[AR] N1 engines (was Re: clusters and reliability...)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Mon, 25 Jan 2016 14:11:55 -0500 (EST)
Chris Jones wrote:
> ... Showing that great minds think alike (or payload designers
> often underestimate their requirements) the Soviet N-1 first stage
> originally was designed with 24 engines in the first stage, and grew by
> the same 25% engine count (also by adding the additional engine(s) in
> the center) when they needed "more power".
According to Siddiqi's book, it wasn't so much general growth in payload
mass, as the top-level decision to use a single launch for lunar landings.
Previously the intent had been an EOR mission, putting *three* N1 payloads
together in LEO. But the August 1964 decree that finally gave approval
and funding to the Soviet manned lunar program explicitly called for a
single-launch mission. Siddiqi says there seems to be no contemporary
documentation on why this was done, and there are conflicting accounts in
people's personal recollections; it was probably some combination of not
wanting to look inferior to the US, and simple economics of using fewer
expensive launches (in a program that never had Apollo's national-crisis
priority, and consequently was always underfunded).
Even with adoption of an LOR mission profile, and determined attempts to
reduce spacecraft mass, the mid-1964 N1 design's 75t payload wasn't
enough. Hence a number of N1 design changes, including six more engines.
On Mon, 25 Jan 2016, Hugh Blair-Smith wrote:
I read (in a secondary source, admittedly) that the expansion from 24 to
30 engines was driven by fault tolerance...
Given that the liftoff mass rose by about 25% (Siddiqi: 2200t->2750t),
and one of the minor design changes was "flexible" throttling that gave
effectively about a 2% increase in engine thrust, preserving T/W would
mean adding 3-4 engines. 6 seems overkill, so it's at least plausible
that fault tolerance was a goal, although other reasons are conceivable.
Certainly some degree of fault tolerance was achieved: the first N1
lifted off successfully with two engines out.
can you point me to a primary source that settles this point?
Given that (according to Siddiqi) there seems to have been a lot of
acrimony within the Korolev bureau about the single-launch change and some
of its consequences, a single primary source might not be enough to settle
it! That said, my first thought would be to look in Chertok's massive
"Rockets and People", since he was high up in the bureau at the time; it
would be in volume 4, "Moon Race", and I haven't gotten to that point in
reading R&P yet.
Henry
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