Other factors which made the LH2 high risk was the requirement for a common
bulkhead to shorten the SII stage
which had never been done before. 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. Truly amazinging
Ken
On Fri, Apr 28, 2023 at 1:43 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Fri, 28 Apr 2023, roxanna Mason wrote:
A high-level NASA advisory committee eventually sold everyone on
liquid-hydrogen upper stages,
This fact still amazes me because of the potential risk against such a
high priority program, Apollo to the moon by the end of the decade.
All this was happening in late 1959, before Apollo even existed. When it
did come into existence, over the following year or so, it was primarily
an Earth-orbit spacecraft -- the successor to Mercury -- with a stretch
goal of lunar orbit circa 1970. Lunar landing was beyond the planning
horizon, although there were vague hopes that it could be done in the
early-mid 1970s with modified Apollo hardware.
Even so, they *did* concede that the focus on LH2 incurred some risk, but
at the time there was great optimism about the potential of LH2, and
little appreciation of its practical problems. Once the technology was
sorted out, it would surely be much like kerosene, only with far higher
Isp. Failing to adopt it for Saturn would doom NASA's new rocket to early
obsolescence.
Two or three years later, the situation was starting to look rather
different... but by then hardware development was already well underway.
With a new crash-priority program to put together, NASA couldn't afford to
throw everything out and start over; the old program plan was in the
trashcan, but reusing as much as possible of its hardware seemed essential
for meeting the near-impossible deadline.
(In the end, much of that hardware actually was gone by deadline time, but
derivatives of some of it were still there, and most of the rest helped
out along the way.)
Henry