Commercial GPS Turns 25: How Unwanted Military Tech Found Its True Calling | Hacker News Reader

Commercial GPS Turns 25: How Unwanted Military Tech Found Its True Calling

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64 pointsmr_golyadkin25 comments

GPS is one of the coolest things mankind has ever put together. I'm always amazed that his stuff was even considered in the 70s/80s.

By far the biggest misconception about GPS is that the GPS satellites somehow know where you are, or that your device transmits something to the satellite. I don't think this article does a good job of making that clear. It's kind of pandering to the paranoid. Granted, if you have a phone with a GPS receiver, it's totally possible/probable that your location is being reported through some other means (like the cell network).

If you have a phone in your pocket your location is already known within a certain bound of error because the cells can triangulate you, for that you don't even need a smartphone with GPS.

http://en.wikipedia.org/wiki/Mobile_phone_tracking

If you don't want to be tracked, don't carry a transmitter in your pocket.

Since we're in a thread about GPS, I don't think it's too pedantic to point out that GPS and cellular tower positioning use trilateration and multilateration respectively rather than triangulation.

> By far the biggest misconception about GPS is that the GPS satellites somehow know where you are, or that your device transmits something to the satellite.

I didn't think that was a common misconception, but then, in the article:

>> The military immediately — finally — [realized the spying benefits of GPS].

The bracketed piece is a link to http://www.army.mil/article/7457/gps-goes-to-war---the-globa... which talks about the military using GPS for straight forward positioning, not a word about spying.

That's really shoddy writing.

Yeah, really bad. The "unwanted" strikes me as completely unjustified: that it had to compete for extremely scarce post-Vietnam War '70s defense dollars is hardly remarkable, and there seems to be little excuse, the author's bio says he's "been reporting, reviewing and ranting about consumer electronics for 30 years", which should make him about my age, i.e. if wasn't politically etc. aware in part of the '70s, they were very recent history. Even the time line as quoted in the work is inconsistent:

"By the early 1970s, several competing GPS ideas emerged, and the battling projects caused military paralysis until a serendipitous four-hour weekend meeting in November 1972...."

Now, maybe it's just because I definately lived through that period, but I kinda thought 1972 was part of "the early 1970s".... Very sloppy writing.

In the tin-foil-beanie community, it's not quite as common a belief as chemtrails, but more so than the deep-underground-military-base meme.

> GPS is one of the coolest things mankind has ever put together. I'm always amazed that his stuff was even considered in the 70s/80s.

Why? The 1980's were already the modern era of technology. By 1980, we had nuclear power (1956), hypersonic human flight (1959), fiber optics (1965), manned moon missions (1969), integrated microprocessors (1970), cell phones (1978), TCP/IP (1978), and satellite TV (late 1970's).

It's kinda sad that we're now going backwards on nuclear, abandoned mainstream supersonic flight altogether, only had one moon landing and still don't have a strong fiber coverage...

A often overlooked feature of GPS is that it actually gives you line of sight information to all satellites of the constellation not only a position. So pretty amazing extraction techniques and 3D reconstructions are possible.

http://www.cc.gatech.edu/~summetj/papers/kim_iswc_08.pdf

http://www.cs.technion.ac.il/RESEARCH_DAY_13/POSTERS/nir_her... (quite big poster)

And in the reverse use case this enables shadow forecasting and faster positioning based on known environment and shadow maps:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3574707/

http://www-user.tu-chemnitz.de/~maob/nt/paper/Bauer2013.pdf

Another cool thing about GPS is that it helps up predict weather.

http://en.wikipedia.org/wiki/GNSS_radio_occultation

Basically, a satellite in orbit (which already knows where it is) will measure the time delay to a GPS satellite as the line of sight skims the edge of the atmosphere. The ray path will be affected by the refractive index of the atmosphere, which depends on its humidity and temperature. This allows temperature and humidity to be calculated for a range of altitudes as the line of sight moves, and is remarkably accurate - so much so that other observations are calibrated against GPS measurements.

I recently read Paul Lutus's book about his solo sail around the world in the late 80's. He mentions using satellite navigation and I was curious what this was since the adventure preceeds GPS. It turns out it was a system called TRANSIT that was operated by the US Navy.

http://en.wikipedia.org/wiki/Transit_(satellite)

http://arachnoid.com/sailbook/

I'm surprised they didn't mention ground-based predecessors to GPS: http://en.wikipedia.org/wiki/Omega_Navigation_System

Not one word about nuclear detonation detection?

AFAIK, that's done by a totally different set of satellites.

Nope still done with GPS [1]. There was talk in 2013 about dropping it for cost savings.

[1] http://en.m.wikipedia.org/wiki/Global_Positioning_System

Heres the money quote: "GPS satellites carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an electromagnetic pulse (EMP) sensor (W-sensor), that form a major portion of the United States Nuclear Detonation Detection System.[76][77] General William Shelton has stated that this feature may be dropped from future satellites in order to save money.[78]

Some also carry bhangmeters - devices for detecting nuclear explosions named after a variety of cannabis!

http://en.wikipedia.org/wiki/Bhangmeter

"the joke being that one would have to be on drugs to believe the bhangmeter detectors would work properly"

Can't believe I've missed the only opportunity to mention bhangmeters - indeed a fun fact.

Originally, since it started in 1963, long before GPS: https://en.wikipedia.org/wiki/Vela_(satellite)

Bundling that mission into GPS satellites was an obvious way to save costs and very possibley get better results.

There's something I've always wondered and maybe here is the right place to ask it, but what is the practical and theoretical accuracy of the GPS? Can it track the position of a device in, say, a radius of 2 feet? It always looked to me like GPS measures are pretty coarse by design or are limited by the government for security purposes (e.g. launching missiles).

Nominal accuracy of "pure" GPS is 15 meters. Using Differential GPS (which uses additional signals from ground stations)gets you down to 10cm in the best case.

There used to be an additional limitation called "selective availability" where the military deliberately introduced errors in the clock siginal to reduce accuracy to about 100m, but this was switched off in 2000.

Note that most modern GPS receivers usually achieve much better than 15m accuracy in normal use.

http://www.gps.gov/systems/gps/performance/accuracy/

I can personally say that ~1.5-2m accuracy is definitely achievable even with a cheap entry-level receiver like the ones integrated into smartphones, when there is a clear view of the sky and good weather.

Edit: It seems my phone does have DGPS, so that accuracy is not just "raw GPS".

That's really outstanding, I didn't expect that.

GPS comes in two flavors, SPS (standard positioning service, your standard civilian positioning) and PPS (precise positioning service, for the military).

The SPS specification[1] says you should expect 95% of reported locations to be within a 9m diameter circle (ref 3.8.3). Realistically, though, you can get much better, and a lot of receivers get within 2-3m.

Up until about 2000, there was thil thing called Selective Availability[2] (aka SA). This limited civilian performance to much worse (95% ~20-30m) by some clock dithering techniques. During-SA and post SA accuracies are very different.

In order to support airplanes using GPS for precision landing, the FAA rolled out WAAS[3], which is a wide-area augmentation system that broadcasting atmospheric correction data (specialized just for the US; there are other national systems). GPS+WAAS gets you to within a meter or so. [3]

If absolute position isn't important, but relative position is (say, if you're measuring the movement of two tectonic plates relative to each other at a fault), there's this neat thing called RTK. This gets you relative positions (in the field) on the order of millimeters[4].

[1] http://www.gps.gov/technical/ps/2008-SPS-performance-standar...

[2] http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_P...

[3] http://www.navipedia.net/index.php/WAAS_Performances

[4] http://hemispheregnss.com/DesktopModules/EasyDNNNews/Documen...

One of my coworkers at General Dynamics did a slide show on GPS potentials in 1981 which of course was long before it was real. It seemed like science fiction at the time. Hard to imagine how we would do without it today.

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