# Mach Projectile Tracker

• February 24th, 2009, 01:18 AM
GPSMach
Mach Projectile Tracker
Track the source and destination of a supersonic projectile with 3 microphones.

http://www.geocities.com/jongiff2000...ile_Solver.xls

I have worked out the math. All that's left is the electronics.

http://mypeoplepc.com/members/jon8338/math/
• February 24th, 2009, 04:19 AM
Megabrain
Bin there done that! - British Army 1970's GSR (Gun sound ranging). It was being developed in another part of the establishment I was working in at the time. Today I understand they use Radar and not sound, since heavey local noise can upset things. The idea was simply to pinpoint the exact location of enemy artillery allowing return fire, (the modern Radar system can pinpoint the firing position using just the last moments of a projectile's track). Even more modern, The US has a GPS Guided shell which can change course and therefore fool any tracking radar!

IF the projectile is supersonic you might find the sound arrives after the projectile has arrived at it's destination.
• February 24th, 2009, 07:47 AM
Harold14370
If it is okay to have somebody input the times manually, it's easy. Just take the 3 microphones and input each to an oscilloscope or digital recorder. Set it up to trigger on a certain threshold signal from the microphone. Then you can read the difference between the peaks of the pulses off the display.

http://cnx.org/content/m11902/latest/
• February 24th, 2009, 01:12 PM
GPSMach
Every point on the cone of the shock wave is synchronous with the projectile, so the shock wave arrives at the 3 microphones not after the projectile reaches its destination. There is, however, a delay due to the half angle of the cone.

I knew this problem was already solved when I decided to solve it for myself. In 1983 a professor in my Vector and Tensor Analysis class told us about it. One of his students solved it for the military and patented it. I just wanted to solve it to see if I could do it. It was made to be used on helicopters. One microphone was at the rotor and two others on the skids. If anyone on the ground fired at them, they knew where to return fire. The speed of their gun bullets has to be known, but other than that, this system is already up and running in the military.

If the projectile departs from a straight line of fire, this solution fails.

The oscilloscopes would be useful in developing a prototype for the system. Once the design is finished, it should be able to read the microphones, input their coordinates and arrival time differences, and calculate the projectile's destination before it gets there, as well as the projectile's source. As I don't own an oscilloscope, (probably a 3-trace digital is needed), I only pose this problem for those of you who might want to take on the project yourselves. You'd also need a gun to test the outfit (be careful).