But it's the wrong satellite, Grommit.


Andy G4JNT
 


I can't imagine that a range of decision makers can be that foolish or forced by government pressures.    Anyone know the real story? (and, more to the point, are allowed to revel properly)

Back in 1990, long before GPS, I worked on a satellite location system based on two way transponders carrying spread spectrum signals for ranging.   The    LOCSTAR project.  I don't recall the full constellation, but think is was two sats in Geostationary and worked with a-priori information on approximate (eg country, location beforehand.   Probably just aimed at just part of the World like Eu.     The US had a not-dissimilar system, GEOSTAR in the pipeline.  NOt sure whether it went ahead fully.

LOCSTAR was cancelled part-way through because, we know now, but didn't then,  people had looked to the future and seen GPS coming along .

There's nothing inherently wrong in principle with a location system based on LEO satellites.  TRANSIT did it in teh 1960s using V/UHF - but not to anyhting like such accuracy.  100s of metres ISTR

If used in the same way as GNSS, they'd all have to carry highly accurate clocks Cs or Rb  which is totally infeasible (? nowadays ?).   But it's not unreasonable to use them as transponders carrying a ranging PN sequence transmitted from the ground.   Then the same correlation techniques can be carried out by users as with satellite generated PN codes.  Of course, satellite ephemeris will have to be known to cm accuracy if it's to match the performance of GNSS.   But given this, and a transponder payload with good phase stability for the PN code it's feasible I'd have thought.

The  ground station requirements are a bit frightening though.

As for mass produced low cost receivers.  IF the frequency band is around the same as GNSS, ie L-Band, I can see all those GNSS chip set manufacturers just yawning and building in compatibility.   After all, they upgraded from GPS to GLONASS,  Beidou, Galileo and I think there's another they work with now as well all in one tiny module costing a few quid.    It's all just IP/Firmare/juggling with numbers.

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