NIAC

[jdbenner]

ijuin,The point is not that Pressure fed rockets will weigh or perform as well as turbine fed rockets.  The point is that we are trying to optimize the cost, and performance will have to be sacrificed for that goal.

Propellant is cheep compared to every other factor in space launch, so why save it?

[jdbenner]

The Performance (as in High Specific Impulse and Low mass fraction) of the lowest stage is the least critical.  Any extra weight in that stage does not go in to orbit, nor does a previous stage have to cope with that weight.