Mounted behind the SR-71 Blackbird RSO’s cockpit, this unit (that was affectionately dubbed “R2-D2” after the Star Wars movie came out in 1977) computed navigational fixes using stars sighted through the lens in the top of the unit
The SR-71, commonly referred to as the “Blackbird,” was a long-range, Mach 3+ strategic reconnaissance aircraft that evolved from the Lockheed A-12 and YF-12A models. Its maiden flight occurred on December 22, 1964. The first SR-71 in service was delivered to the 4200th (later known as the 9th) Strategic Reconnaissance Wing at Beale Air Force Base in California in January 1966.
The Blackbird represented a complete departure from previous aircraft. As famed Skunk Works designer Kelly Johnson noted in an article on the Lockheed Martin website, every aspect of its design required new inventions.
Lessons learned from the A-12 program led the US Air Force to determine that operating the SR-71 safely needed both a pilot and a Reconnaissance Systems Officer (RSO). The RSO managed a complex array of monitoring and defense equipment on board, including an advanced Electronic Counter Measures (ECM) system to block most tracking and targeting radar, as well as the Nortronics NAS-14V2 Astroinertial Navigation System (ANS).
The Smithsonian Institution states that the ANS enabled the SR-71 to quickly determine its position using celestial navigation.
Positioned behind the RSO’s cockpit, the unit—nicknamed “R2-D2” after the release of Star Wars in 1977—calculated navigational fixes by observing stars through a lens at the top of the device. These fixes continuously updated the inertial navigation system and provided guidance with a precision of at least 90 meters (300 feet). Modern aircraft and missiles still use upgraded versions of this technology as a backup to GPS.
About the ANS RSOs, they were known to say, “No one can jam or shoot down the sun, the moon, the planets, or the stars.”
Flying the Blackbird was extremely demanding and required complete focus, yet pilots were exhilarated by the intense and complex nature of their duties. “At 85,000 feet and Mach 3, it was almost a religious experience,” said Air Force Colonel Jim Watkins. “Nothing had prepared me to fly that fast… My God, even now, I get goosebumps remembering.”
After reaching its designated speed and altitude, the SR-71 crew would shift their attention to the reconnaissance mission, gathering intelligence on potentially hostile targets using onboard cameras and sensors. The pilot was responsible for flying the aircraft and monitoring automated systems. At the same time, the RSO operated the cameras, sensors, and the crucial Astroinertial Navigation System (ANS). In the 1960s, the ANS functioned much like a modern GPS, except it relied on reading stars since satellite navigation was not yet available. The SR-71 required highly precise position tracking—within 575 meters (1,885 feet) and 91 meters (300 feet) of its flight path—even while flying at high speeds for up to ten hours.
The ANS enabled the SR-71 to identify targets in enemy territory accurately. Acting as a gyro compass, it could detect Earth’s rotation even while stationary on the runway. The RSO’s position readings always closely matched those given by the ANS. Different stars were used for navigation on each mission, depending on the flight’s destination. When flying in the southern hemisphere, only the stars visible from that region were selected (though it’s not confirmed if such missions occurred).
On July 2, 1967, during a training mission, the ANS malfunctioned, and SR-71A #17972, flown by Jim Watkins and Dave Dempster, unintentionally crossed into Mexican airspace—marking the Blackbird’s first international mission.
The ANS functioned by simultaneously tracking at least two stars from an onboard catalog and, with the help of a chronometer, calculated the SR-71’s position over the ground. Before each mission, the system was programmed, and the flight plan, along with the aircraft’s initial alignment, was stored on a punched tape. This tape directed the aircraft’s route, indicating when to turn and when to activate or deactivate sensors. The stars were observed through a special quartz window located behind the RSO cockpit, and the dedicated star tracker was capable of detecting stars even during daylight.
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Photo by Lockheed Martin, U.S. Air Force, Star Wars/Kristen DelValle and Daderot Own Work via Wikipedia
