
The origins of GPS, and the pioneers who launched the system (2010) - fanf2
https://www.gpsworld.com/origins-gps-part-1/
======
leggomylibro
It's amazing how far we've come in a few decades - the article says they
started testing the CDMA system on the ground in New Mexico less than 50 years
ago. 20 years ago "Garmin" was a noun that meant "fancy mapping/navigation
device". Today you have a global map in your pocket, you can buy $10 modules
to use the constellation, and 1:24000 scale geospatial data is free for the
asking from the USGS.

[https://www.usgs.gov/core-science-systems/national-
geospatia...](https://www.usgs.gov/core-science-systems/national-geospatial-
program/national-map)

I wonder how we'll be navigating 50 years from now.

~~~
Rebelgecko
One of my favorite parts of the Woodford/Nakamura report mentioned in the
article is that when they list the ideal requirements a new system should
satisfy, they say that receivers should be cheap and portable.

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

~~~
beerandt
The previous navy / army prototype systems were roughly tractor trailer sized,
and only got your position within a few kilometers.

------
tverbeure
If you want to learn more about what makes GPS tick, here’s a home made
receiver that was build from the ground up. A stunning project with an
incredibly detail writeup.

[http://www.aholme.co.uk/GPS/Main.htm](http://www.aholme.co.uk/GPS/Main.htm)

One of the things that really caught me by surprise is that the GPS signal is
way too weak to be detected out of the noise in isolation. It’s only possible
to receiver it if you know what to expect:

“All GPS satellites transmit on the same frequency, 1575.42 MHz, using direct
sequence spread spectrum (DSSS). The L1 carrier is spread over a 2 MHz
bandwidth and its strength at the Earth's surface is -130 dBm. Thermal noise
power in the same bandwidth is -111 dBm, so a GPS signal at the receiving
antenna is ~ 20 dB below the noise floor. That any of the signals present,
superimposed one on another and buried in noise, are recoverable after bi-
level quantisation seems counter-intuitive! I wrote a simulation to convince
myself.

GPS relies on the correlation properties of pseudo-random sequences called
Gold Codes to separate signals from noise and each other.”

~~~
sand500
I guess this lets anyone overcome the "COCOM Limits"?

[https://en.wikipedia.org/wiki/Coordinating_Committee_for_Mul...](https://en.wikipedia.org/wiki/Coordinating_Committee_for_Multilateral_Export_Controls#Legacy)

~~~
Doxin
You can already overcome COCOM limits partially by buying the right receiver.
If you build your own receiver you can do whatever the hell you want.

COCOM limits are the equivalent of client-side form validation.

------
nexuist
Fun fact: in 1992 a group of political activists broke into a cleanroom
containing GPS satellites and started smashing them with axes. They called the
event "The Harriet Tubman-Sarah Connor Brigade."

[https://www.theatlantic.com/technology/archive/2015/03/the-f...](https://www.theatlantic.com/technology/archive/2015/03/the-
failed-attempt-to-destroy-early-gps/386656/)

~~~
beerandt
Very interesting, I hadn't ever heard about this.

>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.

------
drmpeg
Sad to learn that Dr. James Spilker has passed away this year. I worked with
him at his company Stanford Telecommunications from 1983 until 1992. He was
quite a character back then and was an avid body building enthusiast.
Sometimes he'd come to work all buttered up with tanning lotion.

[https://engineering.stanford.edu/news/james-spilker-jr-
fathe...](https://engineering.stanford.edu/news/james-spilker-jr-father-gps-
has-died-86)

------
ngold
This is hilarious. My dad started gpsworld. Glad to see it's still alive.

------
karmicthreat
GPS is one of the most amazing technical onions I've ever dealt with. I've
just been scratching the surface of it with understanding positioning for a
robotics project. I kind of wish I had an opportunity to do more paid work
with it. But it seems to be the realm of PHDs.

One of StarLink's biggest overlooked opportunities I think is radically re-
engineering a GPS like system that can work indoors and outdoors as well as
offering some pose estimation capability. It would make implementing robots
way easier.

~~~
OldGuyInTheClub
Not sure what level of detail you're seeking but I've enjoyed Michel van
Biezen's video series on GPS:
[https://www.youtube.com/watch?v=16xHIBmul_o&list=PLX2gX-
ftPV...](https://www.youtube.com/watch?v=16xHIBmul_o&list=PLX2gX-
ftPVXXGdn_8m2HCIJS7CfKMCwol)

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

~~~
throw0101a
A Stanford University lecture series that is "only" 65 videos:

* [https://www.youtube.com/watch?v=o1Fyn_h6LKU&list=PLGvhNIiu1u...](https://www.youtube.com/watch?v=o1Fyn_h6LKU&list=PLGvhNIiu1ubyEOJga50LJMzVXtbUq6CPo)

A few of the longest ones are only 26 minutes, and some are less than 10, so
it's actually bad as all that.

~~~
OldGuyInTheClub
Well, this is embarrassing. MvB's title says 100 episodes but he has completed
18 as of this time. I had only gotten to Ep. 15 so I didn't twig to the work-
to-go until just now.

I'll update my original and check out the Stanford course as well.

------
oh_sigh
What did the rest of the world think of GPS when it first came out? Was it a
shock to the USSR that we gained those capabilities?

~~~
chiph
It came as an unpleasant shock to Saddam's Iraq, because it allowed US armored
forces to navigate accurately through the desert and drive him out of Kuwait.

[https://www.scientificamerican.com/article/gps-and-the-
world...](https://www.scientificamerican.com/article/gps-and-the-world-s-
first-space-war/)

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.

~~~
coin
Rumor has it that the Air Force temporally turned off SA so that civilian GPS
receivers used by US military forces could get high accuracy positions.

~~~
colechristensen
SA (Selelective Availability) was disabled in 2000 by an act of Congress and
according to gps.gov

>The United States has no intent to ever use Selective Availability again.

I wouldn't be surprised if SA was turned off during that war.

