I know that Newton's theory of gravity fails to predict certain features of Mercury's orbit in comparison with GR, and also fails to predict the bending of spacetime around a star shown by the path of light. And perhaps one or two other failures which I forget. But I've read that Newton's laws are adequate for calculating pathways of spacecraft in the solar system, and are used by NASA and presumably other space agencies for their flights, because GR is so much more complicated to use. So, what is the current status of Newton's theory of gravity in physics? Is it considered a special case of Einstein's theory, or an entirely different theory? Is it considered valid in the realms it covers, or outdated and overturned? Does Einstein's theory *contain* Newton's? Is Euclidian flat space which I believe Newton uses, a special case of curved GR space, valid only for smaller realms like the solar system, or could Euclidian space be said to be able describe also a large large area of the universe, say several long walls of galaxies together? If a flight path to another star say, 400 million light years away were calculated with Newton's laws, would it be in error as compared with a calculation made with GR? As the laws of physics break down in a singularity, could Newton's laws be said to break down above a certain size of spatial area?