O.K. I want to change my guess for number of engines from 31 to 27.And this isn't just because Musk informed us that the thrust is going to be higher than previously hinted at. It's also because I realized that, while 31 gives a very nice, minimum diameter packing pattern with a single center engine (like the F9), having a single center (landing) engine is probably not appropriate or desired here. It's unlikely that the BFR could land on a single engine - just too heavy. 3 centralized engines would probably be appropriate. And the nice symetrical, minimum pattern for 3 center engines comes out to be 27.
Quote from: GORDAP on 09/26/2016 04:36 pmO.K. I want to change my guess for number of engines from 31 to 27.And this isn't just because Musk informed us that the thrust is going to be higher than previously hinted at. It's also because I realized that, while 31 gives a very nice, minimum diameter packing pattern with a single center engine (like the F9), having a single center (landing) engine is probably not appropriate or desired here. It's unlikely that the BFR could land on a single engine - just too heavy. 3 centralized engines would probably be appropriate. And the nice symetrical, minimum pattern for 3 center engines comes out to be 27.3 center engines is much worse than 1.If any of those 3 center engines fail, then it's crash and burn.But with many more engines, the landing burn can be done with center engine + ANY two engines that are on oppisite sides of the craft.
I'm revising BFR diameter down to a range of 10 - 12 m based on Musk comment on raptor being comparable to Merlin size but carrying 3x thrust.That completely rules out 15 m diameters, a vehicle that size is approximately 9x the base area of F9, with triple thrust density of Raptor would lead to 27x the thrust of F9 or something close to 45 million pounds of thrust, 3x times what Musk has aimed for.Fundamentally the 15 m speculation was nothing more then a crude attempt to multiply the thrust of F9 by a factor of 9 while completely ignoring the thrust density improvements that come from the full-flow staged combustion cycle.
Target BFR thrust stated by EM and Raptor announced thrust seems to indicate 25-27 Raptors which is still too many for my liking.
42 engines!!!! good god!That will be like 25 million pounds of thrust at liftoff!!!!
3 center engines is much worse than 1.If any of those 3 center engines fail, then it's crash and burn.But with many more engines, the landing burn can be done with center engine + ANY two engines that are on oppisite sides of the craft.
Musk: spaceship can serve as own abort system from booster, but on Mars, either you’re taking off or you’re not. #IAC2016
Asked about abort modes for launcher @elonmusk said "make it very reliable ... you do not have parachutes for commercial airliners" #IAC2016