On Mon, Feb 28, 2011 at 03:05:37PM -0800, I wrote:
> Quoting Nathan Bergey <nat...@psas.pdx.edu>:
> OEM's have a tracking loop (google Costas loop) typically with a 1Hz
> bandwidth (source: a GPS INS book I have. It's at home at the
> moment). Some OEM units can change the loop bandwidth to something
> higher, but with poorer accuracy and greater likelihood of loosing
> the satellite lock. The result is this: if the GPS accelerates
> (relative to the satellite) above a certain rate (some GPS OEMs
> advertise 4 g's) the correlator cannot change the carrier tracking
> frequency fast enough to keep up, so the signal lock is lost.
> Another approach is to adapt the rocket to work with the GPS. This
> would get you the tracking, but not necessarily the altitude unless
> you can unlock the GPS (ITAR restriction). The OS GPS or GPL/GPS
> could really shine here.
> I'd say one could do this with a 2 stage rocket using a slow first
> stage, a slow second stage, and long launch rail. The key is to keep
> the OEM GPS acceleration under 4 G's the whole way. Hybrids might
> have an advantage here with long slow burns.
Note that they don't say you need continuous GPS tracking, just that you
need at least one GPS measurement above the altitude threshold. So, as
long as the GPS recovers during the coast phase, before apogee, that
Of course, independently from their criteria we *want* a GPS unit that
works continuously through the flight.
- Josh Triplett
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