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I am looking for a GPS module that I can use in a high-altitude project. The problem I have discovered is that GPS manufacturers are required to place a set of restrictions on GPS modules. The restrictions set a maximum speed and altitude at which the device should stop functioning. Basically, this limits someone's ability to build a cruise missile.

From what I understand, it is not illegal to have a GPS receiver without these limitations, it is illegal to export it from the U.S. without considering it a weapon.

If I am not mistaken, GPS is also used to track some satellites in orbit, so as long as the orbiting satellite is not in geo-synchronous orbit or further. Obviously, these GPS receivers do not have the limit, as both the height and velocity would far exceed the mandate.

Does anyone know of a GPS unit that does not have these limitations, or, is there a unit that allows you to flash the firmware and manually remove the limitations?

Link to mention of limitations: http://en.wikipedia.org/wiki/CoCom#Legacy

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    Interesting question - what 'high altitude project' would this be? Assuming not cruise missile ... balloon? Are the speed and altitude issues BOTH considerations for you? – Simbamangu Feb 5 '12 at 7:33
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    @Simbamangu No cruise missles, just a high-altitude balloon. But, I would like to find a receiver with none of the limitations, then I can go for a satellite launch...OSCAR, ftw! – Jonathan Feb 5 '12 at 7:58
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    If you have a follow the links at the bottom of the wikipedia page, one mentions a Trimble embedded GPS module that is known to work for balloons; the article suggests that trial-and-error is the only way to figure out what does and doesn't work! – Simbamangu Feb 5 '12 at 12:15
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Here's a page that discusses several models of GPS that are known to work in balloon applications: http://ukhas.org.uk/guides:gps_modules

It looks like the COCOM limits are imposed differently by manufacturers - some use an altitude 'OR' speed limit check, the others use 'AND'.

My next question would be just how much 3D accuracy you would get out of a GPS unit at 100,000 feet!

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The US Government GPS Standard Positioning Service Performance Standard, appendix A, guarantees coverage up to an altitude of 3000km. Accuracy of a standard receiver would in no way be reduced at high altitude. High velocity is a bit different - the increase dopplar shift requires a receiver to search a large frequency range in order to lock on to the signal broadcast.

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