In article ,
Pat Flannery wrote:
...When the Russians ran into similar problems, they responded
by clustering smaller chambers instead, which worked.

Right up till they got to their 30 engined N-1 Moon rocket it worked,
then it didn't work.

There was nothing intrinsically wrong with the N-1 design; it simply was
an overly-rushed and cash-starved development program, e.g. with *no*
ground test of the full first-stage propulsion system, and the
politicians' patience ran out before debugging was finished.

The Saturn V, with somewhat more time and a lot more money, still had
serious bugs as late as Apollo 13. By luck -- quite a bit of luck in the
case of Apollo 13's second stage -- none was catastrophic.

There is also a great deal of propellant feed plumbing weight associated
with such an approach.

The big feed lines for a handful of large engines aren't light either.
There *is* extra plumbing mass with a many-engine cluster, but the
difference comes from second-order effects.

...just how unrealistic von Braun's space plans were, based on
the proposed launch rate alone- as huge V-2 technology based ships put
small payloads into orbit at the rate of four launches per day:
http://www.spacedaily.com/news/rocketscience-03zzf.html

Some of us don't think four launches per day is at all unrealistic --
although it might have required a somewhat different vehicle design --
viewed from a clean-sheet-of-paper perspective, rather than from the
stifling trap that we've gotten ourselves into in the last few decades.
Bell shares a fundamental error with most of today's Old Guard rocketry
establishment: he thinks today's incredible stupidities are laws of
nature, that the Emperor couldn't *possibly* really be standing there with
no clothes on.

The landing approach would have been interesting if you flew it by the
seat of your pants; Armstrong had a "fun" landing after getting the LM
into hover mode. Trying to do it with a bigger lander would have been
even more fun.... particularly figuring out exactly where you are going
to land at once you started your descent.

A lot of Armstrong's problems were because he was improvising a landing in
unfamiliar terrain. And *that* was the result of, to put it bluntly, a
mistake he made earlier: he had his attention inside the LM looking at
the computer alarms, when he should have left those to Aldrin and kept his
mind on navigation and his eyes on the surface. Nowadays, this is a
standard lesson all pilots learn -- you must divide responsibilities, it's
a lethal mistake to have *everyone* preoccupied with troubleshooting and
nobody flying the damn plane -- but it wasn't part of the gospel then.
And the Apollo 11 crew probably wasn't all that well integrated, simply
due to shortage of training time, so Armstrong may not have been all that
confident in Aldrin.

With more eyes watching -- say, a dedicated navigator -- this would have
been much less of a problem. And with no computer, you don't have
computer alarms. :-) The only big question is whether you abort the first
landing attempt when you realize you're coming down well off course, or
try to correct. (If you abort, the *next* ship has the proper correction
cranked in ahead of time.) Probably you try to correct, because the
navigator catches the growing discrepancy early.

...one of the big problems would be the weight of the
lander; the LM was fairly small and had robust landing gear to take a
less than perfect landing, trying to get landing gear and spacecraft
structure that could handle a fairly rough landing on a far larger
lander would be challenging, to say the least.

Not a trivial issue, although eased considerably by assembling the lander
in space so you're not wrestling with packaging constraints too. And the
LM landing gear turned out to be drastically overbuilt.

What matters is not so much how big the lander is, as how well it responds
to the controls. Large size and poor control authority don't *have* to go
together.

Years ago I read
someone's comment about the direct ascent Apollo variant where the whole
spacecraft was to land on the Moon, the gist of it was that the lander
was going to weigh about as much as an Atlas ICBM...

The problem was more that it was going to be as *tall* as an Atlas, and
that the constraints of launch from Earth meant that the crew were going
to be at the top. Which made for very awkward problems of adequate view
for the landing, the issue that finally sank EOR. This is much less of
a concern with a space-assembled vehicle.

and we couldn't get
one of those to take off reliably, much less have it gently touch down
without exploding.

A problem that had very little to do with its mass.

Getting a heat shield to take those reentry heats would have been a real
problem given the state of technology at the time, and Titanium and
Inconel metallurgy for spacecraft structure wasn't nearly as finessed as
it later became...

You don't really need high-temperature structures if your thermal
protection is good. And suitable steels make quite good high-temperature
structures -- more heat-resistant than titanium -- although they're rather
heavy.

But an adequate heatshield would indeed have been a problem; von Braun's
ideas on that aspect were naive, in hindsight. The difficulty is not so
much materials technology -- notably, there would be nothing very
difficult about making an ablative heatshield, even with WW2 technology,
so long as you weren't too worried about how much it weighed -- as the
insight that reentry bodies should be *blunt*. It took quite a while for
people to realize that; it wasn't obvious.

The biggest problem though would have lack of space
experience; you'd still need something like the Mercury and Gemini
programs to get a handle on how to work in space.
IMHO, if you had gone gung-ho at the project at the end of W.W.II, you
might have been able to shave 5-10 years off of the timeline...

Assuming somebody hits on a suitable approach to the heatshield problem,
say five years for the first orbital scout flights, another five for a
heavy ferry and construction start on a station, and five more to finish
the station, fly a scout mission around the Moon, and gear up to attempt a
landing. Maybe 1960.

You might be able to cut a few years off that if it's a crash program from
the start, aimed at a lunar landing soonest rather than systematic
progress while building infrastructure. That would mean (as Pat says)
tolerating both failures and loss of life, and a certain amount of
conspicuously wasted money. And perhaps a bit of luck.

The one area where von Braun's original concepts might have hit a serious
technological snag would be the extensive reliance on orbital assembly
work done in spacesuits...

One could have used the Soviet automated docking technique, something
that we still should develop- but won't- because of the perceived threat
to manned spaceflight.

There has been quite a bit of development work on automated docking in US
labs; what is lacking is funding for flight tests, and that is closely
tied to a lack of any real requirement for it (given that all US station
flights are manned anyway).

Anyway, with a von Braun approach, both the ferry and the station's tug
are manned, so that's not an issue. The problem is that you have to
rethink both the station design and the moonship design to be *modular*,
so that you are plugging modules together rather than riveting girders
together. That may also require one more rev of the ferry design, to give
it a larger cargo hold -- not necessarily more cargo mass, you can outfit
the modules from within once they're connected up, but more cargo volume
so you can launch a reasonable module shell in one piece.

(Well, and there would have been the small matter of his favored assembly
orbit -- the "two-hour orbit" -- being right in the middle of the inner
Van Allen belt...)

You mean the _von Braun_ belts in this scenario; the lack of experience
with solar storms would also be a problem.

Even in WW2, if I've got the dates straight, people understood that solar
flares produced radiation; the neutrons from upper-atmosphere particle
hits at high latitudes are detectable on the ground.

Mind you, the crash-program timing I noted above is unfortunate, in that
it may put your first lunar expeditions during the nasty solar maximum
of the late 50s.

The belts would be discovered by early orbital scout flights, cosmic
radiation being recognized even then as an area of concern. In the real
world, while nobody (well, except for Nick Christofilos and a handful of
other people acquainted with his highly-classified work) was expecting
trapped-radiation belts, cosmic rays had been known since 1911 and their
intensity outside the atmosphere was a serious unknown... as witness the
fact that the major science instrument on the first US satellite was a
cosmic-ray detector.

Some of the scout pilots might get rather high doses while finding out the
extent of the problem, mind you.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |