Author Topic: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)  (Read 41879 times)

Offline speedevil

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #40 on: 07/06/2018 11:23 PM »
I forgot a detail (I told you it was crude thing) With 1.5 km/s left, standing on the Moon surface the BFS... won't go anywhere. Indeed in order to escape the Moon, it's 2.5 km/s. Past Moon escape, aerobraking can do the job. <snip>
I remember Steve Pietrobon did excellent calculations that showed the system might be even better with some refueling in LLO. Which makes sense.

In this threadwas discussed LLO refuelling - in short - refuelling in LEO, followed by topping off in EEO, and transferring fuel to a tanker in LLO gets you around 100 tons landed on the moon, for 7ish launches of BFR.

Offline woods170

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #41 on: 07/07/2018 04:06 PM »
Uh, I don't think there will be real windows.  Too heavy and a safety risk. 

I guess you've never heard of transparent aluminium?

And no, I don't mean the stuff Scotty mentioned on Star Trek IV.

See here: https://en.wikipedia.org/wiki/Aluminium_oxynitride
And here: https://hackaday.com/2018/04/03/whats-the-deal-with-transparent-aluminum/

Actual windows on BFS, made from Aluminium_oxynitride, could very well work and would be lighter than windows made from fused silica (aka glass).
'Transparent Aluminium' has been available for close to 4 decades, and has failed to be used in any big windows for spacecraft (e.g. the ISS' Cupola). Unlike it's sci-fi namesake, it does not behave like bulk Aluminium (or Al alloys) when formed into large sheets, being a ceramic after all. Great for small non-loadbearing bulletproof windows, not so great for huge load bearing windows.

The same problem applies in a large extent to glass. However, space windows made from glass are actually a lot cheaper to produce than space windows made from transparent aluminium. That's the real reason why you don't see aluminium-oxynitride windows on the ISS.

Online Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #42 on: 07/07/2018 04:56 PM »
“Transparent aluminum” is nice and all, but if you’re really worried about micrometeorite impacts (etc), then at least one of your layers should be polycarbonate.



This blend used on motorcycle windshields is particularly effective. Even if hit with a large, gram-sized meteorite, it’ll just punch a small hole (which has a low leakrate which can be fixed at the crew’s leisure, say half a cubic meter per minute, giving them about half a day until oxygen levels get dangerously low), it won’t shatter.

Astronaut helmets are usually made from polycarbonate.

I honestly don’t think having a huge window like that is a big risk if you make it out of toughened polycarbonate on the inner layer (outer layers need to be heat resistant or will need covers during reentry, or both). Ability to put a metal cover on the inside or outside if one of the outer window layers is compromised during transit would address most of the rest of the risk.
« Last Edit: 07/07/2018 05:06 PM by Robotbeat »
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #43 on: 07/07/2018 05:00 PM »
Also, polycarbonate is fairly strong and is better for radiation shielding per unit mass than glass or “transparent aluminum.”
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline jpo234

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #44 on: 07/07/2018 07:35 PM »
https://twitter.com/VoltzCoreAudio/status/1015645483816050690
Quote
Hey @elonmusk, I had a thought cross my mind about BFR. Will it be able to launch & land in most or all weather conditions similar to how the Soyuz can launch in a blizzard? Seems like an important ability for an on schedule E2E transport and orbital refueling missions.

https://twitter.com/elonmusk/status/1015648140341403648
Quote
Yes. All-weather. ~300km/h high altitude winds. ~60km/h ground winds. It’s a beast.

https://twitter.com/VoltzCoreAudio/status/1015649406802989056
Quote
Woah that’s seriously impressive! Do those stats also apply to the BFS during landing?

https://twitter.com/elonmusk/status/1015654917782978560
Quote
Ground winds would
« Last Edit: 07/07/2018 07:39 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 speedevil

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #45 on: 07/07/2018 08:02 PM »
Quote from:
Yes. All-weather. ~300km/h high altitude winds. ~60km/h ground winds. It’s a beast.
From this thread.
Quote from: speedevil
]For 60MPH winds, 30m/s, area of 58*9m, neglect that it's somewhat aerodynamic for safety margin, and you end up with 50 ton or so forces that need to be counteracted on landing - 25 tons per RCS cluster.[/url]

So, each RCS cluster must be able to do somewhere on the order of 10 tons 'outward'  if it's going to land vertically.

Impressive landing performance, and at least 1/15th G or so per axis in orbit, with a full refuelled stack and payload.
'sporty'.

Offline jpo234

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #46 on: 07/09/2018 12:13 PM »
https://twitter.com/elonmusk/status/1015648140341403648
Quote
Yes. All-weather. ~300km/h high altitude winds. ~60km/h ground winds. It’s a beast.

I just looked. According to Wikipedia, the Launch commit criteria for F9 are ground winds up to 56 km/h. For Atlas V the ground winds can be up to 61 km/h.

So BFR would be less of a beast than Atlas V?
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 Hominans Kosmos

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #47 on: 07/09/2018 01:00 PM »
https://twitter.com/elonmusk/status/1015648140341403648
Quote
Yes. All-weather. ~300km/h high altitude winds. ~60km/h ground winds. It’s a beast.

I just looked. According to Wikipedia, the Launch commit criteria for F9 are ground winds up to 56 km/h. For Atlas V the ground winds can be up to 61 km/h.

So BFR would be less of a beast than Atlas V?

Not unless it also has equivalent higher altitude wind tolerance, what's the landing wind constraint on Atlas or F9? I know it's landed in pretty stormy seas before, but has the wind been so high?

Offline speedevil

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #48 on: 07/09/2018 02:28 PM »
Not unless it also has equivalent higher altitude wind tolerance, what's the landing wind constraint on Atlas or F9? I know it's landed in pretty stormy seas before, but has the wind been so high?
If you are considering launching and know you are going to be landing in a stormy area, if you take 'only' 2/3 of your nominal payload, that gives you 800m/s or so of delta-v spare.

You can use this spending an extra couple of minutes landing, or do much more of the landing at half the speed to reduce stresses.

Offline Lar

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #49 on: 07/10/2018 05:29 AM »
... what's the landing wind constraint on Atlas or F9? I know it's landed in pretty stormy seas before, but has the wind been so high?

I don't think the Atlas has any landing wind constraints (since it doesn't land) but I might be wrong...
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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline marsbase

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #50 on: 07/10/2018 07:04 AM »
I don't think the Atlas has any landing wind constraints (since it doesn't land) but I might be wrong...
Yes, how quickly we have become accustomed to the expectation of re-usability. It just makes sense.

Offline Hominans Kosmos

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #51 on: 07/10/2018 09:25 AM »
I don't think the Atlas has any landing wind constraints (since it doesn't land) but I might be wrong...
Yes, how quickly we have become accustomed to the expectation of re-usability. It just makes sense.

You've taken my sarcasm far too seriously, perhaps. It is known the Atlas does not land, but it's also why it having looser launch ground wind constraints is irrelevant in isolation.

Offline ZachF

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #52 on: 07/11/2018 06:23 PM »
Quick little comparo I did of the BFR and other rockets.

The shading of the tanks corresponds to the density of the fuels. I think this is a good way to compare the insides of a rocket and get a "feel" for it's mass.
« Last Edit: 07/11/2018 06:35 PM by ZachF »

Offline biosehnsucht

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #53 on: 07/11/2018 09:49 PM »
Cool comparison, but ... Shouldn't the little empty "triangles" next to the BFS header tanks be filled in with Methane, and not empty?

Offline Hominans Kosmos

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #54 on: 07/12/2018 05:07 AM »
Additionally it appears the sub-tanks on Spaceship extend a bit too far down, if you look at page 12. The main methane tank also is missing it's additional bottom lobe, a dome below the main dome, as seen on pages 12, 14, 15. Makes the thrust structures for mid-engines much shorter while increasing propellant volume
« Last Edit: 07/12/2018 05:09 AM by Hominans Kosmos »

Offline johnfwhitesell

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #55 on: 07/12/2018 01:26 PM »
I think page 12 has a bad angle to look at that part of the layout.  14 makes me think it's like ZachF drew it.

Offline ZachF

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #56 on: 07/12/2018 02:13 PM »
Cool comparison, but ... Shouldn't the little empty "triangles" next to the BFS header tanks be filled in with Methane, and not empty?

That doesn't appear to be the case in this rendering:


Additionally it appears the sub-tanks on Spaceship extend a bit too far down, if you look at page 12. The main methane tank also is missing it's additional bottom lobe, a dome below the main dome, as seen on pages 12, 14, 15. Makes the thrust structures for mid-engines much shorter while increasing propellant volume

These are quick little low-fidelity doodles, if you try to get too detailed on drawings like these it can have the opposite effect and get messy.

I debated even showing the landing tanks at all, because Elon himself said (during the IAC2017 speech) he didn't like the current design and it was probably subject to change. The tank design for the first stage is a complete guess on my part based somewhat on the original ITS S1 design. Therefore, neither the first stage nor second stage landing tank architecture in my picture will likely resemble what the official BFR layout will be, because the real/final layout is essentially unknown. I perhaps should have included this disclaimer in my original post but didn't.
« Last Edit: 07/12/2018 02:15 PM by ZachF »

Offline gideonlow

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #57 on: 07/12/2018 03:04 PM »
Cool comparison, but ... Shouldn't the little empty "triangles" next to the BFS header tanks be filled in with Methane, and not empty?

That doesn't appear to be the case in this rendering:


It's a minor but valid point: Given that the inner/landing tanks are submerged in the outer/main tank, it's safe to assume that the apparent gaps in the 2-D diagram are indeed part of the propellant volume. 

Offline rakaydos

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #58 on: 07/12/2018 03:45 PM »
Cool comparison, but ... Shouldn't the little empty "triangles" next to the BFS header tanks be filled in with Methane, and not empty?

That doesn't appear to be the case in this rendering:
I'm pretty sure you are confusing the fuel pipes for the upper tanks going around the landing tanks on two sides, for a solid shell that's been cut away.

Offline woods170

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 4 (Post Speech)
« Reply #59 on: 07/13/2018 06:36 AM »
Cool comparison, but ... Shouldn't the little empty "triangles" next to the BFS header tanks be filled in with Methane, and not empty?

That doesn't appear to be the case in this rendering:
I'm pretty sure you are confusing the fuel pipes for the upper tanks going around the landing tanks on two sides, for a solid shell that's been cut away.
This.

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