spacex SpaceX's "BFR/BFS/MCT" Thread -- Facts, Conjecture, Math and Hypothesis

[DocM]

Counting the minutes to details of one huge SOB 

 

 

[DocM]

Perhaps Gwynne Shotwell just had a brain fart and misspoke, but OTOH she may have leaked the first syllable of BFR's actual name: 

 

Mock.....

 

Mockingbird?

 

Or, perhaps they're fans of the Hunger Games series....

 

Mockingjay?

 

 

Edited August 13, 2016 by DocM

[Jim K Global Moderator]

nooo...not Mockingjay... that isn't even funny.  

 

Mockingbird is alright.  Being the size of it ... the SpaceX Ostrich would have worked (kidding) or the SpaceX Condor ... or the Gyrfalcon.  hmmmm

 

Well, whatever it is called ... can not wait to see it spread its wings.

[Draggendrop Veteran]

IMHO......September 27th is the Mars presentation, which would mean "all talking points have pretty much been finalized" and will correspond to an unveiling of a "mock-up" model of the architecture.

 

Just a slip up mention of a mock up that she has seen many times and of which will be used as a visual reference with the presentation.

 

 

[DocM]

That interpretation has absolutely zero fun factor (even though you're likely correct)

[Draggendrop Veteran]

I'm sorry..........       ( sulks while walking down the hallway )  

[Joe2mercs]

Some useful information has appeared:

 

a) The spec of the Falcon Heavy has made reference to 22,200 kg to GTO and most recently 8,000KG to GTO from which I assume the former is the expendable figure and the latter is the reusable figure.  This would imply that the amount of fuel required to arrest the horizontal velocity and land the second (middle) stage is considerable since the payload weight penalty, from these figures, suggests it is 64%; somewhat higher than the speculative 50% that I had been assuming.

 

b) Information on the Raptor engine indicates that it is three times the thrust of the Merlin 2D.  If the octaweb design is carried forward then a single core (FalconX) with nine Raptor engines would weigh about 1600 tons; about the same as a Falcon Heavy.  If this is the case then there is some great logic to it (read this to mean that I wish I had seen it earlier!). By establishing a market for payloads to GTO using the Falcon Heavy it would only require a sideways transition for these payloads to be lifted instead by a Falcon X.  This fee generating service would effectively recoup the development costs of the Falcon X and allow SpaceX to gain extensive experience of its use before committing it to a Mars mission.  The BFR would consist of three cores (of the the Falcon X) with a take off weight of 4,800 tons and payload to LEO of 110 tons (reusable mode).  Four launches of the BFR would lift enough material to orbit to enable the assemble a fully fuelled Mars colonial transporter capable of landing 100 tons on Mars' surface.

 

The reveal of Elons plans should be especially interesting and, for me, September cannot come round soon enough!

[BetaguyGZT]

Current projections show it to be a 15m or even possibly an 18m hull, single-core design. All-CH4/LOX engines, (so far) looking like two stages.

 

No announcement has been made or even hinted at about Falcon X or FH-X designs at all. To everyone's knowledge, Space X isn't discussing a full refit to Raptor-based engines to replace the Merlins in the S1. Is such a refit possible? Sure. All of their irons are in the Commercial Satellite, BFR, Falcon Heavy, CRS, Commercial Crew Program and Red Dragon fires right now. SpaceX has turned the corner, finally, on the stuff that's been put into motion when the Company started operations. They're too busy to do much else right now. Give them a couple of years to get some outstanding projects caught up.  

[DocM]

My $0.02

 

1) Raptor

 

Raptor is a family of engines, mostly 3D printed using the Inconel super-alloy and titanium. Known types:

 

a. BFR booster (sea level optimized)

 

b. BFS (vacuum optimised)

 

c. USAF upper stage engine (vacuum optimised) for Falcon 9 and Falcon Heavy, a >$100 million shared funding project just for the prototype. Most likely more for the stage after the engine is qualified

 

The USAF upper stage Raptor is due by Dec. 31, 2018.

 

A Raptor is on the test stand at McGregor, most likely the BFR booster.

 

Thrust levels per engine to be determined. Musk stated 230t for the BFR booster due to thrust/weight optimization, but that was months ago and not necessarily the current trade. 

 

2) BFR

 

Most likely 15 meters in diameter, roughly 50% wider than Saturn V

 

Most likely composite in structure, given SpaceX negotiating a $2-3 billion buy of composites from Toray. 

 

Musk said about 15,000,000 lbf of thrust, roughly 2x Saturn V

 

Given the 230t thrust, 27-30 engines in the booster stage. Maybe less if the per-engine thrust is higher.

 

3) BFS should be at least as wide as the booster, so 15+ meters. IF it's length is about 3-4x it's width this could mean a vehicle length of 45 to 60 meters. 15x45-60 meter spaceship is a flipping Battlestar.

 

4) spitballing the masses (pure guesswork)

 

Many mass optimised rockets have a thrust/weight ratio at liftoff of about 1.3. If we divide this into the 15,000,000 lbf thrust that gives a total stack mass of about 11,538,462 lbs, or about 5,230 tonnes.

 

If we use the 4:1 booster:upper stage mass ratio rule of thumb we get a loaded & gased up BFS mass of about 1,308 tonnes.

 

Subtracting BFS from stack mass, we get a booster mass of about 3,922 tonnes.

 

IF the liftoff mass ratio is lower, say 1.15 or 1.2, then these masses get a lot larger.

[DocM]

"If we use the 4:1 booster:upper stage mass ratio rule of thumb"

 

Meant 3:1, I think. It's late 

[Draggendrop Veteran]

You guys are making this a fun thread.....

 

Proceed.....please.

[Joe2mercs]

Don't get me wrong about the Raptor. I am not saying it will substitute the Merlin engines on the Falcon 9 but that it is the payloads themselves, to be carried on the triple core Falcon Heavy, that will be suitable for a single core Falcon X (which I anticipate be powered by nine Raptors).  The experience of operating and landing triple core Falcon Heavy rockets will provide the basis for operations when the Falcon XX (BFR) as I think it will consist of a triple core Falcon X.  I know that this does not sit well amongst all you 15m diameter core enthusiasts but for me it just seems the most logical progression of design and experience.  The figures I listed on June 8th with regards to rocket mass and diameter might look like trivial guesses but they were each calculated; 4080 tons of methalox fuel can be contained within a 15m diameter X 30m long conjoined tank.  I am now of the opinion now that the diameter of a single Falcon X core will be about 7m only.  The upper stage fairings however, as they are on the current Falcon 9, can be a great deal wider (perhaps 15m or 18m diameter).  With three 7m cores together in a BFR the combined cross sectional are will be greater than that of the Saturn Vs 10m.  Needless to say with each core containing 9 Raptor engines the combined thrust from 27 of them will massively exceed that of the Saturn V.  I have just one more thing to do now and that is to bake a humble pie as, no doubt, Elon will soon be making me eat it :-)

[DocM]

Except that a 3 core BFR was ruled out by Musk during a speech at MIT, and this has been repeated. It'll be an enormous single core with between 9 and 30 Raptor engines depending on how much thrust each Raptor delivers. About 15,000,000 lbf of thrust, per Musk.

 

12.5 meters is the minimum for 30 of the 230t Raptor engines, but 15 meters gives more clearance and keeps the stack around 350-400 feet. Narrower and, to maintain the required propellant volume, the stack stretches to 450-500 feet. That (and 3 cores) makes GSE more complex.

[Joe2mercs]

There is a crazy part of me that wants to see an enormous priapic tumescent phallic BFR, and if Elon pulls it off (by which I mean, of course, he reaches his goal) then I will be cheering loudly.  I still think that canabalizing Falcon Heavy payloads and launching them on a single methalox core would be the logical and economically cautious route towards a reusable heavy lift vehicle, but then again I am not Elon Musk and he has habit of rewriting the rule book on these matters :-)

[DocM]

Interplanetary Transport System....I like it!!

 

 

 

Edited September 18, 2016 by DocM

[Joe2mercs]

  I was right earlier when I said it was likely that our speculations would all be wrong.

42 Raptor engines on a 12m diameter hull of 122m height.  A take off mass of 10,500t (thrust of 13,033t) delivering a payload of 300t (2.8%) to LEO. First stage: 12 x 77m; 6975t of which 275t (3.94%) is dry mass.  

I'm off now to eat my humble pie in the corner :-)