Quote from: DJPledger on 09/29/2017 10:18 amEven 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).
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.
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.
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.
Quote from: DJPledger on 09/29/2017 09:40 amPoint 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]
Quote from: DJPledger on 09/29/2017 11:15 amQuote from: toruonu on 09/29/2017 11:09 amQuote from: DJPledger on 09/29/2017 09:40 amPoint 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.
Quote from: toruonu on 09/29/2017 11:09 amQuote from: DJPledger on 09/29/2017 09:40 amPoint 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.
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.
Hey can anyone explain the flat, shuttle-like bottom? Slightly uptilting wings like dream chaser seems much more intuitively self-stabilising.
Quote from: ZachF on 09/29/2017 05:32 amQuote from: bregallad on 09/29/2017 05:29 amMy 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.
Quote from: bregallad on 09/29/2017 05:29 amMy 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.
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?
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.
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.
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.
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 itThey 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.