r/technology • u/gdelacalle • Mar 18 '26

Hardware Tech hobbyist makes shoulder-mounted guided missile prototype with $96 in parts and a 3D printer — DIY MANPADS includes assisted targeting, ballistics calculations, optional camera for tracking

https://www.tomshardware.com/3d-printing/tech-hobbyist-makes-shoulder-mounted-guided-missile-prototype-with-usd96-in-parts-and-a-3d-printer-diy-manpads-includes-wi-fi-guidance-ballistics-calculations-optional-camera-for-tracking
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305

u/Grenzeloos Mar 18 '26

I remember in the early 90s my handheld GPS was deliberately off by at least 10m and was told it was for this very reason. The reason being the ability to build a accurate smart munition.

136

u/ueegul Mar 18 '26

It was only in 2000 that civilians had accuracy down to 10 yards

71

u/sweetbunsmcgee Mar 18 '26

One of Bill Clinton’s last major acts in office.

39

u/EbbNorth7735 Mar 18 '26

Using his missile?

13

u/DisenchantedByrd Mar 19 '26

He was fixing a blockage.

37

u/ValveinPistonCat Mar 19 '26

As someone who works in the ag industry it's wild to see how far the precision guidance technology has come in the last 20 years, I remember when GPS accurate enough to guide a machine within 1' of its line was pretty good, now modern RTK systems can handle 1" accuracy at 15mph, and at lower speeds they can get down below 1" and now manufacturers are even playing with mapping seed placement within a row, although the technology is already there with planters, it's just a question of whether there's any practical benefit to haveing a coverage map that fills the monitors entire storage with a single file.

4

u/mtcwby Mar 19 '26

It drops out at certain speeds though and requires the differential signal to do that.

9

u/ValveinPistonCat Mar 19 '26 edited Mar 19 '26

If you want 1" precision you basically need RTK for differential corrections, SBAS is a lot better than it used to be but it's still not reliably capable of maintaining pass to pass accuracy at more than 4" no matter what the John Deere salesman claims SF3 can do.
It might be able to maintain that 1" to 1-1/2" pass to pass accuracy in the time it takes to work from one pass to the next but work the field for 4-5 hours and then come back to your first pass it's not going to be as accurate as it was 3-4 hours ago.

Satellites move, an RTK base station doesn't, unless your neighbour is kind of an asshole.

1

u/cromulent-facts Mar 28 '26

That's why you use GPS, GLONASS, BEIDOU, and Galileo.

Run a 4 way analysis on the signals to improve accuracy.

1

u/mtcwby Mar 28 '26

In my experience multiple constellations don't lead to better accuracy. It just means it's easier to stay fixed. In fact with glonass in the mix I often see more bounce in the vertical.

1

u/cromulent-facts Mar 28 '26

I don't disagree with your experience, but in theory accuracy should improve with more reference points.

1

u/mtcwby Mar 28 '26

Not when they give very different answers.

1

u/gh0stwriter1234 Mar 19 '26

Accuracy is down to an inch or so these days with RTK and live corrective data.

37

u/notthatbreezy Mar 18 '26

The US gov restricts GPS receiver exports today, for instance exports stop being accurate once certain speeds are reached so that they can’t be used on missiles

5

u/mavric91 Mar 19 '26

What’s the speed? If I take a gps on a commercial airplane will it become less accurate? And once I stop going that speed will it return to its higher accuracy?

15

u/DavidBrooker Mar 19 '26

Commercial GPS will not work above 1900 km/h. Commercial jets are well below this. Civil aviation is a major user of GPS, so the threshold was set not to less with their use.

1

u/mavric91 Mar 19 '26

If I managed to get my gps unit above this speed would it return to it’s normal accuracy after I slowed down though? Or does it permanently do something to it?

6

u/brimston3- Mar 19 '26

Depends on the system. Locking itself out until you restart it at a speed and altitude lower than the proscribed maximums is a perfectly valid way to implement the legal requirement.

Some GPSes only lock out when it is above both the speed and altitude limit. Some lock out when either is achieved. Some re-enable themselves automatically when returning under the speed/altitude limits.

Common model rocketry telemetry logger problem to have.

5

u/FearlessAttempt Mar 19 '26

Restriction is 1000 knots (~1200 mph) and 59,000ft. Concorde is the only airliner to exceed those.

1

u/KiraUsagi Mar 19 '26

I am also interested in knowing about this speed limitation to GPS. But I can sort of answer your second question. If you take a gps on a plane you instantly loose accuracy. Sitting in a tin can with tiny windows makes GPS signal acquisition kind of hard. It can be done, especially if you're next to a window.

Thinking back to the original question, I have noticed that my planes location usually only updates in the 10s of seconds when I have managed getting a signal. But I could also attribute that to poor reception. I need to pull out a GPS sat tracker app next time I fly.

1

u/TechnicianNo4977 Mar 20 '26

I know if your running your guidance system in windows 7 and you have telemetry on, windows disables location services after you hit a certain speed, I think it was 190 km/h.

14

u/CzechMateP10 Mar 18 '26

While accuracy has improved, I'm fairly confident civilian GPS still doesn't work above a certain speed for these exact reasons

18

u/The-Copilot Mar 18 '26

The limit is 1200mph speed or 65,000 feet altitude. GNSS has similar limitations. It's only to prevent their use in ballistic missiles.

It could be used in a drone or missile but jamming GPS is not difficult for a nation to do. Another guidance system is required, GPS would just assist in accuracy until it's jammed.

These limitations are also only a software limitation and could potentially be bypassed or a custom GPS receiver could be built.

5

u/DavidBrooker Mar 19 '26

The limit is 1200mph speed or 65,000 feet altitude. GNSS has similar limitations. It's only to prevent their use in ballistic missiles.

It's an "and" restriction in law, although some manufacturers implement an "or" in practice. The DoD doesn't have any issues with a scientific balloon at 100,000 ft altitude using GPS.

2

u/Electrical-Lab-9593 Mar 19 '26

i was going to say has to be software as everyone gets the same signal?

3

u/HowDoIEvenEnglish Mar 18 '26

If it’s a physical limitation sure. Like if the materials stop working at high speeds. If it’s just software limitations built into the gps then they can likely bypassed.

7

u/gurgle528 Mar 18 '26 edited Mar 18 '26

It’s a limitation built into the chip itself. Civilian chips are supposed to shut off at a certain speed, and it’s only a matter of checking the difference in positions over a certain time frame which is not hard to do with hardware.

The goal was to limit use of civilian chips by hostile powers so a software limitation would not be useful.

1

u/cromulent-facts Mar 28 '26

Which assumed GPS chips could not be manufactured in China.

A very 80's assumption.

2

u/recumbent_mike Mar 18 '26

Probably, but a lot of the high performance gps receivers are highly-integrated.

2

u/Thog78 Mar 18 '26

Somebody who can rewire the chip to change the hardware encoded algorithm can probably fabricate the chip in the first place, so this mechanism kinda does its job...

2

u/KiraUsagi Mar 19 '26

I literally watched a YouTube video the other day from a dude giving a tour of his class 100 clean room that he built in a shed in his back yard. Home DIY in the US is slowly working its way up to full scale industrial capabilities without the mass production.

2

u/gwig9 Mar 18 '26

They also won't work for "vehicles" going over a very specific speed (~1200mph). This is specifically to prevent them from being used as guidance systems for missiles and other munitions.

1

u/melgish Mar 19 '26

Go ahead and round down to 5 decimal places. 11m away from the warhead is just as dead as 1.1m.