The problem with the Big Dumb Booster concept is one of economics and demand. A BDB (defined as a high payload, low specific performance vehicle built to shipbuilding tolerances and materials rather than aerospace grade construction) is a vehicle for boosting high bulk materials to Low Earth Orbit (LEO) with a significantly greater tolerance for catastrophic launch than typical payload such as a high value satellite (e.g. an 80% or 85% success rate would be considered acceptable versus the standard of 95% for moderately valuable payloads or 98% for high value payloads). Such a system, by itself, would not be suited for deploying satellites, although if accompanied or supported by a space tug could be used for deploying constallations of satellites (provided they were sufficiently robust or protected from flight environments). The payload that would be most suitable for this application would be fuel, bulk materials, or large simple structures such as space station modules. At the time that the BDB concept was in vogue, there was considerable enthusiam for large scale habitable structures, up to structures the size of O’Neill habitats and Bernal spheres, and indeed, such structures would require a BDB to lift major components. However, once it became apparent how expensive it would be to construct even stations of moderate size (supporting a crew of a few dozen people) and the amost complete lack of any credible commercial applications, the actual market for BDB type vehicles was essentially nil. It probably didn’t help that NASA was institutionally focused on the STS (‘Shuttle’) as its singular heavy lift platform regardless of its substantial limitations.
Another major issue with the BDB concept is prosaic but problematic; transportation and handling of structures that are essentially the size of a frigate by land or rail is extremely difficult. Size and mass is what drove the size of the Shuttle Solid Rocket Boosters and the requirement that they be built in segments and assembled in the field. Similarly, the choice of facility for the STS External Tank was dictacted by the ability to transport via barge. The ET is essentially at the lower end of BDB-class vehicle, and really, is the largest practical structure to handle on land. Such vehicles also require very large processing and launch facilities that would dwarf the Saturn/STS Vehicle Assembly Building and the complementary structures at Baikonur. Truax’s Sea Dragon concept got around this by assembling, towing, and launching the vehicle in the water, thereby never requiring any ground based T&H equipment or launch facilities. However, it should be pointed out that no one has ever attempted to launch an orbital launch vehicle in such a manner and the logistical problems of operating a launch platform in mid-ocean are greater than anticipated at the time, as evidenced by the experience with SeaLaunch. There is also the issue of sealing the payload against salt water intrusion and making the critical systems on the launch vehicle sufficiently corrosion resistant to withstand being submerged in a marine environment for indefinite duration.
In short, while the concept was innovative, it would also come with a new set of challenges to overcome. I think it could be done, but without demand for haulage of bulk cargo to orbit there just isn’t any incentive to develop the vehicle and processes for doing so.
Do you mean “shedding tankage” but keeping the propulsion system? The problem with that is that conventional launch systems have the propulsion system attached to and mounted below the tankage. There have been proposed systems which feed propellant from side tanks (called propellant crossfeed) and then drop them once they have been depleted, leaving the main stack to fly, but because of the thrust to weight ratio it is usually necessary that those tanks also have their own propulsion systems, and the complexity of feeding the engines from different systems isn’t judged to be worth the gains in performance (although at least one contractor is attempting to develop that kind of system). And because the requirements for upper stage propulsion (lower thrust, better propulsive efficiency, longer duration) or different than for ground level propulsion, carrying the same engines throughout the flight comes with a substantial weight penalty that can only be mitigated by altitude compensating nozzles and reusable vehicles.
However, modular approaches and parallel staging have been proposed and used in a number of vehicles, the most radical of which was the Otrag rocket which would have used clusters of parallel, pressure-fed stages which would be cheap to manufacture and fault tolerance, with outer stages being expended in the same fashion as solid rocket boosters only en masse. I personally question the viability of this design based upon construction issues, but in general concept it was certainly workable. The Conestoga rocket was a less radical version of this concept. However, the more tanks/engines/motors or other separate hardware you have to expend results in greater complexity, more individual parts to test (and that can fail) and generally more problems than any efficiency gains that might be provided. Two or three relatively simple stages containing as few engines as needed to obtain the required thrust levels are, at least from the standpoint of a conventional launch vehicle, probably the way to go to reduce the costs for space access.
It should be noted that a lot of costs savings are not on the design of the vehicle itself or any performance advantages, but by reducing the labor and handling costs on the ground, i.e. making the vehicle easier to manufacture and transport, more tolerant to manufacturing variances and normal handling, faster to assemble and fuel, and requiring less ground crew and facilities. This has never been the focus of the NASA space flight program (which has frankly become as much of a jobs program as a space flight program) and there is much low hanging fruit. However, there is the danger of removing too much oversight and checkout and resulting greater potential for error or overwork of the ground crew. The right balance of robustness, ease of maintenance, and performance is delicate, and has to be weighed against costs and the fickle market demand which gutted a number of potentially successful efforts in the late 'Nineties and early 'Zeros to develop alternative launch vehicles and platforms (e.g. the Kistler K-1, t/Space CXV, AirLaunch Falcon SLV)
In my personal opinion, the X-33 and VentureStar (X-33 was the subscale technology demonstrator, the VentureStar would have been the full-sized operational vehicle) was an attempt to do the right thing the wrong way. In concept it was a reusable SSTO launched vertically and capable of a runway landing, requiring significantly less infrastructure than the STS. However, instead of a program of incrementally improving the state of the art to get some minimial payload (e.g. a crew of 4-6 astronauts and 1000 kg of cargo) to orbit, NASA Lockheed Martin attempted a number of radical innovations that would make it a (marginally) heavy lift vehicle capable of being refurbished and flown in a matter of days, which essentially neglected every lesson learned from the development and operation of the STS. The massive insulated internal tankage required to carry the cryogenic hydrogen fuel was the real killer to this program, and the metallic thermal protection system–touted as being lower maintenance than the problematic ceramic tiles on the Shuttle Orbiter–was not nearly as robust as originally promoted, demonstrated by even the relatively moderated conditions of the F-15 tests. The one innovative technology that was well developed–the linear aerospke engine–has never been used or even seriously proposed for another vehicle. Although Lockheed is reportedly still working at low levels on the X-33, I have significant doubts that it will ever be a viable configuration to reduce access cost to space even if the technical issues with the tank materials and thermal protection systems are resolved.
Stranger