Mike Nichols – “Astro Navigation in Aviation”

February’s meeting provided another twist on the vast subject of astronomy when Papworth resident, Mike Nichols, talked to us about astro navigation. Mike spent a career in aviation, flying with the RAF and civilian airlines, including a stint with private planes for VIPs. Mike started his career in the days before GPS was invented as a navigation aid.

He began his talk with the story of a plane that got lost over the South Pacific when flying from the tiny island Pago Pago to Norfolk Island off the coast of Australia. The pilot was told to line his clenched fist against the Sun and estimate the number of degrees elevation. In this way, he could give the controllers an idea of his position, and eventually land safely, because of the simple principle behind astro navigation. This is understood by thinking of a light on top of a mast. The closer you are to the mast, the higher the light will appear and when further away, it will appear lower.

The system of astro navigation (initially just for ships of course) was invented in around 1875 by Marc St Hilaire, a French Admiral. Instead of lights on masts, celestial bodies are used instead; these include the Sun, Moon, Venus, Mars, Jupiter and Saturn, as well as 57 named stars. For navigation on aircraft, the naval sextant has been modified so it remains stable in flight and is heated to avoid being iced up when protruding from the fuselage in a perspex canopy. With a special marker to increase the precision of measuring the elevation of a body, this system proves to be remarkably accurate, perhaps to within a few miles. Mike showed some pictures of instruments used on the Hercules aircraft and the Apollo missions. The advantages of astro navigation over modern GPS are that it is simple, free and emits no signals from the aircraft. Of course it can only work if the sky is clear and the turbulence is light. Rather soberingly, the V bomber nuclear strike force was trained to use astro navigation in the event of approaching Russian targets so as to be “radio silent”. Luckily, they never had to try it out.

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