The SR-71 Blackbird Astroinertial Navigation System was affectionately called R2-D2 after the Star Wars movie came out in 1977
No other reconnaissance aircraft has ever flown through such dangerous airspace with the same level of safety and freedom as the SR-71 Blackbird. It holds the record as the fastest aircraft powered by air-breathing engines. Its capabilities and mission successes made the Blackbird the peak of aviation technology during the Cold War.
Lessons learned from the A-12 program led the U.S. Air Force to conclude that the SR-71 could only be operated safely with two crew members: a pilot and a Reconnaissance Systems Officer (RSO). The RSO managed the extensive suite of monitoring and defensive systems on board. These included an advanced Electronic Counter Measures (ECM) system capable of disrupting most search and tracking radars, as well as the Astroinertial Navigation System (ANS).
Regarding the ANS, RSOs often remarked, “No one can jam or shoot down the sun, the moon, the planets, or the stars.”
Flying the Blackbird demanded absolute focus and left no room for error. Yet its pilots were exhilarated by the aircraft’s complexity and the intense rush 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 goose bumps remembering.”
Once the SR-71 settled into its cruising speed and altitude, the crew’s attention shifted fully to the mission: gathering intelligence on hostile and potentially hostile countries with an array of cameras and sensors. The pilot was responsible for flying the aircraft and monitoring the automated systems to ensure they were functioning correctly. At the same time, the RSO operated the cameras, sensors, and the critical Astro-Inertial Navigation System (ANS). The ANS was essentially a 1960s-era GPS, but instead of relying on satellites, it navigated by tracking the stars. This was necessary because, before modern satellite navigation networks, there was no other way to guide the SR-71 in the remote regions where it flew. The Blackbird had to determine its position with an accuracy of about 1,885 feet (575 m) and stay within 300 feet (91 m) of its intended flight path, all while traveling at extreme speeds for as long as ten hours at a time.
The ANS supplied precise target coordinates deep inside hostile territory. It functioned as a gyrocompass capable of sensing the Earth’s rotation while the aircraft was still on the runway, before the SR-71 took off. The RSO could note the exact coordinates of a specific point on the runway and then compare them with the ANS readout. The two almost always matched exactly. The same stars were not used on every mission; the system selected stars based on the region of the world the aircraft would be flying over. When operating in the Southern Hemisphere, it relied solely on stars visible from that part of the sky.
On July 2, 1967, Blackbird crew members Jim Watkins and Dave Dempster flew the first international sortie in SR‑71A #17972 after the ANS malfunctioned during a training mission, causing them to inadvertently enter Mexican airspace.
The ANS operates by simultaneously tracking at least two stars from an onboard catalog and, using a chronometer, computing the SR‑71’s position over the ground. Before each flight, the system was programmed, and the aircraft’s initial alignment, along with the full flight plan, was stored on punched tape, which instructed the jet where to fly, when to change course, and when to switch the sensors on and off. The stars were observed through a special quartz window located behind the RSO’s cockpit, and a dedicated star tracker allowed the system to detect stars even in daylight.
Later, after the film Star Wars was released in 1977, the ANS earned the affectionate nickname “R2‑D2.”
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Photo by Lockheed Martin, U.S. Air Force, Star Wars/Kristen DelValle and Daderot Own Work via Wikipedia
