Ironically, I moved from the Aerospace industry into software/technology product space primarily because there were more jobs, more opportunity to create/join start-ups and the diversity of opportunities from a sector perspective. If you are a skilled software developer, there are MANY opportunities in defense sector - just look at Lockheed, etc. career pages. You'd likely need to find something in your own country as most jobs require security clearance of some level for nationals. However, this should not prevent you from getting started in working with SW products, commercial or open-source, that the industry depends on.
Some things to look into:
1.) Research how to work with large data sets and make sense in trying to identify trends, predict fail modes, and study the types of data space companies collect. SpaceX collects tons of data in a single flight! What would they do with it, how would they analyze? Learn which tools help you do that. Knowing how to code, leverage APIs, get systems to talk to each other: All critical skills needed to support rocket scientists!
Check out things like..
2.) Computer modeling and sim: Computational fluid dynamics
Go check out Anderson, Tannehill and Pletcher CFD&HT texts on CFD to get the gist of the field, then play with os tools like...
I'd get started with those and figure out how you can help ISRO in Bangalore or any supporting contractors on national missions.