SR-71 Goes South
When the SR 71 flew in the Southern Hemisphere, the navigation system had to be adjusted.
The SR-71 conducted brief operations from the remote island of Diego Garcia in the Indian Ocean in 1978 and 1979. During these deployments, the aircraft flew briefly in the Southern Hemisphere, which highlighted a unique technological limitation regarding the SR-71's complex Astroinertial Navigation System (ANS).
Southern Hemisphere Navigation and Diego Garcia
The Problem: The SR-71’s ANS was one of the first automated celestial navigation systems, designed to track pre-programmed stars through a quartz window day or night to maintain incredible precision. However, mission planners only loaded the Northern Star Catalog into the system.
The Incident: As crews crossed the equator heading toward Diego Garcia, the system lost its ability to track the stars and guide the aircraft automatically. The crew was forced to dead-reckon their flight path until they reached the island, and relied on a specialized northbound return route where the system could reacquire Northern Hemisphere stars.
Base Facilities: In 1978, the U.S. Air Force dismantled one of the climate-controlled SR-71 hangars at Beale Air Force Base in California and shipped it to Diego Garcia to shelter the deployed jets.
Diego Garcia Details
Location: A coral island in the Chagos Archipelago in the central Indian Ocean.
Strategic Role: It serves as an isolated, highly strategic military hub (Naval Support Facility Diego Garcia), featuring a massive runway long enough to handle heavy bombers and shuttle operations.
A few years ago I wrote to SR-71 pilot Buz Carpenter about his mission in the southern hemisphere.:
The mission to Diego Garcia was a planned mission to exercise the assets we had on the Island. I flew this with my last RSO, Tim Shaw and as we approached the equator in the Indian Ocean we lost our star tracking automatic navigation capability.
The technicians had not realized that Diego was south of the equator so we would need both the North & Southern star Catalogs. We dead reconned the Island. Funny thing when we took off the next day or two days later we still did not have a Southern Star catalog. The plan was a takeoff, refuel, and climb over Daigo Garcia to take a fix and then take up a northeast heading taking us back to Okinawa. We would continue this heading until we were near the equator and our loaded Northern Star Catalog would guide our Astroinertial navigation system to once again provide accurate guidance for us which it did. The rest of the flight was uneventful returning to Kadena.
John Murphy and I had been part of the ops team that set up Diago Garcia a few years earlier under President Carter.
`Bux Carpenter
Thank you, Buz.~Linda Sheffield
@Habubrats71 via X
