Hello kalyan!! yes , you can go for aerospace in Btech after completion of diploma as mechanical engineer.But,there are few colleges that offers lateral admission to diploma holders in B tech aerospace engineering.every institute has their own entrance examination in which you need to get qualified.All the best!!

hello aspirant,
after diploma in mechanical engineering you can join b.tech aerospace engineering course. diploma candidates join from second year of b. tech course. every state has a lateral entry entrance exam which you need to clear to join b.tech course. some deemed university has their own entrance test.