Author Topic: Developing the BFS - Phase 1 Big Falcon Hopper (BFH) Discussion - THREAD 2  (Read 535020 times)

Offline RoboGoofers

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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?


of course this video says the laser takes off the oxide layer, which you might want for a LOX tank, but I assume that commercial steel LOX tanks have a coating to prevent oxidation so they would apply something similar.
« Last Edit: 01/22/2019 03:17 pm by RoboGoofers »

Offline Lars-J

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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.


1. The three connecting cylinders that provide structural support for the legs would subtract from the LOX volume, and
2. We don't know how high (or low) the LOX top dome will be placed, so any volume calculation is highly speculative. The dome might be welded around the support beams, since it seems to be in multiple parts.
« Last Edit: 01/22/2019 07:52 pm by Lars-J »


Offline JamesH65

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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?

Cool  tool, but very expensive. But I suspect that would not be a problem for SpaceX.

Or... just clean it?


of course this video says the laser takes off the oxide layer, which you might want for a LOX tank, but I assume that commercial steel LOX tanks have a coating to prevent oxidation so they would apply something similar.

Offline scdavis

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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?

It’s 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.

I read "Ignition! An informal history of liquid rocket propellants" by John Clark last year at the recommendation of this forum -- really a great read and learned a lot. One of the things I learned was that even a tiny amount of unexpected material - dirt, grease, rags - can lead to a catastrophic explosion when the oxidizer comes in contact with them. This was a frequent cause of rocket engine explosions in the author's experience testing generations of rocket engines.

If I remember correctly, common practice is to "passivate" a tank and engine channels by flushing with inert gases. I believe that they also will flush with something active in a controlled manner to eat up an compounds that can be oxidized, but with an oxidizer that is less "robust."

I'm not sure I'm saying all this correctly, so more experienced members will need to chime in. But that book leads me to think that it's super important to have a totally clean oxidizer path before you try lighting anything up.

Offline Restless

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Elon has stated that the smooth-skinned orbital prototype of Starship will be complete by June and will fly later this year.

Do we have any clue where it's being built?

Is it somewhere on the Texas Gulf Coast, like Port of Brownsville?

Hard to imagine something so big could be built without the space community not knowing where......

Offline Jcc

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Elon has stated that the smooth-skinned orbital prototype of Starship will be complete by June and will fly later this year.

Do we have any clue where it's being built?

Is it somewhere on the Texas Gulf Coast, like Port of Brownsville?

Hard to imagine something so big could be built without the space community not knowing where......

Elon said they are building the pieces of it Hawthorne now. To be assembled somewhere near Brownsville we presume. Interesting to see what kind of a transporter they come up with for it.

Offline dorkmo

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any ideas on helium tanks? will they use COPV? or could a smaller SS tank fit inside these? wasnt there something like that on one of the original diagrams?

Offline Jcc

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any ideas on helium tanks? will they use COPV? or could a smaller SS tank fit inside these? wasnt there something like that on one of the original diagrams?
They don't need helium. Autogenous pressurization of the tanks by vaporizing LOX/Methane.

Offline Johnnyhinbos

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any ideas on helium tanks? will they use COPV? or could a smaller SS tank fit inside these? wasnt there something like that on one of the original diagrams?
They don't need helium. Autogenous pressurization of the tanks by vaporizing LOX/Methane.
True that it may, I’m not sure it’s 100% correct to say they won’t need helium. I think non- engine derived high pressure gas may still be required from time to time. For example, doesn’t the Raptor still need something to spin up the turbos during startup?
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Offline envy887

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any ideas on helium tanks? will they use COPV? or could a smaller SS tank fit inside these? wasnt there something like that on one of the original diagrams?
They don't need helium. Autogenous pressurization of the tanks by vaporizing LOX/Methane.
True that it may, I’m not sure it’s 100% correct to say they won’t need helium. I think non- engine derived high pressure gas may still be required from time to time. For example, doesn’t the Raptor still need something to spin up the turbos during startup?

They will probably have high pressure GOX and methane on hand, stored for the pressure-fed RCS. But they might also use helium to press the tanks while connected to ground support.

Offline matthewkantar

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Where they're going they won't have helium.

Matthew

Offline envy887

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Where they're going they won't have helium.

Matthew

They also won't have subcooled props, or an atmosphere that is going to crush the tanks when the autogenous pressurant gases condense into them. There are some advantages to pressing with helium on the pad that don't really apply anywhere else.
« Last Edit: 01/23/2019 02:05 am by envy887 »

Offline MickQ

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Is it possible that the leg support triangle is removed when the top dome is welded in ?
Would the dome be strong enough ?

Offline mwood

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Is it possible that the leg support triangle is removed when the top dome is welded in ?
Would the dome be strong enough ?

No need to remove. The dome can be put on top and the triangle remain inside the tank for support.

Offline Nomadd

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Is it possible that the leg support triangle is removed when the top dome is welded in ?
Would the dome be strong enough ?

Good question. But since that triangle will take most of the load from the legs hitting the ground on landing and the up to 600 ton static load when fueled, I'd bet they'll stay.
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Offline Elmar Moelzer

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True that it may, I’m not sure it’s 100% correct to say they won’t need helium. I think non- engine derived high pressure gas may still be required from time to time. For example, doesn’t the Raptor still need something to spin up the turbos during startup?
Musk himself has stated before that they do not want to use helium. They plan to use autogenous pressurization because Musk severely dislikes helium for pressurization. Given the problems they have had with helium tanks, I can't blame him.

Offline Robotbeat

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Mars is the main reason they cannot use helium.
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Online meekGee

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Mars is the main reason they cannot use helium.
IIUC, SH won't use Helium either, and it's not going to Mars.

I think Musk doesn't like expendable stuff. He is scarce, SH is large, and SH will fly very often.

I think He is out no matter how you look at it.
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Offline livingjw

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True that it may, I’m not sure it’s 100% correct to say they won’t need helium. I think non- engine derived high pressure gas may still be required from time to time. For example, doesn’t the Raptor still need something to spin up the turbos during startup?
Musk himself has stated before that they do not want to use helium. They plan to use autogenous pressurization because Musk severely dislikes helium for pressurization. Given the problems they have had with helium tanks, I can't blame him.

You can get as much high pressure OX or CH4 as you want by pumping LOX or LCH4 into high pressure tanks and raising the temperature until desired pressure is reached.

John

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