This is a common problem in navigating a vessel at sea. Convert your sphere to Lat and Long then calculate the Great Circle track. The Reference I use is 'the American Practical Navigator by Nathaniel Bowditch". You can obtain a copy from the Defense Mapping Agency. Request Pub 9 both volumes. Vol 1 has the definitions and Vol 2 has the math. Here is a link: https://permanent.access.gpo.gov/lps22411/Bowditch.pdf