Author Topic: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)  (Read 23235 times)

Online Chris Bergin

Third discussion thread for Elon's second BFR overview at the IAC. Yes, we are looking at a new section for all BFR, per it not being just about Mars.

Open discussion, but everyone has to be civil and posts need to be useful. No "You're concern trolling". No "Wowzers. LOLZ. Cool" <---true, but that doesn't add to anything. No posts with masses of smilies, or it just looks silly, especially when quoted several times.

Most of you know we're going for quality over quantity here, best we can. Bad posts will be removed. Don't quote bad posts (or your post will be removed too, obviously). Report to mod if you see a bad post (against the above rules) - some of you didn't take note of this on thread two and those posts were removed (you were warned!)


New Articles (more to follow) :

 [September 29, 2017] The Moon, Mars, & around the Earth - Musk updates BFR architecture, plan

 [October 4, 2017] Sputnik at 60: Ambition ties first satellite to SpaceX’s BFR, Mars plans

 Previous major discussion thread:
  IAC 2017 -- ITS (BFR) v0.2 Pre and During Speech

 Live Thread from the event:
  IAC 2017 --Elon Speech

Full video:



Additional NSF Articles Of High Relevance:

 [March. 7, 2014] SpaceX advances drive for Mars rocket via Raptor power
 [Aug. 29, 2014] Battle of the Heavyweight Rockets – SLS could face Exploration Class rival
 [Sept. 27, 2016]SpaceX reveals ITS Mars game changer via colonization plan
 [Jul. 24, 2017] Includes Subscale BFR on 39A

 Major NSF L2 Resources:

 L2 Level: Evaluations And Renderings - Thread 2 (Includes link to Thread 1)
 ITS Cargo Modules AIAA - by the Author
 Rocket and Spacecraft Traj Sim
 The Evolution of the Interplanetary Transport System Overview
 SpaceX McGregor, includes Raptor Testing and photos
 Master All SpaceX Pads Updates, Photos and Status, including for BFR


NSF Public Threads:
 
   Discussion before and during the 2017 presentation:

      IAC 2017 -- ITS v0.2
      9m ITS Development Updates and Discussion Thread

   
   Discussion after the 2016 presentation:
 
      ITS Propulsion – The evolution of the SpaceX Raptor engine
      ITS Development Updates and Discussion Thread

9m ITS Development Updates and Discussion Thread 2

Elon's presentation at IAC 2016:



SpaceX: ITS Video from 2016:



Offline jpo234

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1 on: 10/06/2017 09:48 AM »
It's interesting how close Richard Heidmann came in his analysis:
http://planete-mars.com/mars-colonization-transport-main-findings-of-our-analysis/

BFR really looks almost exactly like he imagined (except for the horizontal landing.

« Last Edit: 10/06/2017 09:49 AM by jpo234 »
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Online Lar

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #2 on: 10/06/2017 03:27 PM »
Great first post to start tne new thread. But I'm not ready to give as much credit as you, the general outline was already known at the time of this study and the OML is going to be basically bullet shaped.... Also the study includes an "emergency capsule" which I think we know is out.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline MikeAtkinson

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #3 on: 10/06/2017 04:05 PM »
It's interesting how close Richard Heidmann came in his analysis:
http://planete-mars.com/mars-colonization-transport-main-findings-of-our-analysis/

Of the 13 points in his analysis, it looks like he got 9 (perhaps 10) wrong.

Offline oldAtlas_Eguy

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #4 on: 10/06/2017 04:10 PM »
Great first post to start tne new thread. But I'm not ready to give as much credit as you, the general outline was already known at the time of this study and the OML is going to be basically bullet shaped.... Also the study includes an "emergency capsule" which I think we know is out.
The mentality for where the "emergency capsule" comes from is the idea that this is still an experimental vehicle with very high risks. Musk wants this vehicle to be like an airline not a combat aircraft.

Redundancies, both similar systems and use of dissimilar systems. The only problems for risk are the main engines of the SC and the prop tanks. LOX is an inherently dangerous liquid. To get the risks of a composite LOX tank down to that of an airliner will take a lot of testing both on the ground in destructive tests and many flight tests to get statistical data on behavior in the actual flight regimes to them correct deficiencies in the tank design.

Engines like for F9 would be isolated by ballistic barriers as well as protection of piping and tanks, which allows for a RUD of any specific engine to not cause a LOM or a LOC event. But since the engine redundancy does not use dissimilar redundancy but similar redundancy it like the tanks must be tested extensively on the ground and in flight looking for those design "errors" and software "bugs" in the engine and engine controllers that keep engine failures from being a design fault to being a somewhat random manufacture or wear fault.

If the reliability of those two systems can be made to be very high then the overall safety of the SC and even the Booster can be made so that large numbers of passengers can ride in relative low risk similar to that of an airliner.

A P2P system that has a significant in-flight emergency of about 2 times per year and a LOC event once every 2 or three years but at flight rates of 4 times a day per launch site with 200 launch sites gives a yearly flight rate of the P2P usage of ~300,000 flights/year and a LOC (crew and passengers) event of 1 in 1,000,000 flights.

The key here is that a highly fully reusable vehicle (1000 gas-n-go) is possible to achieve these reliability numbers but a expendable and a low level partial or even fully reusable vehicle (10 reuses) would not reach the reliability levels needed to be airline like safety levels. The expendable and partial reusable and low reusability fully reusability vehicle does not have the engineering safety margins to get high reliability. These vehicles would still be much like an experimental aircraft with the similar LOC number values requiring some sort of crew escape.

Online edkyle99

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #5 on: 10/06/2017 04:16 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle

Offline envy887

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #6 on: 10/06/2017 04:18 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle
By expending the booster it can get 250 tonnes to LEO.

Offline QuadmasterXLII

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #7 on: 10/06/2017 04:23 PM »
Is anyone else spooked by all this talk of "no need for an escape system, we'll be safe like an airline?" The parallels with the shuttle program seem almost too obvious.

Offline oldAtlas_Eguy

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #8 on: 10/06/2017 04:32 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle
By expending the booster it can get 250 tonnes to LEO.
It puts the fully reusable payload to EXPD (expendable) payload at the 60% value. Something we have known for quite awhile for efficient fully reusable designs vs a same size vehicle expendable design as the best case possibility for a fully reusable vehicle vs that same vehicle used as an expendable.

In general not something from this graph, as the vehicle gets smaller this factor gets worse. For F9 it has been hypothesized that this value between a fully reusable F9 and a EXPD F9 would be 40%. So on a 22mt EXPD payload to LEO you would get only a max of 8mt of payload with a fully reusable F9 without any margins (margins here are mainly for engine out which reduces significantly the payload). With margins the payload could be as low as 30% that of EXPD F9.

Offline Lars-J

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #9 on: 10/06/2017 05:01 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle

Looks like expendable payload numbers to a low earth orbit. (It matches the known 22t to LEO for expendable F9)

An interesting comparison, but not that meaningful since the plan is to always reuse.

Online edkyle99

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #10 on: 10/06/2017 05:03 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle
By expending the booster it can get 250 tonnes to LEO.
Booster and "Ship" both expended versus Booster and "Ship" both recovered?

 - Ed Kyle

Offline Lars-J

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #11 on: 10/06/2017 05:04 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle
By expending the booster it can get 250 tonnes to LEO.
Booster and "Ship" both expended versus Booster and "Ship" both recovered?

 - Ed Kyle

Expending both is my assumption, otherwise the comparison to expendable F9/FH makes less sense.
« Last Edit: 10/06/2017 05:04 PM by Lars-J »

Offline Kaputnik

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #12 on: 10/06/2017 05:09 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle
By expending the booster it can get 250 tonnes to LEO.
Booster and "Ship" both expended versus Booster and "Ship" both recovered?

 - Ed Kyle

Expending both is my assumption, otherwise the comparison to expendable F9/FH makes less sense.

Although in practise you could presumably refuel the ship in orbit and bring it back anyway.
Waiting for joy and raptor

Offline su27k

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #13 on: 10/06/2017 05:12 PM »
Is anyone else spooked by all this talk of "no need for an escape system, we'll be safe like an airline?" The parallels with the shuttle program seem almost too obvious.

Yes, but fortunately they don't need to fly people on BFR for quite a while yet, a dedicated cargo version and automated landing helps a lot.

Online AncientU

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #14 on: 10/06/2017 05:13 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle
By expending the booster it can get 250 tonnes to LEO.
Booster and "Ship" both expended versus Booster and "Ship" both recovered?

 - Ed Kyle

Expending both is my assumption, otherwise the comparison to expendable F9/FH makes less sense.

I think it is an attempt to allow apples-to-apples comparison with all other (expendable) rockets.  Believe that at SpaceX there is neither an interest in ever expending any stage(s), nor is the BFR architecture at all optimized for throw-away launches... that said, this vehicle is approximately equivalent to a pair of SLS Block II vehicles in IMLEO if one must compare throw-away throw weight.

By the way, this payload corresponds to a payload mass fraction of 5.68% (250/4400t).  Saturn V was 3.88%; Energia was 3.96%; F9 FT is 4.15% IIRC.  (!)
« Last Edit: 10/06/2017 05:23 PM by AncientU »
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Offline oldAtlas_Eguy

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #15 on: 10/06/2017 05:27 PM »
Is anyone else spooked by all this talk of "no need for an escape system, we'll be safe like an airline?" The parallels with the shuttle program seem almost too obvious.

Yes, but fortunately they don't need to fly people on BFR for quite a while yet, a dedicated cargo version and automated landing helps a lot.
A item would be to get the gas-n-go reuse rate to over 50 ideally to 100 or more. This creates a very mature design with a individual unit statistical database on failures and causes of failures. At lower reuse rates (5 to 20) the statistical data is less precise and can be full of assumptions and miss critical items. The other item is total flights of the system in the 100's before significant numbers of persons flying on any one flight. Number of passengers kept artificially low like a dozen for LEO, Lunar, and Mars initial manned flights. To get the high total flights in 100's could take as long as 10 years from the first successful flight of a Cargo/Tanker.

Online John Alan

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #16 on: 10/06/2017 05:29 PM »
Can anyone explain this slide in Elon's presentation?  He skipped over it quickly and didn't discuss its meaning.

 - Ed Kyle
By expending the booster it can get 250 tonnes to LEO.
Booster and "Ship" both expended versus Booster and "Ship" both recovered?

 - Ed Kyle

Expending both is my assumption, otherwise the comparison to expendable F9/FH makes less sense.

I think it is an attempt to allow apples-to-apples comparison with all other (expendable) rockets.  Believe that at SpaceX there is neither an interest in ever expending any stage(s), nor is the BFR architecture at all optimized for throw-away launches... that said, this vehicle is approximately equivalent to a pair of SLS Block II vehicles in IMLEO if one must compare throw-away throw weight.

By the way, this payload corresponds to a payload mass fraction of 5.68% (250/4400t).  Saturn V was 3.88%; Energia was 3.96%; F9 FT is 4.15% IIRC.  (!)
Using the above expendable figures and other 2017 presentation numbers...
Can we possibly deduct the empty weight and tank volume sizes of the Booster?...  ???
« Last Edit: 10/06/2017 05:31 PM by John Alan »

Online AncientU

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #17 on: 10/06/2017 05:45 PM »
Is anyone else spooked by all this talk of "no need for an escape system, we'll be safe like an airline?" The parallels with the shuttle program seem almost too obvious.

The missing factoid is that the BFR/BFS will fly the same vehicle repeatedly to build up not only a statistical data base on the launch system's reliability, but also on that specific flight hardware.  Recall that shuttle flew for 30 years, and the only disasters were associated with the launch system -- not reusable vehicle related. 
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Online edkyle99

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #18 on: 10/06/2017 06:31 PM »
By the way, this payload corresponds to a payload mass fraction of 5.68% (250/4400t).  Saturn V was 3.88%; Energia was 3.96%; F9 FT is 4.15% IIRC.  (!)
I've been trying to rocket-equation this, with little success. 

Here are the "knowns".
GLOW 4400 t
Thrust Liftoff 5400 t, ISP = 330/356 sec
Ship dry mass 85 t
Ship Mp 1100 t
Ship Thrust 775 t (4 engines) ISP 375 sec
Ship Thrust 347 t (2 SL engines) ISP 330/356 sec

These imply a first stage mass = 4400 t - 1185 t = 3215 t
Unknown is first stage propellant mass fraction. 
When I plug the known numbers into the rocket equation, I get a first stage PMF required to be 0.97938 to get 250 tonnes to 9,200 m/s ideal delta-v (LEO).  That's unrealistic because the first stage ends up with 20 tonnes lighter dry mass than the second stage "Ship".  With PMF1 a more "reasonable" 0.96, I get total ideal delta-v = 9061 m/s, not usually good enough for LEO, but it depends on the details of the ascent.  To get 9200 m/s with PMF1 = 0.96, payload maximum is 235 tonnes.

S1:  3215 t > 128.6 t, ISP 347.4 sec, delta-v = 3734 m/s
S2:  1185 t > 85 t, ISP 375 sec, delta-v = 5479 m/s
PL:  235 t, delta-v total = 9217 m/s

When I try to model the reusable alternative, assuming 10% propellant saved for first stage flyback landing and 6% for second stage retro and landing, I get only 105 tonnes of LEO payload, as follows.

S1:  3215 t > 437 t, ISP 347.4 sec, delta-v (ascent) = 3265 m/s
S2:  1185 t > 151 t, ISP 375 sec, delta-v (ascent) = 5446 m/s
PL:  105 t, delta-v total = 9211 m/s

Rough guesses, obviously, but I've yet to match the SpaceX charts.  When I try to model the 20 tonne GTO mass, the numbers don't converge at all.  I get no payload to GTO.

 - Ed Kyle


« Last Edit: 10/06/2017 06:40 PM by edkyle99 »

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #19 on: 10/06/2017 06:48 PM »
Maybe the ship mass includes the mass of the cabins and other crew accommodations that wouldn't be there in the satellite launcher variant?

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