Author Topic: Developing the BFS - Phase 1 Big Falcon Hopper (BFH) Discussion - THREAD 2  (Read 487306 times)

Offline Chris Bergin

Thread 2 on what has become one of the biggest areas of interest over the last month or so (at time of writing).

Resources:

Discussion Thread 1:
https://forum.nasaspaceflight.com/index.php?topic=47022.0

UPDATES ONLY Thread:
https://forum.nasaspaceflight.com/index.php?topic=47120.0

L2 SpaceX Boca Chica Photos/Videos Update Thread (now a new standalone thread out of L2 SpaceX Pads and Facilities due to the surge in content):
https://forum.nasaspaceflight.com/index.php?topic=47107.0

---

Please remember, these threads run at 17,500 mph. A lot of people tend to have them on "notification" (an e-mail arrives with a new post). You can imagine how much they shout at the mods when that new post link sends them to "HA! It's SOOO shiny" ;) So aim to make your post useful/adding to the conversation.

Moderation here is never personal, it's just the foundation of the forum (we started it in 2005 at which point SDC - the main space forum of the time - was dying due to threads turning into food fights and moderators giving up in frustration). We'll annoy a few "I just want to chat!" types, but it's always got to be quality over quantity, especially during this era of the internet. I always said I'd never allow NSF's forum to turn into the dark days of SDC.

I'll shut up now and start the thread ;D
« Last Edit: 01/05/2019 01:17 pm by Chris Bergin »
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Offline Johnnyhinbos

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Thanks for the new thread layout Chris!


And poor choice of words on my behalf when I asked for a comparison between the BFH and the Crew Dragon "stack". What I meant was the Dragon 2 mated to its trunk, as shown here. I think this would give a nice human scale reference between what essentially is the future of SpaceX crewed spaceships - kinda a Generation 1 (Dragon 2) and Generation 2 (BFS/Starship) side by side.


I just don't have the photo chops to do it justice myself...


John
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Offline cuddihy

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Seen several comments along the lines of “SpaceX giving up on composites for BFS.” My bet is no, they haven’t.
Although structure and fuel tanks will be stainless, it’s possible the “people tank” will still be CF structure. If they develop a CF all-contained module for passengers, it likely would be significantly lighter and cheaper than all that structure out of metal, just as it was for the interstage on F9. A CF “passenger module” or “payload module” could be inserted into appropriate space, whether at the top or as many are speculating based on BFH so far just above the engine bay, as needed for a crew, cargo, or tanker BFS (with only bigger tanks instead).

Offline meekGee

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Nobody knows what the holes are for, but I'll suggest that if they are for RCS, then they are not "too low" in the body, since the bottom section is so much heavier.  If you were to multiply each linear vertical foot by the mass contained in it, the rocket will warp...  The bottom section will take a good 80-90% of the rocket, and the entire shiny section would be just a small nose cone... 
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Offline envy887

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Seen several comments along the lines of “SpaceX giving up on composites for BFS.” My bet is no, they haven’t.
Although structure and fuel tanks will be stainless, it’s possible the “people tank” will still be CF structure. If they develop a CF all-contained module for passengers, it likely would be significantly lighter and cheaper than all that structure out of metal, just as it was for the interstage on F9. A CF “passenger module” or “payload module” could be inserted into appropriate space, whether at the top or as many are speculating based on BFH so far just above the engine bay, as needed for a crew, cargo, or tanker BFS (with only bigger tanks instead).

The pax compartment will be constantly pressurized, for obvious reasons. The F9 interstage is not pressurized, so I don't think comparing those structurally will tell us much.

Offline Johnnyhinbos

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Looks like it's about to get placed on the can!

50_Caliber, just wanted to remind you and others that when commenting on a post in an Update thread you should make sure to do it in the Discussion thread - NOT in the update thread. It's the only way we can preserve the update thread for, er, updates (and in this case photos that are in fact updates).

Otherwise you are breaking the hearts of literally thousands.

This post serves as an example.
« Last Edit: 01/05/2019 02:48 pm by Johnnyhinbos »
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Offline Johnnyhinbos

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I think this counts as an update, as it's sent from Elon and is therefore more validation (though we don't need any more) this what is being built in Boca Chica is indeed a flight article.

https://twitter.com/elonmusk/status/1081573955591258113

(Mods please move to discussion if you deem more proper)
John Hanzl. Author, action / adventure www.johnhanzl.com

Offline NGC 4258

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As seen in photos thread, an official render of the completed BFH.
We can lick gravity, but sometimes the paperwork is overwhelming.

Online kevinof

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First hop in 4-8 weeks and maybe we were correct that it is a compromise bell on the Raptor to suit both sea-level and vacuum.

https://twitter.com/elonmusk/status/1081572521105707009
« Last Edit: 01/05/2019 02:57 pm by kevinof »

Quote from: Elon Musk
Engines currently on Starship hopper are a blend of Raptor development & operational parts. First hopper engine to be fired is almost finished assembly in California. Probably fires next month.
Quote from: Elon Musk
Aiming for 4 weeks, which probably means 8 weeks, due to unforeseen issues

Am I the only one that doesn't know how interpret these tweets together?

How can they expect to do flight tests in a month (or even 2) if the 'first hopper engine to be fired ... probably fires next month'?

Also I still don't understand from Elon's answer if the Raptors already mounted on the hopper are working engines or not.

The only logical explanation I can think of is that they ARE in fact working engines, but SpaceX is waiting to test fire a fourth one in McGregor before flying the hopper.
Is this possible?
« Last Edit: 01/05/2019 03:06 pm by AbuSimbel »
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Offline jpo234

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As seen in photos thread, an official render of the completed BFH.

Can anybody do some Kremlinology what the lack of a SpaceX logo means? Thinking SLS here...

Basically: That's not a SpaceX rocket, that's an American rocket...
« Last Edit: 01/05/2019 03:05 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 Johnnyhinbos

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https://twitter.com/elonmusk/status/1081572521105707009
https://twitter.com/elonmusk/status/1081575156990894082

Am I the only one that doesn't know how interpret these tweets together?

How can they expect to do flight tests in a month (or even 2) if the 'first hopper engine to be fired ... probably fires next month'?

Also I still don't understand from Elon's answer if the Raptors already mounted on the hopper are working engines or not.
My takeaway (and for me it’s clear, but obviously subjective) is he used “engines” not bells, nozzles, or mockups, so those are actual engines mounted in there.

However because they’ve changed materials (SX500 stainless steel for example) and potentially other things on a new iteration that has yet to be fired, they may not be the actual flight engines used for hopping.
John Hanzl. Author, action / adventure www.johnhanzl.com

Offline su27k

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https://twitter.com/elonmusk/status/1081572521105707009
https://twitter.com/elonmusk/status/1081575156990894082

Am I the only one that doesn't know how interpret these tweets together?

How can they expect to do flight tests in a month (or even 2) if the 'first hopper engine to be fired ... probably fires next month'?

Also I still don't understand from Elon's answer if the Raptors already mounted on the hopper are working engines or not.

Yeah, this is a bit confusing. A direct interpretation is:
1. The current engines consists of real engine parts from dev Raptor(s), but they only serve as placeholder, they don't intend to use them.
2. The engine they intend to fly hopper with is still being assembled, they'll tested fire it and then install it on hopper (or maybe install it first then test fire?). Anyway this sounds like the engine is the critical path for the first flight. Also notice he used singular form for engine, so initial hop may use one engine.

https://twitter.com/elonmusk/status/1081572521105707009
https://twitter.com/elonmusk/status/1081575156990894082

Am I the only one that doesn't know how interpret these tweets together?

How can they expect to do flight tests in a month (or even 2) if the 'first hopper engine to be fired ... probably fires next month'?

Also I still don't understand from Elon's answer if the Raptors already mounted on the hopper are working engines or not.
My takeaway (and for me it’s clear, but obviously subjective) is he used “engines” not bells, nozzles, or mockups, so those are actual engines mounted in there.

However because they’ve changed materials (SX500 stainless steel for example) and potentially other things on a new iteration that has yet to be fired, they may not be the actual flight engines used for hopping.

So if they want to fly the hopper in 1-2 months is it possible they intend to forgo acceptance testing of the engines on a test stand?

Edit: or maybe they're going to use just a single engine at first as su27k suggested...
« Last Edit: 01/05/2019 03:12 pm by AbuSimbel »
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Offline MikeAtkinson

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It would make sense if Elon mis-tweeted and meant to say:

"Engines currently on Starship hopper are a blend of Raptor development & operational parts. First hopper
 Starship orbital engine to be fired is almost finished assembly in California. Probably fires next month."

Offline Johnnyhinbos

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https://twitter.com/elonmusk/status/1081572521105707009
https://twitter.com/elonmusk/status/1081575156990894082

Am I the only one that doesn't know how interpret these tweets together?

How can they expect to do flight tests in a month (or even 2) if the 'first hopper engine to be fired ... probably fires next month'?

Also I still don't understand from Elon's answer if the Raptors already mounted on the hopper are working engines or not.
My takeaway (and for me it’s clear, but obviously subjective) is he used “engines” not bells, nozzles, or mockups, so those are actual engines mounted in there.

However because they’ve changed materials (SX500 stainless steel for example) and potentially other things on a new iteration that has yet to be fired, they may not be the actual flight engines used for hopping.

So if they want to fly the hopper in 1-2 months is it possible they intend to forgo acceptance testing of the engines on a test stand?
Elon mentioned test firing next month, so gives four weeks after potential initial test fire to qualify and install in the BFH and still make the 8 week window. Conversely could do initial hop tests using installed engines as I would guess the plumbing connections etc would mostly stay the same.
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Offline jpo234

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So if they want to fly the hopper in 1-2 months is it possible they intend to forgo acceptance testing of the engines on a test stand?

Edit: or maybe they're going to use just a single engine at first as su27k suggested...

It's just 450 miles from McGregor to Boca Chica. I can't imagine that they would risk their hopper just to save a few days.
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 Lar

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The tyranny of Twitter is that no answer is ever as nuanced and detailed as one might wish it to be.

My guess is that these engines are placeholders.. all the connection points for plumbing, mounting, wiring, etc are correct, and their shape is correct, but they aren't intended to be functional since they are a "blend of development and operational parts". By having correct shape and correct interfaces a lot can be ensured to be correct. Engineering drawings don't always let you find every interference. Even if they are from solid models although that helps a lot.
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Offline OxCartMark

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Replying to something from thread 1:
Quote
Do you think that for the production Starship they will return to FSW? Supposedly it delivers welds on stainless with better high temperature properties than more prosaic welding techniques.

No, for FSW you need to use a much harder tougher metal as the stirring tool, and as hard and tough as Stainless steel becomes when cold-worked there really aren't any viable materials.

If you want to go that route then ultrasonic welding (rubbing metal on metal at ~10-20kHz ~0.001mm oscillation) is the way to go.  Doesn't ruin the strength of the cold-worked (tough and hard) stainless being welded like MIG or TIG or laser welding does.

No, tungsten carbide is many times harder than stainless steel and is a common FSW tool material.  It'll FSW stainless just fine.  And toughness of the tool material is of little relevance.  I think where the difficulty comes in in FSWing this would be that stainless requires higher forces and because of the scale BFR very long structural members in the FSW apparatus (arms, gantries etc, however they would choose to do it) woud be needed to reach the areas being welded so a very large beefy machine would be needed.  But dooable it seems if that's the chosen path.

Edit/Lar; Edited in the quoted post as it's easier to read than the screenshot.
« Last Edit: 01/05/2019 03:37 pm by Lar »
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Offline ajmarco

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https://twitter.com/elonmusk/status/1081572521105707009
https://twitter.com/elonmusk/status/1081575156990894082

Am I the only one that doesn't know how interpret these tweets together?

How can they expect to do flight tests in a month (or even 2) if the 'first hopper engine to be fired ... probably fires next month'?

Also I still don't understand from Elon's answer if the Raptors already mounted on the hopper are working engines or not.

Just another interpretation of Elon's comment is that he mentions hopper tests in 4 weeks but nothing about using the engines for that test. So both could be true.

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