I believed that for an accurate and fast estimation, the GPS system required ASIC/FPGAs "expensive" propietary architectures, more than one receptor along the fuselage (allowing for measuring Euler angles), etc.
I don't know much about that. I thought they used fancy ASIC/FPGA stuff in satellites so they could fix them over the wire when the chips got holes punched through them by very fast dust.
I believe carrier-phase correction (in dgps) is more much harder at speeds greater than 1/2 a wavelength per message duration. By Shannon-Nyquist, there's not enough information to disambiguate the direction of the phase error, so you have to mix in more information from somewhere. Maybe that's what fancy dual antenna systems are doing.
One off-topic question, is the hardware is not a limit, why some GPS modules are limited to about 20km of altitude? is this done deliberated? and this is not an actual limitation in firmware/hardware? I can not see why the system could work at 13km of altitude and not at 20km, the atmosphere layer is the same, the signal/line of sight should be better, etc.
Section 11, part (c)
Global Positioning System (GPS) or similar satellite receivers; (1) Capable of providing navigation information under the following operational conditions; (i) At speeds in excess of 515 m/sec (1,000 nautical miles/hour); and (ii) At altitudes in excess of 18 km (60,000 feet)
Note the "and"; logically I guess that means one or the other is ok, just not both. I don't know how that works out in practice.
Chris Gough
On Tue, Feb 14, 2012 at 11:29 AM, Chris Gough
<address@hidden> wrote:
About GPS measuring Ground Speed and ECEF Position at high velocity, I really do not know about how the accuracy is affected, Doppler effect, etc.
It's not physics, it's firmware. Limits are result of treaties.
See section 11.
But it seems that you need an expensive GPS module.
The firmware/hardware isn't more expensive, only the paperwork. You have to prove you won't pass it on, among other things.
Chris Gough
Héctor.
On Tue, Feb 14, 2012 at 2:34 AM, Chris Gough
<address@hidden> wrote:
> Does the paparazzi code accomodate velocities as large as Mach 2- Mach 3?
I don't know, sorry (don't see why not though, try it in
simulation...). Maybe someone else can comment on that.
Do I understand you correctly:
* the rocket will go directly where you aimed it, it's not actively "navigated'
* the autopilot is not responsible for maintaining vertical attitude
* your instruments require a constant orientation (roll in the
rocket's frame of reference) during the preiod between boost and apex.
* your experiments require position and attitude logging during the
same flight phase.
Chris Gough
> Best regards,
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Héctor
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Héctor