It's 1000 knots and 60,000 ft, and this is only to meet U.S. ITAR export requirements. There's nothing inherent about the civilian GPS signal itself that preven

It's 1000 knots and 60,000 ft, and this is only to meet U.S. ITAR export requirements. There's nothing inherent about the civilian GPS signal itself that prevents you from computing a fix beyond those limits. For example, you could buy one of these: https://www.sparkfun.com/products/10981 https://www.sparkfun.com/products/10981 and then design a baseband yourself. I'm currently aware of at least three people that are working on this or have already done it. You'll need to actually take the time to learn how GPS works, and it'll probably take you about a year, but it's definitely possible.