It was designed to be lauched off of a track with a rocket sled:
Cool idea, but you are faced with a dilemma. The design probably wouldn't have worked with just a rocket sled and internal propellants.
The vehicle likely would've had to be larger to make near-orbit, or external tanks or booster rockets may have been needed.
Also, the aerodynamics are questionable, but that can be ignored for Orbiter.
You're dilemma would be whether to stick to the original plan and overpower the engines vs. giving the vehicle an extra boost.
Cool idea, though. Bonus points if you can drop a dirty nuke on NY City and hit Central Park!