The SR-71 Blackbird Astroinertial Navigation System was affectionately called R2-D2 after the Star Wars movie came out in 1977.
No reconnaissance aircraft in history has operated in more hostile airspace or with such complete impunity than the SR-71 Blackbird. It is the fastest aircraft propelled by air-breathing engines. The Blackbird’s performance and operational achievements placed it at the pinnacle of aviation technology developments during the Cold War.
Experience gained from the A-12 program convinced the US Air Force that flying the SR-71 safely required two crew members, a pilot and a Reconnaissance Systems Officer (RSO). The RSO operated with the wide array of monitoring and defensive systems installed on the airplane. This equipment included a sophisticated Electronic Counter Measures (ECM) system that could jam most acquisition and targeting radar and the Astroinertial Navigation System (ANS).
About the ANS RSOs were known to say, “no one can jam or shoot down the sun, the moon, the planets or the stars.”
Piloting the Blackbird was an unforgiving endeavor, demanding total concentration. But pilots were giddy with their complex, adrenaline-fueled responsibilities. “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.”
But once the SR-71 reached cruising speed and altitude, it was time to focus on the mission, which was to collect information about hostile and potentially hostile nations using cameras and sensors. The pilot’s job was to handle the aircraft and watch over the automatic systems to make sure they were doing their jobs properly. Meanwhile, the RSO handled the cameras, sensors, and the all-important ANS. The ANS was the 1960’s version of GPS, but instead of using satellites to locate itself, the ANS used the stars. This is because before the invention of the modern satnav networks there wasn’t a way to navigate the SR-71 in the areas where it operated. The SR-71 needed to be able to fix its position within 1,885 feet (575 m) and within 300 ft (91 m) of the center of its flight path while traveling at high speeds for up to ten hours in the air.
The ANS provided specific pinpoint targets located in hostile territory. It was a Gyro compass that was able to sense the rotation of the earth, while still on the runway before the SR-71 would take off. The RSO could use his coordinates of the spot ….of one place …on the runway …then read of the ANS. They were almost always exactly the same. Not always were the same stars were used on every mission, as they used the stars depending on what part of the world they were going to fly to. If flying in the southern hemisphere they used only the stars that were seen there.
On Jul. 2, 1967 Blackbird crew Jim Watkins and Dave Dempster flew the first international sortie in SR-71A #17972 when the ANS failed on a training mission and they accidentally flew in to Mexican airspace.
The ANS works by tracking at least two stars at a time listed in an onboard catalog, and with the aid of a chronometer, calculates a fix of the SR-71 over the ground. It was programmed before each flight and the aircraft’s primary alignment and the flight plan was recorded on a punched tape that told the aircraft where to go, when to turn, and when to turn the sensors on and off. The stars were sighted through a special quartz window (located behind the RSO cockpit) and there was a special star tracker that could see the stars even in daylight.
Later on after the Star Wars movie came out in 1977, the ANS was affectionately called R2-D2.
Be sure to check out Linda Sheffield Miller, Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Facebook Page Habubrats for awesome Blackbird’s photos and stories.