I think something like a theoretical SpaceX HLV will come on the scene if the private companies are successful at medium lift. However, they need a decade or two building experience, refining technology, and making profits at medium lift. We need heavy lift in the meantime.
Getting NASA out of medium lift is a really big step. It stops wasting money making medium lift vehicles like the shuttle or Ares I that need too much infrastructure for their capability. It encourages the commercial companies to develop. However, NASA is still the best bet for heavy lift, and will be IMO until about 2030.
Ok, I concede the point about the FAA. Forget NASA as a regulatory agency.
The following link is on a NASA site, so you could argue it has some NASA "bias", but nonetheless I think it is fairly solid. EELVs at very high volume are $75 to $150 million per launch, depending on configuration (ie. Delta II vs. Delta IV Heavy). Currently, realistic costs could fall in the $150 to $200 million per launch range. Current actual costs can creep up a lot higher when there are low launch volumes.
http://science.ksc.nasa.gov/shuttle/nex ... V_main.htm
A shuttle launch has often been quoted at around half a billion, or $500 million, over the last decade. Here is a NASA site claiming $450 million:
http://www.nasa.gov/centers/kennedy/abo ... e_faq.html
When you include orbiter refurbishment, mission costs, and payload integration you can get up to $1.3 billion:
http://en.wikipedia.org/wiki/Space_Shuttle_program
A JS-246SH should also cost about $500-600 million. You have no orbiter to refurbish, but you use up an extra engine per launch and your SRBs are a bit more expensive (5 segment instead of 4).
So, a shuttle derived HLV costs between 2.5 to 4 times the cost of a heavy EELV to launch ($150 vs. $600, if we do a best case scenario for the EELV, $200 vs. $500, if we do a best case scenario for the SDLV). You get around 120 tons to LEO with the SDLV vs. 25 tons with the EELV. In other words, the SDLV still gets more pounds of payload to orbit for the same money. If we take the arguments some people make that EELVs are costing substantially more than $200 million per launch, then the SDLV looks better and better.
With the SDLV you avoid the dead weight of docking mechanisms for the different parts, as already mentioned in this thread. Dead weight reduces mission capability, and it increases costs (you're paying for payload you don't really use).
Then, also consider: a monolithic 120 ton vehicle will be significantly more robust (structurally sound) than a segmented vehicle constructed from multiple parts. Also, there are costs associated with on-orbit integration. You'll need yet another launch to send astronauts up to spend time finishing integration, even if the modules dock automatically. Integrating on the ground is cheaper, if the launch cost is the same, let alone less.
I share the frustration of other space enthusiasts, but, quite frankly, chemical rockets will always be mostly throw-away systems, and will always cost at least millions of dollars per launch. They will never be systems which individual families can use to get off the earth's surface. The only real game changers are tethers, a space elevator, and new physics that allow something like a gravitomagnetic drive.
Carbon nanotube composites combined with scramjets will likely make a spaceplane possible. Scramjet technology is pretty much there. Carbon nanotubes aren't quite there, yet. If no truly unexpected hurdles are encountered, they should be advanced enough to make a spaceplane and a space elevator feasible within a few decades. The spaceplane will make crew launch fairly cheap, but still not within reach of the average person.
I suspect that the theoretical SpaceX HLV will cost less than a JS-246SH when it eventually materializes. Perhaps $200-$300 million in today's dollars to launch 120 tons to LEO. If it turns out to be profitable to mine asteroids and other planets for resources, and good fusion powered interplanetary ships are available for flying around the solar system, there will be commercial companies willing to fly cargo up on such vehicles at such prices, and to fly workers up on spaceplanes. You will then get solar system colonization, slowly. The only way it can happen faster is with a "game-changer" breakthrough.
