The main issue there on the
Saturns was the manufacturing of very large, very thin ones.
This is partially true,The RL-10 powered Centaur was an order of magnitude
smaller than S-II so scaling up usually presents problems
The other part is the bulkhead had to also be insulated unlike Atlas which
was a simple sheet of stainless steel.
Ken
On Sun, Apr 30, 2023 at 12:08 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Fri, 28 Apr 2023, roxanna Mason wrote:
Other factors which made the LH2 high risk was the requirement for a
common bulkhead to shorten the SII stagewhich had never been done
before.
No, Atlas already had a common bulkhead -- in fact, about the most minimal
common bulkhead imaginable, a single thin sheet of stainless with LOX
above it and kerosene ullage space below it. And the Centaur folks were
already working on a LOX/LH2 common bulkhead. The main issue there on the
Saturns was the manufacturing of very large, very thin ones.
Additionally the insulation was put on the inside immersed in the LH2.
This is why there was no ice and thick frost on the outside of the stage
like the SI-C stage did on the LOx tank.
Ditto for the SIV 3rd stage.
Only on the third stage, actually. Douglas's list of advantages for the
internal insulation quietly failed to mention its one big snag: it was
heavy, because it needed compressive strength to transmit pressure loads
(pressurization and hydrostatic) out to the metal wall. It made the S-IV,
and then the S-IVB, easier... but the S-II was too performance-critical to
accept the weight penalty, and NAA had to use external insulation. After
some early difficulties, they eventually settled on using spray-on foam --
in fact, the original Shuttle ET foam was an improved version of the S-II
foam.
Henry
