Mission profiles vary greatly, depending on distance between operating base and target areas as well as other factors. From a forward operating location (FOL), it may be possible to access a target area using a single-legged, 1-hour mission. Where range to target is greater, mission is multi-legged. Where extra range is required for a mission, top-off refueling is performed after takeoff, before ascent to the first supersonic leg. During supersonic leg, airplane altitude increases as fuel consumed. Reconnaissance legs are flown at higher altitude and speed to optimize survivability. The above is a simplified diagram of both single and multi-legged missions. The diagram shows the airplane returning to original base; however, depending on mission plan, it may land at an alternate base.
Source: SR-71 Reconnaissance System, Executive Handbook