When the Space Shuttle system was new, NASA planned a Shuttle-C for Cargo. The winged orbiters would be replaced by a cargo pod, powered by the same Space Shuttle Main Engines (SSME) and Orbital Maneuvering System. Without the burden of wings or crew compartment, this configuration could lift twice as much payload to orbit without risk to crew. During the first Bush administration, Shuttle-C was promoted as a heavy-lift vehicle for the Moon and Mars. The new booster's cost, over 5 billion USD, led to it being abandoned.
On June 17 before the Augustine Commission, Shuttle Program Manager John Shannon described this "Sidemount" booster, similiar to Shuttle-C. Because so many components are common with Shuttle, this could be built for about 6.6 billion USD. This is slightly more than the shutdown costs of Constellation (2.5 billion) combined with the proposed R&D budget for boosters (3.1 billion). For an extra cost, the Sidemount booster could be human-rated. A Moon mission would launch Orion with an extra stage to boost the crew into lunar orbit for rendezvous with the lander. Launch Complex 39 and much of the Shuttle workforce would be maintained.
As promising as Commercial Crew is, terminating all of Constellation might be foolish. A Crew Exploration Vehicle is needed to move beyond Earth orbit. The parts to build Sidemount already exist, along with people who know how to build and launch them. Abandoning the production of tanks and Solid Rocket Boosters would lose those technologies indefinitely. Laying valuable people off would be a poor reward for a successful Space program. When the President visits Kennedy Space Center on April 15, he should consider building a new rocket.