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]This brings up the question of "what do we have now that replaces this thing?"

AviationNow reports Two-Stage-to-Orbit 'Blackstar' System Shelved at Groom Lake?.

A large "mothership," closely resembling the U.S. Air Force's historic XB-70 supersonic bomber, carries the orbital component conformally under its fuselage, accelerating to supersonic speeds at high altitude before dropping the spaceplane. The orbiter's engines fire and boost the vehicle into space. If mission requirements dictate, the spaceplane can either reach low Earth orbit or remain suborbital.

The manned orbiter's primary military advantage would be surprise overflight. There would be no forewarning of its presence, prior to the first orbit, allowing ground targets to be imaged before they could be hidden. In contrast, satellite orbits are predictable enough that activities having intelligence value can be scheduled to avoid overflights.

Photo credit: www.aviationnow.com/Aviation Week & Space Technology