These may be interesting times. Everyone try to stay safe out there.

Two considerations:
1) Make sure that the calculations for propellant tankage weights are not based on the propellant mass, but the volume and the required internal pressure. Don't forget the LH2 will require some insulation to prevent cryo-pumping of the air even if frost is acceptable. The low density of the hydrolox system will generate tanks nearly twice the volume of the kerolox. This is where the MacDac/Boeing original trade studies went awry for the Delta IV.
2) The only costs that ratios with GLOW are the engines and the launch facilities. Kerolox engines are simpler, smaller, and feature a higher T/W ratio than the equivalent hydolox, especially at higher chamber pressures. Concrete is cheap, engines are expensive.

In the end, costs ratio more by the inert weight rather than gross. Is the inert weight of the hydrolox system less?

The original parallel burn concept, the Atlas, was done so not for performance, but to avoid an air-started engine and the associated failure mode.

Sadly, we seek simplicity and find complexity.

I do not think the flight J-2 would be suitable for SL operations, running with a 763 psi chamber and a 27.5:1 nozzle has an exit plan pressure of roughly 1.8 psi (I guessed a ratio of specific heat of the exhaust of 1.3). On the image of the J-2 in Wikipedia I noted that there appears to be a restriction ring at the exit plane. Perhaps a modification of the engine could be used from the ground, but there would be some development.

Why not just increase the F-1 strap-ons to 5 and air start the second stage? The Titan IV's air started the first stage just prior to jettisoning the solid stage 0's. For a given GLOW, I would expect higher performance anyway as this operational variant would save the high energy LOS/LH2 for the higher energy portion of the launch.

How about that staunch conservative JFK and his bro. who set us all on the path to the Moon? Perhaps you should reevaluate your sources and assumptions.

It should be pointed out that the ICBM/SLBM fleets have somewhat divergent requirements than space launch vehicles. They are pre-integrated with their payloads, extensively and periodically tested with dynamic payload simulators and are saddled with a completely different set of operational and safety processes.

There is a second path directly to the responsive launch that shares increased costs with the strategic missile fleet. One could now buy the rocket, or rockets of your choice then pay to store and maintain them. For the fastest response, the payloads should also be built and pre-integrated with the launcher. As these are government, national security customers, they can move themselves to the front of the launch facility line any time they feel the need. This operational concept was discussed at Boeing some years ago for a commercial project, but was deemed too costly. So far, it seems, so does the military.

An excellent bit of history that we so rarely hear about. Bravo.

Probably not. Might have to argue that it would benefit his children or even grandchildren. To a business person, even this is sketchy. We seem to be in a position something like we were in 1850 with respect to rail transportation. We had some viable technology and experience, but had not put in the massive investment needed to link both sides of the US with it.

Even with the carrot of gold in California, it took nearly twenty years to establish the first link in 1867. Even then, thousands of square miles of property were given to the rail companies to get them interested. Shiny metals have an over-sized motivational factor; can the carrot of virtually unlimited power availability do the same? Realistically, probably not. We understood how to extract, process, and the market value of gold. Other than the market value, we are on the leading edge of technology to generate and deliver power from space. True, we have done some systems studies in the 1970s and again this last decade or so, but we have no experience at handling, transmitting and receiving the 100's of MW to GW levels of power needed to make space power practical.

So what else? No extraterrestrial materials can compete on cost with what we can extract or reprocess on the surface. Virtually all the orbital material processing experiments lead only as far to support surface processing methods. Even if the optical fiber process requires the orbital environment to be successful, it is such a limited, "boutique" market that I can't imagine that the raw materials for processing won't be launched from the surface.

Without a relatively near term market there will sadly be no massive private investment.

You are quite correct.

When that one collision happens, your numbers change though (It has a few times now, so this is not just academic). Assuming the numbers in the article, the original 34,000 large objects turn into 33,999 or 33,998, resulting in an additional 15,000 pieces between 1 and 10 cm for 915,000, and another 200,000 >1 cm bits for 128.2 million. Then the centuries tick by. Every decade we delay at the current rate the cost of cleaning things up will add another 200,000 pieces.

Based on the numbers oldengg provided alpha in the exponential equals about 0.0017 with time in years (N=No*e(alpha * t)). Left to itself, the time to double is about 400 years (and double again in another 400). Now this analysis is grossly simplified and assumes that all collisions are created equal, none of the resulting debris de-orbits quickly due to the perigee being dropping to a rapidly decaying altitude etc. It may give an appreciation of the issue. Even though the evolution is slow for us humans with our short lives, it will continue. Do we care? Do we assume that there will be technology in the future to either mitigate this condition or make it irrelevant?

If we are adding an additional load of objects by the thousands, alpha will increase. It will not decrease without removing the sources of additional particles.

Long range ballistic transportation is only a few hundred fps short of orbit. The difference between orbital vehicles and suborbital is not the required propulsion and propellant as much as the decreased requirements for environmental control and life support systems.

An interesting paper. What would our activities look like in 10's to 100's of million years? One thing is for sure, the dinosaurs did not harness satellites for communications. They, or remnants of them would still be in evidence for us to study.