Friday, February 15, 2013

Asteroid DA14 and Diamond DA20s

As I write, the asteroid DA14 is passing its perigee, its closet approach to Earth.  I am not afraid of it hitting me, nor am I afraid of it actually hitting a GPS or other navigational satellite directly.

I was worried about the perturbation of a satellite's orbit due to a 1.9E8 kg asteroid passing nearby.  As you are aware, GPS depends on having a super-accurate model of the satellite's orbit, and any error in computing the satellite's orbit translates directly into an error in your GPS estimated position.

My first thought about flying today was to make sure that I am prepared to revert to non-GPS navigation.  No, I take that back, not just prepared, but I need to actually make non-GPS navigation primary.

But after a back-of-the-envelope calculation of the gravitational attraction between a 1.9E8 kg asteroid and 2E3 kg GPS satellite I am not so worried.  Still, the lesson remains: many things beyond human control affect the accuracy of GPS navigation, and we as pilots need to maintain our ability to navigate without GPS.

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