What about current space missions?? Also, I heard from my friends that nowadays people no longer use Newton's theory of gravity for the current space missions. How true is this?

And which one of these is majorly in practical use. Einsteins general relativity or Newton's Theory of Gravity??

In my school I was taught only about Newtons Theory of Gravity and I'm definitely not very well versed in Einstein's general relativity.. but I would like to get some expert opinions on this.

Another question.

I was explaining to my friend about calculating earths mass. I came to a suggestion that earth mass could be calculated, but only with the knowledge of G, by say tossing a ball onto the ground and using Free fall acceleration(g) in newtons theory of gravity equation. But without the knowledge of G how did they come to know about earths mass? How did they compute value of G in the first place? Cause I don't see a practical/empirical way to compute Gravitational pull between two objects.

Thanks