In article ,
says...
It does not necessarily mean that it is the optimal design from an
engineering point of view. It's the design that makes the most business
sense.


It may not even be that. Certainly no one here is advocating 'optimal
engineering design' as a GOAL, although that usually makes the most
business sense.


Depends on what you mean by "optimal engineering design". For example,
missiles are optimized for long storage times and for minimum size and
mass for a fixed payload size. The requirement to store them on subs
and in smallish launch facilities drives the requirements. But, they
are not in any way shape or form designed for minimum manufacturing
costs. In terms of overall program costs, that's just not a big
consideration.

Put those same engineers on a launch vehicle program and they'll design
an "optimum" launch vehicle with different engines on every stage,
maximum ISP engines (at the bleeding edge of what the materials can
take), and stages which have to be transported by barge and by over-
sized cargo aircraft. Different stages will have different fuels
driving up handling complexity and costs at the launch pad. All those
little things add up to launch vehicles which are far more expensive
than they need to be. Why? Because "we've always done things that
way" and "performance uber alles"!

The revolution brought by SpaceX (and somewhat by Blue Origin) isn't at
all technology driven. There was no magic breakthrough technology that
drove down costs (like SABRE engines). There is absolutely nothing
technically challenging about how they've designed their engines and
launch vehicle stages (to date anyway). But what they have done is
optimize for lower cost at every step of the process. Lower development
costs, lower testing costs, lower build costs, lower transportation
costs (Falcon stages are transported by semi-truck), lower integration
costs (horizontal integration), and etc.

On top of that, both SpaceX and Blue Origin are pursuing reusability
with a tenacity never before seen in the industry (space shuttle SRBs
and orbiters were refurbished after flight over many months, so they
don't really count). That will be the next step towards even cheaper
access to space.

Jeff
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