Question

astronatus use fountain pen and they failto write but they not use pencil to write why

Answer 1

because if the pencil breaks so as there will be zero gravity it can cause damage by going into the system or can cause sever injuries to the astronomers by going into their eyes

Answer 2

I remember this exact Q was asked in the movie 3 idiots by amir khan.the reason is the broken graphite tips have a great threat to the eyes.