What are the benefits of a PhD? (Engineering)?

Firstly it's not so easy to become a researcher at NASA or ESA or Virgin Galatic . Secondly , you don't need to do PhD if you want to specialise into spacecraft propulsion , a master degree would work perfectly for it . Search for jobs as a researcher / tester at NASA etc. Search on Google and you will find plenty of best universities for your future . But if you are still interested in studying PhD then go for it . Maybe it will work out good for you in future .