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With upcoming GNSS systems that have better accuracy than GPS, could there be an GNSS based attitude indicator? Does maybe one already exist?

I could imagine having 4 sensors (front, aft, left wingtip, right wingtip) that then calculate the attitude.

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    $\begingroup$ Then what would be your backup in case of a GNSS/GPS outage? Part of the reason for Gyros is to have separate systems that can be cross-checked against each other. $\endgroup$ – abelenky Sep 6 '18 at 14:15
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    $\begingroup$ Even today, differential GPS accuracy is about 10cm, which is perfectly sufficient. The inaccuracy from wing bending is larger than that. $\endgroup$ – Rainer P. Sep 6 '18 at 15:29
  • $\begingroup$ Researchers at Stanford University had working prototypes 20 years ago. They worked, but not very practical or cost effective when compared to a solid state ADHRS which came about the same time. $\endgroup$ – Gerry Sep 6 '18 at 16:51
  • $\begingroup$ I visited a search and rescue cruiser some years ago that used three GPS receivers to calculate true heading at sea. $\endgroup$ – Cpt Reynolds Sep 6 '18 at 20:49
  • $\begingroup$ Which GPS signal in particular are you referring too? All of them in general? $\endgroup$ – jCisco Sep 10 '18 at 1:20
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Part of the attitude determination on the ISS is done that way. The size of the space station makes for a larger measurement base then on an aircraft, but the idea is the same. Further, the ISS has an unobstructed view of the navigation satellites, and has lower rotation rates than one can expect on an aircraft, which makes it an easier problem. But, a quick search finds plenty of research for doing the same for aircraft.

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I suppose you could but what benefit wound a GNSS based system offer over traditional gyroscopic and AHARS based attitudes systems while offering better redundancy against a system reliant on outside radio sources and risks with system outages, etc?

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There has been quite a bit of research on the topic and units have even been built. Ultimately it will trickle its way out there if the price of the unit drops below AHARS or Gyro equivalent units and its accuracy is equal or better than modern AI's. However you can get a good, small, drop in, AHARS style AI for fairly reasonable (considering the cost of avionics). The FAA seems to allow GNSS signals to supplement AHARS data I cant find a copy of TSO-C4c which outlines the certification limits for pitch and bank instruments but may shed more light on the topic.

Side note: to escape the mechanical dependence of gyros and if you want something different than what your run of the mill AHARS unit has, some of the newer high performance stuff uses a Ring Laser Gyro.

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