Physics/regarding relativity in GPS
I would like to know whether (Einstein's) relativity corrections are used in GPS or not. Some people who oppose relativity say that the corrections are not used. Since you have worked in Space shuttle, please clarify whether relativity is used or not.
I was not involved with GPS during my Space Shuttle time. My responsibilities involved a group of electronic devices in the flight control system. I left the program in 1981 after the first launch. GPS was only partially operational in 1985.
I Googled [relativity correction gps] and the first hit provided this link.
This site describes corrections for "errors" that are explained by Special and General Relativity. I reviewed some of the other hits Google gave me and learned that there is serious controversy regarding need for the corrections. There are many sites discussing the need for the corrections and many sites disputing the need for them. Some of those who dispute the need also dispute relativity, others merely say the system would work well without the corrections for relativity.
The sites disputing the need say that the system would perform with the required accuracy even if the corrections were not made. They claim that as long as the time kept by the clocks in all 24 GPS satellites remain the in sync with each other, it doesn't matter if those clocks run slower than Earth-bound clocks. I never found any of the sites supporting the need for the corrections responding to the arguments of the other group of sites.
I don't have the information or time required to educate myself sufficiently to referee this dispute. I'm sorry, I can't settle the issue for you.