In article ,
says...

On Sunday, February 22, 2015 at 10:48:08 PM UTC-5, Jeff Findley wrote:
In article ,
says...
Seems rather optimistic speculation.

Not at all. What was optimistic was the assumption that NASA funding
would continue at the same level as it was during the height of
Apollo/Saturn development. That assumption was proven false.

We need rockets about 10 times as powerful, and about 1/000th the cost
of 20th century technology.

In terms of size, no, we don't. Saturn V would have been enough.
Falcon Heavy would be big enough too, given enough launches.


Most Mars mission profiles from the 70's I recall, envisioned a nuclear upper stage. In the Saturn V configuration we're talking the 3rd stage, I believe.
Such technology was very close at hand in the early 70's but as you point out the funding had been cut off much earlier. Jeff, do you recall if there were other, pure chemical configurations based on Saturn V (either via fuel depot and/or multiple launches)? I keep remembering the timeline of ~1986 being tossed around as a "realistic" deadline for the first Saturn V derivative Mars missions. Of course that was all before we got the Space Truck fever!

Note that even with a nuclear upper stage, you still needed a lot of LH2
to "fuel" it, so the cryogenic storage problem would still need to be
solved (at least to the point of "good enough") with nuclear.

When you look at those sorts of details, nuclear wasn't really "needed".
It was part of the "everything and the kitchen sink" R&D that came with
Apollo/Saturn's blank checks.

Either a nuclear upper stage or cryogenic fuel depots could have been
used with conventional LOX/LH2 engines (J-2 wasn't a bad engine for its
time and had upgrade potential, just as the F-1 was being upgraded to
the F-1A).

In terms of cost, I'm not sure we "need" three orders of magnitude in
cost reduction. Besides, we're well on our way to big cost reductions.
SpaceX is disrupting the industry with its low cost, and they've yet to
reuse a single first stage booster. Give them 5 to 10 years, and I'll
bet they'll demonstrate low enough launch costs for manned Mars missions
(if NASA would stop throwing billions down the SLS rat hole and instead
spend that money on actual Mars vehicles).

Were that there were a way to convince Congresspeople that building Mars vehicles atop the soon to be existing commercial fleet would keep as many people employed as is building yet another redundant rocket.

And of course let's not forget the sheer cost of SLS operations. Which sets a very high barrier to entry for ANY mission that would attempt to leverage it.

The biggest barrier to putting men on Mars is the myth that "heavy
lift", in the form of a very large expendable vehicle, is needed. What
is needed is low cost launches measured in cost per kg to LEO. Falcon
Heavy with reusable booster and core first stage is a step in the right
direction.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer