Congress is tearing NASA apart with its porkulous rocket, all the while not giving it anything to put on that rocket, except maybe giant wads of paper.
But what if we could put together a new heavy lift launch vehicle without going through the expense of a completely new rocket?
One of the interesting features of the Shuttle stack is the external tank, which is mounted to a pair of solid rocket boosters, which suspends not only thousands of tons of cryogenic fuel, but the hundred tons of shuttle above the pad. That fuel in the ET is feed to the shuttles main engines, and between the five engines, the entire stack is lifted, even though there are no engines on the ET.
If we did the same thing, mounting anywhere from four to eight existing liquid boosters around an ET, filling it and the boosters with fuel, cross feeding them, but omitting the engines under the ET, we should be able to loft very heavy loads without actually "building" a new rocket. Best of all, that ET, or Core, could be modified to a host of far reaching purposes, employing the standard payload nose, plus the aft end in the studied but never implemented "Aft Cargo Carrier" configuration.
These boosters, be it the Falcon, Delta, or Atlas, are all either already internally configured as boosters, or are proposed on paper to be. So whatever modifications would be minor, and mostly related to the cross feed function.
Basically, with anywhere from 4 to 8 medium lift rockets strapped together, depending on the intended payload, any amount of fuel we want to put in the Core, we should be to launch at least a couple hundred tons into orbit, plus the Core for wet workshop operations. We could put a fully loaded Core tanker full of fuel up to L1, recirculation, docking, and power equipment included. We could launch a fully loaded Mars Shuttle, with propulsion units in the Aft Cargo Carrier, covered by a faring, and all the interior furnishings in the nose, just waiting for venting of leftover fuel, and assembly. Theoretically, we don't even have to jettison the boosters. Imagine lofting a core and eight boosters whose only cargo is an aft cargo carrier sporting decent engines and landing struts, and enough fuel to land the whole thing on the Moon. Those boosters could laid gently down, and used as habitable volume for dozens.
This way, NASA can concentrate on mission specific alterations to the core, commercial space can provide the boosters, and we get the lift we need.