The tooling no longer exists for the Saturn V and it's not as simple as just dusting off the plans and building more. See decade-long history (and billions of dollars spent) of the Aries/SLS program to see how it's not so simple building a new heavy-lift rocket. Now, redesigning/rebuilding the Saturn V would have been a quicker, simpler and cheaper route to take, I grant you that, but even that isn't as simple as you seem to think.
Political and economic consideration, not an engineering challenge. The original Saturn V was thrown together in approximately a decade for roughly $46 billion, ignoring precursor work. The Soviet N1 had roughly similar capabilities and was put together in an equivalent amount of time. So was the Soviet
Energia for Buran, which was only just shy of the Saturn V in LEO capabilities. It's not nearly as challenging as you think, it's a question of its priority for the people signing the checks. Given NASA's annual budget lately, and those of other space agencies, one can infer how high that priority is. (Hint: it isn't.)
In any case, the launch vehicle is actually typically one of the smallest costs associated with large space systems. It's usually the cost of the payload itself and the R&D associated with it that has the biggest part of the cost. Breaking up the launch (which, for the tenth time, is not what Zubrin called for) is actually going to drive up your overall costs considerably.
If you're only making a few shots, sure. For anything with a long enough operational record, unit flights will dominate the total cost of the endeavor. Interestingly, there is also a sweet-spot to be hand in total number of units assembled versus individual cost, due to economies of scale. Even if a larger vehicle is more efficient per flight, several smaller vehicles may wind up being cheaper overall. That's just in theory though.
In any case, the launch vehicle is actually typically one of the smallest costs associated with large space systems. It's usually the cost of the payload itself and the R&D associated with it that has the biggest part of the cost. Breaking up the launch (which, for the tenth time, is not what Zubrin called for) is actually going to drive up your overall costs considerably.
In actual practice, you're still wrong. Doing some
rough math:
Falcon 9 Heavy cost: ~$100 million per launch
LEO payload: 53,000kg
Unit rate: $1886/kg
Delta IV Heavy cost: ~$435 million per launch
LEO payload: 27,569kg
Unit rate: $15778/kg
Space Shuttle cost: ~$762 million per launch
LEO payload: 24,400kg
Unit rate: $31229/kg
Saturn V cost: ~$1.28 billion per launch
LEO payload: 120,000kg
Unit rate: $10666/kg
It's cheaper to break it up into smaller, more economical launch vehicles, and Falcon 9 outperforms Saturn V by over a factor of 5 on launch economy. Your argument only holds if there is a particular item that requires well more than the 53,000kg launch limit, of which just about the only thing that would qualify is a fission reactor for an electric power source. Given Zubrin's intense distaste for VASIMR, I doubt there's anything in his proposal that does in fact require full launch weight per throw. If there was, as the first point demonstrates, putting together a new launch vehicle would not be that hardif the financial backing and political will existed in the first place, which it would have to for this to even be an issue.
That would fall under the 'host of other problems' that I mentioned. For one, the plan is already modular, requiring at least 2 launches a year of super-heavy rockets that don't exist. Breaking it up into components means adding propulsion/service stages for each component, docking nodes, structural and plumbing additions, etc. It adds drastically to the complexity, mass and cost of the overall system.
This is more valid, but it's not like you're just going to seal some docking clamps on some modules and flit off to Mars. The behavior of a ship under thrust (admittedly depending upon the scale of thrust) is going to necessitate more rigorous construction than that. These issues have already been well studied in modular assembly of modern ships and other large vehicles. That's not to say those techniques will translate 1:1 to orbit, but more or less everyone is familiar with the need for some orbital assembly being required.
In Zubrin's case, Mars Direct can avoid this by being broken down into smaller, more mission-specific modules which can still fulfill the majority of their time-critical functions (e.g., fuel production) while having more esoteric functions enabled by on-site construction by the astronauts. The specifics of how to do that are beyond this conversation, but it's not hard to see how it could be done.
And again, he specifically talked about launching things in single-lift operations on Saturn V class rockets. Not sure if you missed that point or somehow interpreted that I assumed that. I didn't, his plan expressly calls for it.
Plans can be modified and it doesn't take a rocket scientist to see how. Zubrin was writing what was basically a best-case playbook, not an infinitely flexible field manual. A little imagination goes a pretty long way in adapting it.
I just build satellites and new cold-gas propulsions systems in my spare time. The hell would I know?
And someone who builds racing boats is an expert on nuclear subs, eh?
Ok dude.
