Hobbes said:
SteveO said:
I would like to point out that the developement freeze is imposed on SpaceX by NASA. SpaceX likes incremental development, making small changes to almost every successive rocket, tweaking it to get a little bit more performance every launch, as opposed to making the design what they want from the beginning and sticking with it. NASA is pretty adamantly opposed to this, because they feel that each change in the rocket introduces the possibility of a previously unknown safety issue. To be fair, they have a point -- the loss of AMOS-6 was a textbook example of such an occurrence. SpaceX had introduced densified propellant, oxidizer and even densified helium pressurization fluid, to fit more into the same tanks and to push more through with the same pumps. The densified helium caused some of the oxidizer to freeze solid, which eventually caused the loss of the vehicle and it's payload. However, at the same time it was tweaks like densification that allowed Falcon 9 to reach the kind of performance that makes reusability viable at a low cost.
But anyway, one of the criteria NASA has set for commercial operators to human-rate their rockets is to launch exactly the same design, with no changes *at all* for a given number of times, IIRC 9. SpaceX has chosen "Block 5" to be this point where the development of Falcon 9 ends. Now, of course, all their development engineers had no more work to do on the F9, so it of course makes sense for them to start working on the next big thing.
;D)
