John, > I just got a quote from KVH yesterday for their new 6DOF FOG IMU system -- > $25,000 and 10-12 weeks delivery. It looks like we will be sticking with > the Crossbow FOG for a while, although I am keeping my eyes out for either > a good integrated GPS / IMU that could reduce GPS position jumps, or a set > of gyros accurate enough to gyrocompass.
You might want to check with some of the "low-cost ELV" companies. I know that at least Microcosm and Aeroastro have both developed fairly low-cost IMU/GPS guidance packages that are supposedly good enough to fly an ELV all the way to orbit. In at least Microcosm's case, I know that they supposedly cost less than $30k. That's a heck of a lot for ameteurs, but might be within
These are almost certainly basically what we have -- a FOG based IMU and a separate GPS that outputs position. Our current system should also also be capable of guiding a vehicle to orbit. There is a tighter level of integration that is possible if the core GPS resolving algorithm also has access to inertial data as it weights the values from the various satellites. This can get rid of the occasional discrete steps in position that GPS systems give as they transition from satellite to satellite. A few meters isn't relevant for an orbital vehicle, but it matters for precision landing and maneuvering.
Just using differential GPS will probably be a lot easier.
John Carmack
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