I am working on a Low to Medium fidelity orbit analysis tool. My key factor here is speed, I am analyzing constellations with 500 - 1000 satellites and want to be able to perform the analysis in under ~1 min. Now that is another story in its self, but I am analyzing specific cases of circular orbits which makes the propogation significantly easier.
My problem I am running into is converting from ECEF to ECI for access analysis. I know there are plenty of functions that use IAU reductions which I have used and tested. My problem is they take a decent bit of time and memory (for me 5-10 seconds is alot).
I have been referencing Vallado and it states a majority of the difference comes from Earths rotation. I have an efficient algorithm to calculate GAST, but I want to know what amount of error I am inducing by just accounting for earths rotation (meters, kilometers, tens of kilometers etc)?
I have found this nice tool ECEFtoECI which he claims can get accuracy compared to STK on the order of cm's. I seem unable to reproduce his information. Any insight would be greatly appreciated.