Re:Decades-Old Mystery Put to Rest: Why Are There X's in the...
by planteen on Wednesday October 12, 2016 @04:37PM
(#12696249)
> The article says "focusing", but they were probably used to get more precise orbital elements for satellites. This was pre-GPS, and calibration across geography on a planetary scale was tough.
My guess is that they served a function for calibrating ground control points rather than orbital elements. Even today, NORAD publishes orbital elements (TLEs) for spacecraft deduced by radar (and also optical means). I think other radio ranging techniques were also used before GPS. Trying to point at Earth-fixed point with only an inertial attitude (without a position/velocity) seems really tough.
Today, lots of CubeSats don't have GPS, so they eagerly await getting TLEs from NORAD. It seems like this Twitter is always the first with new data:
My guess is that they served a function for calibrating ground control points rather than orbital elements. Even today, NORAD publishes orbital elements (TLEs) for spacecraft deduced by radar (and also optical means). I think other radio ranging techniques were also used before GPS. Trying to point at Earth-fixed point with only an inertial attitude (without a position/velocity) seems really tough.
Today, lots of CubeSats don't have GPS, so they eagerly await getting TLEs from NORAD. It seems like this Twitter is always the first with new data:
https://twitter.com/TSKelso