Bypassing US GPS Limits For Active Guided Rockets

Kristian von Bengtson writes with a link to a short guest post at Wired with an explanation of how his amateur rocket organization Copenhagen Suborbitals managed to obtain GPS receivers without U.S. military limits for getting accurate GPS information at altitude. Mostly, the answer is in recent relaxations of the rules themselves, but it was apparently still challenging to obtain non-limited GPS hardware. "I expect they only got the OK to create this software modification for us," von Bengston writes, "since we are clearly a peaceful organization with not sinister objectives – and also in a very limited number of units. Basically removing the limits is a matter of getting into the hardware changing the code or get the manufacturers to do it. Needless to say, diplomacy and trust is the key to unlock this."

Re: Huh

[interkin3tic]

Ah, so I'm basically wrong. I'm trying to make a joke about inaccurate GPS and making uninformed posts to slashdot, but I've got nothing. So I'm just going to say "Good to know, thank you!"

Re: Huh

[slew]

Ever looked how many DIY GPS receivers are out there? On a six figure budget it wouldn't be much trouble getting something made.

Although there are many so-called DIY GPU receivers out there, all of them I know about use off the shelf GPS modules (like the MTK3339 or perhaps some of the SiRF stuff), not doing the RF stuff themselves. There are some people making the RF stuff as DIY projects, but then they have to stuff the signal into an FPGA and drive the thing with a lump of software.

Having tried the later myself, I can tell you it's generally a bit finicky even in the simple case. I suppose if you know what you are doing you might have better luck (because of w/o a lot of experience, ionospheric noise modelling isn't very easy, it's much easier to just average stuff and hope for the best). Another roadblock is that most folks I know don't have many 60K/Mach velocity platforms to test on to perfect their dopper shift algorithms (remember, the satellites are moving too and you have to account for that)...

I don't think you are just going to download some DIY GPS receiver in the webosphere and have to work for missle guidance applications.