Author Topic: Elon has changed BFR design again - what does this mean  (Read 151339 times)

Offline Slarty1080

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Re: Elon has changed BFR design again - what does this mean
« Reply #1000 on: 12/06/2018 07:03 PM »
Here's what I don't get.  You can make a thin walled stainless tank as long as it's shape is maintained by high internal pressure, at least when you need good structural strength.  And that pressure would be like what, 4 atm?  Which is great in the tanks but not so good for the large portion of the ship that houses people.  Could you get away with balloon walls and low pressure if you had ring bulkheads (floors) every 2-1/2 M or so?  Hmmm, just thinking.
I believe that the liquid oxygen tank that SpaceX tested to destruction ruptured at 2.2atm and designed max pressure was 2atm. Also the habitation module would contain a large number of decks with the possibility of running cross supports to hold up the floor and brace the walls. That said I suspect 1atm would be quite sufficient anyway.
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Offline edzieba

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Re: Elon has changed BFR design again - what does this mean
« Reply #1001 on: 12/06/2018 08:16 PM »
Tank walls can get toasty and then dump heat to the cryogens inside. Hab module walls cook the occupants if they get toasty, so TPS would be needed. If you need to apply TPS, may as well make the hab section out of something self-supporting anyway and 'sit' it on top of the tanks.

Offline barnter

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Re: Elon has changed BFR design again - what does this mean
« Reply #1002 on: 12/06/2018 10:00 PM »
My guess is 360 covering of pica and rotate during re-entry.


CRS-16: Love the partial test.

Offline niwax

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Re: Elon has changed BFR design again - what does this mean
« Reply #1003 on: 12/09/2018 12:16 AM »
ALARM ALARM ALARM

https://twitter.com/elonmusk/status/1071572534921900033

Metal Starship confirmed
Which booster has the most soot? SpaceX booster launch history!

Offline Draggendrop

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Offline jpo234

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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 KelvinZero

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Re: Elon has changed BFR design again - what does this mean
« Reply #1007 on: 12/09/2018 01:03 AM »
Let me end any heavy metal puns with this:..
(edit: argh. too late :) )


Offline Lemurion

Going to a heavy metal is definitely counter-intuitive.

The only thing I can think of is that even though it probably lacks the strength to weight ratio of carbon fiber the shift to metal construction must let them cut enough weight elsewhere to make it worth the switch.

Offline barnter

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Re: Elon has changed BFR design again - what does this mean
« Reply #1009 on: 12/09/2018 01:11 AM »
Hotblack Desiato approves!


Online docmordrid

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Re: Elon has changed BFR design again - what does this mean
« Reply #1010 on: 12/09/2018 01:17 AM »
About a week ago Musk liked this PhysOrg article about high entropy alloys

Link...
« Last Edit: 12/09/2018 01:19 AM by docmordrid »
DM

Offline speedevil

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Re: Elon has changed BFR design again - what does this mean
« Reply #1011 on: 12/09/2018 01:45 AM »
Going to a heavy metal is definitely counter-intuitive.

The only thing I can think of is that even though it probably lacks the strength to weight ratio of carbon fiber the shift to metal construction must let them cut enough weight elsewhere to make it worth the switch.

Maybe the 'question' got reframed to 'what can we get flying in 2019'.
I've noted in the past that doubling BFS2017 structural mass so you have 80 tons ish of payload has little effect to the practicality of Mars. Or, indeed, of any near-term payload.

Online meekGee

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Re: Elon has changed BFR design again - what does this mean
« Reply #1012 on: 12/09/2018 01:47 AM »
Rockets are meant to be shiny :)

I am very happy with this.  Was never at ease with composites, since the environment and mission durations are so unprecedented.

Metal structures are a much better known quantity.

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Offline Rocket Science

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Re: Elon has changed BFR design again - what does this mean
« Reply #1013 on: 12/09/2018 01:49 AM »
Going to a heavy metal is definitely counter-intuitive.

The only thing I can think of is that even though it probably lacks the strength to weight ratio of carbon fiber the shift to metal construction must let them cut enough weight elsewhere to make it worth the switch.
Carbon fiber likes to go up in flames, unless it's carbon-carbon...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline KelvinZero

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Re: Elon has changed BFR design again - what does this mean
« Reply #1014 on: 12/09/2018 01:57 AM »
Anyone care to hazard a guess whether the First stage will still be carbon?

I always liked the way the upper and lower stages looked like they could share a lot of commonality.. but how true was that? wouldn't the plumbing for 31 raptor require wider pipes making almost nothing exactly the same? Would the tanks need to be heavier too? What commonality actually is possible?

Offline GalacticIntruder

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Re: Elon has changed BFR design again - what does this mean
« Reply #1015 on: 12/09/2018 02:26 AM »
Sea Dragon. 8mm thick steel sheeting. Sea Launch. Cheap and known. It makes sense. They could go back to 12m diameter to throw over 150mT+. Won't be 550mT though like ITS or Sea Dragon.
« Last Edit: 12/09/2018 02:29 AM by GalacticIntruder »
Watch out for those pesky corners, they have teeth.

Offline Ludus

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Re: Elon has changed BFR design again - what does this mean
« Reply #1016 on: 12/09/2018 02:31 AM »
So like dropping the Vacuum Raptors, payload to orbit takes a hit from heavy metal, but it was still more than they needed for near term purposes anyway. If it lets them do it faster and cheaper itís good. They get v1 operating and have an upgrade path laid out, sort of the last few years of changes in reverse. More carbon fiber, vacuum raptors, bigger, more raptors. 450 tons to NEO or Mars.

Offline Draggendrop

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Online meekGee

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Re: Elon has changed BFR design again - what does this mean
« Reply #1018 on: 12/09/2018 03:55 AM »
So I'm wondering if the switch to stainless is enabled by the switch to skydiver reentry..


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Offline speedevil

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Re: Elon has changed BFR design again - what does this mean
« Reply #1019 on: 12/09/2018 04:05 AM »
Sea Dragon. 8mm thick steel sheeting. Sea Launch. Cheap and known. It makes sense. They could go back to 12m diameter to throw over 150mT+. Won't be 550mT though like ITS or Sea Dragon.
Booster has changed to a refitted OCISLY with 80 raptors.
This launches up to four F9s to 2km/s, and gets around 200 tons to LEO.
F9S1s are caught in the normal manner up to four at a time with JRTI, suborbital.
Total cost of propellant for the barges, $2M or so per launch,

(I note that this is a joke*)
* This week.

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