Author Topic: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 1 (Pre-and-During Speech)  (Read 247331 times)

Offline kevinof

  • Full Member
  • ****
  • Posts: 1594
  • Somewhere on the boat
  • Liked: 1869
  • Likes Given: 1262
Interesting to read the responses where - the fans and the doubters. I take what EM says with a pinch (large) of salt.  This stuff is way more complicated than he thinks and delays will happen. Happens in every complicated project - Do I dislike him for giving unrealistic dates - not at all.

What I like is that he's stepping up to do this. Probably won't make 2022 but who cares. At least he's got a vision, a plan and he's going to put his money, his time and his team into it. What's not to like?

And to the doubters here, what's the alternative? Sit on our asses waiting for what? The same stuff over and over again? No thanks.  I'll take Musk's ambition and plan any time and I'll expect delays and changes in the plan - that's all part of pushing the envelope but one thing you can be sure of is that they will get there. There are some very smart people in Space X who now know what it takes to get this stuff done.

Looking forward to it.

Offline DJPledger

  • Full Member
  • ****
  • Posts: 807
  • Liked: 506
  • Likes Given: 33568
Even if you have a very reliable engine the more engines you put on a 1st stage increases the risk that one will explode that may cause LOM. So a 9 engine BFR should be more reliable than a 31 engine one. Hopefully BO is watching SpaceX closely and that they do not make the same mistake as SpaceX with the engine no. on their NA and will dev. an engine with sufficient thrust that NA has the same engine no. as NG or F9.

But you also gain redundancy. Losing one engine out of 31 (without causing a RUD) should be safer than losing one out of 5 (F1 on Saturn V).
Yes I agree with you for benign engine failures but the more engines you have the risk of a catastrophic engine RUD causing LOM increases.

Offline tyrred

  • Full Member
  • ****
  • Posts: 920
  • Seattle
  • Liked: 750
  • Likes Given: 20640
The only reusable booster as of today has an engine count of 9.  This is not definitive proof that this is the optimum number of engines for any given booster.  Methinks a bit of superstition should be discarded.

Offline FinalFrontier

  • Senior Member
  • *****
  • Posts: 4490
  • Space Watcher
  • Liked: 1332
  • Likes Given: 173
I will clarify once again as a final thought here. I am not of the opinion that changing the engines would solve anything. Developing a larger or even an "F-1" class engine would require yet another engine development program and would be vastly more expensive. It would also carry a very high risk of being vastly harder to build if the lessons learned from previous engines of that size, or that approached that size, are any metric at all. The designers of said engines had absolute hell getting the things to work.
That is to say nothing of said engines would behave when exposed to retro flow and retro propulsion regimes that SpaceX would be using for this vehicle.  Raptor works right now, although without inside data it's anyone's guess exactly how well it works. But they have built it and it works. It is based on their existing experience. From a technical and more importantly a financial standpoint this is quite literally the only option especially if you want to see a vehicle anywhere remotely near this timeline. You cannot just swap engines and other pieces of a rocket out this is not legos. The vehicles are designed around the engines and the performance of said engines not the reverse and it HAS to be this way because performance dictates how much propellant you need and how you need to size your tanks. Which by the way, changes the vehicle size, structures, flows, loads, frictional heating, base heating, shock heating, vectors and control, and the aerodynamic chord and so many other things. You cannot just swap out the engine you will have to start over from scratch. Even with Falcon 9, going from Merlin 1-C to Merlin 1-D resulted in almost an entirely new vehicle.

So no, changing the engines is a bad bad idea. With that said however, how a 31 engine cluster on a 9 meter vehicle will perform, particularly with engines that operate at higher pressures than anything ever seen before in the history of liquid rocketry, how that will behave is a big series of questions. And to here and say "oh its still less complex than the a vehicle that is built out of flight proven hardware and engines (FH)" is absolutely ludicrous.
« Last Edit: 09/29/2017 11:05 am by FinalFrontier »
3-30-2017: The start of a great future
"Live Long and Prosper"

Offline toruonu

Point to point travel on Earth for people on BFR will never happen as the system will never be anywhere near as safe as modern airliners. It may happen for ultra fast transit of cargo though. You can't put a price on human lives while lost cargo can be replaced.

I've never understood this fixation that human lives are invaluable. Sh*t happens all the time. Millions die in various accidents related to transportation. What's so different about that here.

In fact, from US Department of Transportation. Here's the value of human life:

$9.6 million (Department of Transportation, Aug. 2016)[17]

Offline mgeagon

  • Full Member
  • *
  • Posts: 157
  • Hong Kong
  • Liked: 255
  • Likes Given: 3
So lets all teach EM on how to design a simple very reliable BFR system.

1. Give Raptor sufficient thrust that only 9 are needed for BFR with subscale version for ship.
2. Reduce Raptor Pc to around 15MPa for greatly increased reliability.
3. Make BFR/ship system slightly larger to offset lower engine performance due to lower Pc.
4. EM needs to be converted to KISS.
5. Needs to get Starlink to work to get the money for large engine dev.

For a reusable booster the optimum engine no. is 7-9 so BO has got it right and so has SpaceX with F9. Hopefully BO with design it's NA with 7 or 9 engines of moderate Pc.

I fully agree with you that a large cluster of high Pc engines has the potential to cause no end of problems.

I am speechless over this comment. You do realize that Elon Musk is the founder and chief engineer of the most successful launch vehicle provider currently in existence? One the Russians and Europeans have been losing market share to for years and whose technology has completely disrupted the entire industry. We "all" will not be educating him, but perhaps you can give your presentation at next year's IAC conference.

Offline DJPledger

  • Full Member
  • ****
  • Posts: 807
  • Liked: 506
  • Likes Given: 33568
Point to point travel on Earth for people on BFR will never happen as the system will never be anywhere near as safe as modern airliners. It may happen for ultra fast transit of cargo though. You can't put a price on human lives while lost cargo can be replaced.

I've never understood this fixation that human lives are invaluable. Sh*t happens all the time. Millions die in various accidents related to transportation. What's so different about that here.

In fact, from US Department of Transportation. Here's the value of human life:

$9.6 million (Department of Transportation, Aug. 2016)[17]

Lets face it. No rocket is ever going to be remotely as safe for transporting people than modern airliners. BFR will be a lot less safe than modern airliners. You know which I would rather fly on.

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 4286
  • Liked: 887
  • Likes Given: 201
Hey can anyone explain the flat, shuttle-like bottom? Slightly uptilting wings like dream chaser seems much more intuitively self-stabilising.

Offline DJPledger

  • Full Member
  • ****
  • Posts: 807
  • Liked: 506
  • Likes Given: 33568
Point to point travel on Earth for people on BFR will never happen as the system will never be anywhere near as safe as modern airliners. It may happen for ultra fast transit of cargo though. You can't put a price on human lives while lost cargo can be replaced.

I've never understood this fixation that human lives are invaluable. Sh*t happens all the time. Millions die in various accidents related to transportation. What's so different about that here.

In fact, from US Department of Transportation. Here's the value of human life:

$9.6 million (Department of Transportation, Aug. 2016)[17]

Lets face it. No rocket is ever going to be remotely as safe for transporting people than modern airliners. BFR will be a lot less safe than modern airliners. You know which I would rather fly on.
Airliners. Because you lack the courage to go to Mars.
Rocket engines are pushed far closer to the limits of materials and chemistry than turbofan engines on modern airliners so LV's will never get as remotely as safe for human transportation as airliners.
« Last Edit: 09/29/2017 11:31 am by DJPledger »

Offline toruonu

Rocket engines are pushed far closer to the limits of materials and chemistry than turbofan engines on modern airliners so LV's will never get as remotely as safe for human transportation as airliners.

That assumes that you run them at max thrust you dare because you want to squeeze out every gram of usable payload. However if you're transporting ~800 people + their cargo (say 20-30kg/person, average person 80-90kg) you transport ~90t of cargo. That's around half of BFR capability and you want to limit the G loads as you have standard travellers. I'd guess the engines are going to be running on partial power, nowhere close to their max capabilities for that hop.

If I had to choose I'd take the BFR in an instant.

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 3079
  • Liked: 722
  • Likes Given: 821
Hey can anyone explain the flat, shuttle-like bottom? Slightly uptilting wings like dream chaser seems much more intuitively self-stabilising.

The word you're looking for is dihedral. It provides some positive stability, but you don't always want that if the vehicle has adequate control authority. Indeed fighter aircraft are deliberately unstable to allow faster/easier manoeuvring.
Dreamchaser has its origins many decades ago, and things have moved on since then.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 3079
  • Liked: 722
  • Likes Given: 821
Just a thought on engine count and reliability.
Modern telemetry/EDS systems must be streets ahead of those from the N1 days. I am guessing here, but does it not seem likely that we can now festoon an engine in sensors relatively easily and cheaply, and with faster, more powerful computers, catch problems as soon as they arise? Leading to rapid throttling back or shutting down of sickly engines. Knowledge is power, and all that.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Dante80

  • Full Member
  • ****
  • Posts: 893
  • Athens : Greece
  • Liked: 835
  • Likes Given: 539
Rockets are not going to be as reliable/safe as aircraft in the following 100 years. Sure.

This is not the question or the goal though. The goal for them is to become reliable/safe enough for the proposed tasks at hand.
« Last Edit: 09/29/2017 11:48 am by Dante80 »

Offline Ekramer

  • Member
  • Posts: 65
  • Hertfordshire, England
  • Liked: 62
  • Likes Given: 76
My concern with point to point isn’t capability, it’s cost. Anyone have any idea what cost would be for 200 passengers just counting fuel?

Methalox fuel is about $0.20/kg.

Figure a little under $1m to fuel ITSy.

So $5000 per person just figuring the cost of fuel. $10,000 tickets isn’t too unreasonable for wealthy and businesses.

First Class New York to Shanghai one way is about $10,500 for a 15 hour trip.  If Elon can do it for $15,000 in 90 minutes, then the Jet Set becomes the Space Set and the whole airline industry is disrupted.  And remember you get a prolonged weightless experience thrown in, so Blue Origin, Virgin Galactic and other space tourism is disrupted.

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 4286
  • Liked: 887
  • Likes Given: 201
Rockets are not going to be as reliable/safe as aircraft in the following 100 years. Sure.

This is not the question or the goal though. The goal for them is to become reliable/safe enough for the proposed tasks at hand.
I heard somewhere that rockets are simpler than jets. I don't know if that applies to ones with all the bells and whistles.

One advantage: you have a lot more control over what goes into them, so long as you can avoid pigeons getting into the gas tanks :)
« Last Edit: 09/29/2017 12:09 pm by KelvinZero »

Offline su27k

  • Senior Member
  • *****
  • Posts: 6414
  • Liked: 9100
  • Likes Given: 885
So no, changing the engines is a bad bad idea. With that said however, how a 31 engine cluster on a 9 meter vehicle will perform, particularly with engines that operate at higher pressures than anything ever seen before in the history of liquid rocketry, how that will behave is a big series of questions.

Of course there will be challenges and questions, that's what you employ all those fine engineers for. BTW when they announced FH their head count is about 1500, right now they're at 6000.

Quote
And to here and say "oh its still less complex than the a vehicle that is built out of flight proven hardware and engines (FH)" is absolutely ludicrous.

Not ludicrous, just a little extreme. There's one aspect BFR is definitely less complex FH: It has only one staging event, while FH has 2 (or 3 depending how you count it). I believe Musk specifically said FH booster staging is something to worry about since it couldn't be tested on the ground.

Offline titusou

  • Member
  • Posts: 59
  • Tokyo
  • Liked: 86
  • Likes Given: 0
Scaled comparison ;p

Titus

Offline su27k

  • Senior Member
  • *****
  • Posts: 6414
  • Liked: 9100
  • Likes Given: 885
AMOS-6. Vehicle exploded because they had no idea how to handle super dense cryogenics and despite being warned multiple times that composites don't play nice with cryogenics they ignored the warnings. People WITHIN SPACEX giving these warnings by the way. They had previous buckling with helium tanks prior to this.

This is survival bias, you're picking one example where they were wrong while people giving advice were right, you're ignoring the countless times when they were right while people giving advice were wrong. Hell if Musk listened to his friends' advice to stay out of launch market, there would never be a SpaceX.

Offline su27k

  • Senior Member
  • *****
  • Posts: 6414
  • Liked: 9100
  • Likes Given: 885
There is absolutely no way this vehicle will exist and fly by 2022. Carve it in stone it's not going to happen. They can't even solve the problems they already have and now they just want to throw out all their existing systems? More importantly it should tell you alot when this thing is so expensive they would have NO CHOICE but to throw out their existing systems to build it

They are shooting themselves in the foot with this. Big time. And you will almost certainly see them lose contracts over this idea if they insist on it. Nobody wants to take that amount of risk.

If you haven't noticed, a lot of existing launch vehicles are being thrown out: Ariane 5, H2, Delta IV, probably Atlas V too. And their replacements all have fairly aggressive timeline with first launch in 2019/2020. Their customers are not panicking, there's an orderly transition planned for each one, why do you think SpaceX wouldn't plan something similar?

And what risk? You do realize for a fully reusable vehicle it can afford to fly several test flights before taking any customer payload? And we already have commsat customer signing up to New Glenn even though Blue Origin hasn't orbit anything and New Glenn is about 35x of the size of their current vehicle, the customers are not as risk averse as you think.

As for solving their current problems: That's what they're doing right now, but you need to plan for the next step before the current step is done, that's just common sense, especially for space projects where it takes a long time to start anything. What do you want them to do? Just don't plan anything until they got all the current problems solved? Why do you think NASA is planning DSG when they haven't get SLS/Orion flying yet?
« Last Edit: 09/29/2017 12:38 pm by su27k »

Offline jebbo

  • Full Member
  • ****
  • Posts: 940
  • Cambridge, UK
  • Liked: 608
  • Likes Given: 309
There's been much discussion of the BFR, but it strikes me that with a (optimistically) launch only 5 years away, and 7 for people, there's been no discussion of other aspects.

For example for the 2022 launch, the goals are:
- confirm water resources.
- identify hazards
- Land power, mining and life support infrastructure

Which implies all sorts of things: choice of site, design of equipment, etc.

Is there a thread that discusses such things?

--- Tony

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0