Time and Space

Once again my friends and colleagues at Gogo Business Aviation in Broomfield Colorado indulged me, in the form of my alter-ego John Sloan, by letting me come and give a talk entitled Time & Space on the historical connection between precision timekeeping and navigation. They taped it and put it on the 'tube. I had a great time, and hopefully I wasn't the only one. Among lots of other things, I describe how both GPS and atomic clocks work.

I did, in my enthusiasm, misspeak a couple of times - that's the hazard of giving an hour long talk without slides or notes - and have made some corrections below.

A big Thank You to the folks at Gogo for sponsoring this.

Corrigendum

1. Despite my saying that the escapement wheel is not a gear (and it's not), I incorrectly referred to it as a gear once or twice.
2. When I gave the example about longitude, it would be 5 hours and 11 minutes before GMT, not after.
3. One of my Ph.D. physicist colleagues remarked that it's not really a different electron orbital shell to which the electron transitions but instead a hyperfine transition. (I'll have to look that up.)
4. In my excitement, I said neutrons have a positive charge when of course I meant it is protons which have a positive charge. (A particularly egregious mistake since I've know that since grade school.)
5. The GPS block IIF satellite has three atomic clocks. not four: two rubidium and one cesium. An earlier model GPS satellite I've studied has two of each.
6. There are a variety of algorithms used by GPS to determine your position; I described one class of algorithms. There are simpler closed-form solutions that work for time measurements from four satellites. And there are even simpler algorithms that work for three satellites, but which don't compute altitude. The iterative solution I describe is the most general one, solving for all three spatial coordinates, for time, and for as many satellites as can be observed.
7. I said the volume of the final GPS solution was fifteen meters across. It's actually about five meters across, or about fifteen feet. That jives with a timestamp resolution of about fifteen nanoseconds (light travels about a foot in a nanosecond), and not the 1.5 nanoseconds I quote in the talk. (Maybe I should break down and use notes or slides, huh?)

John Sloan and Internet Protocol version 6

Once again my good friends at Gogo Business Aviation in Broomfield Colorado have been following my work, this time on the Internet Protocol version 6 (IPv6) testbed that I wrote about in Buried Treasure. They invited my alter ego John Sloan to give a talk about it. The fact that they fed us all pizza may have had more to do with the packed house than the topic at hand. But Gogo has a vast system of cell towers - whose antennas point up - and an associated ground network to talk to aircraft that use their Air To Ground (ATG) network connectivity product. So they know a thing or two about networking in the cloud.

The folks at Gogo recorded the talk, made it available on YouTube, and generously allowed me to share it. You can find the slides for this talk on GitHub.



Thanks once again to my colleagues at Gogo Business Aviation for sponsoring this talk. It was fun!