Aerodynamic losses are greater if you're wider. So you want to go taller if you can
Counterpoint: Falcon 9 is a flying needle if ANYTHING is, and it gets industry-leading mass fraction.
In theory, a sphere is the most efficient shape. But is this an example of where theory and practice fail to meet?Is a sphere actually a complete PITA to build, and all the supposed advantages get swallowed up by the time you've factored in all the additional welds, and the difficulty of transferring loads through it?
Quote from: Robotbeat on 05/26/2017 11:03 pmAerodynamic losses are greater if you're wider. So you want to go taller if you canDon't forget mass fraction. Flying needles are not particularly good at it.I think "squat ITS with fewer engines" is not a bad idea. Saturn V's 1st stage had fineness ratio of about 1:4.
Quote from: gospacex on 05/27/2017 08:23 pmQuote from: Robotbeat on 05/26/2017 11:03 pmAerodynamic losses are greater if you're wider. So you want to go taller if you canDon't forget mass fraction. Flying needles are not particularly good at it.I think "squat ITS with fewer engines" is not a bad idea. Saturn V's 1st stage had fineness ratio of about 1:4.One advantage of a squat ITS (10m) is that there is plenty of room to add engines and go taller. Also accommodates engine performance growth.Similar in some ways to F9 v1.0 situation to current max'd out fineness/length due to M1D performance improvements.
There is certainly a trade between reducing aero losses by lengthening your cylinder, and increased dry mass needed to handle bending loads, and narrowing the launch commit parameters to deal with increased bending loads, and simply cost of retooling/transporting a rocket of larger diameter and how large/many engines can fit on the rocket, etc etc.It's a long and complex trade that will likely be dominated by cost considerations (which includes transportation)..