting shows:
1. The water tower part of the hopper body is 12m high
2. The dome is about 3m high
3. The dome inside the water tower has its edge ~3m away from the water tower upper edge
4. This leaves 6m between the lowest point of the dome and the lower edge of the water tower

So:
1. If it's not common bulkhead design, and we're seeing the lower dome for the upper tank, then the lower tank only has 6m to use, even if we put two dome next to each other for the lower tank, the lower dome of the lower tank would be at level with water tower's lower edge, there wouldn't be space for engines.
2. If we're seeing is the lower dome of a common bulkhead design, its lowest point is 6m away from the water tower's lower edge, that seems to be way too much space just for the thrust structure and engines.

Can somebody who knows what they are doing fire up a decent CAD package and model the possibilities? There are dozens of external renders but no reality based models of the interior, AFAIK.

We know the external dimensions. We have seen the bulkheads. We have educated guesses about the engine size. We have seen the reinforcement for the legs.

IMHO that should be enough to get an idea about the internal layout...
« Last Edit: 01/22/2019 11:35 am by jpo234 »
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline strato1

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I'd be a little surprised if it was common due to the construction technique and insulation, but it's possible.  I also noticed quite a bit of oxidation on the bulkheads so not sure they are stainless.  one pic shows "Head #3", so it might be common.

Putting together some rough numbers as a starting point and working backwards to estimate structural and propellant weights ... have to start somewhere.

o/f pretty well known.  t/w a guess at 1.5.  SF a guess, but domes look pretty close to 1".  shaded areas represent rocket length of propellant weights working backwards.

Offline meekGee

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3. Why build such a large tinfoil hat if there is nothing in it?

They're testing the aerodynamics of the shape?

I doubt it will ever go fast enough that anything interestingly aerodynamic will ever happen with this rocket. If anything I see it as practise. They can't leave the top open or flat, and if they're going to design some some sort of dome or cone to cover it, it may as well be close to the eventual article.

The cone head is there exactly to prevent something aerodynamically interesting from happening during flight.

That, and to show people just how large it is in there.  "ECHO ECho Echo echo echo..."
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Offline meekGee

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Well there's still a bunch of stuff laying around.

- The top dome (and its cap)
- the arced members near the top dome (maybe its interface stiffener to the cylinder?)
- Some 3' tubes
- anything else?

I must have missed something, thats what you get for traveling I guess.

1: Do we know its a common bulkhead design to begin with? The hopper doesnt need top notch mass efficiency. I must have missed that info.

2: If it is a common bulkhead design, why does everyone assume that whats inside the hopper is a common bulkhead? Wouldnt it make sense to have a few meters of engine space and above that the tanks? Would fit with what we see.

3. Why build such a large tinfoil hat if there is nothing in it?

After finding out that the tanks are full diameter, I think it's turning out that as much as practical was made "life like".  This is not a minimalist test platform designed to have "most show for the buck".

The is a maximalist test platform, subject to certain constraints.

I think the entire "ass end" of the rocket - tanks, engines, pressurization system - all of that will be functionally representative of the real thing.

I would not be surprised if there are side thrusters.

We know that high-speed flight is out, and with it, movable brakerons.  We know anything forward of the tanks is just a thin shell.

We suspect that nothing much will attach inside the shell, though structurally it may be possible to build a floor or some other construction anchored to the bottom tube and extending into the shell.
ABCD - Always Be Counting Down

Offline strato1

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Well there's still a bunch of stuff laying around.

- The top dome (and its cap)
- the arced members near the top dome (maybe its interface stiffener to the cylinder?)
- Some 3' tubes
- anything else?

I must have missed something, thats what you get for traveling I guess.

1: Do we know its a common bulkhead design to begin with? The hopper doesnt need top notch mass efficiency. I must have missed that info.

2: If it is a common bulkhead design, why does everyone assume that whats inside the hopper is a common bulkhead? Wouldnt it make sense to have a few meters of engine space and above that the tanks? Would fit with what we see.

3. Why build such a large tinfoil hat if there is nothing in it?

After finding out that the tanks are full diameter, I think it's turning out that as much as practical was made "life like".  This is not a minimalist test platform designed to have "most show for the buck".

The is a maximalist test platform, subject to certain constraints.

I think the entire "ass end" of the rocket - tanks, engines, pressurization system - all of that will be functionally representative of the real thing.

I would not be surprised if there are side thrusters.

We know that high-speed flight is out, and with it, movable brakerons.  We know anything forward of the tanks is just a thin shell.

We suspect that nothing much will attach inside the shell, though structurally it may be possible to build a floor or some other construction anchored to the bottom tube and extending into the shell.

Do you know if the composite tank in LA was just a test article?

https://www.teslarati.com/spacex-bfr-spaceship-prototype-tank-dome-complete-hop-tests/

Offline Slarty1080

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"Moreso than any other single part, the most confusing aspect of Starhopper has to be the apparent condition of its steel tank domes, distinctly covered with a patina of impurities like rust, dirt, dust, and grime." https://www.teslarati.com/spacex-starship-hopper-tank-bulkhead-installation-launch-landing-pad-progress/

Could they be planning to use cryogenic bladders inside the rough, dirty steel tanks?

Itís almost as if they are deliberately trying to shake off the current aerospace mantra that everything must be assembled in an expensive clean room facility. I don't think it does. If they manage it correctly it should not be a problem. No doubt there is some dirt and grime on it but a jet wash would remove most of that and rust is not a problem unless it is going to come loose.

The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades Ö well ... there is now!"

Offline su27k

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Well there's still a bunch of stuff laying around.

- The top dome (and its cap)
- the arced members near the top dome (maybe its interface stiffener to the cylinder?)
- Some 3' tubes
- anything else?

I must have missed something, thats what you get for traveling I guess.

1: Do we know its a common bulkhead design to begin with? The hopper doesnt need top notch mass efficiency. I must have missed that info.

2: If it is a common bulkhead design, why does everyone assume that whats inside the hopper is a common bulkhead? Wouldnt it make sense to have a few meters of engine space and above that the tanks? Would fit with what we see.

We don't know it's a common bulkhead, but pixel counting shows:
1. The water tower part of the hopper body is 12m high
2. The dome is about 3m high
3. The dome inside the water tower has its edge ~3m away from the water tower upper edge
4. This leaves 6m between the lowest point of the dome and the lower edge of the water tower

So:
1. If it's not common bulkhead design, and we're seeing the lower dome for the upper tank, then the lower tank only has 6m to use, even if we put two dome next to each other for the lower tank, the lower dome of the lower tank would be at level with water tower's lower edge, there wouldn't be space for engines.
2. If we're seeing is the lower dome of a common bulkhead design, its lowest point is 6m away from the water tower's lower edge, that seems to be way too much space just for the thrust structure and engines.
And the common and separate bulkhead theories both seem to have spacing issues.

Common bulkhead doesn't have spacing issue if you assume what we're seeing is the common bulkhead itself (i.e. the middle dome).

The problem is if what we're seeing is the common bulkhead (i.e. lower dome of the LOX tank), and assuming the top dome goes above the triangular support beams, the LOX tank volume would be too large. If the tank height is 2.2m (0.8m between top of the beam to top edge of the hopper), dome volume 92m^3 (truncated cone, h=3, R=4.5, r=1.5 (3m top hole)), this gives total LOX volume of 324m^3, or 369t of LOX. Total propellant load would be  471t, that just leaves 29t of structure mass if we assume liftoff T/W of 1.2.

Offline AC in NC

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We don't know with certainty the top is thin shell.  I've seen a pic that it's same type of stainless clad with foil.  Maybe slightly thinner but essentially very sturdy.

Offline jpo234

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The problem is if what we're seeing is the common bulkhead (i.e. lower dome of the LOX tank), and assuming the top dome goes above the triangular support beams, the LOX tank volume would be too large. If the tank height is 2.2m (0.8m between top of the beam to top edge of the hopper), dome volume 92m^3 (truncated cone, h=3, R=4.5, r=1.5 (3m top hole)), this gives total LOX volume of 324m^3, or 369t of LOX. Total propellant load would be  471t, that just leaves 29t of structure mass if we assume liftoff T/W of 1.2.

What if they don't top off the tanks? You have just established an upper bound for the propellant load, after all.
« Last Edit: 01/22/2019 01:31 pm by jpo234 »
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline Tuna-Fish

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Do you know if the composite tank in LA was just a test article?

https://www.teslarati.com/spacex-bfr-spaceship-prototype-tank-dome-complete-hop-tests/

It was likely meant to be used back when the BFR was supposed to be a composite rocket. In the recent set of layoffs, it seems that SpaceX fired most of their composites people, so it seems that the future is now steel.

Offline su27k

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The problem is if what we're seeing is the common bulkhead (i.e. lower dome of the LOX tank), and assuming the top dome goes above the triangular support beams, the LOX tank volume would be too large. If the tank height is 2.2m (0.8m between top of the beam to top edge of the hopper), dome volume 92m^3 (truncated cone, h=3, R=4.5, r=1.5 (3m top hole)), this gives total LOX volume of 324m^3, or 369t of LOX. Total propellant load would be  471t, that just leaves 29t of structure mass if we assume liftoff T/W of 1.2.

What if they don't top off the tanks? You have just established an upper bound for the propellant load, after all.

Yes, they can certainly do that, I guess that's what they did when flying Grasshopper. Although it would be a bit strange if they build a tank without using it to its full potential.

Offline Nomadd

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 The upper bulkhead has three cutouts in the skirt that are spaced just right to go over the triangle. Two of them are blocked off and hard to see, but that could be temporary.
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Offline JamesH65

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The problem is if what we're seeing is the common bulkhead (i.e. lower dome of the LOX tank), and assuming the top dome goes above the triangular support beams, the LOX tank volume would be too large. If the tank height is 2.2m (0.8m between top of the beam to top edge of the hopper), dome volume 92m^3 (truncated cone, h=3, R=4.5, r=1.5 (3m top hole)), this gives total LOX volume of 324m^3, or 369t of LOX. Total propellant load would be  471t, that just leaves 29t of structure mass if we assume liftoff T/W of 1.2.

What if they don't top off the tanks? You have just established an upper bound for the propellant load, after all.

Yes, they can certainly do that, I guess that's what they did when flying Grasshopper. Although it would be a bit strange if they build a tank without using it to its full potential.

Part of its potential is simply the experience of building it. So if they have built a full size one, even if they don't use all the capacity, they have still learnt a lot about building it to its final size. After all, NASA/contractors built a full sized Space shuttle that never went to space, but clearly taught them a lot about building it.

Offline rcoppola

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IMO,  this test vehicle is essentially a Flying Engine Test Stand and real environmental Avionics testbed.

Nothing more, nothing less.
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