I agree with you about reasons Space X decided to start with GG.
Still I disagree with a common opinion about SC as something always
"more complex, more difficult to develop, and heavier" (the quote from
another message).
In fact, the complexity and difficulties in designing SC engines are
results of attempts to achieve highest possible efficiency (that is, at
highest possible chamber pressure). This might (or might not) be excused
if the main goal is a highest performance of the engine.
But things may change when other goals drive the development.
For example, the first Soviet staged-combustion engine 11D33 has low
chamber pressure 5.36 MPa (almost the same as in RD-107/108, and lower
than in some other GG engines). It has been developed in 2 years
without any previous experience with SC, and even without any available
knowledge about this cycle.
Several following Soviet SC engines (RD-0203, RD-253, NK-15) were
developed in 3 to 4 years, and operated at moderate chamber pressure ~14
MPa.
Later on, the Soviet engineers (mainly at Glushko's design bureau) had
tried to achieve the max possible performance at max possible chamber
pressure, resulting in more complex, difficult to develop, and heavier
engines.
What I am trying to say is that today the SC engine is not necessarily
more complex and difficult to develop. In turn, in some aspects it might
be even easier to develop the SC engine operating at *low* or *moderate*
pressure. For example, it is easier to control the HF combustion
instability in thrust chamber, might be easier to develop the turbopump
(because the efficiency of turbopump does not affect the overall
performance of the engine, and due to lower turbine temperature), etc.
Related to that, the experience with Raptor and BE-4 seems to be very
interesting.
BR,
Alexander
On 12/30/2015 02:51 AM, Henry Vanderbilt wrote:
I mentioned a number of likely factors in SpaceX's decision to go with
a gas-generator engine for F1/F9. Engine T:W is only one of them (and
probably a minor one, as subsequent discussion seems to indicate.)
Biggest factor was I suspect greatly lower overall development
time-and-cost-to-market for gas-generator, absent previous experience
with staged-combustion.
As you point out in your previous post, previous experience with
staged-combustion is a huge help in developing a new one without much
expensive time spent destroying test engines. And as you were much
too polite to point out, but I will, the vast majority of practical
experience developing successful staged-combustion engines currently
lives in Russia.