Comments on: Where are we, anyway, exactly? NASA is working on that https://gregladen.com/blog/2012/02/24/where-are-we-anyway-exactly-na/ Sat, 25 Feb 2012 13:58:55 +0000 hourly 1 https://wordpress.org/?v=6.4.6 By: hoary puccoon https://gregladen.com/blog/2012/02/24/where-are-we-anyway-exactly-na/#comment-491492 Sat, 25 Feb 2012 13:58:55 +0000 http://scienceblogs.com/gregladen/2012/02/24/where-are-we-anyway-exactly-na/#comment-491492 GPS was commercially available in 1992 when we sailed across the Atlantic. For $3000 or so, you could get a set that gave latitude and longitude (none of those cute charts) as long as the military wasn’t messing around with it just then. We didn’t have the spare 3 grand, so we had an old SatNav — a previous satillite navigation system. The satillites for that system were expiring and not replaced, so we could easily go four hours between good fixes. That was no problem on the days far from land, but hairraising threading between the Azores islands in the dark. I would have killed for a GPS that night.
We were still better off than two Danish sailors, who crossed with just a sextant, and no radar. They had to stand off the Azores for three days, waiting for fog to clear.

And, of course, whatever system people had, they had to cross check with charts that were often based on sextant readings from the nineteenth century. So, the satillite navigation could be spot on, but the charts a mile or more off.

It makes me laugh when people complain that GPS can be a few feet off. We’ve forgotten how lucky we are.

]]> By: MadScientist https://gregladen.com/blog/2012/02/24/where-are-we-anyway-exactly-na/#comment-491491 Sat, 25 Feb 2012 01:37:10 +0000 http://scienceblogs.com/gregladen/2012/02/24/where-are-we-anyway-exactly-na/#comment-491491 The JPL’s global GPS receiver network has been around for about 20 years or so. Once upon a time you joined the network and in turn received corrections so that you could get better positioning without the GPS ‘P code’. Laser ranging work has been going on for even longer (though the size of the transmitters and receivers has shrunk a bit since the bad old days). For example, the long defunct NASA Orroral Valley Laser Ranging Station (http://www.carnarvonspace.com/wiki/index.php?title=Yatharagga:_Satellite_Laser_Ranging_%28SLR%29_Station) and a long-running nearby successor owned by the Australian government and operated by Geosciences Australia (http://www.ga.gov.au/about-us/news-media/news-2004/mount-stromlo-back-in-orbit.html).

So – instruments may be improving, but this is a very old project (or at least a successor to a very old project).

]]>