Feb 122010

NASA's SDO ready for launch

And coming out to play with your satellite navigation, and possibly satcoms, too, so the launch of the Solar Dynamics Observatory scheduled for today is timely.

After years of such quiescence since the Sun’s last maximum activity in 1985 that some astronomers muttered about a new Maunder Minimum*, the sun has suddenly woken up. Within the next few years we’ll be licked by solar flares and a variety of phenomenae that will reach out and touch the constellations of satellites on which we now depend and nobody really knows what’s going to happen.

Reaching out to touch you - a solar flare

A solar flare is the satellite’s equivalent of being beaten around the head with a baseball bat. Most satellites are protected to some extent against this electrical assault but signals could be lost for hours or days as the massive, broad band of electromagnetic radiation swamps the puny signals of the satellites.

That may actually cause few problems, apart possibly from dynamic positioning operations. If the GPS isn’t there you’re not going to be using it and you’ll rely on other systems.

More of a problem, over a longer term, and more unpredictable, may be that the GPS gets fooled.

GPS assumes that signals travel at the same, and at constant speed, an essential part of knowing the distance of the receiver from the satellite. Between your GPS and the satellites it depends on is the ionosphere. Solar flare radiation can affect the speed at which signals travel through the ionosphere and slow them down. It is not a constant effect so Satellite A’s signals can travel at a different rate from satellite B’s signals and both at a different rate to Satellite C.

Solar radiatioon could lead to signals running slower

In an interview with the BBC, Professor Cathryn Mitchell of the University of Bath says: “We can look at the measurements from the last solar maximum… If we project those forward, it varies quite a lot across the Earth; looking at the UK it will be about 10-metre errors in the positioning… Ten metres out is probably going to be OK for a sat-nav system in a car, but if you’re using the system for something safety-critical like ships coming into harbour for navigation or possibly in the future landing aircraft, you’re looking for much greater accuracy and more importantly, much greater reliability.”

*The Maunder Minimum was a period of quiescent Sun activity that coincided with a ‘mini-ice age’ in the 1800s that lasted for about 70 years.

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