How to become an Astronaut in NASA or ISRO?

To become an astronaut in NASA as a non-US resident it may take a lot of effort and you need to be expert in your field may be communication, remote sensing or any other field. You need to be able to re-invent things according to your requirements and should have a great in-sight in subject.

To be eligible to become an astronaut you need to take aeronautical or aviation engineering after your 12th because most important thing is an astronaut should have great pilotting skills. This will take you one step towards your goal. You can write ISAT exam conducted by Indian Institute of Space Technology which is controlled by ISRO. This way you will be upto date about opportunities to get into ISRO. You can also do avionics from IITs or IISc and apply to astronaut recruitment by ISRO.