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Old October 26th 17, 12:29 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default Were liquid boosters on Shuttle ever realistic?

Jeff Findley wrote:

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.


Most aerospace stuff isn't designed for "minimum manufacturing costs"
because we just don't build enough of them to do that.


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"!


Not necessarily. Depends on what the requirements are. If you're a
commercial outfit trying to compete for launch business, you're going
to want to drive overall costs per launch down. That might make you
decide on designs that don't push the envelope as hard because they're
cheaper to build because you can use cheaper materials and fuels that
are cheap and don't require expensive storage and handling facilities.
Or it might drive you to more expensive practices so that stages are
reusable, using more expensive materials and squeezing more
performance so that you have capability left to get the stages back.

On the other hand, if your primary business is government payloads
you're not going to have to compete as hard to get a share (because
the government won't want all its eggs in one basket) and you might
just push pure performance harder because you can afford to do it.

Back in the 1940's and 1950's, there wasn't a lot of choice but to
push performance because nothing less would get **** on orbit. That
doesn't mean modern missile engineers are obtuse (or even that the old
time ones were).


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.


Actually they haven't. Superchilled RP1 drives up costs in order to
improve performance. Going for reusability drives up manufacturing
costs and design costs because you have to make things that can be
used dozens of times without attention (so you need better materials
and tighter designs without pushing for extra performance, figure out
some way to avoid 'coking' on an RP1/LOX engine, etc). It's the
normal engineering evolution of launch vehicles that was stalled while
most payloads were government.


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.


BFR and the BFR Ship are sort of the end result of that. Reliability
of airliners with the ability to do hundreds of flights with only
routine servicing is the goal.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw