SR71 Astral Navigation ?
Last week I was privileged to attend the SETP symposium and oral history sessions in LA, and for those who missed it - my deepest commiserations, it was a remarkable event.
During the week, we had two presentations on the SR71's development, testing and operations. At one point one of the test pilots mentioned an "astral navigation" system which he said gave ?}120ft of track at cruise (M=3.2) speeds.
So the question to the house is - what was this remarkable piece of technology, how did it work, and why did we bother with GPS if it was really so good? (I'm guessing that at least part of the last answer is continuous sight of sky, but presumably not all of it.)
G
(Currently out of town)