I remember reading a DC-X advocate who explained problems with launch rails. To be taken with a grain of salt of course, but...
Rail types
http://web.wt.net/~markgoll/mg3.htm http://forum.nasaspaceflight.com/index.php?topic=16553.0
Not remotely NASA's fault. Blame Congress for dicking NASA around for decades.
That and the United States Air Force, which insisted on messing with the shuttles size--over HEXAGON
http://forum.nasaspaceflight.com/index.php?topic=29244.0
The entire Space Shuttle stack was a Heavy Lift Launch Vehicle (HLLV, HLV, etc).
The problem was that 100 tons or so was the dead mass on orbit orbiter.
Now that isn't necessarily a bad thing. A big shuttle has mass to help hold station modules--the dog is still waging the tail, as it were.
Remember what happened to the out of control Gemini when it released the Agena? It just made things worse.
The problem is that the right country made the wrong shuttle.
I have always loved the modular Energiya Buran, a true space transportation system.
http://www.k26.com/buran/ http://www.buran.ru/htm/history.htm http://www.buran.ru/htm/mtkkmain.htm
You had liquid fueled strap-on boosters that, had they not been Ukrainian, would have replaced R-7 and UR-500 Proton.
These Energiya boosters, with upper stages, are known today as Zenit--named after a Vostok-based spysat of the same name. These are the LVs used by Sea Launch.
The engine is a four nozzle RD-170-series. Cut two nozzles off, and you get the half-strength RD-180, that Atlas V uses--and is the source of much contention with SpaceX vs ULA.
The RD-170 has as much thrust as Saturn V first stage F-1 engine, and Zenit was to launch a Super Soyuz called Zarya:
http://www.astronautix.com/craft/zarya.htm
Zarya now refers to an ISS segment.
The difference between Energiya and the American shuttle is this: The orbiter had three big hydrogen engines (SSMEs), that fed from hydrogen and oxygen from the big organge External Tank--meaning you had to launch that orbiter just to get 20 tons of payload up there--about as much as Delta IV, Ariane V Titan IV, etc.
Thus the External Tank was very like the drop tank on WWII fighters, or on the Hustler bomber. Since the orbiter had the big hydrolox engines, they could be returned to be refurbished. They took up so much space in the aft boat-tail that it forced the OMS pods into those bumps to either side of the tail fin. The propellant tanks inside them?
--about the size of beach balls.
That is all the fuel that orbiter had to use in space. The three SSMEs were dead once that External Tank blew off.
The Soviet design was better.
They had liquid Zenit strap-ons--so no Challenger disaster, and the hydrogen engines were under the External Tank itself.
This made the orbiter much simpler. No, you couldn't re-use the hydrolox engines, but they were too much of a bother to deal with any way.
The important thing to remember is that Energiya was an Ares V/SLS launch vehicle in its own right. It could carry a simpler orbiter with an aft boat-tail full of fuel, so Buran would have been a more capable orbiter, with nearly 30 tons of payload--or the orbiter could be swaped out with a 90 + ton payload pod like Polyus, even simpler than Shuttle C, which was pretty much just an unmanned orbiter without wings.
And the number of Zenits could be dialed up, to surround the engine equipped Energiya core block, to form Energiya Vulkan, a near NOVA class HLLV.
So the EELV-class Zenit liquid fueled boosters could replace R-7 and Soyuz, you had a heavy lifter for Moon missions, and a shuttle orbiter. A true system.
Since the External Tank had the big engines, the orbiter could fly in a heads up attitude, and there would be no need to have propellant lines run along the surface of the ET, shedding foam on an underslung orbiter, like Columbia.
With Energiya you could launch 90 ton station modules, and a big orbiter to bring 30 tons of raw materials to one side of a space factory, and return 30 tons of processed goods from the other end.
The modular nature allowed greater flexibility--and what is more, this would have helped hypersonic research.
With Energiya's SSME type engines under the External Tank itself, the orbiter could be switched out with hypersonic boilerplanes of near orbiter size..
One orbiter might have a faget straight wing, another might be a giant lifting body, you could have, say a waverider scramjet craft tested at full scale.
Had the United States gone with tis design, the 747 orbiter ferry could have releases a NASP test article for low speed tests, and released the boilerplate from an Americanized Energiya for high speed re-entry tests.
Once the perfect spaceplane design is found, the orbiters would be retired, and the spaceplane scaled up for a true SSTO, TSTO, or whatever.
The Energiya HLV remains, and is used for BEO, station segment launch, etc.
The largest SSTO would have been Star Raker, with 100 tons to orbit. Then, all expendables can finally die, but only after serving as a means to an end--the STS acting as a giant Navaho, allowing full scale tests.
Airbreathing scramjet test articles now are about the size of surf-boards--closer to warheads than airframes.
Energiya Buran was the right STS, but made by the wrong country. Had it been the other way around, 14 astronauts would still be alive, we would have operational RLVs, and mean would be back on the Moon, if not Mars.
We are finally putting SSMEs underneath our External tanks, but keeping an Apollo type capsule atop the External tank.
This is now SLS, the space launch system:
http://www.nasa.gov/exploration/systems/sls/index.html
http://www.nasaspaceflight.com/2014/05/four-shuttle-veterans-drive-sls-uphill-maiden-flight/
I'll take what I can get.
Without the orbiters, things are a bit simpler now.
Here is a brief history on shuttle derived heavy lift
http://chapters.nss.org/ny/nyc/Shuttle-Derived%20Vehicles%20Modified.pdf
http://www.spacelaunchreport.com/sdv.html
An Americanized Energiya was proposed
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910018890.pdf
http://ntrs.nasa.gov/search.jsp?R=1...0shuttle%20derived&Ntx=mode%20matchallpartial
http://forum.nasaspaceflight.com/index.php?topic=6348.0
Take a look at figure 21 in the big pdf below
https://www.aiaa.org/uploadedFiles/...uttle_Launches/ShuttleVariationsFinalAIAA.pdf
This worked out very nicely...The subsonic L/D increased to an estimated 6.02 as a result
Other spacecraft concepts
http://www.buran.ru/htm/family.htm the АКРК Т-4 launcher looks interesting, if a bit small
On the other hand...
http://www.buran.ru/htm/foto9.htm#tupolev_aks