The origins of GPS, and the pioneers who launched the system (2010)

Their threshold for cheap and portable was "Less than 100 pounds, less than $100,000". Definitely shows how far we've come.

Hopefully using OpenStreetMap :D

To think you can download a 48.1 GB PBF-compressed file [1] and get a map of just about every trail and built structure that exists* for free and store it on an SD card the size of a fingernail - it just blows my mind.

* There is better coverage in Western countries unfortunately

[1]: https://wiki.openstreetmap.org/wiki/Planet.osm

https://en.wikipedia.org/wiki/Coordinating_Committee_for_Mul...

It takes the advantages of digital signaling, and throws them out, instead measuring the analog carrier waves directly. That this can be done at such low signal levels is unbelievably impressive.

(The statistical methods involved in getting an initial signal lock are nearly as impressive.)

And the whole thing was a 1980s hack for land surveyors to get better than 100m accuracy while systematically eliminating uncertainty due to Selective Availability (SA).

It's a hack that improved the overall accuracy of the system from ~100m to sub ~1cm, and eventually sub ~1mm accuracy, when used with some other methods.

4+ orders of magnitude improvement! From a hack!

>They used wood-splitting axes to break into two clean rooms containing nine satellites being built for the U.S. government. Lumsdaine took his axe to one of the satellites, hitting it over 60 times.

>They were arrested and faced up to 10 years in prison for destroying federal government property, causing an estimated $2 million in damage.

That seems to be a pretty minimal amount of damage, considering the total cost per satellite.

Also, the article gets some of the technical details quite wrong. For example:

>In 2000, Selective Availability was disabled and from that point on, anyone with a GPS receiver could get location data as precise as the data used for military and missile navigation.

This isn't true.

1) A GPS receiver that works above 60000ft or at speeds beyond 1000mph is still considered a military munition. You can't buy one and you can't leave the country with one, even if it only uses the civilian signal.

2) Selective Availability essentially distorted the timing of the L1 (C/A) (coarse / aquisition) unencrypted civilian signal, resulting in location errors up to ~100m greater than the nominal accuracy of ~16ft. It was the government essentially spoofing it's own signal at varied amounts to introduce uncertainty.

Turning off SA had nothing to do with the encrypted military (P(Y)) signals.

The encrypted (P(Y)) signals (on both L1 & L2) are still very much encrypted, and clearance is still required to obtain a compatible receiver, at significant cost. In practice augmented (agps) and differential GPS technologies produce higher accuracy and precision than the P code alone would, at less cost and hassle.

The new block satellites coming online add some signals for greater accuracy, but the civilian / military signal segregation and encryption still exists.

Nobody is getting guided-missle level navigation.

Edited: 18 parts complete of a planned 100 part series but each segment is only a few minutes long.

We didn't work on the radio level (other than learning about the 2-frequency ionosphere delay measurement as a calculation input), but did the rest of the stack above that including working out programs to derive position from given data input. I was a civil engineer but I think it's a great cross-discipline subject for a lot of fields.

https://www.scientificamerican.com/article/gps-and-the-world...

The NAVSTAR GPS constellation was incomplete at the time, so accurate positioning was only available for 19 hours a day. There weren't enough mil-spec receivers to go around, so some units relied on commercial receivers that parents had bought their sons and mailed them to them.